Steam Turbines - Forgotten Books

S T EAM T U RBINE SPRAC TIC E AND THEORY

H

LESTER G . FRENCH,S . B.

Mechan i ca l Eng ineer

II

Kant ion p ub l ished by The Technica l PressforHil l Pub l ish ing Com pany

NEW YORK AND LONDONHILL PUBLISHING COMPANY

1907

PREFACE

This book had its beginning in the editorial office of Machinery,

New York. For nine years previous to Ju ly , 1 906 , the author

w as editor-in-chie f of M achinery,and it w as during the latter

hal f of this period that the steam turbine became a commercialsuccess in America and final ly reached its dominant position inthe field of electric generating .

Inasmuch as a l ive technical j ournal is constantly in touch with

events in i ts field , the author had an exceptional opportuni ty to

coll ect notes and data on the steam turbine and al l ied sub j ects

during the important format ive period of the turbine , when it w as

more discussed , probably, than any engineering subj ect . Advan

tage w as taken of this opportunity to begin what has grown to be

a large collection of such notes and data, which have served as

the foundation for the present volume .

The author i s responsibl e for various articles and paragraphs

which have appeared in Machinery upon the sub j ect o f the turbine , some o f which are here reproduced in more or less modi

fied form . Most o f the matter in these pages , however , w as wri t

ten especial ly for them and has not been used before .In brief explanation of the contents , it may be said that the

first chapter i s a condensed treati se upon the fundamental princi

ples o f the steam turbine . The second chapter traces its early

development and shows the state o f the art” at the time when theturbine became a commercial success . It is bel ieved that thisreview wil l not only save considerable research , but in connection

with the first chapter will serve to ground the beginner in firstprinciples ; for there is no w ay of accompl ishing this so efi

‘ec tively

as by a study of what others have done .

Much attention has been devoted to the resu lts of tests upon

the flow o f steam, upon the action of steam on vanes and upon the

economic performance of turbines . For compari son with the latter there is al so a review o f tests upon reciprocating engines , and

enough data are included to enabl e an intell igent compari son to

iv PREFACE

be made under different running condit ions , with due al lowance

for the effi ciency of generators and engines .

The mathematical treatment has been l imited mainly to a dis

cussion o f the adiabatic flow of steam and to the principl es of

turbine vanes , which together are the basi s o f al l turbine cal cula

tions . Prel iminary to the calcu lations upon the flow of steam is

a chapter for re ference , upon the propert ies of steam , which in

c ludes , also , an explanation o f the temperature-entropy diagram ,

and data upon the specific heat of superheated steam—subj ects

constantly recurring in modern wri tings upon heat and steam .

The attempt has been to S impl i fy the mathematical treatment as

much as possible , and i l lustrative examples have been worked ou t

w herever it w as thought they would be help fu l .

The commercial and operat ive sides of the subj ect have re

ceived due attention, since no broad grasp of any important en

gineering subj ect can be had by viewing it solely from the stand

point of the technic ist . Under this heading may al so be classed

the treatment that i s given of high-vacuum condens ing systems,

which it i s general l y admitted cause engineers more trouble than

the turbines themselves .

Other reference to the contents seems unnecessary except tosay that the descripti ve part of the text w as intended to be comprehensive

,but free from padding . The author wishes to express

hi s appreciation for ass istance rendered and information given by

many engineers and fri ends ; to the publ ication departments of the

several turbine manu facturing compani es for material so courteously suppl ied ; and to techni cal periodical s from which information has been drawn and to which credit has been given at the

proper places th roughout the text . The author i s especial ly indebted to The Industrial Press

,publ i shers of M achinery , for p er

mission to use matter and engravings that have appeared in thecolumns of that j ournal .

L . G. F.

Bratt leboro,Lt January, 1 907.

CONTENTS

CHAPTERI. STEAM TURBINE PRINCIPLESImp ulse and Reac t ion—Essential Features of the Turbine—HowS team and Water Turbines Difi'er—Difl’erence betw een Turbinesand Piston Engines—Steam Nozzles—Distinction betw eenImpulseand Reaction Turbines—Steam Turbine Typ es .

CHAPTERII. EARLY STEAM TURBINE PATENTS

A Rev iew of the Essential Claim s ofImp ortant Turbine Patents .

CHAPTERIII. SIM PLEIM PULSE TURBINESThe De Laval Steam Turbine— Sp ec ial Ap p lications of the De

Laval Turbine.

CHAPTERIV . THE PELTON AND S IM ILAR TYPES

Rateau’

s Simp leImp ulse Wheel —Riedler-Stump f Turbine—Richards

’

Design—The Kerr Turbine.

CHAPTER V . COM POUNDIM PULSE TuRBINEs—MULTICELLULARThe Rateau Turbine—The Zoel ly Turb ine—TheHam ilton-Holzw arth Turbine.

CHA PTER VI. COM POUNDIM PULSE TURBINES (Continued)The Curtis Turbine—The Riedler-Stump f Turbine.

CHAPTER VII. REACTION TURBINEs .

Parsons Turbines—The Westinghouse-Parsons Turbine—TheBrow n-Boveri Turbine—The Allis-Chalmers Turb ine.

CHAPTER VIII. M ISCELLANEOU S TURBINES AND A PPARATU S .

Com b inedIm p u l se and Reaction Turb ines—The Br it ish -Westinghou se T urb ine—T he Su l zer Brothers T urb ine—T he Lindmark

T urb ine—The Rateau S team Accumu lator System .

CHAPTERIX . STEAM TURBINE PERFORM ANCE—COM PARISON S W ITHTHE STEAM ENGINE .

Conversion Of Pow er Units—Effic iency of Engines and Generators—Calculations involv ing Effic iency—Thermal Unit Basis of Per-i

formance—Tables of Tests on Turb ines—Comparison o f Turbinesand Engines .

CHAPTER X . STEAM TURBINE PERFORM ANCE (Continued)Characteristics of Turbines under Variable Loads—Results of

Turb ine and Engine Tests under Variable Loads—Effect o f

Vacuum up on Economy—Effect of Superheating—Economy w ith

Change in Sp eed .

vi. CONTENTS

CHAPTER XI. EX PERIMENTS ON THE FLOW OF STEAM

Nap ier’

s Ru les—Exp eriments of Brow nlee, Kunhardt , Kneass,Rosenhain, Rateau, Gutermuth and Others .

CHAPTER XII. STEAM ANDITS PROPERTIESNotation and Definit ions—Heat Values for Steam and WaterTemp erature-Entropy Diagram s—Characteristic Equations for

Adiabatic Exp ans ion—Sp ec ificHeat of Sup erheated Steam —Sp ecific Vo lume of Sup erheated Steam .

CHAPTER XIII. CALCULATIONS ON THE FLOW OF STEAM 266

Equations for Saturated Steam—Calculations upon SuperheatedSteam—Steam Nozzle Design—Practical Considerations .

CHAPTER XIV . TURBINE VANES 284

The Vanes ofImp ulse Turb ines—Calculations of Effi c iency and

Elements of Veloc ity Diagram s—Diagram for Pelton WheelDiagrams for Comp oundImpulse Turbines—D iagram s for Re

action Turbines—Tests on Buckets and Channels .

CHAPTER XV . BODIES ROTATING ATHIGHSPEEDAction OfHigh-sp eed Bodies—Methods of Balanc ing—Stresses inRotating Bodies .

CHAPTER XVI. NOTES ON EFFICIENCY AND DESIGN

Calculation of Effic iency—Losses in Turb ines—Temp erature-Eutropy Diagram Ap p lied to Stage Turbines—Examp le in Design.

CHAPTER XVII. THE COMMERCIAL ASPECT OF THE TURBINERelative Advantages Of Turbines and Engines—Relative Sp ace

Occup ied by Turbines and Engines—Space Required for Condensing Ap p aratus—Comp arative Cost of Turbine Outfits and TheirMaintenance—Turbine T roubles—Blade Erosion.

CHAPTER XVIII. CARE AND MANAGEMENT

General D irections—Op erating the De Laval Turbine—Op eratingthe Parsons Turb ine—Op erating the Curtis Turbine.

CHAPTER XIX . CONDENSING APPARATUS FORHIGHVACUUMGain fromHigh Vacuum—Surface Condenser Plants—Jet andInj ector Condensers—Data up on Condenser Performance.

CHAPTER XX . THE STATUS OF THE MARINE TURB INE .History—Atlantic Liners Fitted w ith Turb ines—Turbine Boats of

the Cunard Line—Comp arison betw een Marine Turb ines and Re

c ip rocating Engines .

STEAM TURBINESCHAPTER I

STEAM TURBINE PRINCIPLES .

The steam turbine , l ike the water turb ine , i s based on the prin

c ip le that when a flu id i s in motion its energy wil l be con

verted into mechanical work,i f the flu id impinges on moving

vanes which change its direction o f fl ow and reduce its velocity:

It differs from the water turbine in important particulars , how

ever, due to the facts that water and steam have very different

properties and that the steam turbine , l ike the steam engine , i s

a heat motor and must uti l ize the heat energy of steam .

The Princip le of the Water Turbine i s i l lustrated in Fig . 1 ,

w hich shows the effect o f a curved vane upon a stream o f water .

F ig . 1 . Effects of S tationary and M oving Vanes upon a

S tream .

The l ines w,R

,V

,etc . ,

represent velocities and also show direc

tion of motion. At A the vane i s supposed to be stationaryand the stream glides upon it tangential ly , Without shock , at a

2 S TEAM TURBINESvelocity R

,and l eaves it tangential ly at the same velocity . The

only effect of the vane is to alter the direction of flow .

I f the vane now be given a veloc ity 20 in the direction shown, a

particle of water start ing‘

at a‘

w ill reach po int c by the t ime the

tip of the vane has traveled from a to b . The direction and ve

loc ity of the stream relative to the vane wi ll then be represented

by,

the l ine bc, and i t i s evident that the w ater wil l meet the vane

with cons iderable sho ck and in thi s instance wi l l fai l to touch it

anywhere except at the tip .

To bring about tangential action of the j et while the vane i s

moving,which is essential to smooth and economical running ,

*

either the nozzle must be given a motion 70 , or else the direction

and velocity o f the stream must be changed'

to V,the resu l tant

o f R and w . ( Shown at B . ) The motion of the water relat ive

to the moving vane wi l l then be the same as i ts motion relative

to the stat ionary vane be fore the change w as made . S imilarly ,in leaving the vane the motion r

,relative to the vane i s tangential

and equal to R. But as the stream and vane each has the

velocity 10 at the exi t,the absolute or real veloc ity of the stream

will be the resu ltant of r and w ,or TAT The difference between

V and 7/ represents that part o f the stream veloc i ty which,neg

l eeting losses , has been trans formed into wheel velocityIt ) . We

thus have

*This is the theo retical s tatem en t- o i the cond it ions .

-l-The subj ect of re lative mo tion c an b e made clear by the s imple device herew i th .

Tw o p i ns , 0 and b, are drivenIn a board and a co rd is s tretched betw een them . P lace

an oblong piece o f paper under the cord in the po si tion show n and, ho ld ing it sta

t ionary w i th one hand, draw a d iagonal l ine across the paper by fo l low ing the co rd w iththe po int of a penci l . Remove the p aper and c d ( at the right) w i l l be the l ine draw n .

Again place the paper in i t s former po s i tion and run the penci l along the co rd , at thesame time pu l l ing the paper to the r ight ju st fas t enough so that w hen the penci lreaches the Oppo s i te edge o f the paper po int c w i l l come oppos i te arrow d m arked on

the board . The l ine traced th is time w i l l b e c k .In bo th cases the penci l fo l low edthe same cour se, relative to the board , bu t it s mo tion rela t iv e to the pap er w as no t thesame w hen the paper moved .In l ike manner the m otion , r ela tii '

e to the f ame, o f t he

j et o f w ater in Fig. 1 is d ifferent , w hen the vane m oves , from w hat i t is w hen the vaneis stationary .

STEAM TURBINE PRINCIPLESEnergy given to the moving vane by each pound of water

l/ / 2

2In thi s case , therefore , the effect of the vane is not only to changethe direction of the stream , but toreduce its veloci ty , by which

means its kinetic energy is changed into mechani cal work at the

turbine wheel .Imp u l se and Reac tion.Impu lse and Reaction of a J et—The dynamic pressure uponthe vane of a turbine , which causes the rotation of the wheel , i s

the resu lt of the impuls e and reacti on of the imp inging j et . Ac

cording to older writers in mechanics , an impu lse is a force act

ing in a forward direction and a react ion i s the equa l and Opp os iteforce—a force acting in a backward direction relative to the

impu lse . These are the commonly accep ted meanings , although

strictly an impuls e i s no t a force in the sens e of be ing a

push or a pu l l , but i s a term used to express the same meaningas momentum , when a force acts for a very short time

, as whenone bo dy gives another a sharp blow . A reaction i s properly defined as a force .

GF ig. 2 .Impu lse. F ig . 3 . Reaction.In F ig . 2 is a tank from which w ater i ssues through a nozzleand impinges against a flat surface capable of moving horizontally—in this case the face of a plank susp ended so that i t i s free to

4 S TEAM TURBINESswing. When the water strikes the plank the latter will swingto the right under the pressure due to the impu ls e of the j et .

As the j et leaves the nozzle , however, i t exerts a reaction agains t

the tank , w hich i s equal and oppos ite to the force due to the im

pu lse Of the j et . This may be i llustrated by suspending the tank ,as in F ig. 3 , so that i t i s free to swing , when i t wi l l move to the

left,owing to the reaction Of the j et .

WEIGHTFig . 4 . M easur ing Pressure d ue t oImpu lse.

The explanation of the reaction i s that there i s no pressure

on that part of the tank where the nozzle i s s ituated and the un

balanced pressure on that part d irectly Opposite to the nozzle will

therefore tend to move the tank in a direction oppos ite to thatin which the water i s escaping . The faster the water escapes

,the

greater the pressure requ ired in the tank to give the water i ts

velocity and hence the greater the unbalanced pressure which we

cal l the reac tionf‘<Impulse and Reaction Upon Curved Vanes .—In F ig. 2 the ve

loc ity of the j et i s suddenly checked when i t strikes the plank ,

and there is more or less comm otion of the parti cl es of the flu i d ,causing loss of energy . This i s always the cas e when there i s

impact of the particles against a surface and i s to be avoided byus ing a curved surface so placed as to change the direction of

flow gradual ly without shock or jar, as previously explained .

*The reaction is no t determined so lely by the pressure in the tank . Since action andreaction are alw ays equal , t he reaction u pon the tank mu st b e that due t o the mom en

tum o i the j et . The velocity and w eight o f flu id d ischarged , how ever , and hence the

momentum , depend in part upon the shape of the nozz le, and it s effec tive area, w hichis never exactly equal t o the measu red area, ow ing t o the coefficient of contraction o fthe jet .

S TEAM TURBINE PRINCIPLES 5

Such an arrangem ent i s shown in Fig . 4 , where a nozzle N i s discharging against a plate D attached to the rod R. The rod issupported by gu ides and together with the plate can move longi

tudinal ly. The pressure of the j et against the plate is balanced by

the weight W supported by a cord pass ing around the pul ley Pand attached to the rod R. The plate D is so shaped at the center

as to gradual ly gu ide the particles of water through an angle of

90 degrees , thus avoiding the impact present in Fig. 2 , and the

particles leave the plate in a direction paral lel with its face . It is

evident that the pressure against the plate i s due solely to the

impu lse of the j et and that the reaction of the water in leaving

the plate has no tendency to move the plate longitudinal ly .In Fig . 5 the case is different .Here the water strikes a curvedsurface and i s turned back upon i tsel f through an angle of 1 80

degrees . This surface is therefore acted upon by two forces , both

WEIGHTFig . 5 . M easuring the Combined Effect ofImpu lse and Reaction .

tending to move it to the right . The first i s that due to the impulse

of the j et,just as in F ig. 4 , which acts unt i l the central point C

of the curved surface is reached ; and the second is the reaction

of the j et,which begins where the j et starts to flow backward

and continues up to the edge where it discharges . These forceswould be equal i f there were no frictional or other losses , and

it would requ ire a weight, W,just twice as heavy as the weight

in the first example to balance the end thrust .

6 S TEAM TURBINESEssential Features of the Turb ine.How S team and Water Turbines Difi er.

—In a steam turbine

the energy of the steam , due to its m otion, i s converted into me

chami cal work at the turbine wheel by the use of curved vanes , as

outl ined for water turbines . There are t w o important dist inc

tions between steam and water turb ines however, w hich i t wi ll

be advi sable to refer to here . These are

First, provis ion must be made in the steam turbine fo r con

verting the heat energy of the steam into kinet ic energy , or the

energy of mot ion. To accompl ish this the passages and nozzles

of the steam turbine must be designed to control the expans ion of

the steam in a w ay to augment i ts velocity .In the De Lavalturbine the expans ion i s effected in an

“expanding nozzle” which

directs the steam j et against the blades of the wheel . The wal l s of

the nozzl e diverge in the direct ion of fl ow of the steam so that

its outlet area i s larger than its inlet area,whereas ,

in a water

nozzle the outlet area wou ld be smal ler than the inl et area.

Second , the steam turbine must be adapted to the high veloc

i ties of steam,which have no paral l el in hydrau l i c work , although

veloc i ti es of over 300 feet a second are met with in water p ower

plants on the Pacific S l ope . The enormously high velocity with

which steam flows from an orifice Often exceeds the speed of a

rifle bu l let . The new Springfield rifl e adopted by the Uni ted

States Army gives an init ial velocity to its bu l l et of feet

per second , or over 26 miles a minute , and thi s i s almost exact lythe velocity with which steam at 50 pounds gauge pressure wou ld

i ssue from a nozzle of the best shape when discharging into theatmosphere .In s ingle-wheel impu l se turbines , operat ing und erh igher pressur es and with a condenser veloci ti es of to

feet p er second , or even mo re , are at tained . The problem of dealing with a flu i d capable of attaining such incomprehensible

velociti es cal l s for serious cons ideration . By some means or

other the rotating elements must be kep t wi th in the speed of

safety to guard against rupture of material , cutting of bearings ,etc . , and at the point w here power i s to be used the speed must bewithin the practical l imits of conveni ence .

The Successfu l S teaen Turbine—It will be evident from the

S TEAM TURBINE PRINCIPLESforegoing that the success fu l steam turbine must accompl ish thethree following resu lts

First , as much of the heat energy of the steam as pos s ible must

be converted into kinetic energy .

Second , the wheel must be capable of u ti l i z ing the kinet icenergy of the steam in an efficient manner.

Third , the apparatus mus t run at a moderate sp eed at the point

where i t del ivers its power, and all parts must be kept within the

speed of safety .

The S team Turbine Compared w i th the S team Engine—Thefundamental p rinciple in any economical steam motor

,whether

turbine or piston engine , i s that the expans ive force of the steammust be uti l ized . The direct—acting steam pump , although serving

a very usefu l purpos e,i s one of the most wastefu l steam users in

existence . Steam is supplied to the cylinder at boiler pres sure

throughout the whole stroke . It forces the piston ahead because

of the static pressure back of i t in the boi ler, in the sam e manner

that water wou ld do i f the steam cylinder of the pump w ere con

nec ted to a c ity water main . Such expansion as occurs takes

place in the boiler at constant temperature .

Steam ,however

,i s capable o f much better use than this , be

cause it i s suppl ied with a store o f heat energy which has the

power to make the steam in the cyl inder expand and push the

piston forward,after al l communication with the boiler has been

cut off .In an engine working expans ively steam ' is admitted at

boiler pressure unti l the point o f cut—off i s reached . Up to th is

event the action i s the same as in the steam pump ,but during the

rest o f the stroke the piston i s pushed ahead as a resu lt o f the heat

energy o f the steam encased in the cyl inder .In the steam turbine the process of the expans ion eng ine is du

plicated,except that the fl ow of the steam is continuous instead

of intermittent . It w as explained that steam is first forced into

the engine cyl inder by the pressure in the bo i ler and then i s al

l owed to expand in virtue of its ow n internal heat energy .Inthe turbine the steam is continuous ly pushed into the nozzle bythe higher pressure at the inlet , and during the passage throughthe nozzle it expands continuously because o f its internal energy .

E ach particl e, as i t expands , pushes the particles ahead o f i t for

8 S TEAM TURBINESward at a faster rate and so increases the v elocity of flow .

Al though the turbine and piston engines are different in outward

form,they are equ ivalent in the thermodynamic acti on .

The difference in the form of the turbine and engine i s due

to the fact that the turbine i s des igned to operate by changingthe motion of flowing steam , on the principle of the water turbine ,while the engine i s des igned to operate by the direct pressure of

the steam . The turbine i s a velocity mo tor and the steam engine

a pressure motor.

*

S team Nozz les .

The S tudy of S team Nozz les of GreatImportance.—S ince a

turbine Operates by changing the motion of flowing steam , atten

tion must be given to the proportions of the passages through

which the steam flows .In the De Laval and some other turbines ,the steam flows through nozzles which direct it against the blades

o f the rotating wheel .In other machines it flows through pas

sages between gu ide vanes which form what i s virtual ly a group

of nozzles .In sti l l ot hers of the Parsons type bo th the stationarygu ide vanes and the blades of the wheel have the same funct ions

that a col lection Of nozzles placed side by s ide would have.

Whatever the arrangement of the passages of a turbine , throughwhich the steam passes , thev may be

“

regarded as steam nozzles ,provided the steam fil l s them completely , leaving no air spaces ,just as water fil ls completely al l the space in a water nozzle

used in connection with a hose pipe .In order to understand the

action of steam flowing through the pas sages of a turb ine , i t i snecessary to study its action in flowing through nozzl es of d i fferent shapes , and the principles discovered may then be appl ied in

p roportioning t he ducts or passages of the turbine .

“It mu st no t be imagined that the dr iv ing force in a turbine is the s tatical s teampressu re. Al l turbines der ive their pow er from changes in the mo tion of the w orkingflu id The pressure in a turbine might b e infin i te, y et unless the steam possessed the

requ i si te velocity the tu rbine w ou ld not ac t . On the o ther hand , i f the steam possessedthe requ is i te velocity then the pressure might be—ii that w ere practicable—abso lu telyzero , and yet the turbine w ou ld w ork qu i te normal ly. The statical steam pressure actsequal ly on the back and front of each vane, and hence produ ces nei ther end thrustnor ro tation. As the steam passes through the turbine the d irection of it s motion isal tered by the vanes , and hence these vanes mu s t exer t force on the steam .It is thisforce, or , rather, the correspond ing reaction of the steam on the vanes, w hich cau ses ther o tation and w here, as in the Parsons turbine, the vanes are not symmetrical , an end

thrust. -From “The Theory Of S team Turbines , by Frank Foster , in The Engineering

Review , London, May , 1 904 .


Flori) of S team Through Nozzles —The i llustration, Fig . 6 ,

shows the effects of nozzles of different shapes upon steam flowing

through them. The general form of the j ets i ssu ing from thenozzles is substantial ly as shown by Strickland L . Kneass

,engi

EXPANDS TO ATMOSPHERIC PRES SUREHERE

PHERIC PRESSURE

ATMOSPHERIC PRES SURE

5 8 % OR MORE

ATMOSPHERIC PRES SURE

F ig . 6 Types of S team Nozz les and the Shapes of Jets Discharging from them .

10 S TEAM TURBINESneer of the inj ector department , W i l l iam Sellers 81. Co . ,

inc . ,

Philadelphia,in his “Practice and Theory of the Inj ector.

”In F ig . 6 , five styles of mouthpieces are i l lustrated , and with the ,

exception of No . 5 , steam is supposed to be flowing from some

h igher pressure down to atmospheri c pressure .In No . 5 , steam is

assumed to discharge into a closed c hamber in which the pressure

is maintained at the “cri ti cal” pressure referred to bel ow . The five

styles of mouthpieces are as fol lows :

1 . Short cyl indrical tube , s l ightly rounded inl et .

2 . Nozzle with converging wal l s— such as wou ld be used to

produce a sol id water j et .

3 . Diverging nozzle with rounded inlet and straight taper

s ides .

Jr . Diverging nozzle , rounded inl et and diverging s ides , curved

as -shown.

5 . Same as NO . 1 .

6 . Orifice in a thin plate .

W hile the nozzles shown are supposed to be of a circu lar cros s

section,i t i s evident that it i s the area of the section which is Of

importance and not the shap e of the section . A rectangular

shaped section wou ld answer as well as a c ircular section,for all

practical purposes,and in fact is o ftener u sed for the steam p as

sages between the vanes Of turbines .

A pecul iari ty of the flow o f steam through nozzles i s that the

absolute pressure in the throat o f the nozzl e does not vary greatlyfrom 58 p er cent of the absolute ini tial pressure , unl ess the abso

lute pressure at discharge shou ld be more than 58 p er cent o fthe ini tial pressure . I t can be shown that theor eti cal ly th is shou ld

be the case , although it i s known from tests that the pressure maybe somewhat mo re or less than thi s . The pressure of 58 p er cent o f

the ini tial pressure i s call ed the crit ical pressure and has an important bearing upon the sub j ect of the flow of steam .

Nozzles w ith Parallel Wal ls or Converging Wal ls —Many ex

periments have been conducted on the flow of steam throughnozzles l ike Nos . 1 and 2 and i t i s found that when discharging

into a med ium which has not mor e than 58 p er cent of the init ialpressure ( equal to the cri tical pressure) the veloci ty of discharge i snot far from the constant value of feet per second and the

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12 S TEAM TURBINESthe ini tial pres sure. Beyond the throat the cross - sectional area in

creases just sufficiently to accommodate the rapidly increas ing

specific volume of the steam ( space occupied by uni t weight)which occurs as the pressure drops . When thus proport ioned ,the wal l s restrict the expans ion of the steam in a lateral d irection ,

bu t al low free expans io‘n longitudinal ly . Such a nozzle i s known

as an expans ion nozzle and by i ts use the ful l expans ive force of

the steam is uti l i zed and a very high velocity of ou tflow attained .

A no zzle l ike No . 4 has been found to give sl ightly better resu lts

than one with straight , conical s ides , l ike No . 3 , but i t'

i s more

difficu l t to construct .

Complete expans ion may be obtained in a straight or converging

nozzle by arranging so that the pressure o f the medium into which

it discharges shal l not be l ess than 58 per cent of the higher pres

su re . Under thes e condi tions the steam will i ssue from the nozzle

in straight , paral lel l ine s , or nearly so , since_

there i s no excess

internal pressure to make the j et bu lge , and all the expans ive

force of the steam will be expended in giving velocity to the j et .In the illustrat ion,.

nozzle No . 5 i s intended to show that complete

expans ion may be real ized in a straight nozzle discharging into

a tank in which the pressure i s 58 per cent of the higher pressure .

Orifice in Thin Plate—When steam issues from an orifice‘

in

a thin plate , asIn nozzle No . 6,the swel l ing of the ~j et after

l eaving the Opening is even more marked than in the first two

nozzles shown. This i s b ecause the internal pres sure of the steam

is h igher in the orifice in the plate than at the mou th of the tubesin the first two examples . The steam has an opportuni ty to ex

pand more ful ly before leaving the tubes than i t doesIn pass ingthrough an orifice in a th in plate .

D istinc tion B etw eenImp u lse and Reac tion Turb ines .Impulse S team Turbine—Both water and steam turbines are

grouped into two general classes know n as impu lse and reaction

turbines , or better,into action and . react ion turbines . These

terms are somewhat mis leading ,however

,because all practical

turbines op erate both by the action and reaction of the working

flu id and i t wou ld be cl earer to designate the two types in someother w ay .

S TEAM TURBINE PRINCIPLES 13In Fig . 7 i s a s imple impu ls e turbine having curved vanesagainst which the j et of steam impinges . The expans ion of the

steam is completed within the nozzle, and there is no expansi onin passmg through the wheel passages . The pressure betweenthe vanes is the same as the pressure within the cas ing in w hichthe wheel runs and the steam flows freely through the wheel

passages in virtue of the kinetic energy given i t in the nozzle. The

wheel i s driven ahead , first by the pressure due to the impulse ofthe steam and then, after the vanes have reversed the direction offlow

,by the reaction of the steam .

VANE

Fig . 7. Usua l T yp e ofImpu lse F ig. 8.Impu lse Wheel . in w hich thereWheel . is no Reaction.In Fig . 7 , N

’ i s the nozzle,which may or may not be a diverging

nozzle , according to the pressure against which it is discharging,and W is the wheel . W i th the vanes constructed as shown , there

would be spaces S S not fil led by the steam , since the area of thepassages at these points is greater than at the entrance and exi t .

Some manu facturers , however,make the blades thicker at the center

than near the edges , to maintain a constant area and so avoid pos

s ible eddy currents . Although a so-cal led impul se wheel , i t wil lbe evident that thi s wheel acts bot h by impu lse and reaction. The

chief characteri stic o f this type is that the expans ion occurs whollyin the nozzle or gu ide passages , as the case may be.

14 S TEAM TURBINESWhat wou ld s trictly be an impu l s e wheel i s shown in F ig . 8,

Where the vanes are so curved that wi th the w heel held stationarythe steam wou ld leave them in a direction paral lel with the shaft .

The w heel i s therefore prop elled solely by the pressure against the

vanes due to the impu ls e of the -s team , and wou ld'

be ineffi cient

because the steam w ou ld have a high res idual velocity when i t

le ft the wheel . Such a Wheel i s on the principle -o i the stationaryvane in F ig . 4 , against which the water exerted only hal f the pres

sure that it did when the force of reaction w as taken advantage of .

Reac tion S team Turbines —In Fig . 9 i s the simplest type of

F ig . 1 0.

Tw o forms of Reaction Wheel .

reaction wheel .Here the steam enters the trunni on T,flowing

radial ly outward through the two hollow arms A A,unti l i t dis

charges through the nozzles N N. The arms therefore rot ate ina direction opp osi te to that in which the

‘

steam escapes, and

’

are

driven ent irely by the reaction of the steam . The chief difficultyof thi s type of whee l is the excess ively high speed o f rotat ion .

Supposing the wheel to be p erfectly free to move,i ts momentum

would be equal to the momentum of the escaping steam .The

velocity of the arms wou ld theoretical ly be less than the ~velocityo f the steam onlv in so far as the ma ss o f the arms w as greaterthan that of the steam .

S TEAM TURBINE PRINCIPLES 15In Fig. 10 i s shown a more pract ical form of reactionwheel .Here there is first the impact o f the steam against the buckets ,but the expans ion in the nozzle is only partial and the steamexpands still mo re and acqu ires additional velocity in flowing

through the wheel , provis ion being made for thi s,i f neces sary ,

by having the passages diverge in the direction of the flow , as

shown at V. The steam therefore reacts upon the wheel when i tleaves the vanes as a resu lt of the energy acqu ired in the wheel

itsel f, and this feature gives it the name of a reaction wheel . It

wil l be seen , however , that the wheel acts bo th by the imp u lse andthe reaction of the steam just as in the case of the impul s ewheel . The dis tinc tion betw een the tw o is that in the impu lse

w heel the expans ion of the s team is comp lete w ithin the nozz le

and in the reac tion w heel it is not comp leted until after it enters

the w heel passage. I f i t were possible to attach a steam gauge to

one of the spaces between two wheel vanes , it wou ld show a

pressure equal to the pressure -

of the medium in w hich the w heel

w as turning in the case of the impulse turbine and a pressure

higher than that of the surrounding medium in the case of thereaction turbine .

Shape of Vanes inImpu lse and Reaction Turbines . The il lus

Figs . 1 1 and 1 2 , represent the gu ide vanes and moving

Fig. 1 1 . Shape of Vanes inImpulse Wheels .

vanes of impu lse and reaction turbines respectively .In impulseturbines the wheel vanes are symmetrical or nearly so .In Fig .

1 1, G G are the guide vanes which , i f the fal l of pressure is small ,

need not provide diverg ing passages The w heel vanes at VIhav e both faces paral lel , and the vanes at V are thicker at the

‘ From a p ap er by M . J . Rey read be fore the Soc ie'

t ié deIngene’ u irs Civi ls deFrance. March. 1904 .

STEAM TURBINEScenter than at the edges , forming passages of a uni form width

,

as explained in connection with F ig. 7 .

F ig . 1 2 . Shape of Vanes in Reaction Wheel s .In Fig . 1 2 G G are the gu id e vanes and V V the wheel vanes

showing in a general w av the contour that must be obtained in

reaction turbines .

Steam Turb ine Ty p es .

The S imp leImpu lse Turbine—The simplest possibl e arrange

ment o f the steam turbine is shown in the diagramatic sketch ,Fig . 1 3 , where N i s a nozzle directing a j et of steam against the

vanes of a s ingle wheel W inclosed in a casing . This i s l ike the

De Laval turbine, w hich must uti l ize steam flowing with a velocity

Of to feet a second , and the peripheral velocity of the

wheel shoul d be nearly one-hal f o f this to ut i l iz e the total energyof the steam .In the De Laval turbine the peripheral veloc i ty i sfrequently as high as feet a second or as high as safety will

permit with the strongest material s for the rotating member.

Such high velocity of rotation makes i t necessary to use speedreducing gearing .

Princip le of the Compound Turbine.—In turbines of large

s ize i t i s desirable , and in fact nec essary ,to avoid such high speeds

of rotation and to do away with the reducing gears , and th is

i s accomplished in s everal ot her types of turbines through com

pounding . A compound turbine may be bu i l t either for wateror steam , and it i s entirely po ssible for a water j et to flow at such

great veloc ity as to make compounding desirable for a waterturbine . The principle of compounding is very simple and is thusexplained in Bodmer

’

s text bo ok “Hydrau l i c Motors”I f a turbine i s al lowed to run at a much lower speed than at


the best, the water l eaves the bu‘

ckets with a very cons iderable

ab solute velocity, and there is consequent loss from unutil ized

energy. This energy m ight , however, be useful ly employed indriving a second turb ine , the water, after l eaving the first , beingdeflected by a set of stationary gu ide vanes to cause i t to enter the

SHAFTVELOCIT

ESSURES

Fig. 1 3 . S impleIm Fig . 1 4 . CompoundImpu lse Fig . 1 5 . CompoundImp u lsepulse—De Laval —Ried1er-S tumpf Type.

—Curt i s Type.

Type.

S team T urbine Types .

second wheel at the proper angle . Both turbines could be keyed

to the same shaft and their speed would be much lower than that

of a single turbine driven by the same head of water and util izingit to the same extent . This arrangement wou ld constitute a com

pound turbine and i t i s clear that , instead of two wheels only ,

three or more m ight be employed in the same w ay , the speed being

18 S TEAM TURBINESlower the greater the numb er of w heels . The only obj ect in us ing

a comp ound turbine in pre ference to a s ingle one wou ld be to

reduce the speed in cas es where the head w as great and high

velocity of rotation inconven i ent or impracticable .

CompoundImp'

u lse Turbines .—There are different met hod s of

taking advantage of th is principle o f compounding , the s implest

one of which i s shown in Fig . 1 4 . .Here steam flows through the

expans ion nozz le N which reduces its pressure to that of . the

medium in. w hich the turbine w heels rotate . The steam then

imp inges against the vanes of the whee lIV1. I ts d irection i s

then reversed by the gu ide vanes G and i t next impinges against

the vanes of w heel W2 ,on the same shaft S as the other wheel .In thi s example the action i s the same as out l ined above by Bod

mer, and the steam ,having acqui red its velocity in the nozzl e ,

flows through the passages of the turbine in virtue of i ts inertia.

This plan has been carri ed out in the turbines of Pro fessors

Ried ler and Stumpf , al though the arrangement of the parts i s

d ifferent .

At the bottom of the engravings Figs . 1 3 to 1 7,are diagrams ,

the upper ones of which show the change in velocity and the

lower ones the change in pressure of the steam in the diff erent

steps of its progress .In the first i l lustration the veloci ty o f thesteam increases from a to b , and as i t flows through the nozzle

most of this velocity i s absorbed by the wheel,the height of the

line c d indicating the res idual or unused velocity o f the steam as

i t l eaves the w heel . The lines 1 -2 and 2-3 show that the pressuredrops in the nozzle bu t does not change after the steam strikes

the wheel .In the second i llustration,Fig . 1 4 , the velocity increases in the

nozzle , but in the gu ide passages where no work is done it remains constant , or would do so except for fri ctional l osses , and

final lv in the last w heel the velocity drops to the point e. The

pressures , however , indicated by 1 2-3 are as in the previous case .

Proportions op assages in a Compound Turbine—It wil l benoticed that the height x of the passage through the first wheelW1 ,

in Fig . 1 4 , i s the same as the diameter o f the nozzle,wh i l e

the height of the passages in the gu i de G and the s econd wheell/V2 i s sl ightly greater. T

'

he draw ing i s made in this w ay to


20 S TEAM TURBINES

VELOCITl-ESPRESSURES

PRESSURES

F ig . 1 6 . CompoundImpu lse—Mu lti F ig . 1 7. Compound Reaction—Parcel lu lar or Rateau T yp e. sons Typ e.

S team Turbine Types .

in which the pressure i s stepped down i s cal l ed a s tage, and i t is

know n as a mu lt i-stage turbine .

The S implest form of stage turbine is shown in F ig. 1 6 , which

i l lustrates the principle o f turbines l ike the Rateau and Zoel ly.

This i s in effect a seri es of simple turbines l ike that of F ig. 1 3,

each of which i s in a separate compartment . There are usual lyenough compartments s o that the steam does not have to dropmore than .4 of its ini t ial pressure when flowing from one com

partment to the next, and diverging nozzles are not requ ired .

Steam enters through the gu ide passages N 1 and expands down

STEAM TURBINE PRINCIPLES 21

to the pressure in the first compartment . The pressure withinthe wheel passages is the same as without and to insure a uni formpressure in all parts of the compartment holesHare som etimesmade through the wheel disks . The second set of guide passages N 2 has a larger area than the first to accommodate theincreas ed volume o f the steam and the same is true of the suc

ceeding passages . The velocity d iagram below shows that thereis a smal l unus ed res idual veloc i ty in each case and the pressurediagram shows how the pressures are gradual ly stepped down .

Compound Reaction Turbines—We now come to the reactionturbine of w hich the Parsons turbine i s the most prominent rep ;

resentat ive.In this type the steam expands continuously fromboiler pres sure to vacuum . There are al ternate rows of gu idesand vanes , the latter being attached to the drum on the turbineshaft. The steam flows through a fixed ring of directing blades

N onto a revolving ring of s imi lar blades W and so on, i ts pressure being reduced a f ew pounds , say tw o or three , at each step .

The steam final ly discharges at E . I t wi ll be seen that i f thewheel were fixed and the steam al l owed to fiow . through theturbine the p assages thems elves taken together would constitute

a large expans ion nozzle , and the flow of the steam w ou ld increase from beginning to end as shown in the upper diagramplaced beneath the section of the w heel .

Let the wheel rotate, how ever, and the velocity acqu ired in

pass ing through the firs t gu ide ring wou ld be partial ly absorbedby the first w heel

”

; and .the velocity acqu ired in the next ring o f

gu ide blades would be part ial ly absorbed in the second w heel ,and so on. The l ine o f velocities , there fore , wou ld be representedby a b c d

,etc . , in the middle diagram . The pressure however,

drops gradual ly from beginning to end as represented in the last

This diagram shows that the pressure in the passages of theturbine is maintained higher than the final pressure, which , as has

been explained , i s the characteristic of the react ion principle .In subsequent chapters modifications of these simple types willbe shown

, but what has been gi ven i s bel ieved to be suffi cient toenable the reader to understand the descriptions of the vari ousturbines which follow.

CHAPTER I I

EARLY STEAM TURBINE PATENT S .

I t i s probabl e that the first steam engine w as a tu rbine .InHero ’ s “Sp iritalia, a boo k on pneumatics i ssued in the second or

third century , i s a description of the whi rl ing eol ipile cons i sting

of a smal l hol low sphere mounted on trunni ons , one of which is hol

low for the admission o f steam . The sphere i s caus ed to rotate by

the reaction of steam fl owing from two diametrical ly oppo s ite noz

zles having bent mou thpieces . This i s frequently spoken of as the

beginning of the reaction turbine ; and to Branca,who issued a

w ork ,entitled “

The Machine ,”

publ i shed at Rome in 1 629 ,i s given

credit for the first impu l se wheel . This volume contains an i l lus

tration of an eolipile,in the form of a negro’ s head , placed over a

fire. A blas t of steam proceeds from the mou th and impinges

against the blades of a large wheel whi ch it w as proposed to con

nect by means of cog wheels with a crude stamp ing mill for pu l

verizing drugs . These very early efforts cou ld have been nothing

more than vis ionary schemes,but they are scarcely less imp rac

t icab le than many of the later inventions to be found in the pages

of the patent records . Comparatively few of the steam turbine ihvent ions em body even the first elements of success

,probably be

cause most of those who have directed their attent ion to the sub j ect

have fai led to unders tand either w hat w as requ ired or what meansmust be taken to ac compl ish good resu lts .In selecting from among the great number o f turbine patents

those that appear to have u sefu l featu res, the author has had in

mind the requ irements of the success fu l steam turbine as outl inedin the first chapter, and has no t given space to inventions unless

they seemed to embody at least one ‘

feature that wou l d contribute

toward a practical and operative machine . W i th the exception of*In w r iting th is rev iew t he au thor has draw n on the histor ical mater ial in the

valuable ser ies “Rou es et Tu rbines a Vapeu r , by M . So snow k i , published in the Augu st ,

September , October and November , 1896 , numbers of the“Bu l letin de la Société

d’

Enc ou ragem ent pou r l’Indu s trie Nationale, ” Par i s .He has al so been m ater ial ly

as sisted in his search of the paten t records by the l is t of Engli sh turbine patents inNei lson ’

s treati se, “The Steam Tu rbine” ; and b y a s im i lar l ist o f Un ited S tates p ateh t s

kind ly supplied by M r . Robert A. M cKee, m echanical engineer , s team turbine department , All is-Chalmer s Com pany .

EARLY TURBINE PATENTS 23

a very few patents taken from the French patent records , SpeC1fica

tions o f the inventions ment ioned are to be found either in the

English or in the Uni ted States patent records .

Real and Pic/1 0 11 , 1 82 7.

—This machine operates by impulse and

is one of the earl i est attempts to p roduce a wheel to run at mod

erate speed and at the sam e time util ize a large percentage of the

energy of the steam by the principle of compounding . Certain of

Fig . 1 . Rea l and P ichon Compound Turbine.

the detail s o f the orig inal patent drawing are somewhat obscure ,

but the il lustration has been made to correspond with the text as

nearly as pos s ible . The cylinder A contains a successi on of

disks,B

,which divide the cylinder into compartments . The shaft

F i s turned wi th a seri es of step s up on each of which is carried a

turbine Wheel G,having short radial blades ,H, around its pe

riphery . Steam is admitted from the bo i ler through the pipe 1 at

24 S TEAM TURBINESthe top into the first compartment and flows in the form

'

of j ets

through a series of op en ings , C,against the blades of the first

w heel which runs in the second compartment . The steam nex t

passes through a second seri es of holes in the second disk and im

p inges against the second wheel and so on to the bottom of the

cyl inder,where the steam exhausts through the pipe M . The

shaft and wh ee ls are carri ed by a step bearing and power i s suppos ed to be transmitted through the gears P and Q . The open

ings , C,in the circumference of the disks , B ,

are bored obl iquely ,so the steam will impinge as directly as poss ible against the faces

of the blades . W i th this p lan the pressure wi ll drop only a few

pounds from chamber to chamber, giving the steam a com para

t ively low velocity of fl ow .

Avery Turbine, 1 83I.— The first steam turbine patent to be issued ih the Uni ted States w as to Foster Avery for a reactionwheel of theHero type . S trangely enough , th is i s one of the few

turbine inventi ons that has been developed and put into actual use,and probably i t i s the on ly steam turbine used in commercial work

FE EDGE

I S SUE

2 . Avery Reaction Wheel .

in th is country unti l a cons iderably later date . There were severalof these machines in operation in 1 83 5

,som e of which were used to

drive saw mi l l s near Syracuse , N. Y .In 1 901,Prof . John E. Sweet

contributed a description to the Transactions of the American Society of M echan ical Engineers , accompanying it by a sketch madefrom an original drawing of the Avery wheel

,reproduced m

F ig . 2 .


The arm i s made , with the exception of the end pieces and kni feblades , of tw o pieces of iron brazed together from end to end at

the edges . The openings at the ends of the arms for the steam jetswere by inch . The speed of the tips of the arms w as ,

ofcourse, enormous . M r. Avery states in his notebook tha t the sp eedof the arms of a 7- foot wheel placed upon a locomotive in 1 836

,

which w as put upon a rai lroad near Newark, N. J . , and ended its

li fe in a ditch, w as at one time M y. miles a minute at the p eriphery . A diffi cu lty met with w as the end pressure on the hollowshaft, which w as overcome by running the end of the shaft againstthe edge of a wheel set at right angles . The trouble in Setting upthe packing around the hol low shaft became a serious matter.

Itw as also found that the kni fe edges at the end of each arm werecut away by the steam and requ ired frequent renewal . The noisealso w as very obj

Leroy,—Ih commenting on Avery ’ s invention Prof .

JohnE. Sweet has said that he long had the conviction that expandingnozzles applied to the Avery turbine

, in place o f the plain orificesused , wou ld give the benefit o f expans ion and produce superiorresu lts .

“In a paper presented by John Richards be fore the Technical Society of the Pacificcoast in 1904 and publ ished in the Journal o f the Association of Engineering Societiesfor September , 1 904 , is the fo l low ing account o f the Avery engines , w r i tten byPro fessor Sw eet, a near re lative of M r. AveryIn respect to the history of the

Avery engines , these w ere made 75 t o 80 years ago by Wi l l iam Avery, a local mechanicin Syracuse. There w ere abou t 50 constructed and p u t in u se. One o f the runners

is now in my possess ion ; another , thatIsaw years ago , had a ho l low shaft of perhapsl % -inch bore. The head or runner w as of sw ord shape, the arm 1 by 3 inches at the

center and b y 3 % inches at the end s , the d iameter sw ept being abou t 5 feet . S teamw as admitted through the shaft by means of a stuffing box, passed through the shaft tothe ho l low arms and escaped at a tangential is sue 1A inch by 14 inch , at the rear cornersof each arm , the .ends of w hich w ere stopped by plugs brazed in . Ow ing to the rapidrotation of the arms—1 0 to 1 5 miles p er minu te—the front edges w ere so rapidly cu t

aw ay that replaceable blades made of tempered s teel w ere inserted so they cou ld be

renew ed. The fact that the engine had to be taken to a blacksmith shop every 3 or 4

months for renew al or repairs had more to do w ith it s abandonment than it s lack o f

economy. As to the latter , people w ho knew the facts , or claimed to do 5 0 , said thatw hen they changed t o the common sl ide-valve engines there w as no gain in steameconomy over the Avery engine. Ano ther feature that w orked against the Averyengine w as the stuffing b ox around the shaft, w hich in the hand s of w o rkmen of thatt ime w as ap t to be set u p so as to consume a large part of the pow er in fr iction. Thisw as a natural consequ ence, as the w ear w as rapid . What the resu l t w o u ld have beenw ith a tru ly ground shaft in a metal bush , instead of a tu rned shaft and stuffing box.

making the issues expand ing nozz les and mu l tiple expand ing by 2 or 3 arms in separatecases and connecting to a condenser , is no t know n.It might r ival a pretty good modernengine, i f no t the best. The Avery engines w ere u sed in saw mill s and w o od-w orkingshops o f the time. They had w eak starting p ow er,

'

and did no t need much fo r the

u ses named . They ran at such a fear fu l speed that the reducing mo tion w as a n im

ped imen t. M r . Avery had to employ bands , ,w hich w ere far mo re objectionable than

gear w heels .

26 STEAM TURBINESLeroy i s perhaps the first on record with th i s i dea of the appl ica

tion of the expanding nozzle .He w as a prolific inventor and had

defini te notions about many features now employed in turbines .

Figs . 3 , 4 and 5 show three styl es o f rotating arms that he

proposed for reaction wheels . The nozzle at N is clearly a diverging nozzle , as are also the or ifices in Fig . 5 . It i s uncertain, how

ever,whether he understood the principle of the diverging nozzle

,

because he stat es in one place that a nozzl e in the form of a'

tube,

Fig . 4,will produce a higher steam veloc ity than a funnel- shaped

open ing . This wou ld be true i f the funnel flared too much, as

F ig . 3 . F ig . 4 . Fig. 5 .

LeRoy’

s Reaction Wheels .

seems to be the case . I t i s a curi ou s fact that the author has

learned of recent experiments by a mechani cal engineer who is at

work upon the turbine problem,which show the same resu lt .

When a nozzle flares too much the expans ion of the steam is com

p leted before the end of the nozzle is reached , and the effect of the

d ivergence beyond that point i s to check the flow of veloc ity just asi s the cas e in a water nozzle which diverges .

Leroy w as one of the firs t to propose a compound turbine .Heshows two il lustrat ions of machines— one a reaction and one an

impu ls e turb ine, m which each wheel i s encas ed in a separatechamber .In the react ionturbine steam enters the hollow arms

o f the first wheel through a trunnion at the center and escapes


28 S TEAM TURBINESexperimented on the flow of steam and determined that for

economical resu l ts the peripheral velocity of the wheel must be

very high , and accordingly devised vari ous arrangements for com

pounding with a view to reducing the velocity to a practical rate .In all his compound turbines , however , he adopted the plan of run

ning two or more wheels in oppo s ite directions without stationary

gu ide vanes , as shown in F ig . 6 .Here steam enters through the

nozzle , A,impinging against the blades of wheel C, which rotates

in thedirection of the arrow . The steam then passes through th iswheel and discharges against the blades of a second wheel , E,

ro

tating in the Opposite d irection. Fig . 8 shows how he proposed

to carry the idea sti l l further by us ing several wheels , the alternate

wheels rotating in opposite directions . Sti l l another construction

F ig . 8. Pil b row's M ul ti-Wheel Turbine.

that he proposed i s indicated in Fig . 7 , where the tw o wheel s

rotate on paral lel shafts , as shown, and have incl ined vanes so

located that steam from the nozzl e wil l flow through the vanes o f

both wheels in the direct 1on of the arrows . The buckets are

curved,as in Fig . 6 , and the w heel s , of cours e , rotate in op p osite

directions .

Another interesting invention o f Pilbrow i s i l lu strated in F ig . 9 .

This i s a revers ing turbine arranged with a number of nozzles that

can be shut off or ol

p ened success ively by means of a rotary valve .

The plan of us ingseveral nozzles , which are brought into or out of

action by valves , as used in the De Laval and Curti s turbines ,probably here has its introduction

, and the invention i s of value on

this account . Steam enters the chamber, C,in which is located a


rotating segment that covers or uncovers the nozzle openings ,0 , b, 6 , etc. At A i s the whee l with vanes pointing in one direction

and at B one with vanes in the opposite direction.Hal f the nozzlesconnecting wi th chamber C direct the flow of steam against wheel

A and the other hal f against wheel B . By rotating the segment,

steam can be admitted to either wheel , caus ing the turbine to re

volve in either direction , as desired ; and also the amount of steam

admitted can be adapt ed to the power requ ired . A rotat ing va lveof this description i s not to be advocated as a durable construction.

SEGMEN

Fig. 9 . Pilb row’

s P lan for Revers ing w i th Valve for Contro l ling Nozz les.

Wilson,1 848.

—The inventions of Wi lson rank among the twoor three most important early steam turbine patents . His designsare the forerunners of the present Parsons type .He devi sed several compound reaction turbines m which the steam flowed throughalternating sets of stationary and rotating rings of b lades , expanding gradual ly during its passage through the apparatus . Fig . 10

is a sketch of his most valuable invention . Steam enters at the le ft ,passes through the turbine in a longitudinal direction and exhausts

at the ou tlet at the right . The vanes , a, b and c, are attached to

the drum,D

, and rotate with i t , while d, e and f are stationaryguide vanes . The depth of the vanes increases from inlet to outlet,

30 S TEAM TURBINESW i lson’

s Compo und Turbine.

al lowing for gradual expans ion o f the steam . This is real ly the

Parsons turbine reduced to its s implest elements .

Another type—the radial flow wheel— i s shown in Fig . 1 1 . Here

there are al ternating stationary and moving vanes , and the steam

flows ou twardly through them,at the same time expanding to a

lower pressure .In F ig . 1 2 i s stil l another type in which there i s a s ingle rotating

F1g l l . Wi lson’

s Compound Rad ial-flow Turbine.

EARLY TURBINE PATENTS 3 1

ring o f blades marked B . The steam is expanded and util i zed

upon this one ring o f blades several times in succession by follow

ing a tortuous course back and forth through this ring B . Steamenters at A,

passes through the moving blades to the chamber C,

then returns through the gu ide vanes in this chamber to the cham

ber D ; again it passes through the gu ide vanes to the wheel andinto chamber E then to chamber F

,and so on. These successive

chambers increase in s ize to al low for the increase in the volume of

Ano ther Type o f W i lson Turbine.

the steam as i t progresses through the wheel , until finally it has

passed around the whole circumference and exhausts at the outlet

G. This plan of al lowing steam to act at different points in suc

cession on a s ingle rotating ring of blades , has since been worked

out in various other ways , as subsequent patent specifications show.

Delonchant,I853 .

—The speed reduction problem w as attackedby Delonchant in the same w ay that it w as later by De Laval ; thatis , instead of compounding he proposed to al low his turbine to run

.

at high speed and then used reduction gearing, in the form of the

familiar “grindstone hearing .

” The arbor , B ,o f the wheel , Fig . 1 3 ,

32 S TEAM TURBINESFig . 1 3 . Delonchant .

w as supported on the circumference of anti fricti on wheels , C.Inexplanation he says : “

By the employment of these wheels instead

o f ordinary bearings , not only the rubbing of the first axes wi l l be

replaced by rol l ing frict ion but power wil l al so be transmitted to

the fol lowing part s , without gearing .

”In the i l lustration , A i s the

rotating wheel ; B ,the arbor and at the center i s a steam chest , D D ,

indicated in outl ine only . S team passes from the steam chest

through the passages d d d ; and E is a ring having passages e e e,

used in regu lating the amount of steam flowing through the wheel .

The passages , d d d, are so disposed that by rotating ring E the

passage e e e through the ring wil l be successively cut off from the

steam supply, or el se opened to thesupply . By moving of a

turn one pas sage is closed ; another closes a second passage ,and so on.

Tournaire,1 853 .

—In this y ear Tournaire pres ented to theAcademie des Sciences a paper discuss ing the meri ts of compoundturbines both of the impu lse and reaction types . There is a cop ious

extract from this‘

pap er in the Bu l letin de la Société d ’Encouragement pour l ’Industrie Nati onal e for September, 1 896 , and the factsexplained by him as essential to a successfu l turbine are so inaccordance with modern pract ice as to place him am ong the leading

'


inventors .He says : To overcome the difficulties of high veloc ities the vapor or gas shou ld be made to lose its pressure in a con

tinuous and gradual manner, or by successive fract ions , by caus ingit to react s everal times upon the floats of turbines conven ientlysituated . S ince the differences of pressure are cons iderab le it isnot difficu lt to recognize the necess ity for a large number of successive turbines in order to sufficiently annul the velocity of theflu id j et.In spite of the mu ltip l icity of parts the device must bes imple in i ts action and susceptible of great exactness in construc

tion.

”Tou rnaire bel i eved he fu lfil l ed these conditions by means

of a machine composed o f several wheels , with shafts having thesame axis and driving the wheel which w as to transmit the motion

,

F ig . 1 4 . P lan of Vanesin T ournaire

’

s

T urbine .

by means of pinions . A plan o f the buckets and vanes i s given

in Fig . 1 4,where G G G are the rotating elements and V V V the

stationary elements .He describes the construction of the turbinein detai l

, but these structural features are of l i ttle interest at the

present time . It i s to be noted,however, that he appreciated fully

the necessity for expans ion.He says : “As the vapor wil l expand

in proportion as i t passes from the wheel buckets and directingrings , it is necessary that the passages between them become larger

and larger.

”He also suggests losses from leakage , saying :“A

part of the flu id escaping between the spaces , w hich»i t i s necessaryto leave between the fixed and movabl e parts , will exert no action

upon the turbine -nor will it be gu ided by the directing buckets .

Shocks and eddies wil l be produced at the entrance and exits o f

34 S TEAM TURBINESthe buckets . Again

,The fri ction which the narrowness o f the

channel will render considerable wil l absorb an appreciable part of

the theoretical work .

”As to the structural features he suggests

among other th ings , that“the cogs of the p inions which wil l turn

with great rapidity, shou ld work very evenly withou t shocks andj olts

,and proposes the use o f hel icoidal gears .His turbine

,as

well as some o f the others already de

scribed,i s a vertical turbine rotat ing

on a vertical ax i s .

John and EzraHartman,1 858.

Standing in importance with the inven

tions of W i l son and Tournaire are the

English and American patents of theHartman brothers , from the drawingsof which F ig . 1 5 i s made . The patent

relates to a“mode of obtaining motive

power by caus ing steam or air to im

pinge upon a seri es of chambers with

curved bottoms ranged around a wheel

at o r near the periphery thereof ; and

second ,the general construction and

arrangement of machinery or ap

paratus for obtaining motive power.

”

Fig. 1 5 shows the most important

modification o f the patent,of which

the fol lowing i s the inventor’ s desc ript ion :

“This represents a detai l of the

F ig . 1 5 .Hartman,

s Comp ound third modification wherein we proposeImpu lse Turbine. to employ two wheels , C C1

, bothwheels being fast on one shaft ,I) .

A space i s le ft between the contiguous faces of these wheels for the

reception o f four or more returning chambers , d d , the bottoms of

which are curved in a direction oppos i te to that of the bottoms of

the chambers in the wheels . These chambers in other respects areprecisely s imilar tothose in the wheels and are fitted to a rim which

is bolted or otherw i se secured to the interior of the cas ing G. The

j et p ipe , F, i s at one s ide of the wheel and the d ischarge pipe ,H, onthe Oppos ite side of the second wheel .


36 S TEAM TURBINESinto separate chambers and provided with induction and escape pas

sages .

” The course followed by the steam will be evident from the

engraving . Other patents s imi lar to M onson’ s have been taken

out in later years , notably by T . Bauta in 1 867 and by Parsons , the

inventor of the Parsons steam turbine in 1 893 . These latter are

exactly s imilar in principl e to Monson s and are merely construe

tion patents .

Fig. 1 7.Hoehl , B rakel l Gunther .Hoehl, Brakel l a»Gunther,I863 .

—The turbine produced by this

aggregation of inventors has as i ts onlv novelty an arrangement of

passages by which the steam returns on i tsel f and so i s uti l ized

twice by the same wheel , although an additional set of wheel

blades i s requ ired . Steam enters the chamber A, passes rad ial ly

outward through the gu i de passages B to the wheel blades C, then

discharges into the annu lar chamber D , where its mo t ion i s re

versed . and escapes through E to another set of buckets F . and

final ly to the‘

exhaust chamber G.

Perrigau lt <3" Farco t . —The type of turbine here exemplified 1 5 in

principl e l ike VVilson’

s turbine , in F ig . 1 2 , the latest representative

of which is found in the compound turbine of M essrs . Ri edler and

Stump f , to which reference wi l l be made later. The inventions o fPerrigau lt Farcot took several forms

,but the general principle is

well i l lustrated by Fig . 1 8 herewith .Here steam enters through

the pipe or nozzle A and impinges against the w heel buckets ,passing through to the other side/

of the wheel where it d ischarges


into pipe B . This pipe br ings the steam around again to the inl etside o f the wheel

,al lowing it to discharge a second time against the

buckets of the same wheel , when i t i s again picked up by a secondpipe C,

and so on. The exhaust i s final ly through pipe D .

The arrangement cons ists essential ly in a bundle of bent p ipeshaving openings a, b, e, through which the steam impinges againstthe wheel buckets ; and openings on the other s ide , .r

, y, etc . ,

which gather up the steam flowing from the wheel and bring itround again to the inlet s ide . The ob j ect is to util ize the steam

INLET I)CL C

F ig . 1 8. Comp ound Turbine w i th Only One Wheel .

over and over without necess itating a series o f rotating wheels .

It i s a system that has been tried with vari ous modificat ions , butwithout much success . Its obvious disadvantages are : Largelesses from friction and l eakage , and the wide range of temperatures through which the same buckets must pass , thus causing

condensation and reévaporation as in the steam engine .

M oorhonse,1 877.

—Among the most success fu l typ es of turbineis that having a success ion o f chamb ers in each of which is a s ingleimpul se wheel . There is only a sl ight drop in pressure from chambe1 to chamber, so that the velocity of the steam does not becomeexcess ively high at any point . The latest turbine of this description

i s‘

theHamilton-Holzwarth ,bu i lt bv theHoovens , Owens , Rent

schler'

Co . ,Hamilton, O. , and the earl iest one of . which there isany record is “the invention of Real Pichon

,1 827—the first pa

tent re ferred to in thi s series . The invention of Moo rhouse i s for

38 STEAM TURBINESa turbine on the same plan. As shown in F ig . 1 9 , a, a, a, etc .

,are

the nozzles , and b,b,b,etc .

, the wheel buckets . Steam flows

radial ly outward at each wheel unti l .near the exhaust end , w here

there i s a different arrangement , owing to a smal l er drop in p res

sure between the success ive chambers .

M oorhouse real i zed what previous inventors of this type of

compound impu ls e turbine had not , or at leas t had fai led to sp ec i fy ,

namely , that provis ion must be made for progress ive expans ion of

the steam by a gradual increase in the area of the steam passages .

F ig. 1 9 . CompoundImpu lse Turbine w i th Provis ion for Exp ans ion o f

the S team .His patent i s a broad one and fu l ly covers thi s requ irement as a

general principle , apart from the exact method u sed in i ts appl ication.In his specifications he says '

that his invention cons i sts of a

cylinder bu i l t in sections , each section compos ing a s eparate com

partment . Through the center of the cyl inder passes a revolving

driving shaft upon which is fitted a series of turbine wheels,each

having , at or near i ts circum ference , a sufl‘icient number of buckets .

These wheels are as many in number as the compartments intowhich the cyl inder i s divided . Each compartment contains a turbine wheel , and i s separated from the adjo ining compartment bymeans of a dividing plate or diaphragm . The foregoing is condensed from his specifications . but correctly represents thei r meaning .He then goes on to say


Openings are made in the dividing plates which separate eachcompartment from the adj oining ones , and the area of these Open

ings is proportioned to the pressure of the steam or other drivingflu id

,and to the number of compartments and turbine wheels , and

to the extent to which it i s desired that the driving flu id shou ld beexpanded before being final ly discharged from the engine . By thismeans the driving flu id , admitted at its highest pressure into thesmal lest compartment , passes into the second compartment through

Fig . 20. Rad ial Ou tw ard-flow T urbine.

openings of such area that it expands to a cal cu lated extent . Thesame proc ess is rep eated , etc .

”He says that various form s of turbine may be used , and hi s firstclaim is as follows :

“In combination with a rotary engine,the dividing plates be

tween the compartments provided with openings forming communications respectively of v arying area between said compartments , the turbine wheels in such compartments , and a drivingshaft , substantial ly as and for the pu rpose set forth .

Cu tler,I879.

—This i s a radial outward flow turbine in whichthe compound principle i s used . Steam enters at the bot tom ,

passesto the center and then flows radial ly outward through the passages

40 S TEAM TURBINESbetween the gu ides c e c and the wheel vanes cl d d . The rotating

wheel A has vanes attached to each o f i ts two faces so the pressurei s balanced on each side .

_ Expansion . o f the steam is al lowed for in

part by the increas ing w idth o f the passages and in part by the

fact that the steam is constantly flowing from a smal ler to a larger

diameter o f wheel so t hat the circum ferential area of the passages

constantly increases from this cause as well .Irnray , 1 881 .

—This i s another attempt to apply the compound

SECT ION ON X-Y

Fig. 2 1 . Ano ther Compound Turbine w i th On ly One Wheel .

principle to a s ingle wheel,having a s ingle set of vanes , but differs

somewhat from the turbines of W i lson and Perrigau lt and Farcot .

Steam enters at A,passes through the nozzl e and impinges against

the buckets C C C . These buckets are semi-circu lar in shape , asindicated in the sectional View in the upper l eft-hand corner of the

i l lustration . The steam enters at one s ide o f the bucket , fol lowsthe curved surface o f the bucket , and di scharges into the oppos ite

s ide o f a semi—circular stat ionary bucket or gu ide D .Here thed irection of flow of the steam is again reversed . The steam , as

before , flows around the stat ionary‘

guide surface and dischargesagainst one of the buckets C,

whence it i s carri ed al ong to thesecond stationary bucket , and so on, alternately entering the succes

EARLY TURBINE PATENTS 4 1

sive wheel buckets C C C and the success ive stationary bucketsD D D . It final ly discharges on the oppos ite s ide of the turbinecas ing , at E .In the meantime steam enters at A on the right-handside of the cas ing and zigzags through the lower half of the wheel

in a similar manner, exhausting at E on the left-hand side .

De Laval, 1 883 .

—The first patent o f this noted inventor w as for

a reaction turbine and w as taken out in 1 883 , in several countri es .

According to the specifications , steam ( or other flu id) enters the

Fig . 22 . Tw o Vvl heel s Ro tating in Oppos i te Directions .

wheel at the center through a nozzle, and passes ou tw ard through

hollow curved arms , escaping at their ends , and caus ing the wheelto rotate at high velocity . The wheel shaft drives another shaftat a slow er speed , by means of fri ction wheels

,the requ is i te

pressure between the friction surfaces being obtained by the axial

thrust of the turbine wheel . The principle of this turbine is no di fferent from that of the first American patent by Avery in 1 83 1 , bu ti ts appl ication to centri fugal cream separators , for the extens ivedevelopment of which Dr . De Laval has been respons ible , w as

success fu l and marks the beginning of an important career by this'

inventor in the manu facture of steam turbines .

Babbitt, 1 884 .

—B . T . Babbitt , besides acqu iring fame as a

42 S TEAM TURBINESmanu facturer o f laundry soap , w as bo th an inventor and a me

chanie, and one Of his inventions related to a steam turbine of the

type shown in Fig . 22 . This i s an inward—flow turbine with tw owheels

,A and B ,

having rows Of buckets on their peripheri es . The

wheels rotate in Opposite directions . The steam from the nozzle Nimpinges against the buckets Of the ou ter whee-l , which it is supposed to leave with a cons iderable residual veloc ity , and gives upi ts remaining energy to the buckets of the inner wheel . The chief

novelty Of the invention i s the method Of transmitting power fromthese two wheel s to the slow speed shaft F . The turbine wheels

are mounted concentrical ly on two separate shafts , having the same axis , shownat E . There i s a pinion on the outer endOf each Of the shafts . One Of these

pinions gears with the internal gear C on

one end Of the slow speed shaft F,and

the other pinion gears with the spur wheel

D on the other end Of shaft FIsaac Las t,1 885 .

—Th i s i s another ex

ample where the steam is caused to re

turn upon i tsel f , first flowing radial ly out

ward then revers ing and flowing radial ly

inward , ju st as in theHoehl , BrakellGunther turbine , F ig . 1 7 .In Last’ s tur

F ig . 23 .Isaac Las t bine,however

,compounding is carri ed

further than in the former , there being a

seri es Of wheel s placed s ide by side on the same shaft .In the sketch ,A B C are the different chambers in which the wheels rotate ; a a

are the gu ides for directing the steam against the wheel bucketsand b b are the wheel buckets . One drawing in the patent specifications o f Last has a very modern appearance

,in that he shows

a compound turbine bu i lt up of two parts , the high pressure and

the low pressure , in each Of which is a seri es Of compound wheel s .The high-pressure and low-pressure sections are c onnected by a

pipe , and their arrangement resembles that Of some Of the turbinesbu i lt to-day .

Parsons , 1 885 .

—W'

ith a patent i ssued in several countri es in th isyear, theHon. C . A. Parsons

,who w as the first to place the turbine


44 S TEAM TURBINESthe first del ivering into the second , the second into the third and so

on. Each portion compri ses a set of fixed and a set of moving

vanes , the direction Of motion'

of the actuating flu id being general ly

paral lel , o r approximately so . TO ba lance the end p ressure'

upon

the cyl inder,I mount two s imi lar sets o f rotary parts upon one

shaft, one set being so placed at each side Of the inlet for the actuat

ing flu id that the entering stream divides right and l eft , and the ex

haust takes place at both ends .

“As the speed Of the motor wi ll be necessari ly high , and perfect

balancing Of the moving parts wou ld not be practicable , I give to

the bearings a certain very smal l amount Of elasticity or play com

b ined with a fri ctional res istance to their motion.

”

This re fers to the well—known Parsons construction shown in

F ig . 25 , in which there i s an annulai‘ space , between the shel l Of

the bearing and the pocket for the shel l bo red out in the frame ,fil l ed with a series o f metal rings . Every other ring is bored to fit

the outs ide Of the shell , but i ts outs ide diameter i s smal l er than the

bore of the pocket, as in a a. The al ternate rings b b are turned to

fit the po cket , but are bo red larger than the outs ide Of the shel l .The rings are forced together by a spring s , so that they Offer considerab le res istance to any lateral movement of the bearing.He says “The lubri cation i s effected by

‘ forcing lubricant

through pip-es to the parts to be lubricated and -for this purpose apump can be employed . To prevent l eakage past the shaft at theend covers Of the cas ing , w hich , when steam is the actuating flu id ,

wou ld be inconvenient,I form annular recesses in the covers

around the shaft ends , and place these recesses in communicationwith a pipe in which a partial vacuum is maintained by su i tablemeans , such as a steam jet .

”In the next year, 1 888, Parsons took out a patent in which the

turbine wheels are arranged in groups , each success ive group beingOf larger diameter than the preceding one, to al l ow the steam , as

i t expands , to flow through larger spaces,as requ ired by the in

crease in the specific volume of the steam .He al so proposes to

secure steam-tight j oints at the bearings by admitting water underpressure to an annu lar groove pass ing around the bearing .Hesuggests cutting a sp iral groove on the shaft

, at the section wherethis annular groove occurs , with the idea that when t he shaft i s

EARLY TURBINE PATENTS 4S

revolving at high speed , the spiral wi ll diminish the quantity ofwater forced int o the turbine cas ing by the air pressure , w hen the

turbine is running condens ing .

Altham,1 892 .

—A compound turbine cons i sting of two rotatingwheels

,one inside of and concentri c with the other , i s the invent ion

o f George J . Al tham . The buckets of the inner wheel are arranged

in its outer periphery and those Of the outer wheel in i ts innerperiphery ,

so that steam. will act alternately on the inner and outer

Fig . 26 . Altham T w o-w heel Turbine.

wheel , and successively on the different buckets of both wheels ,the arrangement being such that the wheels rotate s imu ltaneouslyin opposite directions . Fig . 26 shows at the le ft a cross-section

Of the rims of the two wheels in which the buckets are cu t . Theother sketches show longitudinal sections of the r ims . Steam isdischarged from the nozzle into one row of buckets of the outer

wheel , whence it passes to the first row Of buckets of the mnerwheel , thence to the second row of the outer wheel and final ly tothe last row Of the inner wheel . from which it discharges into theturbine casing .In the smal l est sketch, Fig . 26 , the constructionis i ndicated where there i s only a s ingle row Of buckets in eachwheel .In thi s same year patents were granted to J . F . M cElroy

46 STEAM TURBINESfor a turbine with U-shaped channels , but with one set Of vanes

attached to the cas ing . See, al so , Imray ’ s patent Of 1 881 .

Dow ,1 893 .

—When turbines first began to come into promi

nence in this country , the one invented by J .H. Dow w as one of

the three or four that were most frequently mentioned . His firstpatent w as i ssu ed in 1 887 , and later several others were taken out ,

but the one showing the most completely worked out des ign w as

i ssued in 1 893 . All Of the Dow turbines are Of the radial outward

flow type , cons isting Of alternating r ings Of rotat ing and stationary

vanes , and in thi s respect resemble one of W i l son’

s invent ions Of

F ig . 27. Dow ’

s Patent of 1 893 .

1 848.In Fig . 27 , taken from his latest patent,A i s the ring Of

stationary vanes directing the steam against the ring Of rotating

blades B,and C i s another ring Of stationary vanes , D a ring Of

rotating blades , etc . A pecu l iari ty Of the drawing shown i s that

the stat ionary vanes are not cu rved at their inl et ends in a w ay to

gu ide the steam into them in the direction in which it l eaves the ro

tating blades , except as the latter might be designed so that steam

wou ld leave them in the direct ion in which the wheel i s turning ,

which wou ld be an inefficient arrangement . As actual ly con

structed , however, the gu ide vanes were curved correctly and the

turbine w as bu i lt along the lines show n in the re ference to i t in

Thurston ’ s manual Of the steam engine .In the patent Of 1 887there is a s ingle shaft on which are two disks facing each other,having annu lar rows of vanes cut on their inner faces . Between


these two disks is a central stationary disk with annu lar rows ofgu ide vanes cut on each of i ts faces . The arrangement i s shown

in Fig . 28. Steam enters at the center, and flows radial ly ou twardbetween the vanes on each side Of the central disk .In his latestpatent Dow compounds his turbine sti l l further by providing several rotating and stationary disks ranged along the shaft on eachside of the center . Steam enters at the center and gradual ly worksoutward tow ard both ends of the turbine .

Fig . 28. Do w Tu rbine w i th T w o De' Lava l T ufb ine

Disks . w i th Diverging Nozz le.

De Laval , 1894 .

-De Laval ’ s most important patent relates to hi sexpanding nozzle

,in combination with a turbine wheel . It i s in

teresting to note in this connection that the expanding nozzle w as

patented in this country in 1 867 , patent for steam inj ectors .

De Laval , however, w as the first to apply the principle of a diverging nozzle for the expans ion Of steam to a turbine . The twobroadest claims of the patent are the following1 . The combination with a bucket .or turbine wheel , Of a sta

tionary nozzle opening adjacent to the wheel and having its bo rediverging or increas ing in area of cross section toward its discharge end

,whereby the elastic flu id under pressure is expanded

in passing through the diverg ing nozzle and i ts pressure i s con

.verted into velocity be fore the j et i s del ivered against the wheel .

48 S TEAM TURBINES2 . The combinati on with a bucket or turbine wheel , of a sta

tionary nozzle opening adjacent to the wheel and prov ided with a

contracted receiving port ion and w i th a discharge po rt ion having

its bore diverging or increasing in area or cross section toward its

discharge end .

M aison Breguet, 1894 .

—Judging from the i llustrat ion aecom

panying this patent , i t introduces no new principle that w as not

included in the invention ofHartman’ s compound impul se turbine ,the patent for which w as taken out in 1 858. That i s to say ,

the

F ig . 30. From Patent issued to the firm

of B reguet , Paris .

i l lustrat ion shows a converging nozzle in connection with rotat ing

rings of blades alternating with stationary vanes . This i s nothing

more or less than what i s shown inHartman’ s patent drawings .

From the w ay the text of the Breguet patent reads , however, the

inventor apparently had in mind the improvement of the De Laval

turbine , and i f such is the cas e he evidently intended to imply theuse o f a diverging nozzle instead of a converging nozzle in con

nect ion with a compound turbine . Putting this interpretat ionupon the patent i t i s Of importance as the first to be issued upon thiscombination of elements , preceding , as i t does , the Curti s patent

(which introduced the same principle) by abou t two years . The

descript ion o f the invention states that in the De Laval turbine“even with a circumferential veloc ity of the turbine of 420 meters ,


i f the steam has a veloci ty of meters , i t stil l discharges fromthis turbine with a velocity of 4 -10 meters

, and this velocity i s muchhigher when the circumferential velocity of the turbine is less .

The idea that has natural ly come to us i s to uti l ize anew this lostvelocity in a second turbine mounted on the same axis , and even

in exceptional cases in a third , so as to increase the use of the tur

bine . We affirm as our prop erty the invention of the compoundsteam or gas turbine, in which the steam , or gas , after having lost

a part of i ts l ive force in the turbine buckets , final ly loses the re

mainder in the buckets of one or of several other disks mounted

or. the same arbor.

”

Fig . 3 1 . Seger ’ s F irs t Patent .

S eger, 1 894.

—Seger’s turbine has been bu i lt and used to someextent abroad .His first patent specification,

i ssued in 1 893 , showsan arrangement Of wheels indicated in Fig . 3 1 . L ike Pilbrow and

B . T . Babbitt, he seeks to secure a moderate speed of rotation byus ing two wheels turning in oppos ite directions . The steam ,

in

l eaving the firs t wheel , impinges directly against the second without any intervening guide vanes . The turbine wheels are on

separate, paral lel shafts , and at G are the gears by which the

motion of the wheels i s transmitted to the driving shaft, S . N is

the nozzle through wh i ch steam enters, and E the exhaust pas

sage .His claim i s for a steam turbine in which the turbinewheels are p laced in close proximity to each other , and are com

50 S TEAM TURBINESbined with one or more steam condu i ts d ischarging into the s ides

of said wheels in such a manner that the steam passes through the

wheels in the direction of their axes, and in which the shafts are

arranged ou t of l ine with each other so that the wheels only partlyoverlap each other.

”In his patent Of 1 891 , Seger shows wheels arranged on the sam e

axi s,but rotating in oppos ite di rections . A feature of the patent

i s the method for fastening the buckets in diagonal slots cu t in the

F ig . 32 . Arrangement of Wheels .

Fig . 3 3 . Vanes of Seger Turb ine.

wheel rims . The lower view,Fig . 32

,shows these slots

,and in the

upper view the rings , R,forced ins ide the rim

,hold the proj ecting

ends of the buckets in po s ition. This construction wil l be evident

from Fig . 33, where A i s one o f the buckets . At B the bucket i s

placed in the rim and at CC i ts pro j ecting ends are bent Over nuderneath the rim .In 1 897 Seger i ssued an English patent upon an

arrangement of his turbine by which the belted connection couldbe used for driving the low-speed shaft

,F ig . 34

,from which power

i s taken .Here A and B are the turbine wheels rotating in oppo

s ite d irections and attached to the ends o f shafts which carry , at

their outer ends , smal l belt pu l l eys . On the shaft , S , are two pu lleys ,I/V, , W Of equal diameter

,one of which i s fast to the shaft ,


52 STEAM TURBINESF ig. 35 . An Early Pel ton T yp e.

0

pockets of each pair being divided by a tapering ridge in combina

tion with a circu lar steam ring having a circu lar series Of nozzles ;and secondly , pockets as above described , but with a flat inclined

cut-away portion for each , as shown in the sketch .

Rateau,I894.—Professor Rateau , of Pari s , w as one of the ear

l iest to experiment with a steam turbine having a s ingle wheel of

the Pelton type . The essent ial features of hi s Engli sh patent on

thi s are shown in Figs . 36 and 3 7 , which represent the wheel vanes .He intended primari ly to produce a revers ibl e wheel and uses

buckets proj ecting radial ly,with double cancave surfaces , A,

B,

FACE OF WHEEL

F ig . 36 . Rateau’s

'

Revers ing Pel ton Wheel .


F ig. 39, which form a dividing wedge at the center, just as in the

Pelton water wheel . For revers ing the direction of rotation, he

uses steam j ets flow mg 1n the Opposite direction and impinging

against the backs o f the blades . The backs are shaped as shown

at C,with a s ingle concave surface , instead of with the double

curve , in order to avoid'

any obstruction to the steam when running

in the normal d irection. While the singl e curve is less efficient thanthe double curve , i t answers the requ irements for the bri ef periods

during which the turbine has to be reversed .

When the w heel i s to be des igned for forw ard mo tion only ,Rateau presents the construction of Fig . 3 7 . A and B are two

Bot tom of Groove 0

SECTION ONFACE OFWHEEL.

F ig. 37. Wheel for Fo rw ard M o tion Only.

concave vane surfaces and at the rear Of each bucket an inclined

groove , C, i s cut , represented by the dotted l ine , bp , in theupper

view . This al l ows the j ets Of steam to strike the buckets , one after

the other,without interference from the success ive buckets as they

come into position . The sectional views at the right are taken on

the l ine,XY

,looking

,in each case , in the direction of the arrow

drawnunder each view .

While it is not introduced as a definite claim in thi s patent Professor Rateau ment ions that where the speed of the flu idIS toogreat i t may be necessary to arrange these turbines in series on thesame or independent shafts

,in which case the openings of the noz

zles should al l be des igned to del iver the same relative quantityof flu id at the same moment . This he wou ld accomplish by us ingdistributing valves for supplying steam to the nozzles , and having

54 S TEAM TURBINESthese valves all operated positively from the same source so thatthey wou ld act in uni son.

Parsons , 1 895 .

—In the method of govern ing u sed on Parsons

turbines,an osci l latory motion i s given to the throttl e valve by an

eccentri c driven by the turbine , and the extent of this movement

is controlled by a governor.In the i l lustration,A i s a doubl e

seated throttl e attached to a valve stem , B ,which is connected with

a piston , C,working in a cy l inder above the valve chamber. At D

PLAN OF LEVERS

38. Parson’

s Governing Arrangement .

is a pilot valve for controll ing the motion of the piston. The steam

enters the chamber, E , and flows downward through the valve tothe turbine . An Opening from E to the space below the pistonal lows the steam to push the piston upward against a sp iral spring

which pushes it dow nward in cas e the steam pressure underneath

the piston i s relieved . When pilot valve D closes the port leadingfrom the space below the piston

,the pressure maintained under the

pi ston causes the latter to r i se and with it the valve A, but when

valve D uncovers the port . steam escapes from under the piston and


p asses around to the top , and together with the spring serves to

c lose the valve .

A floating lever mechan i sm is used for controll ing the pi lot valve .

At F is an eccentric driven by a worm and worm-wheel , w hich

osci llates lever G about its fu lcrum ,I. At point K,

on lever G, the

leverHi s fu lcrumed . One end of leverHi s connected to thegovernor and the other end to the pi lot valve D. The pilot valve ,there-fore

,i s control led both by the motion Of the eccentric and the

motion of the governor. The eccentric keeps the pilot valve and

hence the main throttle valve in constant osci l lation, whi le themovement Of the governor changes the positions Of the l imits ofthis motion. For examp le , i f the turbine were running with a

l ight load , the valve wou ld osci llate in the lower end of i ts poss iblepath of travel and wou ld shut off steam entirely at each osci l lation ;but i f the turbines were heavily loaded , the valve wou ld be moved

upward by the governor and i ts path of travel wou ld be locatedhigher , so that steam wou ld flow through the valve continuously ,although it wou ld be throttled more or less as the valve moved up

and down under the action of the eccentric .

S ebas tian Z . de Ferranti, 1 895 .

—The patent taken out by thi sinventor i s to be classed withHartman ’ s patent of 1 858 and thato f the Soc iété Anonyme Mai son Breguet , 1 894 , al l three of whichpropose a compound turbine containing certain features employedin the Curtis patents now used by the General Electric Company .

It i s to be noted,however

,that

,l ike his predecessors

, Ferrantifai ls to specifical ly state that he wishes to employ a diverging nozzlein combination with a compound turbine

,which is an important

feature of the Curti s type of wheel , although he says that he in

tends to uti l ize flu id in the wheel,

“after complete expans ion and

the acqu is it ion of the max imum velocity,

” which, under certain

conditions , can only be attained in a diverging nozzle .He advo

cates the use of superheated steam and also re fers to gas turbines .

The following is an extract from his specifications“I construct impact engines in which the working flu id impinges

after complete expansion and acqu i s it ion Of the maximum veloc ity ,upon sem ic ircu lar rotating blades fixed round the rim of a motorwheel . The working flu id enters the blades at a high velocity and

has its direction reversed , a portion o f i ts energy being turned into

56 S TEAM TURBINESF ig . 39. One P lan for Compound ing .

work , and rotates the wheel , and then leaves at the other s ide of

the blades at a dim ini shed , though sti ll high velocity . I then pass

i t through a set of standing semi-circu lar blades Of exactly the same

description as the rotating blades,but with grooves in the opposite

direction, which reverses its direction,bringing it back to the

original direction of motion,when i t strikes the blades Of the second

wheel and del ivers up a further porti on of its energy and comesout at a reduced veloci ty . This proc ess i s repeated unti l the

steam issues from the last set of blades with practical ly no usefu l

velocity , i t having given up nearly al l i ts energy to the rotating

F ig . 40. Fei'rantxs Turbine.


blades o f the wheel The Obj ect i s to convert the whole Of

the energy and pressure in the working flu id into velocity Of t he

particles , which then react backward and forward through therotating and standing blades o f the machine

,thus constituting an

impact mu l tiple re-active engine .

“The engine may be made with one o r more expans ion tubes

according to the p ower i t i s des ired to obtain; More or l ess of these

expans 1on tubes may be used and actuated by the governor according to the power requ ired for the time being The expansiontubes stand tangential ly from the periphery o f the wheel and at a

F ig. 4 1 . A Second P lan fo r Compound ing .

sl ight angle to the s ide of the wheel so as to del iver its workingflu id in the most su itable position.

”

Fig . 39 shows the principle of his scheme , N being the nozzle , G

a set of rotat ing vanes , V stat ionary gu ide vanes reversing

the direction of mo tion, and so on. The des ign of turbine

proposed by him is i llustrated in Fig . 40, where N is a noz zleand G and V the rot ating and guide vanes respectively . therotating vanes being attached to a coni cal drum on the end

of the turbine shaft and the gu ide vanes attached to a cas ingon the turbine .In this design he plans to have an increas ingarea for the steam as i t flows through the turbine , after Parsons

’

plan which i s somewhat contrary to the statement of hisspea ficat ions .In Fig . 4 1 i s stil l another proposed arrangement in which the steam ,

directed by the nozzle, N,

impingesagainst the wheel vanes , W, and i s then taken up by the U-shapedpassages , G1 , and returned to the wheel vanes , where it i s again

58 STEAM TURBINEStaken up by the U-shaped passages , G2 . This is another modifica

fion o f the schemes advanced by W i l son, Perrigault Farco t and

a number of other early inventors , and , as previous ly s tated , later

by Profs . Ri edler and Stump f .

Curtis,I896 .

-The impo rtant group of patents taken out in th i s

year by M r . C . G. Curti s , inventor Of the turbine manu factu red by

the General Electri c Company , cover mo st of the bas ic principles

of thi s turbine . The leading feature of the Curti s machine i s the

combination o f a diverging or expanding nozzle with a compound

Fig . 42 . Curtis Turb ine .

turbine wheel , although other features are included which had

been found by the inventor to be necessary to the successfu l opera

tion Of a turbine of thi s form o f construction . As already stated

previous inventors have patented turbines in which were combined

a nozzle for d irecting the steam against the blades of the rotating

wheels of a compound turbine , but the Curt i s patents are the first

to clearly claim the diverging nozzle as a part of the combination,

and they are, furthermore , the first ones to fu l ly explain a practical

method for carrying out the design so as to make an operative ande conom i ca l mach in e . Wh i l e the r e qu ir em en t s for th e su cce s sfu l operat i on Of a compound impu l s e turb ine were ou t l ine d b yMoorhou se in h i s sp e c ifi cat i on s of 1877

,in wh i ch h e prov ide d for

progre s s iv e exp ans i on of t h e s t eam from in l e t to exhau s t,b y


60 S TEAM TURBINESi t receives an additional impu lse in the gu ide pas sages be for e com

ing in contact with the second set Of vanes . The preferred con

s tru ct i on,however

,and th e one wh ich i s ac tua l l y emp loy e d , is

shown in F ig. 4 3 .Here the steam is expanded in the nozzle , N, to

nearly , but not qu ite the final pressure o f the exhaust p ipe , E. The

balance of the expans ion occurs during the passage between both

the rotating and stati onary vanes , and the pressure with in these

passages is , therefore , s l ightly in excess of the pressure w ith in

the chamber in which the wheel i s rotating .

The il lustrat ion,F ig . 44 ,

i s from the so—cal l ed stage patent

Fig . 44 . Curtis S tage Turbine.

upon the Curti s turbine . The cut shows each stage to be com

posed of one or more Of the compound elements that gO to make

up the tu rbine represented in Figs . 4 2 and 43 .In each of the twostages the wheel-and-bucket arrangement di ffers one from the

other.In the first cas ing are wheel s A and B,each carrying two

sets of rotating rings or vanes , and in the second cas ing i s a single

wheel with two sets Of blades . The advantage Of dividing the

turbine into stages in th is w ay , i s that there is l es s leakage be

tween the gu ide vanes and the wheel vanes , s ince the differences of

pressure are l ess ; and there i s als o less diffusion of the steam since

the number of rows of vanes for the steam to pass through in each

stage is less than wou ld be the case i f al l the rows were combined

together in one cas ing and the steam were compelled to pass

through them in virtue of the velocity acqu ired in the nozzle atthe beginning .


A third patent taken out in this year deals with the problem Of

governing,and M r. Curt is shows methods for changing the quan

tity of steam suppl ied to the turbine without throttl ing the pressure

or reducing the veloc i ty o f flow . Obviously an expanding nozzleof certain proportions i s adapted only to the steam pressure for

F ig . 45 . Curt is ’ P lan for Governing a Compound Turbine.

which it w as designed , and when the pressure i s throttled the noz

zle does not op erate at i ts highest efficiency . I t i s proposed byMr. Curtis to avoid thi s by us ing a nozzle of rectangular crossseet1on with one s ide ad justable in or out , regu lating the quanti tyof steam flowing through the noz zle without making a great changein the ratio of the inl et and outlet areas .In Fig. 4 5 i s a diagramshowing the principl e proposed , where the turbine i s div ided intotwo or more stages . A i s the steam inl et , term inating in a nozzle

62 STEAM TURBINEShaving a sl iding piece, B ,

operated by. the rack , D ,and pinion, C.

This rack gears with another pinion, which transmits motion

through the rack ,E

,to the pinion, F,

and th is in turn Operates a

s imilar s l id ing piece in - the nozzle , directing steam agains t thesecond nozzle .

The claims for the apparatus as used with a com

pound turbine cover first the principle of govermng by changingthe volume without great variations in the velocity Of the steam

Fig . 4 6 . Des ign w i th New Type of Expans ionNozz le .

by means equ ivalent to the above ; and second , the s imu l taneous

and propor tionate ad justment of the several passages leading to

the turbine or connecting the different stages of the turbine .

B ollrnann,1 897

— This invention i s an attempt to combine with

steam a flu id of greater dens ity so as to reduce the velocity of the

j et impinging against the wheel vanes . There have been. many

attempts to accompli sh this resu l t,some inventors preferring to

mix a heavier gas with the steam and others to m ix water or someless volati l e l iqu id , such as Oil , with the steam in a manner s imilar


.to the w ay steam and water are mixed in a steam inj ector. One

of the earl iest attempts to do this w as by Pel letau in 1 838. Otherswho have proposed fairly good arrangements of this character are

M i l lward in. 1866 , Crum lisk in 1 869 , M i l ler and Col l ins in 1 896 ,

and Lundell a year after Bollmann,in 1 898.

The chi ef interest in Bo llman’

s invention centers in a new typeof expans ion nozzle rather than in the plan for using a heavier

working flu id . The nozzle cons ists of an annu lar slot between two

disks B and‘

C,

’

-the'

former of which is adjustabl e. Steam entersthrough the pipe A and flows radial ly out through the annular

slot between the disks . Inasmuch as the diam eter Of this s lot i ssmal l where the steam enters and i s larger where i t leaves , thesteam expands in. flowing through the slot , al though the faces ofthe d i sks do not diverge . Escaping from the nozzl e

,the steam

enters the space D D and there comb ines with air and passesradial ly ou tw ard to the gu i de vanes E E E and the w heel vanesF F F . The plan i s to use this combined flu i d in a turbine workingon substantial ly the principle of the Curtis turbine.

W i th this invent ion the review of steam turbine patents willclose .

“The patents chosen for these pages , while representing only

a part of the best work of inventors o f the past century in per

fect ing the steam turbine , point the w ay by which success hasfinal ly been attained and indicate the directions that the paths ofprogress in this field will most l ikely take in the future . The

author bel ieves that the hints contained in the descriptions Of theseinventions wi ll prove of real value to inventors who are at work on

the steam turbine problem,as they wil l give at . least a l imited idea

of what has already been. accompl ished and will enabl e inventorsto work more intell igently .In subsequent pages reference willbe made to some of the later inventions in connection with descrip tions Of the leading turbines now on the market .

AWORD WITHINVENTORS .In reviewing the patents upon this sub j ect , a great many morefeatures have been found in the specifications which wou ld con

tribute to an unsuccessfu l turbine than to a successfu l one. I twould be out o f the question to point out al l of these , but a few

64 S TEAM TURBINESo f them have appeared so frequently and have b een re—inventedso many times at the expense of the inventor and to the p rOfit of

the patent lawyer and the Uni ted S tates Patent Office that it will

be wel l to give attention to them .

M omentum Turbines —One of these is the scheme propo sed in

the Bollinann patent of 1 897 . I t i s improbable that any turbine

in which the velocity of the steam is reduced by combining with

some other flu id on the principl e of the injector can prove at all

economical in i ts operation. The reason for thi s is that in com

bining the flu ids by any o f the methods proposed the kinetic energy

wil l be reduced ; and in doing work upon the vanes of the wheel s

i t i s kinetic energy which i s des ired . This can be explained as

follow s

Suppose steam , flow ing from a nozzle , to com bine with some

other flu id , as in the cas e of the steam inj ector,where the steam

combines with water. The steam imparts a certain velocity to the

water j et , or other flu id , i f other i s used , and in calculating thevelocitv i t i s necessary to apply the principle Of impact, that

Momentum be fore combining : momentum after combining.

h/Iomentum z massX veloc itv ; and as

weightmass g be ing accelerat ion Of gravi ty

,

momentum :

Applying the above principle,we may calculate the velocity of

the combined j et as fol lows

Let Vz velocity of the steam .

V1=velocity of the combined flu id .

s eight of flu i d (water or otherwise) combined withthe steam .

Then,assuming one pound Of steam to be used , we have ,

V (W+1 ) VI2

VI


Now ,if we suppose all the kinetic energy of the j et be used by

the turbine , the capacity of the j et fo r doing work is represented by

in the case Of the steam , and by

(W+1 ) V1

2

2s

in the case of the combined flu id . Let us assume that one p ound of

w ater or other flu id i s used for each pound of steam . I t i s evident from above formu la ( 1 ) that the veloc ity o f the combined j et

wil l then be one hal f the veloc ity o f the steam , while the weight

wil l be double .

The kinetic energy of the steam,

V2

2g

wil l therefore be two times that of the combined j et , which is

W+1 ) V2

This does not mean that energy has been lost .In this processthe heat energy of the steam is first converted into kinetic energy,giving the steam j et high velocity of flow at the start ; second , partOf the kinetic energy is converted back again into po tent ial energyin the form o f heat or pressure , or both , after the two flu i ds combine ; and the kinetic energy remaining is all that is avai lable fordoing work . I f the turbine i s to be effici ent

,this potential energy

must be uti l ized by converting it again into kinetic energy , and i tmust be acknowledged that so many trans formations wou ld entai l

serious losses , i f , in fact , i t were poss ible to make them at all .

A M isconcep tion of Reac tion—It has been demonstrated manytimes that the reaction of a j et of water or steam is not altered byholding an Obstruction in the pathway o f the j et , unless the Oh

struction i s placed near enough to the mou th of the nozzl e to chokethe flow . This has not been real ized by some inventors who haveschemed on turbines similar to Fig . 4 7 , where steam enters the

66 S TEAM TURBINEShol low radial arms through the trunni on A and discharges at the

orifices B and C. Those inventors who have provided notchessuch as N N for the steam to strike against have not improved theefficiency of the machine in any w ay . L ikewise those w ho have

arranged for two rotat ing elements , one of wh ich may be rep re

sented by the arms in Fig . 4 7 , and the other to cons ist o f a ring

rotating in the opp os ite direction and contain ing blades N N, have

done nothing to improve the effi ci ency . I f th e blades N N are

properly shaped , as , for instance , in the Seger turbine , speed re

F ig . 47. A Useless Cons truction.

duction may be secured by this means , but there wou ld theoretical lybe no improvement in the efficiency . Other inventors have at

tempted to produce turbines , combining the principle of the rotaryengine , in which the blades move through closed com partmentsand the steam

,after impinging against the blades , reacts against

an abutment . None of these various schemes are l ikely to be successfu l , and inventors are advis ed to adhere to the plan o f first p roy iding means for converting as much of the potential or heatenergy Of the steam into kinetic energy as poss ible , and then us ing

this energy to the best possibl e advantage according to the wellproven laws of the hydrau l ic turbine.


S TEAM TURBINESupon the bearings under such condit ions .He there fore adoptedthe flexible shaft , which ,

with the diverging nozzle , i s employed

in the De Laval turbine of to day . These characteri stic features

are represented in the famil iar i l lustration ,Fig . 1 .

General Descrip tion— Fig . 2 i s an external view of an electric

generating set cons isting Of a De Laval turbine direct-connected

to double , direct-current , Bu l lock generators . The generator i s at

the le ft,the turbine at the extreme right , and between the two are

the cas ings inclos ing the speed reduction gears connecting the

turbine and generator shafts . The turbine wheel rotates within

a steel cas ing and on one end o f i ts shaft i s a smal l , doub l e , spiral

Fig . 2 . De Laval Elect'

ric Generating Set .

pini on, which , in the smal ler s izes , meshes with a large , double

spiral gear .In the large sizes two doubl e gears are placed , one on

each side of the pinion,which thus balances the thrust of the trans

miss ion.In the large engraving,Fig . 3 , i s a hori zontal s ectional vi ew Of a

turbine taken in the plane o f the turbine and gear shafts . Startingat the right , W i s the turbine wheel attached to the flexibl e shaft ,which latter i s supported on each side of the wheel by bearings heldin the cas ing by bal l and socket j oints . The pressure within the

tu rbine casmg i s practical ly atmo spheric pressure when runningnon-condensing , and i s equal to the pressure of the condenser whenrunning condens ing . Under the latter conditions , these bearings

70 STEAM TURBINESshou ld be tight to prevent leakage Of air into the cas ing , and theymu st at the same time be able to move sl ightly ,

in case of flexure

of the shaft . They are, therefore , . held to their seats by spiral

springs N bearing against a collar 0 made in the form of a socket .

At the other end of the fl exible shaft are the spiral p inions K,sup

ported on each s ide by bearings C in the wheel cas ing. These

pini ons mesh with the gearsII, as indicated .

The speed reduction between the pinion and gears is about in

the rati o of 1 0 to 1 for -al l s izes of turbines . The speeds of the

turbine wheel s range from about revoluti ons per minute for

a 7-horse-power to for a 300-horse-power turbine ; and the

speeds of the large gears range from about 900 to revolutions

per minute . The peripheral speed of the turbine wheels ranges

from abou t 5 1 5 to feet per second , whi le the peripheral speed

of the gears i s 1 00 feet per second or s l ightly more , for al l s izes .

These speeds of the gear shaft are found to be wel l adapted to

driving generators and other apparatus , such as centri fugal pumps ,blowers

,etc . Such apparatus i s driven through flexibl e couplings

taking power from the outer ends o f the gear shafts . The coup

lings have a series of pins F ,Fig. 3 , securely driven into holes in

the circum ference of the driving disks , and on their outer ends

have rubber bushings E,which fit in corresponding holes in the

disk attached to the shaft belonging to the generator or other

apparatus . These bush ings are fitted with an internal steel bushing D ,

which sl ips over the end of p in F,to protect the rubber.

This brings the wear on the ou ts ide of the rubber bu shing , which

presents a greater area than the ins ide .

The governor,shown at M ,

i s Of compact design and i s carri ed

bya short shaft made a taper to fit in the end Of one of the gear

shafts . The governor controls a throttl e valve and al so, in case of

extreme increase in speed, Opens a valve admitting air to the wheel

casing by means o f the l ever V. The friction o f the wheel rotatingin the air checks its speed .

Nozz les and S tearn Ches t —In cons idering the individual partsof theDe Laval turbine

,the first to be noted are the nozzles which

direct the steam against the wheel buckets . These nozzles are ar

ranged about the circumference of the steel casting which servesas the cas ing for the turbine wheel . The inner end of this cast ing

SIMPLEIMPULSE TURBINES 71

has an annu lar closed space, separate from the wheel chamber,which serves as a steam chest for the turbine, as indicated in

Fig. 3 . The inner ends of the nozzles Open into this s team chest,as in the sectional view ,

Fig. 4 .Here A i s the steam ches t ; B ,the

nozzle ; D,the turbine wheel , and C,

the valve for admitting steamto the nozzle . The divergence o f the nozzles depends upon thesteam pressure to be used and also upon whether the turbine i s to

run condens ing or non-condens ing. I f the latter, the turbine is

general ly fitted with both condens ing and non-condens ing nozzles ,so that in the event of difficu lty with the vacuum the machine can

be operated non-condens ing with a greater degree of economyThe nozzles are turned to gauge on their outs ide and reamed to the

Fig . 4 . Nozz le and Va lve.

requ ired taper on the ins ide . Over 600 reamers of different tapers

are kept in the tool room of the American De Laval company forthis purpo se . The noz zles are s imply driven into place in the

casing ,but are threaded at their inner ends to faci li tate removal by

means of a jam nut . The taper of the nozzles ranges from about6 to 1 2 degrees total taper, and they are located with their outletabout % 3 inch from the wheel blades .

Turbine Wheel and Shaft .— The turbine wheels are all made inSweden, of a special grade o f high carbon steel . They are shap edacc ording to theoretical calcu lations , so

’

as to offer nearly a uni formresistance throughout to the forces acting ; but they are madeslightly stronger near the center . A short distance from the periphery annu lar grooves are turned on each s ide Of the wheel ,making this the weak section,

which wou ld be ruptured first in caseOf excessive rotative speed . To further guard against danger in

72 S TEAM TURBINESthe case of a wheel bursting , the steel cas ing is made stnong enough

to sustain the shock due to flying segments of the wheel ; and sti ll

further, the hubs of the wheel extend into circu lar openings in the

cas ing (Fig . in which the hubs ordinari ly run without touch

ing . But i f the wheel rim. shou ld burst , what wou ld be left of the

wheel wou ld be out o f balance and wou ld cause the hubs to bear

against the casing with gr eat force and thus s low down.

Grooves of the shape shown in Fig . 5 are dri l l ed and mi lled

through the turbine rim in a crosswise d irection ,and in these drop

forged steel buckets are fitted . This construction enables buckets

to be eas i ly renewed , as i s sometimes necessary either because ofwear or accident .

Fig . 5 . Method o fInserting B lades .In the smal ler s ize turbines the wheels are attached to the flex ib le shafts by the method indicated in F ig . 3 . The hubs of thew heels are bored out and a thin steel bushing is drawn into the hubby a nut at one end . The middle port ion of the bushing is bo red

tapering and fits on a taper portion of the shaft, as indicated . This

taper i s the standard 56 inch p er foot used by the De Laval com

pany . After fo r cing the bushing on the shaft,i t i s pinned into

place ; but the wheel can eas i ly be removed by loosen ing the nutand sl iding it off the steel bushing . The wheels for the larger turbines are made as in Fig . 6 .Here the hub i s sol id at the center, buteach end of the hub

i

is recessed and the flexible shaft i s made with

enlarged flanged ends which fit into the recesses and are bolted inplace . The recesses and shaft ends are mach ined on a taper of

V2 inch p er foot .


The pinions are cut directly on an enlarged po rtion o f the shaft

the flexibil ity o f the shaft making an extremely accurate balance

unnecessary since the wheel and shaft reach the cri tical speed , so

cal led , at about to % 3 o f the normal number o f revolutions of

the Wheel, at which point

“settl ing” takes place and the parts p ro

ceed to rotate about their center o fgravity instead of about their

geometrical center .

German—Next in importance tothe turbine wheel , and probably first

in importance in so far as the suc

cessfu l operation o f the turbine isconcerned , are the gears used to re

duce the speed o f the turbine shaftto a point where it i s practicable to

util ize the power. It w as a radicalstep on the part o f De Laval when

he first attempted to run gearing at

so high a speed as these gears

operate , and i t i s safe to say thatprevious to the time when De Laval

demonstrated that gears would run

at a l inear velocity of upward of1 00 feet p er second ,

i t wou ld not

have been supposed possible .

The pinions are made o f .GO or

.70—point carbon steel and area partof the flexibl e shaft . The gears areof mild .20-point carbon steel o f a .

grade similar to that used for loco

Fig . 6 . Section o f T urbine Wheelof th e Larger S izes .

motive wheel tires . For turbines up to 30 horse-power the gearsare of sol id steel but for s izes above that they are made with castiron centers with rims o f mild steel . The teeth are of fine pitch ,

ranging from about . 1 5 inch in the smal lest to .26 inch in thelargest sizes . The success at running these gears at high speed isdue, in part , to the fine pitch and the Spiral angle o f the teeth .

which thus brings a large number of teeth in mesh at one time ,making the working pressure at each tooth very light , and re

74 STEAM TURBINESduc ing the l ikel ihood o f abras ion. The dimens ions of gears and

pinions for four S izes o f turbines are shown in the accompanying

tabl e

PINION S .

GEARS .

Oilz'

ng Arrangements .—In the high-speed bearings oi l ing is

accompl ished by having a shal l ow spiral groove turned in the

shel l,which al l ows the oi l to reach every part of the bearing .In a

1 00-horse-power machine this groove is about % 4 inch deep and

- inch pitch .In connection with the oil ing arrangements for

the bearings,reference shou ld be made to the design of the wheel

cas ing in which the bearings are l ocated . This cas ing is in two

halves,divided on a horizontal plane , and the upper edge of the

lower hal f has an oil groove running around it , as shown. in

Fig . 3 , to catch any drip that may work in between the tw o halves .

The oi l i s carri ed down into pockets in the casting ,where the ring

oilers reach it , and these pockets are piped to a gauge glass, to indi

cate the quanti ty of oi l in them . The oil ing of the various bearings

is effected by means of a s ingle s ight—feed lubri cator having tubesleading to them .

The Governor .

—Reference has now been made to most of the

principal parts o f the turbine,with the exceptions of the governor

and throttle valve which it controls . These are shown in F igs . 7and 8 respectively . The governor i s held in the end of one of thegear shafts by the taper plug K

,Fig . 7 , and i s made cyl indrical in

form , with its outer shel l B B cut l ongitudinal ly into two halves


76 S TEAM TURBINESernor wou ld have

.

power enough to overcome the pressure of the

spring at the connectionH, and the p in 0 wou ld strike the spindleof the valve T,

which latter wou ld admit air to the vacuum cham

ber in which the wheel revolves . This wou ld immediately put an

air brake on the wheel and prevent an acceleration of speed . I f

for any cause the speed becomes excess ive thi s act ion takes place .In a paper read be fore Society of Arts,Boston ,

in 1 904, Charl es

F ig . 8. T hro ttle Valve.

Garri son states To show the acti on of the vacuum breaker

more clearly , I started a 1 50-horse—power turbine with al l nozzles

open , the nozzles being des igned for 1 50 pounds gauge pressure

and 26 inches vacuum; The condens er w as shut down and the

turbine exhausted against the atmosphere , and with these condi

tions the turbine wou l d not come up to fu l l speed with no l oad .

”


Sp ec ial Ap p lications of the De Laval Turb ine .

The turbine , as bu i lt by the several De.Laval compani es

,by

C . A. Parsons Co . in England , and Sautter,Harle Co . in

France , has been appl ied to many special uses besides that of

dynamo driving.In the United States more instal lations o f this

character have been undertaken by the De Laval company than by

any other manu facturer.

App lication to Centrifugal Pmnpa—Unti l recently cent rif

Appl ication Comp ound Centrifugal

ugal pump has no t been cons idered as effici ent as the plunger

pump , mainly because of the low speed and imp erfect design of

such apparatus ; and i t has also been adapted on ly to low li fts .

As the De Laval Steam Turbine company , however , were bu ilding

high-speed turbines,which ran at almost exactly the speeds re

qu ired for maximum efficiency in centri fugal pumps adapted to the

different s izes of turbines , i t w as decided to des ign a series of

pumps,of improved mechanical construction , which would admit

of the high speed necessary , and which w ou ld'

also enable the

pumps to work against high heads . The smal ler uni ts cons i st of a

STEAM TURBINESsingle pump , but the larger uni ts have tw o pumps driven by the

double-gear turbine , one pump being connected to each gear shaft ,perm i tt ing their operation in parallel for low p ressure , and in seri es

when high li fts are des ired . Standard sets are bu i lt in s izes from

7 to 300 horse-power for al l heads up to 300 feet , handl ing from

90 to gal lons p er minu te . Lately a high-pressure pump has

developed with forcing pump having a runner of very

o Fig . 1 0.High-pressure Centr ifugal Pump Connected in Series .

smal l d iameter attached to the turbine shaft and rotating at

extremely high sp eed of that shaft . The centri fugal force

ve10p ed by the runner under thes e condit ions makes i t possible to

pump against heads of 600 to feet, and to use the pump for

boi ler feeding . A runner operating at such high spe ed , however,wou ld force out the water more rap idlv than i t cou ld draw it in bysuction, or under atmospheric pressure only , and hence the pressure

pump is floo ded with water at sufficient pressure to ensure an ade

quate supply , by a pump on the geared shaft .

SIMPLEIMPULSE TURBINESFig. 1 1 . App lication to B low ers of the S iro cco Type.

B low er SetsQ—Another field where the turbine is well adapted isfor direct connection to blowers for water pressures between 4 and

21 inches . The high veloci ty of the turbine makes it feas ible to usesuch blower uni ts for locations and pressures w here the positiveacting impeller blowers have been employed . The turbine is usedin connection with blowers of the Sturtevant and S irocco type.When directly connected to the blowers

,the Whole form s a com

pact unit , and el iminates the trouble from tight belts and heatedbearings met with in attempting to use blowers for high. pressures .

CHAPTERIVTHE PELTON AND SIMILAR TYPES .

S imple impu l se wheels o f the Pelton type have been exp eri

mented with extens ively by Pro fessor Rateau of Pari s and Pro

fessors Ri edler and Stumpf o f Berl in ; although Rateau has now

abandoned this type in favor o f his mu lt icel lu lar turbine , and the

Fig . 1 . Wheel o f Rateau ’

s Turb ine.

manu factu rers o f the Ri edler-Stump f turbines appear to give

pre ference to compound turbines of later des ign. The fact , how

ever , that the Pelton water wheel,commonly known as the

“Hurdy-Gurdy wheel, and its later r ival the Dobl e turbine , have

been so success fu l in Amer i can water-power plants where there isa high head and a high velocity o f water j et at the wheel , makes it

seem probable that steam turbines similar in principle to the

Pelton water wheel wil l be experimented with in this country to a

considerable extent .

THE PELTON AND SIMILAR TYPES 81

Ratean’

s S imp leImpu lse Wheel .—Fig . 1 i s an engraving of

Rateau’

s wheel , a l ine drawing o f which w as shown in the patent

review o f the second chapter.In Fig . 2 are sectional drawings ,showing the detai l s o f the turbine itsel f as constructed from

Rateau’

s des igns .

“A number o f turbines s imilar to this were bu i l t ,

the one represented being direct—connected to a blower.

The Riedler-S tumpf l lf’

li eels* were invented by Pro fessor

Fig . 2 . Rateau’s S impleImpu lse Turbine.

Stump f and developed w ith the ass istance of ProfessorRiedler.

A wheel for a -horse-power turbine is shown in Fig . 3 and thenozzle ring for the same in Fig. 4 .In a turbine of so large a s izeit w as necessary to use a complete ring o f nozzles

,but in machines

of smal l er power one or more segments containing nozzles are all

that are requ ired . The groups of nozzles are connected with a

central distributing chamber by means of radial tubes so arranged*Described in a paper read by Pro fessor Riedler in Germany .

See“Machinery” for February, 1 904 .

S TEAM TURBINESthat steam may be adm itted to one or more of

,the group s a s de

s1red . The buckets are cut into the rim o f the wheel , but the noz

z les are placed obl iquely upon one another in a ring w hich sur

rounds the wheel . The nozzles are of the De Laval type made of

nickel steel, but are square in cross- secti on . They are produced

first in the form of round tubes and the diverging parts are then

F ig . 3 . F ig . 4 .

Wheel and Nozz le Ring for Ried ler-S tump f Turbine.

drawn ou t square and final ly cut off obl iquely . The detai l s of thewheel are indicated in Fig. 5 , which show s s ections of the buckets .I t wi l l be noted that the buckets are so formed as to overlap each

other something l ike the shingles of a roof , instead of being placedone in front of another as in a Pelton water wheel . They are de

s igned to reverse the steam j et through the whole angle of 1 80degrees .In order to reduce the veloci ty of rotation b elow thatobta ined in the De Laval wheel

,Professor Stumpf increased the

diameter o f his wheels from six to nine feet, and he al so found

it expedient to aboli sh the flex ible shaft by giving unusual atten


84 STEAM TURBINESIt is pointed ou t by Professor Stumpf that steam , in revers ing

its direction of flow in a turbine -wheel , acqu ires suffi c ient centrif

ugal force to increase its pressure, frequently by a cons iderable

KETB

S ECTION ON X-Y

Fig . 6 . Subject of S tumpf Patent.

amount , so that in leaving the vanes there i s a sudden explos ive

expans ion of the steam , caus ing a scattering of the j ets . By catching the steam in the return buckets as i t leaves the wheel , and

bringing the streams together in a sol id j et again at the center, he

aims to overcome this action and to produce a more efficient type

of compound turbine .His claims are broad ones , applying to thecombinat ion of admi ss i on nozzles

, a turbine wheel with double

buckets and doubl e return buckets .In F igs . 8 and 9 are tw o arrangements that have been adoptedfor applying the features of the Stumpf patent . The wheel , instead

F ig . 7 .

of having double U-buckets , has a s ingle U—shaped bucket. The

steam flows from the nozzle and strikes against one s ide o f the

buckets , then passes around to the other s ide and escapes to thegu ides , which again change its direction of flow and caus e it to


STEAM ENTERS

Fig . 8 . Show ing Arrangement of Gu ides .

impinge a second time against the wheel . The course of the steam

is indicated by theletters A B C D in the il lustration.InFig. 9 i s the arrangement where there are double U-buckets .

The steam enters through the nozzle in the direction of the arrow

A,the j et divides when it strikes the buckets , flow mg in the direc

STEAM ENTERS

F ig. 9 . M od ified Arrangement of Guides .

86 STEAM TURBINEStion indicated by the arrow s B B and C C,

and final ly impinges the

second time against the bucket s in the direction of the arrow D .In a subsequent chapter further reference wi l l be made to the

Ri edler-S tump f turbine , in which the compound pr inciple is appl ied

by us ing two or more wheel s instead of a s ingle wheel as here

described .

Claims M ade for the Pel ton Type— The best presentation of the

claims for a Pel ton type of wheel for s team turbine purpos es has

been given by John Richards ‘

in a pap er before the Technical

Society of the Pacific Coast in May ,He argues that steam

impul s e wheels as usual ly bu i l t are at fau lt because the blades are

curved in one plane only , and consequently have but one correct

pos ition in the j et throughout the w hole arc o f their movement ; and

furthermore in nearly al l cases are cu t out of sol id metal , and have

angu lar or imperfect corners . Whether the principles enunciated

wil l hold when us ing an elastic flu id l ike steam instead o f an in

elastic flu id l ike water can only be told by experiment . The ‘

ten.

dency of the steam j et is to break up into spray and eddy cur

rents , whereas a water j et wi l l hang together”for a longer p eriod .

This act may have an important bearing on the question of the

spacing of the buckets in a Pelton type of wheel when used with

steam .

The following is extracted from M r . Richards ’ paper , beginning

wi th hi s obj ections to the typ e of bucket employed in impu l se steam

turbines as now constructed ,such as in the De Laval

First.It increases the w eight and number of the buckets about fivefoldin the attemp t to secure imp ingement of the steam j ets normal to the straightfaces of the bucket s .

Second.It distorts the course o f reaction from a p ossible angle of 1 5 de

grees to an angle of 2 0 to 30 degrees required to secure clearance.

Third.It makes necessary a side ap p l ication of the j et , introduc inglateral stress on the w heels and induc ing vibration.

Fourth .It augments, in p rop ort ion to the added number of buckets, theamount of fluid friction. No t to include the resistance of corners .

The number of buckets is an imp ortant matter.It is a sequence of the

angle of imp ingement, and th is again is a sequenc e of the bucket’ s shap e, as

w ill be show n further on. The surface or fluid friction, w h ich offers a con

‘Publ ished in the Jou rnal of the As sociation of Engineer ing Societies , Philadelphia,

September , 1 904 .


siderable resistance and loss, is in p rop ortion to the number of bucket s em

p loyed , and should be considered in this connection.

Most of the steam turb ine bucket s now made have angular corners and ,

w hen there are not such corners, the end w alls of the buckets are so di s tantfrom the j et as to lose reactive effect in that direction. We long ago

learned to keep w ater out of sharp corners in hydraul ic p ractice.

F igs . 10 and 1 1 .

Figure 10 show s how the line of imp ingement varies in resp ec t to the

straight faces of radial buckets , and there is no w ay of securing imp ingement even ap p roximately normal to the straight faces , excep t by emp loy inga large number of buckets set close together. The result is much the same

w hether the j ets be ap p lied tangentially or on the side, as show n in Fig . 11 ,

w here the angle o f entrance is 20 degrees and that of discharge 36 degrees m conform ity w ith the p ractice of the De Laval company .

Fig. 1 2 .

The trend of p ract ice in tangential w ater w heels has been to w iderspaces betw een the bucket s , better angles for discharge, and, recently , touniformly curved buckets , as hereinafter exp lained.In Fig . 11 the entrance and discharge angles embrace an arc of 56 degrees,w hich, by reducing the number of buckets, cou ld be reduced to 36 degrees or

88 S TEAM TURBINESless if the p roblem of ob lique imp ingement w ere out of the w ay . Fig. 12

show s spacing for tangential bucket s to secure an easy discharge at 2 0 de

grees .In the Riedler-Stump f turb ines , the angle o f discharge is 180 degrees .In other w ords , the discharge is op pos ite the j et , but this calls for increased surface, more w idth and w eight for the revo lv ing member, and

exp ens ive w ork in construc t ion, w h ich are hardly offset by countervail ingadvantages , and w hich cert ainly p revent a cheap and general manufactureof the machine.

M r. Ri chards then contends that buckets of steam" turbines

shou ld be curved in al l planes approx imately as shown in F ig . 1 3 ,

taken from a form of water buckets of an advanced type by W . A.

SECT IONON xy

F ig. 1 3 . Buckets Sugges ted by Richards .

Doble of San Francisco . These are of double concave or cup form ,

in order to permit direct and balanced impingement at the various

angles in which they are presented to the jet , and have a centraldividing wedge to permit tangential appl ication. The bucket i s

no tched at A,following the construct ion of certain w ater wheels ,

to permit the passage of the j et b eyond and through the buckets

as they come into position ,so that i t wi ll impinge agains t the

buckets in advance which have reached a posit ion where the j et

wil l act upon them efficiently .He estimates that about one bucketfor each 8 degrees of arc w i l l be sufficient for wheels from 20 to 40

inches diameter. This i s less than one-fifth the number now em

ployed for wheels having the ordinary type of buckets .

Z oel ly’

s Patentsim —In 1 900 a patent w as taken out byHeinrichZoel ly for a turbine wheel o f the Pelton type , but with radial arms .the outer ends of which serve as vanes for the wheel . These arms

decrease in cross- section as they approach the per iphery of the


wheel and thus are proportioned to resist the stresses due to centrif

ugal force , which are greater near the center. The first claim of

thi s patent i s for “the combination in a turbine wh eel of radialbuckets separated from each other fo r a part of their length . eachbucket having its receiving face channeled for the greater portionof its l ength , and a pair of flat disks inclos ing said bucket s fromtheir inner ends for a greater portion of the length of the channeledpart of the buckets .

”In Fig . 1 4 A and B are two sectional views

S ECT ION ON X'Y

SECTION ON M-N

F ig. 1 4 . Wheels Patented by Zoel ly .

of the wheel, C,

an enlarged front view o f one of the blades , and

D and E,enlarged sections of the blade on the l ines x y and m n

respectively .

At F and G are detai ls o f a wheel now used in the Zoel ly tur

bine described in a subsequent chapter.In this type , patented in1 903 , the steam is directed against the blades on one s ide of thewheel and escapes on the other s ide . Sections of the b lades are

shown atH. The first claim is for'

a“turbine blade cons tructed

with a gradual ly increas ing longitudinal th ickness and a longitudinal cavity of substantial ly uni form depth .

”Some of the other

90 S TEAM TURBINESclaims relate als o to the method of clamping the blades in pos ition,

and the use of spacing blocks , b b, between them .

Richards’

Patent—The idea presented in the Zoelly patent of

1 900 i s carri ed a step further in a patent i ssued to J . Richards for

a wheel in accordance with his ideas . The wheel cons i sts of

buckets , B ,l ight in w eight and drop forged on the ends of radial

arms , which are attached to a central nave by pins inserted between

the arms , as indicated in the i l lustrat ion. The buckets are spaced

further apart than i s u sual in turbines , because they are des igned to

be concave and reactive through a cons iderabl e angle of rotation,

and thus wil l absorb the energy of the j et sufficiently throughout

F ig . 1 5 . Turbine Wheel Propo sed by Richard s .

th i s range . The arms of the w heels are no t covered by plates atthe sides

, as in the Zoel ly des ign ; the intention of the inventor

being that the ins ide of the turbine cas ing shal l be machined

smoo th , and the steam al low ed to rotate with the wheel within the

casing. The claim is in substance for a w heel having a s ingle hub ,of a diameter within the zone of d isruptive centri fugal strain, w i th

equ idi stant radial sockets formed therein ; strong radial stems fast

ened in the sockets ; and concave reactive buckets integral ly formedon the extremities of the stems.

Turbine Designed by John Richards .

—In F ig . 1 6 i s a turbine

proposed by John Ri chards and patented by him in 1 903 .In thi sturbine he u ses a wheel l ike that outl ined above . The cas ing forthe wheel is fini shed smoo th ins ide and the steam is suppo sed torotate with the wheel in the cas ing . The gearing of transmiss ion


92 STEAM.TURBINES

Steam i s expanded in the nozzle , N,which proj ects i t against one

s ide of the semi-circu lar buckets , B ,of the wheel . The steam

pass es around these buckets and i s‘

proj ected outward against the

curved surface , C,of the cas ing twice in success ion, wh ich at each

time redirects the steam against the buckets of the wheel . The

curved surface of the cas ing is stepped so that the portion at C1

may be brought nearer to the wheel , and when the steam reaches

the buckets at B 1 i t i s proj ected against the surface at C1. As

draw n,the arrangement i s des igned for a w heel having a p e

ripheral speed of one- tenth the init ial veloc ity of the steam s ince the

steam i s proj ected against the buckets five times in success ion.

The bucket s are semi-circu lar in form .

SECT ION ON X-Y

F ig. 1 7 . Experimental Turb ine o f Levin.

The steam proceed s in a success ion of hel ical whirls after leav

ing the nozzle , and i t i s neces sary that the steam shou ld be com

p letely expanded in the nozzle so that i t will be at cons tant pressure,but have a decreas ing velocity after l eaving the nozzle . The first

claim for this wheel i s for a “mu lt iple impu l se turbine , compri s ing

a wheel having a row o f buckets , an expans ion nozzl e del ivering

into said buckets , and a stationary revers ing gu ide extending fromsaid nozzl e over a number of said buckets , to form a space open

end to end within w hich the motive flu id proceeds in a hel ical

whirl and i s success ively proj ected against the buckets of saidwheel .”

Mr. Levin bu i lt an experimental turbine on this order w hich w as

described in“Power” in May ,

1 904 . One of the int eresting

features i s a widening of the semi-circu lar grooves const i tu ting the

wheel buckets and the gu ide surfaces at the points where the steam


l eaves the grooves , as clearly shown in Fig . 1 7 at D . Thi s is because the steam becomes compressed in pass ing around the curvedsurfaces , and at the points o f escape , the passages are widened to

allow the steam to reexpand to its previous volume .In referenceto fri ctional losses , M r. Levin states that his tests indicate theyare not of prohibitive importance , nor has he found indications ofwear even when moist steam has been used . On the contrary , after

having run the wheel with moist steam ,the buckets were always

coated with a fine blu i sh film , apparently derived from oil carri edover from the boiler.

Fig. 18. Buckets of Kerr Turbine.

C. V. Kerr’

s Turbine—Another patent is that i ssued to Mr.

C. V . Kerr for a compound impu l se wheel o f the Pel ton type . The

buckets are made of drop forgings and of such a shape that theymay be bored out perfectly smoot h by means of a special reamer.

Accordingly , each recess in the bucket on either s ide o f the‘

dividing

wedge has a contour representing a surface of revolution.

Sketches of the buckets appear in Fig . 1 8. The curves o f the interior of the bucket in a transverse direction must obviously becircles in whole or in part , as shown at E ,

whereas the longitudinalsection will show curves el l iptical in shape .

The buckets are attached to steel disks , and in Order to withstandthe great strain he prefers to attach them , as shown at A, by dove

94 STEAM TURBINEStai l ing and upsetting the interlocking parts , or else bv electric weld

ing . Another construction sugges ted i s by riveting, as shown at

E.Expans ion nozzles are used ,

~

of the form indicated at C,

Fig . 1 8, the tip o f the nozzle being rather short inasmuch as the

turbine is divided into stages and only a portion of the pressure of

the steam has to be reduced at each stage . Each nozzle of the

turbine i s controlled b y a hand valve .

The Kerr turbine i s b eing developed by the Kerr Turbine

Company , W ell svill e , N. Y .In Fig . 1 9 i s a diagram il lu strat ing

the arrangement . Steam flows through a series of nozzles and

Show ing Princip le of Kerr T urbine.

impinges against the cups of the first wheel , which i s located in a

compartment by itsel f . I t then flows through another seri es of

nozzles and impinges against the cups of a second wheel in a

second compartment , the cups be ing enough larger to accommo

date the increased volume of the steam at the lower pressure . I tagain discharges into a third chamber, in thi s case against tw o

wheel s . This arrangement i s fol lowed throughou t , there being an

increase either in the s ize of the cups o r in the number of wheelsas the low pressure end i s reached . This design provides for

manu facture in standard parts,because by combining the units

turbines o f widely varying powers can be constructed without

increas ing the s ize o f the individual parts . The governor i s of thethrottl ing type .


96 S TEAM TURBINESOerl ikon,

and the.

American rights have been procured by the

Bal l Wood Engine Company , New York .

R ateau Patent—The main features of the Rateau turbine are

covered by American patents issued to Rateau and Sau tter in 1 903 .

The turbine i s of the compound impu l se type , sometimes cal l ed the

mu lticellu lar turbine , in which are a number of wheel s up on which

the steam acts in successi on, each wheel being in a s eparate com

partment .In Fig . 1 A i s the turbine cas ing , B B ,etc . , are the ro

tat ing w heels attached to the shaft , S ,and C C C are diap‘hragms

forming the s eparate compartments . Steam enters through the

F ig . 2 . Arrangement of

Gu ides in RateauTurbine .

intake pipe at D,passes between a seri es of gu ide vanes at c, where

i t i s directed against the vanes , b, of the first wheel . I t then passes

through the gu ide vanes in the next diaphragm and impingesagainst the next wheel

, and so on, unti l the exhaust space , E, i s

reached . The depth of the gu ide blades and wheel vanes increases

progress ively from the inl et to the outl et,to al low for the increas

ing volume of the steam .

The principle of thi s turbine as thus far out l ined is in no w ay

different from that of Moorhouse (Chapter but Rateau has

introduced an arrangement o f the vanes which is new and is

covered by this patent .In F ig. 2 the first set of gu i de b lades isshown at A. These are few in numb er and are arranged in,

say ,

three groups about the p eriphery of the first disk . After pass ing

COMPOUNDIMP ULSE TURBINES 97

through the wheel the next set of gu ide blades is reached at B ,

which cons ists of a greater number to accommodate the increasingvolume o f the steam ,

and these blades are arranged so as to extendby the first set in the direction in which the steam flows

, as shown.

When the steam reaches the first wheel it wil l be carri ed along a

short distance by the rotation of the wheel before discharging

into the wheel chamber, and a portion of the next set of gui deblades shou ld be located in advance of the previous set . At C thethird set laps by sti ll more, and final ly a point wil l be reached

w here the blades wil l extend around the fu l l p eriphery of thecasing. An advantage of this arrangement over one in whichsteam is first admitted to the turbine around the whole p eriphery

A B C D E

Fig. 3 . Cons truction of Rateau Diaphragms and Wheels .

i s that as the volume o f the steam at the admiss ion point is smal l

the vanes wou ld necessari ly have bu t l i ttle radial depth at thatpoint i f they comprised a fu l l circle , and there w ould be excess ivefri ction of the steam w hen flowing through them .In the Rateauarrangement the steam passages are deeper and the volume ofsteam passing i s large , in proportion to the rubbing surfaces o f

the vanes The reference to thi s in the claims of the patent i s asfollows distributors arranged in the m embranes to


100 S TEAM TURBINESdirect the mot ive flu id directly upon the paddle b lades , and said

distribu tors increasmg in Width,and overlapping each other suc

cessively at one end and no t at the‘

other.

”Rateau al so introduces

features of construction on w hich claims are made , but which are

it : no w ay tied with the blade arrangement mentioned above .

Some o f these are shown in Fig . 3 . At A i s one o f the diaphragms

Fi g . 6 . Group of Diaphragms o r Dis tribu tors for Turbines of

Different S izes .

containing the gu ide vanes . At B, C,

D,and E are typi cal wheel s

cons i sting o f steel disks either flanged around their peripheri esor els e with annu lar channel s riveted to their peripher i es .In thefirst two instances , B and C

,the di sks are dished to add to their

lateral strength and in the last two they are flat .

The vanes , which are curved su itably at the points where the

steam str ikes , are bent on an angle and r iveted to the circumference of the disk . At F and G are enlarged detai ls o f the vanes , the

COMPOUNDIMP ULSE TURBINES 101

second one showing a band or shroud riveted to the outer circumference.

Prac tical Notes .

—Ih designing the turbine,Pro fessor Rateau

attempted to attain the three following main ob j ects : 1 . A highmechanical efficiency together with as l ow an angu lar velocity as

Fig. 7. Pair of Wheel D isks .

possible. 2 . A large and at the same time non—injuri ou s clearancebetween the fixed and moving parts . 3 . The least pos s ible weightof the whole machine , and especial ly of the rotating parts .InFig. 6 i s shown a group of diaphragm-

s or distributors for tur

bines of different s izes . The gu ide vanes are arranged in groupsabout the p eriphery and the number of open ings about each groupincreases about the exhaus t end of the turbine unti l they final lyextend around the whole periphery ; As in an impulse turbine the

102 STEAM TURBINESexpans i on of the steam is complet e in this distribu tor, so that the

steam acts upon the w heel in virtue of its veloc ity , and as the

wheel vanes are symmetr i cal in shape , end thrus ts are practical ly

el iminated . The shaft passes through the diaphragms in bushings

of ant i-fri ction meta l . A pair of w heels i s shown in Fig . 7 .

These are cons tructed as indicated in sketch F ig. 3 .

The bearings of these turbines are ex ternal and by means of asystem of spring packing are kept perfectly tight . The speed i s

controlled by a centri fugal governor acting by vary ing the pres

sure of the steam del ivered to the turbine . By means of a by-pas s

in the main steam pipe it i s pos s ible to del iver steam of ful l pres

sure both to the entrance of the turbine and to a point in the ma

chine nearer to the condenser, thus enabling a h igher p ower than

the norma l amount to be produced by the machine, much in the

same manner that a compound engine may be used wi th ful l

pres sure steam and low pressure cyl inders .

The Zoel ly Turbine.

A s team turbine now attaining a prom inent p lace abroad is the

Zoel ly turbine which has been developed and i s now manufactured

by Escher, Wyss Co . ,Zuri ch , Switzerland , the famous manu

facturers of hydrau l i c turbines , water-wheel governors , etc . A

number of large German firms , of which the Krupps are one, are

repo rted al so to have formed a syndicate for the manu facture and

sale of this turbine on a large scale .

The general arrangement of the Zoel ly turbine i s evident from

the hal f- tone i l lustration,F ig. 8, and the l ine drawing , F ig . 9,

almost without explanat i on. The turbine i s divided into tw o parts ,encased sep arately , and placed far enough apart to permi t a bea r

ing to be located betw een them for supp orting the sha ft at the

center .In F ig . 8 the top of the cas ing of the low -pressure com

partment i s l i fted , exp osing the w heel blades to view , and in

F ig . 9 the same compartment is shown in section. The construe

tion of the high-pressure section i s entirely similar to the low -pres

sure , except that the steam passages have l es s area.

There are ten rotating w heels constructed in the form of cirenlar disks , attached to the sam e sha ft and carrying curved bladeson their peripheri es . For each w heel there i s a set of gu ide vanes


104 STEAM TURBINESfor directing the steam against the rotating blades . These gu ide

vanes give the steam the proper direction of flow and al l ow it to

expand a certain am ount as i t pa5 ses through the gu ide pas sag es ,their funct ion being the same as that of the steam nozzle in the

De Laval turbine and the gu ide pas sag es of the Rateau turbine .

Each w heel rotates in a chamber by i tsel f , the wal l s of wh i ch are

formed by the disks to which the gu i de vanes are attached . The

steam enters at A,Fig . 9 , and passes thro ugh a throttl e valve

operated by the governor, to the high—pressure compartment .Here i t flows through the first s et of gu id e passages , and impingesagainst the blades of the first w heel . The gu ide passages permit

the steam to expand to the somewhat l ower pres sure of the first

chamber and thus partial ly convert i ts p otential energy to kinetic

energy , which i s mainly gi ven up to the rotat ing w rheel , s ince the

steam leaves the w heel at a low veloc ity . The steam now passes

through the passages of the second gu i de d isk , expands to a

l ower pres sure and i s directed against the blades of the second

rotating w heel in the second comp artment , where it again gives

up i ts kinetic energy . When the last step i s reached in the low

pressure compartment the steam final ly exhausts , ei ther into a

condenser or into the ai r .

Guides and’ Wheel Vanes .

-At the beginning of the high-pressure s ection

,the gu ide vanes occupy only a part of the periphery

of the turbine , but tow ard the end o f the low -pressure part theyextend around the who l e circum ference . I t wil l be noted in

Fig . 1 0 that the passages through the gu ide vanes have paral l el

s ides ; that i s , the wal l s do no t diverge as in the nozzles of theDe Laval turbine . This construction i s based on the wel l-known

fact that steam wi ll expand and convert i ts avai labl e heat energyinto kineti c energy , or the energy of motion ,

by flowing through a

nozzle having straight,paral lel s ides

,provided the final p ressure

i s not less than . 58 of the in i tial pressure ; w hereas , i f the final

pressure is less than this,the wa l ls of the nozzle must d iverge in

order to fu lly expand the s team .In the Zoelly turbine the expansion occurs in success ive steps and the pressure does not dropsufli cient ly at any one step to make gu ide passages with divergingsides necessary .

It wil l be noted further,from Figs . 9 and 1 0

,that the passages

106 S TEAM TURBINESthrough the whee l b lades have th eir inner s i des incl ined , produc

ing channels of gradual ly increas ing area. This is no t , however,to al low for expans ion.In thi s turbine , as in others of the impul setype, the pres sure of the steam: does not change in pass ing through

the rotat ing w heel . The pressure i s uni form throughou t the

chamber in w hich the wheel turns , making a drop in pressure in

pass ing through the wheel impos s ible,and hence the only effect of

SHAPE OF GUIDE VANES

BEFORE INSERT ING.

PLANOF GUIDEANDWHEEL VANES

GU I DE WHEELFig . 1 0. Section of Diaphragm and Wheel .

the s loping s ides of the wheel pas sages i s to cause the steam to

flow smoothly , without eddy currents , into the next guide pas

sages , w hich are of larger area than the ones preceding . The conditions under which the s team flows through the wheel are entirelydifferent from thos e which influenc e the flow through the gu ide

vanes , for the latter have a higher pressure on one s ide than on theot her .

Enlarged sec tions of the wheels and gu i des are shown in

F ig . 1 0. Thep rinc ipal difference between the Zoelly turbine and

others of simi lar type , such as the Rateau ,l i es in the construction

of the detai l s of the turbine wheels . These are des igned to permit


108 STEAM TURBINESgovernor acts on a relay valve , m ,

and connects one s ide or the

other to pipes a and b ; a being a pipe leading from a reservoir fu l l

Of a l iqu i d , such as Oil or w ater, under pressure produced by a

rotary pump ; and b a return l eading to the suction well Of the

pump . The tw o p ipes e and f connect each end Of the valve to

the cyl inder g,which is located top Of the throt tl e valve.

Governor Turb ine.

The moving part of this valve is attached to the same stemas the piston h, in the cyl inder g. I f the load on the turbine i s

decreas ed , the resu lt ing increas e in speed raises the governor

lever n,and valve m makes a direct connect ion b etween anand f

and e and b. The l iqu i d,entering cyl inder g,

forces pi ston h

down, which clo'

ses throttl e valve k a corresponding amount , re

duc ing the pressure Of the entering steam . The valve stem is p ro

longed and attached to the end of lever n,and hence the down

ward movem ent of the throttl e valve moves the relay valve in

back to its original pos ition . During th i s return movement Of the

COMPOUNDIMPULSE TURBINES 109

valve m the lever n i Ot s about its le ft hand end ; while , when thelever w as original ly moved by the governor , i t pivoted about itsright hand end . Lever n i s thus w hat is cal l ed a floating lever,the fu lcrum Of w hich is shi fted from one end to the other , according to the conditions . When valve in has been returned to itsoriginal po s ition ,

no further movement Of the throttle valve can

occur unti l the sp eed Of the turbine changes again.

BOILER

F ig . 1 2 . Diagram ofHamilton-Ho lzw arth T urbine.Ham il ton-Ho lzw arth Turb ine

A turbine is being developed by theHooven, OwensRentschler Company ,Hamilton, Ohio , which is On the plan Of theRateau and Zoel ly turbines , but differs in detai ls Of construction.In units Of 750 Kw . and upward the turbine is divided into twoparts , the high and the low-pressure . Steam enters through a

separator and passes through the main inlet valve and the regu

lating valve,al l Of which are below the bed plate . As the steam

flows through the first set Of stationary vanes it forms a comp l etering instead of entering through a part of the ci rcum ference as in

the Rateau turbine . The casing i s d ivided into compartments with

1 10 STEAM TURBINESOne rotating w heel ~in each . Both the stationary and the moving

vanes gradual ly increase in height toward the low -pressure end .

Fig . 1 2 shows the scheme Of the turbine . This is somewhat mis

leading ,in that the stationary nozzles apparently increase in area

from inlet to outl et , a construction that wou ld not be requ ired

with the smal l drop in pressure that Occurs between the different

compartments . The areas do not actual ly increase , however, be

cause the gu ide vanes are so shaped that they are nearer together

at the outlet s ide than at the inl et s ide , and to compensate for this

SECTION ON A-B

SECTION ON C-D

F ig . 1 3 . Cons truction of Diaphragms .

they have to increase in‘

height somewhat from the inl et to the outlet s ides .

Details of Cons tru c tion—In F igs . 1 2,1 3

, and 1 4 are certain

detai l s of construction Of the turbine . F ig. 1 3 shows the sta

tionary discs which are bu i lt up of tw o s ide pieces riveted together.

Each vane i s a separate p iece held by its proj ection at its lowerend

, which fits inan angu lar groove between the two disks at their

periphery . The vanes are Of drop- forged steel and are secured byrivets . After they are in position their outs ide ends are groundand a steel ring is shrunk on.In case it were not desired to extend


112 S TEAM TURBINESThe Governor is . Of the spring-and-weight type and controls the

turbine by throttl ing the steam . It i s constructed on a relay sys

tem and controls the valve by moving a smal l wheel across the

faceOf the rotating fri cti on disk . This d isk is dr iven by a worm

and worm wheel from the shaft which operates the governor. At

normal speed the smal l wheel i s at the center Of the disk and is

moved out Of contact with it by means Of a cam . I f the turbine

shou ld speed up , however, the wheel wou ld be moved a short dis

tance to one side o f the center and the cam wou ld al so move suffic ient ly to al low the wheel to come in contact with the disk and berotated a number Of turns

,thu s closing the throttle valve a sl ight

amount , whereupon the wheel wou ld be returned to the central

position again and the cam wou ld throw it out Of contact with thedisk .

CHAPTER VICOMPOUNDIMPULSE TURBINES (Continued).

The Curtis Turb ine.

The Curtis turbine i s manu factured in this country by the General Electric Company, the large sizes at Schenectady , N. Y . ,

and

the smal l s izes at West Lynn,Mass . The Curti s marine turbine is

being developed by a company headed by M r. Curtis , the inventor,who is conducting extens ive experiments .

NOZZLE

SECOND WHEELSLI DEOPERATEDBY GOVERN

Fig. 1 . Early Form of Curtis Turbine.

Early Type—The mach ine is represented in i ts s implest and

earl iest form in Fig . 1 . It cons ists Of two rings Of curved bucketsmounted upon disks revolving with the shaft . Between the tw o

revolving rings is a group of curved blades in the form of a shortsegment fixed to the interior of the turbine case . The nozzle isOf rectangular cross section ,

so designed that one s ide Of i t can

slide in or out withou t material ly al tering the rat i o between the

inlet and outlet areas of the nozzle . By this means the quanti ty ofsteam del ivered is adjusted to su it the load , and i t i s not necessaryto govern by throttl ing . An earlv turbine Of substantial ly this

1 14 S TEAM TURBINESdes ign

, Of 1 50 horse-power , w as tested at Stevens Institute Of

Technology ,Hoboken , N . J .

S tage Turbine—In its practi cal form the nozzl es are smal ler

in area than in the experimental machine mentioned and are ar

ranged ih group s ; bu t the method of governing is in effect the

same . One des ign that has been used is shown in Fig . 2 . S team

STEAM CHESTNOZZ LE

MOV ING BLADESSTAT IONARY BLADESMOV ING BLADESSTAT IONARY BLADESMOV ING BLADES

NOZZLE DIAPHRAGMMOV ING BLADESSTAT IONARY

BLADESMOV ING BLADES

STAT IONARYBLADES

MOV ING BLADES

F ig . 2 . S tage T urbine. Three Ro tat ing Rings of Buckets inEach S tage.

enters through the seri es of nozzles , forming a broad be lt of steam ,

and the quantity admitted is regu lated by a seri es of p opp et valves ,one for each nozzle . Regu lation i s by opening or clos ing these

valves automatical ly , which has th e effect of increasing or decreas

ing the quanti ty of steam flowing ,as may be requ ired

,without

reducing the ini tial p ressu re . The turbine in Fig . 2 i s a “stage”

turbine , with two stages or elements , each cons is ting of three rotating sets of blades and the necessary gu ide vanes . Each element

i s incased in a separate compartment wi th i ts set Of nozzles .


116 STEAM TURBINESin the patent revi ew Of Chapter I I . , to which the reader i s referred .

Although a mod ified form Of the De Laval expans ion nozzle is

used , the rotative speed Of the wheel i s much lower than in the

Fig . 4 . The Firs t Kw . Turb ine,Ins tal led at the Commonw eal thS tation, Chicago .

De Laval type ,‘

s ince two or more rotating rings of blades are

ployed to uti l i ze the h igh velocity of the steam after i t leavesnozzle .In the De Laval turbine the s ingle wheelnearly as practicable at hal f the vto absorb

Fig 5 . Sectional Elevation of Kw .Turb ine.

118 STEAM TURBINESless than hal f the velocity Of the steam ,

and when the steam issues

from the first set Of blades it has a high residual velocity ; and this ,

in turn,i s taken up in part by the second rotating set Of blades ,

and so on. This construction makes it possibl e to uti l i ze the

energy Of the steam with a comparat ively smal l number Of blades .

For i l lustration,suppose steam to start with a velocity Of

feet a second ; once compounding wou ld reduce the requ ired

veloci ty Of the wheel by two , or to 750 feet p er second instead Of

the feet theoretical ly necessary with a s ingle wheel , and

three rotat ing sets Of vanes wou ld reduce the velocity to 500 feet a

second .

Curtis Vertical Turbines —Th e first commercial turbine bu i lt

by the General Electri c Company w as a 600 Kw . uni t , instal l ed

in their power plant at S chenectady in 1 901 . This machine w as

bu i lt on the l ines advocated by M r. Curt i s , with a horizontal shaft

and two stages wi th groups of w heels in separate cas ings , as in

Fig . 2 . S ince the constructi on of thi s machine al l the turbines of

the 5 00 Kw . s ize and larger have been bu i lt with shafts in a

vertical pos it ion , and the generator placed direc tly over the turbine .

The total weight Of the revolving parts i s borne by a step bearing

at the foot of the shaft , and the shaft i s steadied and al igned by

three bearings , one at the tOp of the generator , another near the

foo t of the shaft , and a third between the generator and the tur

bine . The sectional view,Fig . 5 , shows the arrangement clearly .

The different parts are l ettered as fol lows

A,spring—weighted governor ; B ,

generator ; C,cas ing inclos ing

the three turbine wheels ; D ,step bearing ; E,

ou tlet to condenser ;a,upper steady bearing ; b ,

lower steady bearing ; c , stuffing box

with graphite packing rings ; d ,connection from governor ;

e, mechani sm operating admission valves ; f, by-pass fo r maintaining correct pressure in second stage .

The cons iderations l eading to the verti cal design are stated byone Of the engineers Of the company

,as follows

The relative po sitions Of revolv ing and stationary p arts are definitelyfixed by the step -bearing . The stat ionary p art is symmetrical , eas ilyma chined and free from d istortions by heat . The shaft-bear ings are re

*W . L. R. Emmet, in a paper upon the S team Tu rbine in M odern Engineer ing,read before the Amer ican Society of Mechanical Engineers in 1 904 .


120 STEAM TURBINESF ig . 7 . Bucket Segments—the Up p er One for Low Pressure and th e

Low er One fo rHigh Pressure Sections of Turbine.

pressure of 1 50 pounds to pounds , thereby attaining a

velocity of feet p er second . I t acts upon the two rows of

moving vanes and then,in pass ing through the second set of noz

zles , i s expanded to about 1 8% pounds , again acqu iring a velocityof about feet p er second . It here acts upon the second se

ries of bucket wheels and i s del ivered to a third set of nozzl es ,which expand it to about 3% pounds , imparting to i t a velocityof about feet p er second . After acting upon the third set of

wheels the process is repeated and the steam is del ivered to a

fourth set of nozzles,which expand the steam to about 1 pound

absolute , giving it a veloc ity of feet p er second , wh ich is

absorbed by the fourth set of wheels , and by them the steam is de

l ivered to the condenser with its energy practical ly al l extracted .

Speeds of Ro tation—The speeds at which the various s izesof Curtis turbines (GO-cycle) operate are as fol lows

500 Kw revo lutions p er m inute.

1 ,0m ( 6

900

900

720

720

Fig. 8. Bucket Segment w i th Rim Riveted on.

COMPOUNDIMPULSE TURBINES (Continued) 121In the smal l er turbines the peripheral speed is about 400 feet persecond , and in the larger ones it is reduced to 325 feet p er second .

The Turbine Buckets — The most vi tal po int in a steam turbine

is the buckets , s ince they , and the spaces between them ,must be

shaped correct ly to give the prop er direction of flow and the

Fig. 9 . Bucket Cu tting Mach ine.

highest mechani cal effi ciency , and also to provide for the p rogres

s ive expans ion of the steam . The buckets of the Curtis turbineare cut out of the solid metal by special bucket cutting machines .In the smal ler sizes the blades are cut fro-m the disks compri s ingthe wheels, and in the larger s izes the buckets are cut from segments of steel or bronze and then bolted around the periphery o fthe disks .In Figs . 7 and 8 are shown bucket segments , in the

S TEAM TURBINESfirst instance as they appear after machining and in the second

with a rim of steel riveted on,closing the outer openings of the

curved passages between the buckets .

Buckets are al so made o f drawn metal,the p ieces being set in a

mou ld and fixed in place by pouring molten bronze around them ,

thus forming one of the segments .In al l these constructions the

buckets themselves are l ess in width than the rim of the segment ,so there is no possib i l ity of their coming in running contact with

any of the stationary part s o f the machine .

Whil e the process o f cu tting the buckets produces very nicelv

fin i shed work,i t i s at be st exp ensive, cal l ing for sp ecial machines ,

which have taken a long time to des ign and develop .In al l of

them a s ingle-pointed cutt ing tool i s employed , the tool be ing so

gu i d ed by the m echan i sm that its cutting edge wi ll be in correct

position for cut ting effectively at al l p oints of the cu rve .In oldermachines the too l w as given a motion of rotation around the cir

cum ference of a circ le'

( app rox imately , depending on the shape of

the buckets ) , and as i t passed the bucket segment i t would remove

a chip . The tool w as gradual ly fed into the work as the cutting ad

vanc ed .In the latest type the tool i s given an osci l lating motion,

back and forth across the face of the segment . On the forward

stroke the tool advances for the cut and on th e return withdrawsfor clearanc e . The machine of th is typ e i s partly pneumat ic in its

action, and i s an exceedingly interesting piec e of mechanism

S tep Bearing—In Fig . 1 0 i s a sectional drawing of the step

bearing . I t cons ists of tw o castiron blocks , A and B,one carried

by the end of the shaft and the other held firmly in a horizontal

po s ition and so arranged that it can be adjusted up and down bya powerfu l screw , S . Both blocks are recessed to about one hal f

thei r diameter as shown at C and into th i s recess oi l i s forcedthrough the central bore D

,with sufficient pressure to rai se the

shaft s l ightly and support its weight on the th in film o f oi l which

flow s out between the flat faces of the two b locks . The lubri cant

flowing out fil ls the space surrounding these blocks and ri ses between the verti cal bearing and the sha ft , to the overflow E ,

where

it escapes . The whole structure i s ins ide the base and packing isused , aided by a low steam pressure , to insure that oi l shal l notescape into the vacuum chamber above . The pressure requ ired in


124 S TEAM TURBINESSgeed o f C ond ens ing No . o fha ft . o r Non C u r rent . Vo l tage.

R . P . M . cond ens ing .

S tages .

Non-0 0 nd . 1 D ir . C u rs t 0 6

1

l2

3 A l t . C u r

3 4 D 11’

. C u t

3 4 D C A

The three smal ler s izes have two bearings . The turbine wheels

are overhung on the end of the shaft and the shaft i s in one piece,with the turb ine and armature both mounted on i t . Beginning

with the 75 Kw . s ize and upward the shafts are in tw o pieces and

the sets have four bearings .In the sma l l s izes where the wheels are overhung the fro nt endof the case may be taken off to obtain access to the wheels and

intermediates , and in the larger sizes where four bearings are

provided the upper hal f of the cas ing is removable for the same

purpose.In the fou r—bearing sets the generator and turb ine shafts are

united by a flexib l e coupl ing w hich permits some l i ttle inaccuracyin the al ignment of the tw o sha fts without affecting the op erationof the set . This coupling i s a modification of the Oldham coupling,the necessary flexibi l ity being secured by the use of l inks turningon pins .

The 1 5 and 25 Kw . turbines are of the s ingle-stage type ,having a s ingle group of nozzles and three rows of moving buckets .The larger s izes are mu l ti-stage and have only two rows of moving buckets per stage.

The bearings us ed in t hes e turbines are support ed on spheres .

The l inings are made in two parts and lubrication i s eff ected byforced feed from. a pump which i s geared to the main shaft of the

turbine and suppl ies oi l at a pressure of from three to six pounds

p er square inch .

Governing M echanism .

—~Varions methods o f governing havebeen experimented with by the General Electr i c Company .InSizes of 25 Kw . or less

,governing is effected by throttl ing the

steam pressure by the direct action of a powerfu l centri fugal governor.In the larger s ized machines

,however

,each nozzle or

COMPOUNDIMPULSE TURBINES (Continued) 125

group of nozzles i s suppl ied w i th steam from a poppet valve

operated by means of controll ing mechanism under the influence

of the governor. One method adopted for larger uni ts cons ists in

the use of a hydrau l i c cyl inder with a controll ing valve actuat ed

by the governor. A movement of the control ling valve, caus ed bya change in the speed , admits oi l to one side or the other of thepiston of thi s cyl inder and a movement of the cylinder results ,through the intermediate mechani sm , in the Opening or closing

of corresponding poppet valves . While the governor remains in

any given pos ition the hydrau l ic cylinder i s al so stationary and i slocked in i ts pos ition by confining the oi l in bo th ends of the cylin

der. A movement of the governor produces a correspondingmovement of the hydrau l ic p iston ,

and w hen thi s movement hastaken place the parts come to rest . The motion of the hydraul icpiston i s trans ferred to a shaft running paral lel with the bank ofnozzles and on which is a seri es of cams that actuate the valves .

The Kw . turbine, Fig . 5 , i s controlled by a hydrau l i c gear ofthis type . The hydraul i c cyl inder i s located in a vert ical positionabove the nozzle valves , at the right

,and its plunger moves the

cam shaft one w ay or the other according to the position o f thepi lot valve . The -cam shaft i s plainly vi sible in the engraving.

On some o f the largest machines horizontal cyl inders have been

employed instead o f the vertical,placed between the turbine and

the generator,and with the plunger operating the cam shaft

through a rack and pinion.

M echanically Operated Gear.

—This gear i s a development from

steam-engine practice and i s used on some of the turbines manufactured at the Lynn plant o f the General Electri c Company.

Each nozzl e valve is actuated directly by a pair of reciprocating

pawls , one adapted to open the valve and the other to close it .

The several pairs o f pawls are pivoted to a common moving sup

port , which is osci llated by a rock shaft receiving its motion fromthe turbine shaft through a worm and w ormw heel . At the upperend of the valve spindles are crossheads , in which are millednotches or teeth for the pawls to engage

,and the engagement of

the pawls in these teeth i s determined by the angu lar position ofshield plates controlled by the governor . These plates are set

progressively, one in advance of the other , to obtain successive

126 S TEAM TURBINESactuation of the valves . When more steam is requ ired , a shield

plate permits the proper pawl to engage the crosshead of its valve

and open the valve on the upward stroke ; while i f less steam is

requ ired the shield plates wil l be moved by the governor to such

a posit ion that the proper pawl wi ll close its valve during the

downward stroke of the rock shaft .

Another type o f mechanical gear , that has been appl ied to

smal l er units , has positively actuated valves that are always either

in the fu l l open or entirely closed pos itions . Each valve has a

crosshead and block and i s actuated by a dog cons isting of a smal l

eccentri c strap with a proj ecting arm about s ix inches long , p ro

vided with two hooks , one adapted to pu l l the crosshead block

toward the eccentri c shaft and open the valve and the other to

push the block away from the shaft and close the valve . The

governor controls the engagement of the hooks . The governing

arrangement of thi s gear i s very ingeniou s and sketches of the

mechani sm wil l be found in the 1 906 report of the turbine comm ittee of the National Electric Light Association.

E lec tric Governing—One of the earl i est methods used for con

trol l ing the nozzle valves,and which is stil l employed , i s an elec

tri c system in wh ich the action of the valves i s governed bysolenoids or magnets through which an electri c current passes .In F ig . 1 1 is a diagram showing the principl e of the arrangement .

The governor at G connects with the cyl inder R,on the surface of

which is a seri es of contact points arranged spiral ly , so that as

the cyl inder turns one w ay or the other these points come in con

tact success ively with corresponding points from which the ver

t ical w ires extend and close the c ircuit'

through these w ires in suc

cession.

Referring to the figure : A i s the supply wire for the currentand B the return . The current passes through the switch S ,

which ordinari ly i s closed , and thence to the wire and to the cyl inder . The verti cal wires at the left connect with the magnets be

longing to the various sets o f nozzles,but in thi s diagram the

horizontal wires l eading to one set of nozzles only are indicated ,which accounts for several of the vertical wires having no apparent connections . When the cyl inder R i s so rotated by the governor as to bring two contact points together the current ener


STEAM TURBINESposition that steam under pressure i s admitted to the space above

piston P ,this pressure , in connection with the spring S , forces the

valve to its seat .

Fig. 1 2 . Nozz le Valve. F ig . 1 3 . Curtis Turbine Governor.

Curtis Turbine Governor .

—In F ig . 1 3 i s an outl ine of the gov

ernor for a 500 Kw . machine . The governor i s supported

flange keyed directly to the top of the vertical shaft of the turbine and the whole support ing framework rotates with the shaft .

W W are the two weights fu lcrumed at the points indicated and

as the turbine speeds up the centri fugal force of the w eights pu l ls

the lever L downward against the res istance of the spring S .

IMPULSE TURBINES (Continued) 129

A second spring at S 1i s arranged so that its tension can be in

creased or diminished to change the loading of the governor and

thus bring the speed of the governor within smal l l imits . The

lever L connects with the valve mechani sm .

Ried ler-Stump f Turb ine.

This turbine has been developed and manu factured bv the

Al lgemeine Electricit'

ats Gesel lshaft , Berl in,who have now be

Fig . 1 4 . Buckets and Guides of Compound Ried lerS tumpf Turbine.

come incorporated with a new Berl in organization, known as the

Union El ectri c Company . The obj ect of theUnion Company is toexploit in certain Europ ean countri es important steam turbinepatents

,chi efly those of Pro fessors Ri edler and Stumpf , controlled

by the Al lgemeine Company ; and the Curti s patents , owned by the

General Electric Comp any in this country . As a resu lt o f thisorganizat ion ,

turbines are now being constructed by the A. E.

combining features to be found in bo th the Cu rt i s and the Riedler

Stump f machines .

The Riedler-S tumpf Compound Turb ines .

— The singl e zwheelRiedler-Stump f turbines have already been described in ChapterIV .In the compound turbine o f this design,

in which two o r

more wheels, or else two or more rows of buckets on the same

130 S TEAM TURBINESwheel , are us ed , each wheel i s provided with semi-circu lar buckets .

The steam is proj ected against one s ide o f the buckets of the first

wheel and then as i t escap es from the oppos ite s ide , i t i s col lected by

curved gu ides which carry it around to the next wheel . The

sketch,Fig . 1 4

,shows the arrangement , and i t wil l be noted that

here it i s not nec essary to arrange the gu i des sp iral ly in order to

HIGHPRESSURESTEAM ENTERS

CONDENS ING WATERENTERS

F ig. 1 5 . Comp ound Ried ler-S tump f Turb ine.

circumvent the nozzle as w as done in the cas e of compounding

with the single wheel as described in ChapterIV . The lettersA, B , C, D indicate the direction of the flow of steam in F ig . 1 4 .

When a cons iderable speed reduction i s des ired, t he turbine i s

divided into stages with tw o steps in each stage .In F ig. 1 5 i s a sectional drawing of a tw o-stage turbine,s imilar

in i ts arrangement to the Curti s turbine made in th is country . The


132 S TEAM TURBINESW i th condens ing w ater which enters through Open ings in the pe

riphery of thi s passage . The mingled steam. and water t hen flow to

the center, where they enter between the two rotating disks at R.

The condensed steam and the condens ing water are here thrown

outward by centri fugal force and are discharged through openings

at M M . This novel arrangem ent of the condenser insures tho r

ough intermingl ing of ‘the water and steam and produces a high

vacuum . The shaft of th is turbine and generator instead of being

carri ed on a step bearing at the bottom is supported by a b earing atB , s ituated between the tu rbine and the generator.

F ig: 1 9 .

“

End View of A . E. G. Turbine.

The A. E . G. Turbine— Figs . 1 6,1 7 and 1 8 show three of the

more recent designs'

of the Allgemeine Com pany,in two of which

the principle o f the Curt is type of wheel i s ut i l i zed . The s implest

design i s that of Fig : l 6 , a s ingle stage turb ine, the wheels of whichare made with a double bucket rim .In Fig . 1 7 i s a four- stage tur~

bine with bu t a s ingle wheel in each stage ; whi le in Fig . 1 8 i s acombination o f the two previou s types . .In each o f these des ignsthe turbine wheels are supported by the ends o f the shaft whichpasses through the -bearings and overhangs , while the generator i slocated between the bearings .

Features of Cons truction of the A. E . G. Turbine—The use ofonly two bearings for a generating uni t s impl ifies the cons tructi on

134 STEAM TURBINESto a marked degree, and with a very stiff fram e and a heavy shaft ,gives satis faction. Owing to the stiffness of the frame i t i s poss i

bl e to secure the cas ing to it so that i t i s po ss ible to expand and

contract. The w heel casings are of cast iron provided with rel i ef

valves as a prot ection agains t a pos s ibl e ri s e of pressure. The

wheel i s held on the shaft end by a flange and i s machined out of

a sol id ni ckel steel disk . The steam inlet to the main cut -off valve

and to the steam distributing chest i s through a fine-meshed screen.

The steam from the distri buting ches t i s del ivered to the nozzles

by a number of pipes shown in end view ,Fig . 1 9 . The bearings

are suppli ed with oi l under pressure and are l ined with wh ite

metal . The governor i s fitted direct on the free end of the shaft

and is of the spring type . I t i s placed ins ide the steam distribution

chest and openings which l ead from the latter to the nozzles are

closed or Opened by a steel band .


136 S TEAM TURBINESGeneral Princip les .

—In the Parsons turbine there are alternate

rows of stationary gu ide vanes and moving wheel vanes as in

F ig. 1 .

The steam flows through a fixed ring o f directing

blades , which serve the purpose o f steam nozzles , onto a revolving

ring of s imilar blades and so on,the pressure being reduced a

smal l amount at each step . The revolving rings of blades act

both in the capacity of buckets and nozzles as in any reaction

turbine .

Assume , for i l lustration,that the steam expands from 1 1 5

pounds absolute to atmospheric pressure in i ts passage through

the turbine and that there are 40 rows of gu ides and vanes giv

ing an average drop in pressure of 2% pounds at each wheel . I f

steam were to flow through an expanding nozzle from 1 1 5

pounds to 1 5 pounds absolute , its velocity wou ld be about

feet p er second ; but , by stepping down the pressure and al lowing

it to expand an average of 2% pounds at each stage , the velocityof flow corresponding to the differences of pressure would be

only about 400 feet p er second . I f the Parsons turbine were

purely a reaction wheel , the wheel woul d travel nearly as fast as

the steam when i t l eft the moving vanes , and in the above i l lustra

tion wou ld have a peripheral speed of nearly 400 feet p er second .In the actual turbine the average speed i s much l ess than this ,requ iring more rows of blades and an immense number of blades .In a 400 Kw . turb ine there are 5 8 rows o f gu ide vanes and wheel

vanes , or 1 1 6 rows in all,aggregat ing about blades .

The pressure differences at each el ement or set o f blades gradual ly decrease from inl et to exhau st , instead Of running uni formas in the above example

,s ince

,for a given difference of pressure ,

the velocity of steam is much greater at low than at high pres

sures . Thu s,in flowing from 1 65 pounds to 1 5 5 pounds absolute ,

a difference o f 1 0 pounds,the velocity acqu ired i s only about .

520 feet p er second ; whil e at atmospheric pressure practi cal ly the

same velocity is acqu ired by a drop of only one pound in pres

sure or as much as in the first case . The steam veloci ti esare kept within 1 50 feet p er second as a minimum at the high

pressure end ,and 600 feet p er second as a maximum at the low

pressure end .

REACTION TURBINES 137

Wes tinghouse-Parsons Turb ines .

Des crip tion of Parts —The el emental parts of a Parsons turbine

are the rotor or rotating element , the stator, compri s ing the cas ing

and gu ide vanes , and the balancing pistons . These are shown in

F ig . 2 ,which represents a Westinghouse-Parsons turbine . Steam

enters the chamber B at boi ler pressure through the steam pipe A

and passes to the right through the first group o f blades whichgradual ly increase in height ( see F ig . 1 1 ) to chamber C .Here ,to avoid excessively long blades as well as many sizes o f blades , i t

Fig. 2 . Sectional Elevation of Wes tinghouse-Parsons Turbine.

i s necessary to jump to a larger diameter and the steam flows

through a second set to D and final ly through a third set to spaceE. The balancing pistons a

,b and c are of such a diameter that

the steam pressure against them exactly balances the axial thrustin the d irection of the steam flow . This thrust i s composed o f

three factors : ( 1 ) The static pressure on the end of the drum ; ( 2)the forward thrust on the blades due to the impact of the steam ;

and 3 ) the backward thrust due to the reaction o f the steam in

l eaving the blades . The net resu l t i s a forward thrust . The diameters of the pistons are approx imately equal to the -mean diameters

of the steam areas of the different steps . The pipe F connects theSpace back of the balancing pistons with the exhaust chamber. G

i s a coil for cool ing the oi l c ircu lating through the bearings .

138 STEAM TURBINESIn Fig . 3 i s shown a 4 00 Kw . turbine open for inspection. The

cas ing is made in halves divided longitudinal ly so that the upper

hal f can be removed , exposing the rotor , which may then be rai sed

from its bearings , after the bear ing caps are removed . The

interior wal l s o f the casmg . contain the stationary radial blades

corresponding to those on the rotating cyl inder . S tart ing at the

le ft,i t wil l be seen that there are several rows of blades , al l

of the same height ; then there is a change to blades of a sl ightly

F ig. 3 . 400 Kw . Wes tinghouse-Parsons T urb ine w i th Cas ing Removed .

greater height and there are several rows of this s ize , and so on.

When the mechani cal l imit i s reached for s ize o f blade , the

rotor i s then increased in diameter , giving a greater circumference

and al lowing shorter blades . The correct method ,theoretical ly ,

wou ld be for each row to be a l ittl e higher than the previous one

throughout the turbine . Practical ly , thi s i s neither conveni ent

nor necessary .

A more detai l ed description will now be given o f certain parts

of the turbine , as made by the Westinghouse Machine Company.

Turbine B lades — These were formerly made o f a special cold

drawn bronze,but at the p resent time drawn steel i s extens ively

used . The blades are secured in annu lar rings turned on the out


140 S TEAM TURBINESof fri ction rings

,each being al ternately larger and smal l er than

the ad jacent ring , the smal l ser i es fitting the shel l on the outs ide

and the large ser ies fitting the hol e in the bearing block .In the Westinghouse-Parsons turbine the bearings are made

up of several concentr i c sleeves instead o f the r ings loosely

fitted in the pedestal s . Oil circu lates between the sleeves , and

the capil lary action forms a flu id cushion about the several sl eeves ,which restrains vibration and at the same time gives sufficient

flexibil i ty to al low the shaft to revolve about its axi s of gravity

instead o f it s geometri cal axis . The bearing proper i s a gun

F ig . 5 . Ribbed Disk fo r Water-packed Gland .

metal bu shing which i s prevented from turning by a l ooselyfitted dowel . Outs ide o f this are three other concentric tubes .

Water-Packed Glands .—In any turb ine it i s necessary to p ro

vide glands at the ends of the cas ing to prevent the escape of

steam or the admission of air around the shaft , which latter i s

detrimental in the case of high vacuum . Steam-packed g lands

have been used with success , but the Westinghouse company nowuse water-packed glands .In the cas ing is an annular groovearound the shaft

,in which rotates freely a di sk attached to the

shaft . The disk has vanes on i ts faces,l ike the blades of a

blower . ( See Fig . The compartment i s fil l ed with water ,and when the turbine i s running the water i s thrown outwardand completely fil ls the outer part of the annular space and

prevents the air or steam from pass ing the periphery o f the disk .

REACTION TURBINES 141

A similar device has been employed in the glands o f centri fugal

pumps .*

Lubrication—A smal l pump , driven by a worm and w ormw heel

upon the shaft circu lates oil through a closed system ,compri s ing

in the order o f arrangements , pump , oil cooler , bear ings and

reservoir. The oi l is suppl ied to the bearings at the top ,at one

end where it follows a groove in the top o f the shel l , from which

it i s distr ibuted around the shaft . A forced circu lation under

high pressure is not found to be necessary . The ob j ect i s to

maintain an oi l film around the j ournals so they will never actual ly

come in contact with the bearings .

Governing Arrangement.

Descrip tion of Governor.

—Fig . 6 shows the governing mechan

i sm of the Westinghouse-Parsons turbine . ItIS sub stantial lv

the same as that i l lustrated in the second chapter in connectionwith the Parsons

'

patent of 1896 . The governor i s of the centrif

ugal type with bel l-crank levers , the vertical arms of which carrythe bal l s , and the horizontal arms bear against the spiral spring,

which res ists the centri fugal force o f the bal ls . The tension of

the spring may beadjuste’

d for the purpose of synchroni z ing twoal ternating current generators when running in paral lel . The

main admission valve i s actuated by the piston B ,which is con

troll ed by the pi lotw

valve A. Steam is admitted below the piston

through the annu lar clearance around the main valve stem and

raises the piston against the pressure o f the spring . When thepilot valve A

,however

,uncovers one o f the ports the steam

*A s imple device for packing the shaft of centr ifugal pumpsin a frictionless manner w as introdu ced some year s s ince byM essrs . Robinson B ro thers Co . , o f M elbourne , Au stral ia ,

and described in a recent issue o f London Eng ineering .Itis applicable as w el l t o the pack ing o f the shafts o f steamturbines , w here the effi ciency is impaired by the leakage o f

air into the vacuum end . The idea is ingenio u s in it s verys implicity. The bear ing is cased in w ith an annu lar chamb er F w hich is fi l led w ith w ater . Ro tary mo tion is given t o

t he w ater by means of a d isk o r set o f vanes E attached t o

the shaft. As the d isk is tight upon the shaft , any air t o

reach the interior mu s t pass around t he top s o f the blades .

Th e w ater in which the t ips are immersed ,ho w ever , is under

greater pres sure , due t o centrifugal fo rce, than the pres sureof the atmo sphere can overcome , and thus t he air is effectual ly exc luded

'

w ithou t the entrance o r expend i ture o f w ater w hile the shaft is leftentirely free—Pow er , Apri l , 1904 .

142 S TEAM TURBINESF ig . 6 . Governing Arrangement .

escapes from the space under the piston, through the smal l ex

haust pipe and al lows the spring to close the valve .

The pilot valve i s governed both by the motion of the governor

and the reciprocating motion of the rod C wh i ch i s actuated byan eccentri c driven through a worm and w ormw heel from the

main shaft o f the turbine . D and E are fixed fu l crums and F

i s a floating fu l crum moving up and down with the governor

sleeve. The reciprocating motion of the rod C i s communi cated

to the pi lot valve A and thence to the main valve , admitting

steam to the turbine in puffs ; wh il e the distance that the valve

Va lve Open

When Running L igh t LoadIF ig. 7.Ind icator Diagram Show ing Effect of Recip ro cating

Valve.


144 STEAM TURBINESprovided to admit high-pressure steam to the second drum of the

turbine on overl oads and increase its capacity up to 50 p er cent or

more in excess o f the normal rating . This arrangement has the

further advantage that i t enables much better economy to be main

tained under normal loading than when the primary admiss ion

valve only is used for governing .In Figs . 8 and 9 are diagrams

showing the principle of the valve , and i ts connections , taken

from the patent records"

,and the sectional view ,

Fig . 1 1 , shows

the actual arrangement o f both primary and secondary valves .In Fig . 8 A i s the steam inl et and B is a valve admitting high

pressure steam ,when the valve i s rai s ed , to the port C, which

Fig . 9 . Show ing Connections fo r By-Pass .

connects with the intermediate part of the turbine . Th i s i s

shown in Fig . 9,where steam enters at A ; B is the valve , and C

i s the pipe l eading to the turbine .

The valve , B ,i s hol low

,al lowing the steam to pass through

to the space , D ,where it bears against the under s ide of the piston,

E . F i s a smal l passage l eading from space ,D ,to the space

,H

,

so that under ordinary conditions there wil l be a balanced

pressure on the pi ston E,and the valve wil l be kept seated by the

spring , S . Connecting with the space ,H, in wh i ch the spring islocated , i s a pipe , P ,

l eading to a by-pass in the base of the gov

ernor , shown -at the l eft,which is opened or

'

c losed by a pilot

valve , M ,under control of the governor . Under normal conditions

the pilot val ve wil l be in the position shown,closing the by-pass

and preventing the escape of steam from the chamber,H. Shou ld

the speed of the engine decrease beyond a fixed point,however,

146 S TEAM TURBINESthe governor bal l s wou ld move inward , which wou ld depress the

governor yoke and the pilot valve,M

,caus ing the pi lot to

open and al low steam to escape from space ,H, into the atmos

phere. The resu l t wou ld be an unbalanced pressure on the piston,

E,caus ing it to rai se and compress the spring and open the valve ,

B,al lowing the high-pressure steam to enter the low-pressure

part of the turbine and increase the power .

S ec tional View of Wes tinghouse-Pars ons Turbine—In F ig. 1 1

on the opposite page is a sectional vi ew showing the essential

parts of a turbine , which are l ettered to correspond with the

fol lowing l ist o f part s

S .

—Steam adm ission.

V .

—Adm ission valve to high -

p ressure end . This valve is contro lled bythe governor ( connections not show n) and is o scillated by an eccentricdriven by the w orm and w o rmw heel at right—hand end of main shaft.V

8.

—Auxiliary valve also contro lled by governor and op ened automat ical ly in case of o verload .

P , P , P .

—Pistons o r d isks against w hich steam p ressure acts to balancethe thrust.E, E, E.

—Equalizing p ip es . The tw o up p er ones maintain steam p res

sures against the front faces of balance p istons equal to the p ressures in thestep s or stages of the turbine hav ing corresp ond ing d iameters—the low er

one maintains vacuum p ressure at the back of the large p iston.

T.

—Adjustment bearing for maintaining the exact running p osition of

the rotor and for taking up any unbalanced thrust not p rovided for by thep istons . This bearing is adjusted endw ise to locate the rotor in correctp os ition relative to the stationary p art.R.

—Relief valve.

B .

—Exhaust p assage.

The arrangement of the governo r has p rev iously been described.

Kw . Turbines .

—~The general vi ew,F ig . 1 0, shows a

turbine of thi s power of the type that i s to be used for the initial

equ ipment of the Pennsylvania Rai lroad terminal property in New

York C ity , furni shing electri c power for the trains pass ing through

the tunnel approaches to New York C ity now in construction. The

space occupied by thi s machine i s approximately 27 feet 8 inches

by 1 3 feet 3 inches , and the height to the top of the rai l i s 1 2

feet . I t occup ies‘

less than square foot p er electri c horse

power and develops horse—power p er square foot of floorarea. For the complete uni t

,including the generator

, a space ofthe above width and 4 7 feet 4 inches long is requ ired .


148 S TEAM TURBINESThe machine runs at 750 revolutions per minute . The con

struction i s substantial ly that used in the smal l er machines . To

support the drum a central steel qu i l l i s employed . Hollow forged

steel ends are forced into the ends of the qu i l l and constitute the

j ournal s .High-pressure steam is conveyed to all parts of the

qu i l l structure to el iminate distort ion due to expans ion.

The bearings of these larger machines are of the sel f-al igning

type, s imilar to those employed in generators and cross-compound

engines . The departure from the oi l cush ion j ournal s u sed in the

smal l er machines i s made poss ibl e by the low speed of rotation.

Turbines w ith S eparateHigh and Low -Pressure Cy linders .

Three turbines,aggregating Kw . ,

have been instal l ed in the

immense power plant of the Interborough Rapid Trans it Company ,

New York C ity , to furni sh current for l ighting the New York

subway . The most striking feature of these i s the separation of

the high-pressure and low-pressure sections,which provides for

a central bearing for the turbine shaft,thus reducing the distance

betw een bearings and al lowing a much l ighter shaft . As original lydesigned , these turbines were to be equ ipped with reheaters , placed

between the cyl inders,but the reheaters were final ly omitted .

It w as expected that the drying of the steam and poss ibly i ts

superheating in the receiver,before the steam entered the low

pressure cyl inder,wou ld effect an improvement in economy . Ex

periments at theWestinghouse shops , however, have demonstratedthat such is not the case . Franci sHodgkinson states that “

ex

haustive tests have shown the reheater to be of l ittle , i f any ; valuein increas ing the economy of the turbine when the high-pressure

steam condensed in the reheater coil s w as charged up against the

turbine . An improvement in the separator resu lted in an im

provement in the operation of the reheater,but , notwithstanding

this , no advantage due to the reheater cou ld be observed and i tsappl ication does not seem to be warranted , on account of the

decreased compactness of the machine .

”

Westinghouse-Parsons turbines are no longer bu i lt with tw o

cyl inders , the whole tendency being toward compactness . The

Kw . uni t with inclosed generator,Fig . 1 2 , i s o f the latest

type . The obj ects of encas ing the generator are to reduce the

noise which sometimes i s enough of a roar to be disagreeable , and

150 S TEAM TURBINESto enable a current of air to be forced through the generator for

the purpose of maintaining a moderate temperature and enabl ing

heavier overloads to be carri ed without danger o f overheating.

Th e B row n-B overi Turb ine.

Descrip tion—In F ig . 1 3 i s shown one of the Parsons turbines

manu factured by Brown,Roveri Company , Baden, Switzer

land . The arrangement of the turbine blades and the balancing

Governor of B row n-B overi Turbine.

pistons,including the increased diameter of the drum at the low

pressure end ,are substant ial ly the same as in the Parsons turb ine

as made by the Westinghouse Machine Company in thi s country.

The governor ; which is shown in F ig. 1 3,al so operates on the

same principle,following the l ines laid down in the Parsons

patent in 1 896 . The oil ing is by forced lubrication and the gen

eral arrangement of the valves , governor, oi l p ip ing ,etc . ,

i s clearly

indicated in the engraving .

By-pass Valves .

—M r. Brown of this firm has taken out a

United States patent for a by—pass valve to supply high-pressure

steam to the low-pressure end of the turbine,which is somewhat


152 STEAM TURBINESdifferent from theHodgkinson valve already illustrated . The

invention cons i sts in providing pipes from the steam chest to the

intermediate stages of the turbine and controll ing the opening of

these pipes by the governor.In F ig. 1 5 , steam is admitted through the supply pipe , A,

and

when the thrott l e valve , B ,i s rai sed by the governor , i t will pass

in the direction of the arrows through the valve , C, to the steam

space , D ,whence it wil l enter the high-pressure end o f the turbine .

F ig . 1 5 . By-Pass Arrangement.

The pipes,E

,F and G,

l eading to other points in the turb ine , are

opened to the steam space by movement of the valve , C, which

uncovers s everal ports shown in success ion,when i t i s raised .

Ordinari ly , i t i s kept in i ts lowest pos ition by the spring , S , thus

clos ing al l the ports . I f , however, the speed of the turb ine

decreases under a heavy load the governor wil l admit a greater

quantity of steam through valve D to the steam space , increas ing

the pressure in the steam space and forcing the p iston,P

,upward

against the pressure of the spring,by this means rai s ing the valve ,

C,and admitting steam success ively to the different stages of the

turbine . Brown’s patent al so covers an arrangement,for a s imilar

purp ose , having the valve , C,controll ed directly by the governor.

REACTIONTURBINES 153

TheAl l is-Chalmers Turb ine.

The illustration, Fig . 1 6 , shows the first turbine instal led in this

country of this type . It is now in operation at Utica , N. Y . It is

rated at Kw .,normal load , and runs at a speed o f revo

lutions p er minute . It i s direct- coupled to an Al l i s-Chalmers two

phase,60-cycle revolving-field alternator, Operating at volts .

The uni t has a continuous overload capacity o f 25 p er cent , with

a 3 -hour 50 p er cent overload capacity without exceeding a safegenerator temperature , and capable of a 1 00 p er cent safe momentary overload . Artificial venti lation by means of an elec

trical ly driven fan blower wil l , however , enable the unit to be run

safely beyond its rated overload capacity .

B lading .

—The chie f distingui shing feature is the blading . The

roots o f the blades are formed in dovetai l shape by special ma

chinery,and are inserted in slots cut in foundation or base rings ;

these slots being formed by wspecial machine too ls in such a w ay as

to exactly conform to the shapes o f the blade roots . The founda

tion rings themselves are of dovetai l shape in cross section and are

inserted in dovetail ed grooves cut in the turbine cas ing and spin

dle respectively,in which they are held by key pieces , much in the

same w ay that the well-known“Lewis bolt i s fastened .In order

to further insure the integrity o f the construction,the key pieces

or rings after being driven into place are upset into undercutgrooves .

Another noticeable feature o f the blading is the method o f rein

forcing and protecting the tips o f the blades,which is a point upon

which much thought has been expended by various inventors .Informing the blades a shou ldered pro j ection i s left at the tip . Thisis inserted in a slot punched in a shroud ring ; the slots being

punched by special machinery in such a w ay as to produce ac

curate spacing and at the same time form the slots so that theywil l give the proper angles to the blades independent o f the slotsin the base ring . A fter the blade tips are inserted in the slots inthe shroud rings they are riveted over by special ly arranged pneumatic machinery .

The shroud rings are channel shaped with outwardly proj ectingflanges which , after assembly in the turbine , are turned and boredto give the necessary working clearance . The flanges of the chan


156 S TEAM TURBINESF ig . 18. Tw oHalf-rings of B lades—the Larges t and the Smal les t in

the Turbine.

absence of the u sual l ow—pressure balance piston. Instead of

being at the h igh-pressure end , as formerly arranged , i t i s at the

low-pressure end , and by making this p iston in such a w ay that i tscircular area i s equal to the annu lar area of the pistons used in the

older construction, the low-pressure balance p iston can be much

smal ler. Instead of reducing the leakage past thi s p iston by means

of “dummy packing,

”as in the high-pressure and intermediate p is

tons , and as used in the low-pressure pistons of the older construc

F ig. 19 . From a Pho tograph , Show ing Uniformity of B lad ing.

158 S TEAM TURBINEStion,

a labyrinth packing of radial baffl ing type has been adopted ,thus el iminating smal l axial cl earance in this turbine . The advan

tage claimed for this construction is the u se of smal l er working

clearances in the high-pressure and intermediate balance pistons .

Wil lans <5“ Robins on Turbine—The Al l i s—Chalmers Company

have effected an al l iance with the Turbine Advisory Syndicate of

England , which includes M essrs . W illans Robinson,the high

speed engine bu i lders of Rugby , and several other well—knownEnglish firms . Their turbines are s imilar in construction to those

manu factured by Wil lans Robinson,both being made under the

Ful lagar patents .In Fig . 20 i s a Wil lans Robinson turbine

with the top cas ing removed and which shows certain of the

features of construction more cl early than the il lustrations p reviously given.In this figure A i s the rotor

,B the top cas ing, and

C the admiss ion valve . D i s the steam chest in which is the valve

controlled by the governor,admitting steam through the pipe E

to the high-pressure end and through pipe F to the low -pressure

end in case of overl oads . At G are tw o of the balance pistons ,while atHi s the smal l low -pressure balance pi ston previously re

ferred to in the description of the Al l i s-Chalmers turbine . I t willbe noted that all connections

,such as pipes and valves

, are attached

to the lower hal f of the cas ing , so that the upper hal f may be removed without disturbing any Of the fittings .


160 S TEAM TURBINEShas al so been experimented with by The Westinghou se Machine

Company in this country , the double—flow arrangement i s adopted

to el iminate end thrust and a long’

drum is obviated by having

the turbine divided into‘

tw o or more stages , in the first of which

the steam acts on t he impu l se principle'

and in the second , or

last , of which it acts on the reaction principl e . Fig .

‘

1, taken from

the patent records,shows the general features of the design,

although the turbine as actual ly constructed is different in some

o f the detai l s .

Steam enters through the valve at the center and flows to the

right and left through nozzles (not shown) in which it is ex

panded to a cons iderably lower pressure . The nozzles direct the

steam against a seri es o f impu l se blades at A,cons isting of two

rows o f moving and one row of stationary vanes . I t then passes

to the longer seri es of blades which may be entirely o f the reac

tion or Parsons ty pe ; or may start at B with several rows of im

pu l s e vanes , divided into two or more pressure stages , and end

with the reaction blading at C. A feature of the design i s that

the drum is of constant d iameter, instead of in steps , as in the

regular Parsons turbine , the reaction part o f the drum cor

responding to the last stage or step in the Parsons turbine and

the expans ion previous to thi s point be ing taken care o f in the

impu lse section of the turbine .

As made by the Briti sh company,the drum o r cyl inder i s a

single forging carried on the sp indle by a central supporting diskand stiffening disks of th in steel fitted into the ends . The impul se

blades are carri ed by steel rings shrunk onto the drum and thereaction blades by grooves in the drum itsel f . Steam is expanded

to about 60 pounds in the impu l se section by means of the nozzlesand two rows o f rotating blades .

A vertical turbine , combining both the impu l se and reaction

principles , i s manu factu red by the Uni on Machine Company ,Essen, Germany , and a horizontal one i s manufactured by Sulzer

Brothers , Winterthur, Switzerland . A sectional el evation of thelatter i s shown in Fig . 2 . Steam enters through valve A

,pass ing

through the two impu l s e wheels at B . I t then flows through the

passages of the reaction wheel , C,thence around to the other s ide

through the passages o f reaction. wheel D,to the exhaust space E .

162 S TEAM TURBINESI t i s des igned that the thrust of reaction wheel C shal l be balanced

by that of wheel D . The admission valve A i s an osci l lating valvecontrol led by the piston P,

which in turn i s governed by the aux

iliary valve V. This latter valve i s given an oscil lating motion by

the w ormw heel W and the position of the valve is at al l t imes de

term ined by the position o f the governor.

The Lindmark Steam Turb ine.

It has been known for some time that the De Laval Steam

Turbine Company , Stockholm , Sweden ,were developing a com

F ig . 3 . L indmark T urbine.

pound steam turbine for u se where greater power i s des ired than

i t has been found advisabl e to attempt to supply with the s ingl ewheel De Laval turbine . This new turbine i s made under the

patents o f T . G. E. Lindmark ,the first of which w as i ssued in th is

country in 1 902 . Along substantial ly the same l ines as the L ind

mark inventions are patents taken out by P .I.Hedlund and con

s igned to the same company . At present no information con

cerning the Lindmark turbine i s avai lable other than given in the

patent records , but inasmuch as a new principl e is involved in the

operation of this invention, i t wil l be of interest to explain thefeatures of this turbine in so far as i s now poss ible .

Fig . 3 i s a representation o f a typ ical turbine containing the

turbine wheels , A, B , C,D and E

,attached to the shaft , S ,

and


164 S TEAM TURBINESa lower pressure in the d irection o f the arrow . The nozzle issupposed to be proportioned so as to give complete expans ion

, and

the pressure wil l accordingly drop from a to b,whil e the velocity

wil l increase from c to d as indicated by the diagram below the

nozzle .

At B the diverging part of the nozzle i s cut away so that the

steam does not have the . opportunity to fu l ly expand unti l it hasle ft the nozzle . The pressu re

,there fore

,will gradual ly drop from

a to b,at which latter point the steam leaves the nozzle and sud

denly expands to the lower external pressure , producing a suddenchange

,b,in the curvature of the pressure l ine . Inasmuch as the

expans ion i s not complete in the nozzle,the velocity l ine does not

ri se to as high a point as in the previous case .

At C the nozzle is shown l engthened out so as to produce over

expans ion ; that i s to say ,when the steam reaches point .r in the

nozzle it i s expanded down to the external pressure of the medium

into which the nozzle discharges,and beyond this point the steam

will expand a few pounds below the outs ide pressure unti l , say ,

point y i s reached . After th is the pressure wi ll rapidly ri se again

unti l i t reaches the external pressure at the mouth of the nozzle .

The Ac tion in the Lindmark Turbine.

—It i s th is latter action

which takes place in the diverging passages of the Lindmark

turbine .

The appl ication of the principle can best be explained by re

ferring to the detai l sectional sketch of the Lindmark turbine

shown in Fig . 5,which represents hal f of one of the wheels and

the connecting passages . Steam enters through the inlet and

passes through the w heel in the direction of the arrow ,and thence

to the exhaust chamber,whence it escapes through the valve B .

Suppose fifst the turbine wheel to be blocked so that i t wil l not

tu rn, valves A and B to be wide open, and the steam to flow freely

through the turbine . At points 1,2,3,4 and 5 , are openings to

which gauges may be attached for determining the pressure at the

different points . The steam passages , C and D,wil l now act l ike a

converging and diverging nozzle . At 1 the entering steam will

be at boi ler pressure ; at 2 the pressure with in the wheel casing

wi ll b e substantial ly that at the throat o f the nozzle , or about

910 o f the bo i l er pressure ; at 3 i t wil l be sl ightly lower ; and

MISCELLANEOUS TURBINES AND APPARATUS

at 4 nearly as low as the pressure in the exhaust space indicated by

the gauge at 5 . ( See“Steam Nozzles ,

”Chap . I . )

Ac tion, Wheel B locked, Exhaus t Valt/e Par tially Closed.

Now ,suppose valve B to be closed as much as poss ible without

increas ing the pressure , 2 , with in the wheel chamber . The pressu re at 1 will obviously remain as before

,and the expans ion in the

passages, C,

of the wheel will,as before , carry. the pressure at the

throat of the nozzle to % 0 of the ini tial pressure . After the

steam enters the diverging space,D

,however , over- expans ion will

occur just as in nozzle C,Fig . 4 . Probably the lowest pressure

EXHAUST

Fig. 5 . Enlarged View of Pas sages .

will be at or near the point where the gauge is attached at 3 , and

from there on the velocity will decrease and the pressure wi ll in~

crease so that the gauges at 4 and 5. will indicate a pressure con

siderab ly higher than that in the wheel chamber at 2 , but lowerthan the ini tial pressure at 1 .

Action w ith the Wheel Rotating— Final ly i f the wheel now

be supposed to turn,instead of being blocked as be fore

,and the

exhaust valve sti l l be partial ly closed , the principle of the steam’ s

action will remain the same,the only change being due to the

altered velocity of the steam owing to the fact that part o f thevelocity will be absorbed by the vanes of the rotating wheel .

166 STEAM TURBINESUnder these conditions the velocity of flow when the steam reaches

the entrance to the diverging port ion wil l be less than before and

this wil l produce an effect , which , according to the experiments

of Lindmark,will reduce the pressures somewhat at points 4 and 5 .

The Lindmark turbine is a react ion turbine, s ince the expans ion

o f the steam and increase in velocity occur in the passages of the

wheel vanes and the curvature given to them . i s s imilar to that

employed for reaction wheel s o f other types .

THE RATEAU STEAM ACCUMULATOR SYSTEM .

Turbines for Low -Pressure S team—One of the most interest

ing appl ications of the Rateau turbine i s in employment wi th low

pressure steam suppl i ed from engines working intermittent ly , such

as roll ing-mil l engines , hoisting engines , et c . The maj ori ty of

such engines are w orking under wastefu l conditions .

* They

usual ly op erate under widely varying loads , frequently with onlya smal l degree of expans ion and u sual ly exhausting freely into

the air. Professor Rat eau has given special attention to the em

ployment of waste steam from such engines and has obtained

sati s factory resul ts by means of hi s regenerat ive accumu lator Of

steam combined with low-pressure turbines . The accumu lator i s

intended to regu late the intermittent flow of steam before i t pass es

to the turbine, and cons i sts essential ly of a tank containing sol id or

flu id materials w hich play the part of a flywheel for heat.

Descrip tion of the Accumu lator.—In his

’

paper b efor e theAmerican Soc i et y of Mechanical Engineers in June, 1 904 , Professor Rateau gave the fol l owing description of his accumu lator '

The steam collec ts and is condensed as it arrives in large quantities in theap paratus , and is again vap orized during the time w hen the exhaust of thep rincip al eng ine dim inishes or ceases . The necessary variations for con

*Trials of modern w ind ing engines frequently show a s team consumption of 6 5 to 80

pounds p er horse-pow er in mineral ho isted , w hile 100 to 120 pounds is no t uncommon,

so that al low ing 20 p er cent condensation in the cyl inders and passages of the engine,there is d ischarged into the atmosphere by su ch an engine a minimum of to

pound s of steam p er hour w hich is total ly lo st. This steam is theoretical lycapable o f developing 500 t o 600 horse-pow er if suppl ied at atmospher ic pressure and

exhau sted at a vacuum o f 2 7 inches . Ro l l ing mil l engines frequently consumepounds o f s team p er hour , w hich is theoretical ly capable of developing over horsepow er in expand ing from atmospher ic pressu re to the vacuum of an ord inary condenser ,even after dedu cting 20 p er cent for condensation losses—From paper by LeonceBattu , read at a meeting o f the Western Society of Engineers, September , 1904.


168 STEAM TURBINESinto the body of the liqu id itself, Fig . 7. The low -

p ressure turbine, fed bythe regular flow w hich com es from the accumulator, and w orking, for ex

amp le, betw een an adm ission p ressure of 1 5 p ounds p er square inch and a

vacuum at the condenser of 2 7 inches of mercury ( back p ressure Of

p ounds) can furnish an electric horse-p ow er for about 3 1 p ounds of steam

p er hour.In st eel w orks, w here revers ible steam rolls are emp loy ed con

sum ing about.45 ,ooo p ounds of steam p er hour, it w ill be easy t o develop ,

by means of accumulators and turbines , an extra outp ut o f over electric horse-p ow er.

Accumulators are fitted with several accessori es which are

necessary for the ir success fu l Operation . One of these i s an

SECTION c cl efgh SECTION ab

F ig . 7. Accumu lator w i th Water onl y .

automatic rel ief valve to al low the steam from the engine to

escape into the atmosphere of the condenser i f the turb ine should

not requ ire al l Of the steam exhausted by the main engine. An

other i s an automatic expans ion valve provided so that l ive steam

from the boi ler may be admitted to the turb ine, shou ld the main

engine be temp orari ly shut down or i f sufficient exhaust steam i snot avai lable . There shou l d al so be a steam check valve and a

w ater check valve , the former for shu tting Off the accumulator

from the turbine when the main engine i s shut down and the tur

bine is suppl ied wi th l ive steam only ; whi le the latter i s used to

prevent the w ater in the accumulator returning tow ard the main

MISCELLANEOUS TURBINES AND APPARATUS 169

eng ine , through the exhaust supply pipe , when the eng ine i s shut

down.

Calcu lations for an Accum ii lator.

*—TO cal cu late the weight ofwater or cast iron necessary fo r an accumu lator , we must know1 ) The total weight of steam

’

required by the turbine p er hour ;

( 2) assume a length of time for the accumulator to operate without a steam supply ; and ( 3 ) assume an al low able drop in tem

perature of the accumu lator w hi le the steam supply is shut off and

the turbine is in operation . For example,suppose the turbine to

consume pound s of steam p er hour ; the durat ion of the stopto be one minute ; and the range o f temperature 1 0 degrees F .

Let s eight of steam used by turb ine during stoppage ofsteam supply .

Then G

At atmosph eri c pressure one pound Of steam contains 966

B . T . U . Whence , the accumu lator must be able to del iver

36 .6X 966 : 3 5,400 B . T . U

S ince the specific heat Of w ater i s one, the weight o f waternecessary to del iver this quantity o f heat w i th a range o f temperature Of 1 0 degrees F. i s

1 0pounds

,o r about tons .

I f the accumulator were to contain cast i ron ins tead of water,

the specific heat of wh i ch is a weight o f iron wou ld be re

qu ired about 9 times as great as for water .Hence,for cast iron

we have

tons .

Tes ts on Rateau’

s Accumu lator Sys tem .

— The first plant of thistyp e to be instal led w as at the Bruay 'M ines , France. The ac

cumulator w as Of the type shown in Fig . 6 , and a draw mg o f theGI)aper by Leonce Battu , Wes tern Society o f Engineer s , Sep tember , 1904 .


172 S TEAM TURBINEShowever

,for use with the turbine and a vacuum of 28 inches or

more has been maintained during the cool weather. The turbine

has four wheels , each with a s ingle r ow of buckets . When theturbine is receiving steam at atmospheric pressure , without moist

ure, the guarantees provide that the steam consumption shal l notexceed 36 pounds p er kilowatt hour at fu l l load and 40 pounds athal f load

,back pressure being two inches . At four inches back

pressure these figures are respectively 4 5 and 50 pounds . Tests

made on the machine at the factory showed even better p er

formance. It i s est imated that the turbine will increase the out

put of the engine or engines that supply steam to it about 6634;p er cent instead of the 25 p er cent usual ly expected from theappl ication o f a condenser .

CHAPTERIXSTEAM TURBINE PERFORMANCE—COMPARISONS WITH

THE STEAM ENGINE .

There will be found in thi s chapter the resu lts o f a number o f

tests upon turbines o f different types .In these the steam con

sumption i s usual ly given in pounds p er electrical horse—power

p er hour, or in pounds p er kilowatt hour.In the maj ority o fcases turbines are direct—connected to electri c generators

, and the

power i s most readily measured by the electrical instruments o f

the switchboard,which show the outpu t o f the generator instead of

the actual power developed by the turbine .In factory tests,how

ever,before the turbine is shipped

,the brake horse-power i s often

determined,s ince means are usual ly at hand for attaching an

absorption dynamometer . This plan is followed at the works of

the Westinghouse Machine Company , Pittsburg ,Pa.

Kilow at ts and E lec tricalH0rse—Pow er.

—The power del iveredby the generator i s expressed in kilowatts or in electrical horse

power,the latter being the equ ivalent , in electric uni ts

,of me

chanical horse-power . For. converting ki lowatts to horse—powerand horse-power to kilowatts

,we have

1 kilowatt horse-power : 1 .34 horse-power, nearly .

1 horse-power : 0.74 5 9 kilowatt : 0.746 kilowatt,nearly .

Tabl e I . wil l be o f ass istance in converting the more usual

values o f kilowatts to electrical horse-power and o f electricalhorse-power to ki lowatts .

Tabl e I I . gives steam consumption in pounds p er electri cal

horse-power hour corresponding to steam consumption p er kilo

watt hour,taken at hal f-pound interval s , within the l imits usual ly

met with in practice .

Table I I I . g ives steam consumption p er kilowatt hour corresponding to consumption p er electrical horse—power hour.Indicated

,orInternalHorse-Pow er .

— There is no such thingas the indicated horse-power of a turbine , because no indicatorhas been

,and probably none can be

,devised to show the internal

power developed . While an indicator might show the energy o f a

174 S TEAM TURBINESj et o f steam discharged from a nozzle , i t wou ld be practical lyimposs ible to register the amount o f energy given up by a j et to

the blades o f a compound turbine ,‘

where'

the losses might be

greater or l ess , according to the des ign, load , and other running

conditions .

Engineers are so famil iar with the water rates of reciprocating

engines on the bas i s o f the indicated horse-power , that in com

paring a turbine with an engine i t i s usual to reduce the figures

for the steam consumption of the turbine to terms of the indi

cated horse-power of a reciprocating engine having the same

el ectrical output , or brake horse-power, as the case may be .

TABLE I .

CONVERSION OFHORSE POWERINTO KILOWATTS AND KILOWATTSINTOHORSE POWER.

1 KW . H. P.

1H. P . KW .

Number . Number .


176 S TEAM TURBINESComparing Turbine Performance w ith Eng ine Performance.

*

-Calcu lations o f thi s character must take into account the effi

cienc ies of engines and generators, data upon which wil l shortly

be given. The actual calcu lations involve nothing more difficu lt

than the principles of percentage .

Examp le : Let a turbine uni t del iver 500 electrical horse

power,and consume pounds o f steam p er hour . Its rate o f

steam consumption wil l then be pounds p er elec

trical horse-power per hour. What wou ld be the ind icated horsepower

,and the consumption p er indicated horse—power p er hour ,

of a reciprocating engine having the same rate of consumption

per electrical horse-power p er hour ? Assume the engine to be

direct-connected to a generator,the effici ency o f the generator to

be 95 p er cent , and the mechanical effici ency o f the engine 94 p er

cent . The combined efficiency will then be

The indicated horse—power : 500—2 The steam con

sumption p er indicated horse-power p er

pounds . The latter cou ld have been obtained directly by

mu l tiplying the water rate fo r the turbine , 1 5 pounds p er el ectri cal

horse—power p er hour , by thus :

It i s to be noted that in these comparat ive calculations , where

we estimate engine performance for compari son with turbine re

sults, we use the efficiency o f the engine

-driven generators , not of

turbine generators .

*In a paper u pon the Cur tis tu rbine , read by Chas . B . Bur leigh be fore the New

England Rai lroad Club, Apr il , 1 905 , are calcu lations of the lo s ses in engines and

generators , as fo l low s : Let u s take a Cu r ti s turbine guaran tee o f 20 pounds of

s team p er kilow att hour and figu re w hat the reciprocating engine guarantee p er

ind icated horse-pow er shou ld be to ju s t equal it . Tw enty pound s p er kilow att houris equ ivalen t to pound s p er e lectr i cal horse-pow er hour . To startw ith , w e mu st make ou r tu rbine tes t w ith instruments mounted on the sw itchboard ,and the loss in the condu ctor s from the generator to the sw itchboard being 1 p er

cent , w e mu st dedu ct this 1 p er cent o f or pounds .

pounds . Next w e mu s t dedu ct the generator loss , w hich , s ince the generator isdesigned to meet the engine speed , is in most cases more than as though the idealgenerator cou ld have been u sed and the generator adapted to i t. We Shou ld , there fore,al low at leas t 5 p er cent generator loss . Thus , 5 p er cent of and

pounds p er brake horse-pow er . We are now back to the engine, bu t the

ind icator card does no t take into account the fr iction losses in the engine, so thesemust be deducted , andIthink y ou w i l l agree w i th m e that 7 p er cent is fair for th is .

Seven p er cent of and pounds p er ind icated horsepow er . There fore :

A turbine guarantee of 20 pound s of s team p er ki low att hour ,An engine guarantee of pounds of steam p er ind icated horse-pow er hour ,Or a tu rbine guarantee of pounds o f s team p er electrical horse-pow er hou r ,

are identical .

S TEAM TURBINE PERFORMANCE 177

Efficiencies of Engine-type Generators —TableIV . has beenprepared from data furni shed by manu facturers o f generators .

TABLEIV .

EFFICIENCIES OF ALTERNATING AND DIRECT CURRENTENGINE—T YPE GENERATORS .

ALTERNATING CURRENT GENERATORS (ABOUT 2 300 VOLTS).

Per Cen t Effi ciency .

S p eed .

MLoad . 54 Load . Load . Fu l l Load . 1% Load .

DIRECT CURRENT GENERATORS .

Per C ent Effi ciency .

Vo l ts .

Load . Load .34 L oad . Fu l l Load .

Efficiencies of Turbine Generators .

—In estimating the brake

horse-power of a turbine , having given the electrical horse-power ,or vice versa

,there must be an al lowance for the efficiency o f the

generator driven by the turbine .In the De Laval turbine outfits,twin generators are used ,

which reduces the size of each generator by about one hal f, and

the efficiencies are low on this account . M edium S ize generatorsfor these turbines

,say o f 200 Kw . capacity , have an efficiency

ranging from 88 to 91 p er cent between one hal f and fu l l load ,

i f for direct current .In alternating-current units o f the samecapacity , the efficiency vari es from 86 to 92 p er cent, betweenone hal f and fu l l load .

A test upon a Kw . A. C . generator for use with a

Westinghou se-Parsons turbine , reported by A. W . Mattice in the

178 STEAM TURBINESElec trical World

,February 20, 1 904, showed efficienc ies of 86 p er

cent at quarter load , 93 p er cent at hal f load , and 96 p er cent at

fu l l load . Also , a report of a test upon a 400 Kw . A. C. generator

for Parsons turbine , normal voltage of 440,by F . P . Sheldon

Co . ,Providence

,R.I. , contains the fol lowing figures :

Guaranteed Efficiency . M easured Efficiency.

p er cent p er cent

91

Tests on an Al l i s-Chalmers Kw . A. C . turbo—generato r,reported in The Engineer, February 1 , 1 906 , showed the fol lowing

efficiencies

f/z load , 97 p er cent fu l l load , p er cent

1M

Al ternating current generators of the type used with the Curt is

turbine , 500 Kw . and over , have efficienc ies ranging from 96 to

p er cent at fu l l-load . These generators have a high electrical

efficiency,because the Curt i s turbine runs at a favorable speed for

the generator ; and a high mechani cal efficiency ,owing to the

smal l fri ction of the vertical shaft .

M echanical Efficiency of S team Engines .

—The importance of

being able to make a just compari son between the performance

of steam turbines and steam engines makes it essential to care

fu l ly cons ider the subj ect o f engine fri ction,so that proper al low

ances may be used when reducing electrical horse-power to

equ ivalent “ internal” horse-power .

The friction loss o f steam engines remains very nearly con

stant at al l ordinary operating loads . Professor Thurston has

treated the subj ect exhaustively in papers to be found in theTransac tions of the American S ociety of M echanical Engineers ,volumes V I I I . , IX . , and X .

,and his conclus ions

,as well as those

of others who commented on his investigations , were that i t i s

substantial ly correct to cons id er the fri ction loss constant under

varying loads .He found this loss to be influenced to a much

greater extent by the degree o f lubri cation,change in speed , steam


180 S TEAM TURBINES5 .In Prof. Thurston ’

s p ap ers up on the friction loss in steam engines,p reviously referred to in this chap ter, are rep orts of several tests :( a) A 50 horse-p ow er, Straight Line, h igh-sp eed eng ine, non-condensing ,

had a constant friction load of about 3 horse-p ow er,or 6 p er cent of full

load, g iv ing an effic iency o f 94 p er cent. ( b) A comp ound , condensingeng ine. had a friction horse-p ow er of 44 w hen develop ing 347 horse-p ow er

and a friction horse-p ow er of 40 w hen develop ing 185 horse-p ow er.

( c ) A 16 x 30 Porter-Allen eng ine had a friction horse-p ow er of

w hen develop ing 142 horse-p‘

ow er and at 84 horse-p ow er. The lasttw o engines ( b and c ) p robably had full load efficiencies o f about 87 and

90 p er cent, resp ectively .

6.In addition to the above, reference may be made to the internalfriction o f large p ump ing engines , w hich is usually about 10 p er cent.The famous Leav itt p ump ing engine at the Boston sew age w orks show ed

an efli c iency of 90 p er cent, and the ChestnutHill, Mass , engine by the

same designer had an efficiency o f 93 p er cent.

Summary of Engine Fric tion Tes ts .—Tests 1

,3 and 4 give the

combined efficiency of engine and generator, for three large units ,ranging

,

from 850 to horse—power,one of which i s vertical .

These are all modern, Corl i s s-type engines . Taking the two

horizontal engines,the efficiency of No . 3 i s 90 p er cent and o f

No . 4 93 p er cent , at about normal load . The average effi ciency

of No . 4 at the different loads i s 90 p er cent . I t wou ld seem that

for large engines of thi s type an estimate of 90 p er cent wou ld be

conservative for combined effic iency at normal load . For vertical

engines the combined efficiency wou ld be higher, reaching 94 p er

cent ( as a safe figure) in the large S i zes .In the l ight of the above efl‘ic iency tests the following tabl e of

the mechanical efficiency o f engines has been prepared

T ABLE V .

MECHANICAL EFFICIENCY OF ENGINES AT OR NEAR THEIRNORMAL LOAD .

Effi c ienc y , Per Cent .Engine .

Eng ine and

G enera tor .

Large Vert ica l Cor l i s s , Compo und .

LargeHor izon ta l Cor l i ss , Compo u nd .

LargeHorizonta l , T r ip leHigh S peed . S imp leSma l l and Med ium-s izedHor izonta l , Com p oundLarge Pump ing


The Thermal Unit Basis of Performance.In comparing theresults of engine and turbine tests , and especial ly where boiler

pressures differ or superheated steam is used , the effi ciencies

shou ld be calculated on the bas is o f the heat units contained in thesteam . Under conditions o f varying pressure or o f superheat the

pounds o f steam p er horse-power p er hour do not indicate the

amount o f heat energy contained in the steam .

Calcu lations are given herewith to i l lustrate the heat-unit

method,taken from .a report of tests upon a 400 Kw . Westing

house—Parsons steam turbine , by M essrs . Dean and Main. The

efficiencies for superheated steam are figured by us ing as the

value for the specific heat of superheated steam . These calcu la

tions will prove o f ass istance shou ld the reader desire to recal cu late

any tests on the heat—uni t bas i s .

CALCULATION OF EFFICIENCIES OF 40 0 Kw . T URBINE.

Brake horse-p ow er develop edC orrespond ing ind i ca ted or interna lh orse

ipow er of a recip roca t ing engine

B . P.

T o ta l s team u sed p er hou r , p ou nd sS team u sed p er interna l horse-pow er p er

ho ur , p ound sAbso lu te s team pressu re , p oundS uperhea t (exact figures) 0 109 Deg . F. 181 Deg . F.

T emp era tu re cond ensed s team . Deg . F Deg . F . Deg . F.Hea t in one p ound o f d ry satu ra ted s teama t ab o ve p re ssu res , B . T . U .Heat in su p erhea t p er ound , B . T . U . (ont he b as is o f sp ec rfi c ea t

T o ta l hea t in one p ound o f s team , B . T . U .Heat o f l iqu id in cond ensed s team , B . T . U .Hea t u sed b y tu rb ine p er p ound , B . T . U .IIIFrom the above the fol lowing re su l ts are ob ta ined

Case ofDry S team.

B . T . U . used by turbine p erB . T . U .

182 S TEAM TURBINESB . T . U. used per internal horse-power per minute ,

B . T . U.

Thermal efi’ic iency p er cent .

Case of 1 00°

Superheat.

B . T . U . p er minu te , B . T . U .

B . T . U . u sed p er internal horse-power p er minute ,B . T . U .

Thermal effic iency,

O.1 843 : 1 8.43 per cent .230.1 2x778

Case of 1 80°

Superheat.

B . T . U. per minute , —60z l 37,625 B . T .

‘

U .

B . T . U . used p er internal horse—power p er minute ,—2 B . T . U .

Thermal effi CIency , 0 1 943 2 1 9 4 3 p er cent .21 8.33X 778

Resu lts of Turb ine T es ts .

Tables VI. to XVI I . , inclus ive , contain results o f tests uponturbines of di fferent types and show in condensed form what .

economy may be expected of turbines operating under differentconditions .


184

Number.

S TEAM TURBINEST ABLE V I I I .

T EST S ON 30 0H. P . DE LAVAL T URBINE DYNAMO .

Pres su res

Lb . sq . in. gau ge .

(DEAN AND MAIN . )

Su perhea t , Vacu um ,

Degree s F .Inches .

S team U sed

p erHo u r .

Tes ts w i th Sa tura ted S team—Av erage Res u l t s .

Ab ove BelowG o ve rno r Go vernorVa l ve . Va l ve .

T es ts w i th S

Average o f 7 and 8.

TABLE IX .

333

SUMMARY OF DEAN AND MAIN TEST S ON 300H. P . DE LAVAL T URBINE.

Rela t ive S t eam Cons ump t ion a t D/fi'

er en t Lead s .

G roup No .

Sa tura ted S tea m .

100%865559%36%

Sup erhea ted S t eam

Increase fo rDim ini shing

Load s , referred t oMaximum Load .

Saving (a t the Tu r bz’

ne) by i lze Use of S up er /ma t ed S t eam .

L d h L d hS teiam Dry S team

oa w it oa w it u se p er u sed p er

gggggéac

zfSu p erhea t Satu ra ted BrakeH. P . BrakeH. Ped S team . S team . w i th Su p . w i th Sat .

S team . S team .

505 24430

32291950

Average R esu l t s .

490642823033

3062


TABLE X .IISCELLANEOUS T ESTS ON PARSONS T URBINES .

*

Tes t No. 1 . 75 -A’

w . Con t z'

nu ons Cu r r e nt Tu r bof or B anbur v ,

14 1 0

142 0

Tes t No. 2 . 200-K w . Cont z'

nu ous Cur r e nt Tu r bo or S/zz’

p ley

57 2755

181 27 . 3166 28 0 100 27

Te s t N 0 . 3 . 3 7 5 -K w . Tar bo-Al t erna tor for O n ndee.

Tes t No. 4 . 30 0-K w . Tur bo Al t er na t e r .—Hu l ton Col l iery .

00000

Tes t N 0 . 5 . 3 00 -Kw . Tu r ba-A l tern a t or . De Beer s Exp los z’

ve Wor ks

Tes t N o . b .-Kw . T ur bo-Al t er na tor—Ne w eas t le -on -Tyne C o .

196 76

197 84

196 76

199 77200 68

Af t er 16 month 3’u se th e fo l low ing figu res w e re o b tained

9266

Tes t No. 7. 1 ,5 co Kw . Tur bo -A l ternato r for S/zefi ela'Corp or a t ion .

W i th vacu um au gment or , and inc lu d ing 4 5 0 l b s . s team p er hou r u s ed b y i t .

141 1 13154 0 0

*From a pap er b yHon . C has . A . Pa r sons , G . Gera ld S to re and C . P Mart in , p resented b efore t he B r i t ishIns t i tu te o f E lectr ica l En gineers , ay , 1904 .In summ ar izIng the tes ts o f t hi s ta b l e , and o ther tes ts u pon h is tu rb ines , Mr . Par sons s ta te s : “ItW 111 b e seen tha t und er cond i t ions o f, say , 1 10 po und s s team p res su re and 100 d egreessuperheat , and a va cu um o f 27 inches . t h e consumptions in rou nd numb ers are as fo l

low s : A 100 Kw . p lant takes abou t 25 po und s o f s team p er Kw . hou r a t fu l l load ; a 200Kw . takes 22 p o und s ; a 500 Kw . 20 ound s ; a Kw . 19 pound s ; a Kw . 18 pound s ;and a Kw . 16 po und s . These gures are d er ived from averag es o f a large numb ero f tes ts tha t have b een mad e from time t o t ime . W i tho u t su perhea t t h e consump t ionsare abou t 10 p er cen t m ore .

”

186

p resented b e

S TEAM TURBINESTABLE X . (CONTINUED).

A t S top Va lve . S t eam Used p erHou r .

W ith ou t vac uum augm ent or .

3

0

Par sons Tu r ba-A l ter n a t or Sup 1 fed t o F ra nk/or t by M e ss r s .

B r ow n ,B aver i Lo .

5

55

5

5

5555

CO

CO

ACQ

QD

IONUI

TABLE NO . XI .

T ESTS ON PARSONS T URBINES ,WHEN RUNNING NON-CONDENSING .

*

At S to p Va l ve . S team U sed p erHo u r .

BackPres s ure , Va cu um , Rig

eedér

Lb .

8er SqInches .

\1'

ln au ge Imu te

Tes t N o. 1 . 25 0-K ] w . Con t zn u b us -Cu r ; ent .

—M e ssr s . Gu i nness , Son 59-9

144 0 25 1 5 50

138 0143 0

Test N o. 2 . 3 00 -Kw . Tu r bo-A l t er na t o r .—Hu l t on Col l iery .

0 0

0

Te s t N o. 3 . 5 oo-Kw .

“

Tu r bo A l te r na t or . Met r op ol i tan E . C. C o.

000 500

*From a

tp ap er byHon . C ha r les A . Par s ons . G . G era ld S tor ey and C . P. Mar t in ,

o re t he B r i t i shIns t i tu te o f E lectr ica l Eng ineer s , May , 1gt 4 .IResu l t es t ima ted by th e au thor from curve p lo t ted in or i g ina l p a per .


188 S TEAM TURBINESTABLE XIV .

TESTS ON soo Kw . CURTIS T URBINE, CORK (IRELAND) ELECTRICTRAMWAY AND LIGHTING Co .

’

s STATION .

*Ini t ia l Su p erS team U sed p erHou r .

“

Pres su re hea tl b . sq

'

. in. Degree sGau ge . F ,

*Elect r ical Review (Engl ish), Nov . 18, 1904 .

TABLE XV .

TESTS ON zoco Kw. C URTIS T URBINE .

*

Revo l uIni t ia lt ions p er Pres su re ,

L112S t efim p er

M inu te . Gau ge .

W ou r.

*T es t b y A . R. Do d ge , S chenectad y , N . Y . Rep o r ted by Au gu s tH. Kru e s i , in a

p ap er b efore th e Na t iona l E lectr i c L i gh t As socia t ion ,June , 1905 .

STEAM TURBINE PERFORMANCE 189

T ABLE XVI.TEST S ON 40 0 Kw . ( 580H. P . ) WESTINGHOUSE—PARSONS T URBINE.

*

S team Used

p erHou r .In i t ia l Sup erPre s sure , hea t , Vacuum ,Ibis‘qgé

n. D e

greesInches.

Pound s

Resu l ts w i th A p p ro x im a t e l y 100° F. S u p er hea t .

3 1% Over load . 150 9157Fu l l Load (256Over load ). 156 7384

77% Load . 154 572841% Load 153 27 10 3508

Resu l t s w i th A p p r o x im a te l y 180° F‘

. Su per hea t .

32% Over load . 15 1 182Fu l l Load (276Over load ). 154 181

R esu l t s w i th Dry , Sat urat ed S te am

26% Over load . 153Fu l l Load (275 Over load ). 15477% Load 15642% Load 156

Resu l ts w i th D ry S team and Poor Vacu um202 Over load . 152Fu l l Load (2% Over load). 155

W i th 100° Su p erhea t t h e Sp eed of ro ta t ion w a s R. P. M . at fu l l load ; at 31%over load i t d rop ped and at 41% load i t increasedW i th Dry S team t he sp eed w as R . P. M . at fu l l load ; at 265 over load i t d rop

p ed and a t 4253 load i t increased W i th tu rb ine running l igh t sp eed increased

ll‘Test s mad e at t h e w orks o f t he b u i ld er s b y Dean and Ma in in 1903.

190 S TEAM TURBINESTABLE XV I I .

TEST S ON A 1 2 50 Kw . T URBINE FORINTERBOROUGHRAPIDT RANSIT CO NEW YORK .

*

Load Car ried by T u rb ine S team U sed p erHo ur .

Re su l t s w i th Dry ,

R e s u 1t s w i t h 75°

23 .05

28 . 1

Tes ts upon a 5 0 0 Kw . Curtis Turbine at New port, R.I.—ACurti s turbine at the Newport , R.I. , power house of the OldColony Street Rai lway Company ,

a description o f which plant will

be given later, w as tested by GeorgeH. Barru s , consu lt ing en

gineer , Boston,Mass i This turb ine is one of the earl i er two

stage ty pe and had been in'

continuou s service nearly a y ear when

the test w as made . The resu l ts with dry ,saturated steam ,

1 5 0

pounds ini t ial pressure , and two inches back pressure in the con

denser,are tab u lat e d herewi th for d ifferen t l oads

,toge th er

*Tests made at the Westinghou se M achine Company ’ s P lant , and reported by A. M .

Mattice, Chief Engineer .

+TheIron Age, M ay 5 , 1904 .

F . S u per hea t .

790

. 0385

6

8

.02

{Q

t—l0

0

03

0

0

C

0

0 .Q

01

O0

01

Sa tu ra te d S te a m .


192 S TEAM TURBINESTABLE XV I I I .

EXAMPLES OF STEAM CONSUMPTION OF T URBINES. BEST RESULTSOF T ESTS QUOTEDIN THIS CHAPTER

S team U sed erHrp o n

Es t ima ted Sigr

ic

éent

Nomina l Equ ival’

ntasssnri

l

e

c

Tu rb ine . Consum pPow er . Po und s Pound sP d t

' in es t imat

p er p erou

g5

ing 1 .H. P .

B .H. P . E .H. P .

Per W °

Resu l ts .

2 3 4

Res u l t s w i th Sa t u ra ted S t eam .

De Lava l 300H. P .

Rateau 500H. P .

Z oel lv 500H. P .

Cu rt is (Amer ican) 500 Kw .

Wes t inghou se -Par sons 400 Kw .

Wes t inghou se -Parsons 1 350 Kw .

Resu l ts w i th Su p erh ea t ed St eam (M o d era t e S u p er be at , no t

e xceed ing

De Lava l 800H. P .

Z oel ly 500H. P .

Cu r t i s (Engl i sh) 500 Kw .

C u r t i s (Am er ican) 500 K w .

Parsons 300 Kw .

Par sons 1500 Kw .

Par sons 3000 Kw .

Wes t inghou se Parsons 400 Kw .

Wes t inghou se-Par sons 1250 Kw .

Resu l ts w i thHig h l y Su perb ea t ed S t e am (Su pe

Cu r t i s (Amer i can) 500 KW .

C ur t is (Amer i can) 2000 Kw .

Parsons 3000 Kw .

Wes t ingho u se Par sons 400 Kw .

Engine efficiency alone (withou t generator) for uni ts of from

400 to 500H. P ( or 300 to 400 93 p er cent .Engine efficiency corresp onding to the 300H. P . De Laval

turbine , 92 per cent .

Chart for Es timating Rate of S team Consump tion—Ii resu lts

on any other efficiency bas is are des ired , they may be eas i ly cal

cu lated,or they may be obtained by the aid o f the accompanying

chart , Fig . 1 . On th is chart the figures at the le ft are pounds of

steam p er electr ical horse-power p er hour. The incl ined l ines arefor

fvarious effic ienci es , and at the top are corresponding values

for pounds of steam p er indicated o r brake horse-power p er hour .

Obviously , al so , i f brake horse—power units are assumed to be at


Pound s S team p erInd i cated or B rakeHorse Pow er p erHour .

22 21 20 19 18

Pound s S team p er K i lowat tHour .

F ig. 1 . Chart for Estimating Rate of S team Consumption.

the left , indicated horse-power units corresponding can be foundat the top . The incl ined l ine labeled “kilowatts to horse-power”

is for the purpose of converting kilowatt units at the bottom tohorse-power units at the left .

Examp le toIl lus trate Use of Char t. —Following the dottedline , we find that 20 pounds o f steam p er kilowatt hour : 1 4 .9

pounds p er electrical horse—power p er hour. Assuming 90 p er

cent eflic 1ency , the equ ival ent steam consumption p er indicatedhorse-power p er hour i s found by retracmg the dotted l ine fromthe point unti l it meets the 90 p er cent l ine ; then extendingupward unti l i t reaches the point

,which gives the requ ired

rate of consumption.

194 S TEAM TURBINESTABLE XIX .

EXAMPLES OF TESTS UPON RECIPROCATING ENGINES OF EXCEPTIONALLYHIGHECONOMY , SHOWING BEST RESULT S OBTAINED .

8 6q-aI‘ 2 8

“

53 A th r'

t4. u 0 1ngw e

3 5 8 3 330 3 3 3 2y

k 3 33 8 r: o r:

O o0

ca cs 8 <0 0

04 0.

W es t inghou se Vert i cala t Brook l yn N .

Ro c k W OOd -Wh ee l o cka t Na t i ck , R.I

McInt o sh and Seymo ur

a t Web s t er , Ma ss

Ri ce and Sargent a t

Brook l ynRi ce and Sa rgent a t

Phi lad e lp hiaHo r izonta l , Fou r-val veLeav it t Pump ing Eu

1ne at Ches t nu tHi l l .l ass 2 7 25 E. F . M il ler in Tech

n o l og y Quar t er ly ,V o l 1X .

Bes t Reciprocating Eng ine Performance—In Table XIX . are

a few best resu lts” selected from tests upon several very economi

cal engines . Many other resu l ts as good as these cou ld have

been tabu lated , but the ones given are indicative of what i s nowattained under the most favorabl e conditions . It i s conservative

to say that compound engines may now be bu i lt to produce an.

indicated horse-power on pounds o f steam p er hour, with

saturated steam . W'

ith a high degree of superheat the long

sought 1 0—pound mark has nominal ly been passed , but i f the re

sults were recal cu lated in terms of the equ ivalent rate of con

sumption o f saturated steam,by us ing the heat uni t method , i t

woul d be found that they barely reached 1 0 pounds .

Average Engine Performance—S ince the resu lts in Table XIX .

are from picked tests , and are exceptional,Table XX . i s given,

which fairly represents what the ordinary high-grade engine wil l

do . This table i s made up from the resu lts o f tests upon fourvalve, comp ound

‘

condensing engines , publ ished in Barrus’

En

gine Tes ts . They are not selected tests, bu t are from 23 engines

in commercial operation and are average representat ives of theirclass . We find that one of the resu lts fal l s below 1 2 pounds

,five

13

Eng . Recor d ,May 28,

1904 .

F . W . Dean, Tr ans .

A . S . M . E . , 1895 .

F . W . Dean, Tr ans .

M . E . , 1898.

D . Wsj

acob u s , Trans .

A . M . E . , 1903.

D .Wsj

ac ob u s , Trans .

A . M . E . , 1904 .

Barru s ’ Engi ne Tes t s .


196 S TEAM TURBINEShave some means for estimating the steam consumption o f en

gines under the supposition that superheated steam is used . Data

for th is are afforded by tests upon a

'

Belgian engine of 250 horse

power, which has establ i shed a remarkable record for economy .

The tests are summarized in Tabl e XXL ,and undoubtedly are

rel iabl e , as they were made by Professor Schroeter , one of the

most experi enced experimenters abroad . The tests start with

saturated steam and Show the extremely low steam consumption,

for an engine of this s ize , of 1 2 .

-08 pounds p er indicated horse

power hour. The items following thi s one give the consumption

for different degrees o f superheat . The resul ts Show that for

every 1 00 degrees superheat the steam consumption p er horse

power p er hour w as reduced one pound , or p er cent ; and

that the consumption,expressed in terms of equ ival ent con

sumption of saturated steam , w as reduced (71 0 pound .

Comparing Turbine and Engine Resu lts .

—The reader has at

his disposal in the last three tables,together with Tabl e XV I I I . ,

suffi cient information to form an Opinion upon the comparative

rate of steam consumption of turbines and engines when operat

ing at their most economical loads . Due al lowances,however

,

must be made for s izes o f machines , conditions o f operation,such

as steam pressure,vacuum ,

superheat , etc . This i s very impor

tant , as ent irely erroneous Opinions are Often formed where such

al l owances are no t made . Taking pounds , previously men

tioned , as a conservative figure fo r the most economical engines

usmg saturated steam ; and pounds as a safe figure for theaverage high-grade engine , we shou ld then have the estimated

rate o f consumption for each,with different degrees of super

heat , as follows , taking the Belgian figures as a bas i s

M-

os t Economical Engine.

W ith Saturated 1 00 Degrees 200 Degrees 300 Degrees

Steam . Superheat . Superheat . Superheat .

1 ° 5

Ave-rageHigh-Grade Engine.


Comparing these figures with those of Tabl e XV I I I . ,

‘ i t seemsprobable that the reciprocating engine wil l

,under exceptional ly

good conditions , Show a l ittle better economy than the turbine ,w hen running at i ts most economical load ; but that what we havecall ed the “

average high-grade engine” appears to about equal

the turbine in i ts rate of steam consumption at most economical

loads .In the next chapter the question of variable loads wil l becons idered .

Economy of Smal l Engines and Turbines—The author hasseveral t imes seen i t stated by English engineers that in s izes of

500 Kw . and less the engine i s more economical than the turbine ,but that as s izes increase the economy of the turbine improvesmore rapidly than that of the engine, and in the larger powers the

turbine is equal or superior to the engine .

* This view seems to

be borne out by the facts i f the four-valve compound type o f eng ine be taken forcompari son. Engines of this type of from 300

to 500 Kw . capacity are exceptional ly economical and are rea

sonably so in stil l smal ler s izes . The same is true of the Wil lansengine, used so extens ively in England . When we come to thesingle-valve

,high-speed engine

,however , which isIn such general

use in this country,there is no doubt that its rate of steam con

sumption can eas i ly be improved upon by the turbine . The Gen

eral Electric Company , the bu i lders of the Curti s turbine , recognize thi s fact and do not provide for as complete expans ion ofthe steam in turbines o f smal l s izes as in their larger machines ,S ince i t i s not necessary to do so in Order to compete with thehigh-speed engine .

*In d iscuss ing the paper by Parsons , S torey and M artin, before theIns titution of

Electr ica l Engineers, May , 1904, E. J . Fox said Taking figures of steam economyas given by M r. Parsons, for d ifferent sizes of tu rbines, there is no diffi cu l ty w hat~soever in the reciprocating engine giving equal ly good resu l ts u p to the KW .

size. From 100 up to Kw . , the resu lts obtainable w ith reciprocating engines are

better. When you come to the Kw . s ize, there is very l ittle d ifference betw een

the tw o ; and final ly w i th the Kw . size,Ithink there is no doubt a cons iderabled ifference in favor of the -turbine.

CHAPTER XIn a steam engine , and in certain turbines , l ike the Parsons , in

wh ich latter there i s an auxi l iary valve to admit steam to the low

pressure end in case of heavy overloads , the lowest steam con

12 13 14 15 16

LB. STEAM PER l .H.P. PERHOUR.

F ig . 1 . Co rl iss Engine Curve.

sumption p er horse-power hour occurs at or near the normal load .

A decrease in‘

the load below its normal point causes an increase in

the rate of consumption ; and an increase in the load above the

normal point produces a l ike effect , though to a l ess degree .In F ig. 1 i s a steam consumption curve for a Corl i ss engine.

The most economical load is at point A,S ituated on the curve at

the extreme l eft , and points C and B ,above and below A,

re

spectively, areboth to the right of A. These tw o extreme points

represent the consumption at 50 p er cent overload and underload ,


200 S TEAM TURBINESwere no by

-pass the turb ine wou ld not be abl e to carry a load

above Kw . ,and we Shou ld have a curve extending from

A to B,s imply, l ike the lower part of the engine curve . The gov

cruor in this type of turb ine is virtual ly a throttl ing governor and

the rate of steam consumption gradual ly decreases , as the load

increases , unti l the b y -pass opens , when the rate increases,s ince

the steam which enters the low -pressure end through this valve i s

not used to so good advaii tage.

Curves for Turbines of the Rateau Type—In Fig . 3 i s a steam

rate curve for a Rateau turbine , plotted from Table XII. , ChapterIX . This turbine , al so

,i s regulated by a throttl ing gov

ernor and the curve resembles the sections from A to B of the

Corl i ss engine , and the Parsons curves , F igs . 1 and 2 . The most

17 18 19 20

LB. STEAM PER E.H.P.HOUR.

F ig . 3 . Rateau Turb ine Curve.

economical , and al so the max imum ,load carri ed the Rateau

turbine is at point A,at the upper end of the curve

,Fig. 3 . The

normal load is at point C,and the fractional loads are at the suc

cessive points indicated . Turbines of th i s type cannot be strictlysaid to have overload capacity , and their normal rated load must

be fixed at some point below the most economical load,in order

to give the machine the equ ivalent of overload capac ity. Pro

fessor Rateau , however, has proposed the use of a by-pass valve ,

S TEAM TURBINE PERFORMANCE (Continued) 201

in which case the performance in respect to variable loads wou ld

be substantial ly the same as in the Parsons type fitted with thisdevice .In Fig. 4 are three curves plotted from tests in Chapter IX .

on the 400 Kw . Westinghouse-Parsons turbine,given in Table

XVI. , the Rateau turbine , Table XII . , and the Zoel ly turbine ,Tabl e XI II . The curves are placed in their correct relative posi

tions so that compari sons can be made . It should be noted that

1 18 19 20

LB. STEAM PER E.H.P.HOUR.

power and are modified somewhat by the efficiency of the gencrator, while the Westinghouse curve i s ‘based on brake horsepower. The similarity of the curves

,however

,will be apparent .

Curve for the Curtis Turbine—This turbine operates under

curve , Fig . 1 ; though theoretical ly it shou ld continue up to point0 . From load to 1 111 load the change in steam consumption i s

202 S TEAM TURBINESvery slight , but from load to load it is rapid . The increased

consumption at l ight loads in this turbine i s due to internal losses ,such as fri ction,

diffus ion and eddying of the j ets , radiation, etc . ,

which are nearly constant and therefore absorb a larger p er

centage of the power at l ight loads than at heavy loads . Com

paring this curve with that of the Rateau turbine , we find the lat

ter resembles that part of the Curt is curve lying between a point

at about load and load . The upper part of the Curtis curve ,where there i s cons iderable variation in power with only sl ight

variation in rate of steam consumption,i s absent in the Rateau

22 23 24 25

STEAM PER K.W .HOUR, LB.

F ig. 5 . Curt is Turbine Curve.

curve . This i s explained by the fact that in the Rateau , or any

turbine which governs by throttl ing only,there are not only the

constant internal losses just mentioned in connection with the

Curti s turbine , but there are al so losses due to the throttl ing of

the steam ,and the tw o together cause the steam rate to increase

more rapidly with a drop in load than in the Curti s turbine , where

the steam is not throttl ed .

Curve for the De Laval Turbine—In the De Laval turbine conditions are very similar to those found in the Curti s turbine .

While regu lation for smal l changes in load is effected automatical ly by throttl ing ,

for wide variations in load the several

steam nozzl es are opened or closed bv hand ,as requ ired . TWO


204 S TEAM TURBINESCy linders, 11 and 19 by 24 ; revolutions, 160. Tests g1ven by A. K. Mans

field, Proc. A. S . M . E. ,1897.

4 . A McEw en, tandem -comp ound, non-condens ing , high-sp eed engine.

Cy linders, 9 and 16 by 14 ; p ressure, 112 p ounds revolutions, 265. Testedby Prof. R. C. Carp enter, Proc. A. S. M . E ,

1893 .

5 . A Flem ing, four-valve, tandem-comp ound, condensing engine, of

500 horse—p ow er. Cylinder ratio ,1 to p ressure, 150 p ounds . Re

p orted by B . T . Allen, Proc . A. S . M . E. ,1904 . These tests have been

criticised because the steam p ressure w as allow ed to drop in the bo iler at

light loads .It is p robable, how ever, that this variation did not greatlyaffect the results , since the high-p ressure adm ission valves throttled the

steam at light loads , so that ful l bo iler p ressure could not have been realized in the cy linder in any case.

6. A Rice and S argent, comp ound engine (Corliss typ e) w ith cylinders20 and 40 by 42 inches . Steam p ressure, 150 pounds ; vacuum , 28 inches ;revolutions , 120. Tested by Prof. D . S . Jacobus for the builders .In obtaining figures from the tests upon the above engines , and

al so from the turbine tests in this chapter, the method followed

has been to plot curves for the rate of steam consumption under

vary ing loads , and from those curves to take the figures at such

points as were des ired . For example,the resu l ts of an engine

test might not give the steam consumption at exactly hal f load ,bu t by plotting the curve for such . resu lts as were given,

the hal f

load consumption cou ld be approx imately determined . Figures

wi ll be given without showing the curves,except where they have

previously been

“The fi gures given below are the tabu lated resu l ts from w hich the cu rves for the

engine tes ts w ere plotted . Of each group of figu res, the fir st co lumn contains the

ind icated horse-pow ers and the second co lumn the correspond ing steam consumptionsin pounds p er horse-pow er hour .

Engine No .I.1 94

1 75

1 50

1 1 7


The turbine tests selected for compari son are the following,taken from data in Chapter IX .

No . 1. 300H. P. De Laval. Fourth test in Table VII., w ith sup erheatedsteam . Results in term s of electrical horse-p ow er.

No . 2. 300H. P. De Laval. First test in Table VIII. , w ith saturatedsteam . Results in term s of brake ho rse-p ow er.

No. 3. 500H. P. Rateau. Table XII. Results in electrical horsepow er units .

NO. 4. 5004H. P. Zoel ly . Table XIII. The results in the table w ere con‘

verted into term s of electrical horse-p ow er before p lotting curve.

No . 5 . 500 Kw . Curtis. Table XIV . Results in p ounds p er kilow atthour.

No . 6. 500 Kw . Curtis turbine at New p ort, R.I. The figures for thismachine w ere taken from a curve p lotted from the results of tests byGeo .H. Barrus and given in a p ap er by W . L. R. Emmet before the

Engineers’

Club of Philadelp hia, in March,1904 .

No . 7. Kw . West inghouse-Parsons, w ith by—p ass valve. Table

XVII. Results in term s of kilow atts .

No . 8. 400 Kw .

t

w estinghouse-Parsons . First and third tests, Table

XVI., one w ith sup erheated steam and one w ith saturated steam . Re

sults in term s of brake horse-

p ow er. Th is turb ine had no by-p ass .

Comparison of Tes ts under Variab le Loads —One w ay of comparing tests under variable loads i s to set a percentage l imit for

the rate o f steam consumption and then determ ine how great avar1at ion in load the engine or turbine will permit without exceeding this l imit .The author has assum ed a l imit of 1 0 p er cent increase in the

rate of steam consumption above the most economical rate , and

then determined the approximate variation in power for each

turbine or engine,corresponding to the 1 0 p er cent variation in

the steam rate .

The variation in power w as found in p er cent of the maximum

power developed by each turbine or engine , and i s as fol lows

Turbine No . 1 . Variation in power,5 5 % o f maximum power.

( 6

No . 2 . 6070No . 3 . 3 5 70No . 4 . 3 5 %No . 5 . 60%NO . 6 . 60%No . 7 . 5 5 70No . 8. 50%

206 S TEAM TURBINESOn the same bas i s we have the fol lowing resu lts from the U l r

gine tests of which a l i st has been given

Engine No . 1 . Variation in power , 60% of max imum power .

NO. 2 .4 5 %

No . 3 .5 0%

No . 4 . 65 70

No . 5 . 70%No . 6 . 5 5 %In reviewing these resu lts , i t s eems fair to discard the figures

for turbine tests Nos . 3 , 4 and 8, s ince these particu lar turbines

were not fitted with a by-pass to admit high-pressure steam to the

low -pressure end ,but are of a type requ iring the by-pass to give

the best resul ts . The remaining tests indicate that for a 1 0 p er

cent variation in the rate of steam consumption'

the variat ion in

power developed by the turbines averages 5 5 to 60 p er cent .

The engine tests quoted give an unusual ly good presentation Of

the claims of the steam engine . The Six tests are from five differ

ent types of engines , and include both s imple and compound .

The only resu l t apparently open to question i s the one of 70 p er

cent variation for engine No . 5 . Only one test w as made upon

this engine at very light loads , and as the only w ay of checking

that test i s by means of the curve drawn through points plotted

for cons iderably larger loads , the resul t o f 70 p er cent does not

appear well establ i shed . This engine ought to do as well as eu

gine No . 4 ,however

,which gave 65 p er cent . I f we cal l the

variation 6 5 p er cent, instead of 70 p er cent , the average engine

resu l t for the whole group wil l l i e between 5 5 and 60 p er cent, or

the same as in the case o f the turbines .

Direct Comparison of Engine and Turbines—In F ig . 7 are

plotted three curves showing the rate o f steam consumption, nu

der different loads , of a Curti s turbine , a Westinghouse-Parsonsturbine , and a Ri ce and Sargent engine . The first i s the 500 Kw .

turbine at New port , R .I. , tested by GeorgeH. Barrus ; thesecond the Kw . turbine reported in Tabl e XV I I . , and the

third the 850H. P . compound engine referred to previously in


208 S TEAM TURBINESDeductions from Curves of Fig. 7.

—The Curtis turbine p ro

duces the flattest curve , while there is not much to choose between

the Ri ce and Sargent and the West inghouse curves , s o far as thisfeature is concerned .In point o f economy , the engine i s eas ily inthe lead . This engine , however, has proven i ts el f to be excep

t ional ly economical , while the 5 00 Kw . Curti s turbine as thenconstructed had only two stages and wou ld not run With -as low

steam consumption as the larger, three or fou r- stage machines .

It wou ld lead to erroneous conclus ions to accept this diagram too

literal ly as an example o f what may be expected from engines andturbines in general , when operating with variable loads . The diagram is a s ignificant one

,however , and inevitably leads to the

conclusion that a compound Corl i ss engine is able to hold its ow n,

in compar i son with turbines , provided the variation in load is notover 40 or 5 0 p er cent above or below normal load .

Engine Performance from an Operative S tandpoint.—In con

nec t ion with the above compari sons of turbines and engines under

variabl e loads , the author wishes to point out tw o important

facts : F irst,that the water rate load curve of an engine does not

represent its true performance where the load is rapidly fluc

tuat ing . The rapidly changing cyl inder conditions that ex ist

when the load is fluctuating lead to increased condensation and

consequent waste of steam that does not occur when an engineISunder test at certain fixed loads .

Second , that in the tests quoted the overloads were not more

than 50 p er cent above normal load and in most cases were less

than thi s .In one w ay this adds to the interest of the compari sons

because it shows what turbines wil l do with in ranges o f load under

which reciprocating engines general ly operate ; but in another w ay

i t i s not fair to the turb ine,because the practice now i s to design

turbines to carry much heavier overloads than can the steam en

gine . I t i s not usual for engines to run with loads greater than50 p er cent in excess of their normal load

,i t being advisable to

put in a larger engine when this point i s reached . Corl i ss engines

fitted with two eccentri cs can carry overloads as great as 100

p er cent , provided the vacuum can be mainta ined , but not withgood economy . The tendency always i s to instal l a steamengine large enough to safelv handle the overloads

,and then l et it


operate at an average load considerably below the normal load forthe balance of the time . This i s i l lustrated in a striking mannerby tests made by students o f Cornel l University upon 3 5 street

rai lroad power plants during a per iod of 1 2 years . These resul ts

have been gathered by Prof . R. C . Carpenter and grouped accord

ing to the type of There were eight tests o f compoundcondens ing engines of the Corl i ss and S imilar -types

,and the main

results of these are given in Tabl e I . They show the same char

acteristics as the others o f the 3 5 tests , not quoted here .

T ABLE I .

SUMMARY OF TESTS ON COMPOUND CONDENSING ENGINES OF THE CORLISSAND SIMILAR T YPES

,IN STREET RAILWAY PLANT S

A verage

Taking the average resu lts , the average load on these enginesw as less than hal f their normal load , and they were running dayin and day out on a steam consumption o f pounds per horsepower hour, instead o i the 1 3 or 1 4 pounds that s imilar engines arecapable of at normal load , i f in good condition.How the TurbineImproves upon Engine Performance—Whati s the answer of the turbine to thi s condition of affairs Theturbine, first of all , i s not sub j ected to serious losses from internal

condensation and under a rapidly fluctuat ing load should Shownearly the same economy as indicated by the water rate loadcurve. This is o f great importance in street railw av work .

Second , the resu lts that can be secured with a turbine under

heavy overloads are indicated by a test upon a Westinghouse‘S ibley J ournal of Eng ineering , December , 1904 .

210 S TEAM TURBINESParsons 400 Kw . turbine , by F . P . Sheldon Co .

,mechani cal

engineers , Providence , R. I .

This turbine showed the u sual resu l ts under loads varying from

V; to the normal rating ; but in addition— and this i s the 1m

portant point— demonstrated its abi l ity to carry an overload of

1 00 per cent with an increase in the rate of steam consumption of

less than 1 0 p er cent .

TAB LEII.PERFORMANCE OF WESTINGHOUSE—PARSONS T URBINE UNDER VARIABLE

LOADS ,INCLUDINGHEAVY OVERLOADS .

S t eam Pr ess ur e 15 0 L b . Absol u t e; Va cu um 2 8Iu c/ies .

S t eam Consump t ion—Pound sp er B .H. P . p e rHo u r .

team Su p erhea ted 100 Degrees .

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0

The meaning of thi s i s that a turbine can be instal l ed withreference to the average l oad that i t has to carry , instead

“

of

with reference to the maximum load,as in the case o f the steam

engine , and then trus t to the by-pass to take care o f the overloads .

The turbine will then be Operat ing at or near i ts point o f best

economy most of the time, and being of smal ler power than a

steam engine for the same work,wil l not , at l ight loads , drop to so

smal l a percentage of the normal load as will the steam engine .

The recent practice o f encasing the turbine generator and cool ing

it with forced air c ircu lation makes the generator amp lv able to

handle overloads and the generous condens ing systems used with

turbines Should preclude a serious drop in vacuum under excess iveoverloads .

Taking into account the operative conditions of engines and

turbines as they exist , the author i s incl ined to the op inion thatthe turbine wil l surpass the engine under fluctuating loads . Thisconclus ion appl ies d irectly to the Parsons type , fitted with a by

pass valve . Enough data have not been publ i shed in respect to


212 S TEAM TURBINESfigures are u sual ly quoted on this bas i s , i t i s not always , and we

doubt i f it i s u sual ly , poss ibl e to maintain so good a vacuum in

commercial Operation. A ccordingly,what we want to know is

,

how much the steam consumption of a turbine will be increased byth is drop in vacuum .

Turbine Tes ts w ith D ifferent Vacuums .

— The most complete

tests o f turbines under di fferent vacuums have been made at the

shops Of the Westinghou se Machine Company,and are reported in

their turbine catalogue .

*In Tabl e I I I . i s a summary o f tests

upon a 750 Kw . turbine compiled from this source , and in TableIV . i s a summary of tests upon a KW . unit .Tabl e I I I . gives resu lts under different loads for vacuums of

28 and 26 inches , respectively , and with both saturated and super

heated steam .It i s evident that the increase in steam consumptioni s more marked at l ight than at heavy loads , and the average in

crease for the two inches difference o f vacuum is p er cent

with saturated steam and p er cent with superheated steam .

TABLEIV .

ECONOMY OF KW . WESTINGHOUSE—PARSONS TURBINE WITHDIFFERENTVACUUMS . T ESTS WITHSATURATED STEAM .

Po und s S team p er E.H. P. p erHou r .

\Vi th 25 -InchVacu um .

Increa s e in S team Consumption on a ccount o f Dro p in Vacu um from 28 t o 26Inches :Load , E .H. P . ,Increa se p er c ent .Load ,

E .H. P . ,Increa se p er cent .Load , 400 E .H. P . ,Increa se p er cent .A verageIncrea se p er cen t .

*In a turb ine, the benefit derived from a good vacuum is much more than in a

recipro cating engine, every one inch Of vacuum betw een 23 inches and 28 inchesafl ec t ing the consumption on an average abou t 3 p er cent in a 100 Kw . , 4 p er cent ina 500 Kw . , and 5 p er cent in a Kw . turbine, the effect being mo re at highvacuum and less at low .

—Hon . Chas . A. Parsons in a paper before theIns titu tion o f

Electrical Engineers , M ay , 1904 .


TableIV . gives resu l ts under different loads for vacuumsvarying by inches from 28 to 25 inches . The average increase insteam consumption when the vacuum drops from 28 to 27 inchesis p er cent ; from 27 to 26 inches , p er cent ; from 26 to 25inches , p er cent, which shows that the drop from 28 to 27inches ae cts the results nearly twice as much as the drop from26 to 25 inches . The average increase , as summarized at the bottom of the table , for a drop in vacuum from 28 to 26 inches

,i s

p er cent . We see from this,and the previous table that a loss

of two inches of vacuum , below 28 inches,causes in these cases

an increase in steam consumption of say from 1 0 to 1 5 p er cent .A turbine , therefore, rtmning on 20 pounds of steam p er Kw .

hour, with 28 inches vacuum , might be expected to use from 22 to23 pounds i f the vacuum w as reduced to 26 inches—qu i te a l ikelycondition.

The diagram ,Fig . 8. w as plotted from the tests upon the

V acuum inInches .

Fig. 8.

214 STEAM TURBINESH . P . turbine and shows the steam consumption at different

vacuums . Curve A i s for the load of 400H. P. ; curve B fOIH . P. ; curve C for H. P. ; and the dotted curve D for

the average of the three loads . This chart Shows graph ical ly the

tw o facts already pointed out , that a change in vacuum has a

greater effect at l ight than at heavy loads , and that the effect i s

more marked at high than at low vacuums .

The Effec t of Sup erheating.In the tests upon the De Laval and Parsons turbines in the

last chapter are data upon the gain ( at the turbine) throughthe use of superheated steam . Whil e such resu lts have l ittle or

no s ignificance , unless computed on the heat-uni t bas i s , i t i s be

lieved to‘ be , and probably is , the case , that superheated steam is

desirable for turbine use.In the summary of tests upon a 300

horse-power De Laval tu rbine in Table IX .,the gain from super

heating is about 1 p er cent for every eight to 1 0 degrees super

heat .In their report upon the tests of a 400 Kw . Westinghouse

Parsons turb ine , already referred to‘,Dean and Main estimate the

gain from superheating to be one per cent for each 1 0 degrees , upto 1 80 degrees superheat

,which w as the l imit Of their tests . This

figure i s corroborated by Parsons , who , in the paper before theBrit ish Institute of El ectri cal Engineers

,from which Tables X .

and XI . are quoted , says ,“Every 1 0 degrees superheat up to about

1 50 degrees F .,affects the consumption abou t 1 p er cent .

Reason for Gain from Superheated S team—The gain from

superheated steam in the turbine comes from reduced fri ction be

tween the rapidly flowing steam and the passages Of the turbine ,and between the steam and the surfaces of the rotating wheel s .In the steam engine the gain from superheated steam is due to thereduction of cyl inder condensation

,resu lt ing in l ess loss from re

evaporation of thi s moisture at the lower pressures during the latter part of the stroke

,and during exhaust . The ini tial condensa

tion Of saturated steam enter ing an engine cyl inder i s often as

much as 40 or 50 p er cent , and thi s i s partly or entirely prevented

when the steam is superheated , depending upon the degree 0‘

superheat .In the turbine the effect of superheated steam is als'

to reduce condensat ion,which always occurs when saturated


216 S TEAM TURBINESdefini te relation to the velocity of the steam ,

as determined by the

proportions of the turbine , or otherwise there wil l be d isastrous

impact of the steam against the vanes .In the Curti s turbine at

the Newport station, tests were run to determine the variation in

steam consumption with a variation in the speed . At revolu

tions p er minute , the water rate p er kilowatt hour w as about

pounds ; at revolutions , about pounds ; atrevolut ions

,about and at revolutions , abou t 27 pounds .

This shows that at first the decrease in speed produced only a

smal l effect on the economy ; but later, as the Slower speeds arereached

,the steam consumption increases very rapidly .In a paper upon steam turbines* by Ernest N. Jansen,

tests are

quoted upon several turbines running with varying speeds . W i tha 400 Kw . Westinghouse-Parsons turbine at revolutions p er

minute , or hal f of the des igned Speed,there w as an increase of

25 p er cent in the steam consumption.

*Publ ished in the J ournal of the S ociety of Naval Archi tec ts , 1904 .

CHAPTER XIEXPERIMENTS ON THE FLOW OF STEAM .

Nap ier’s Ru les for the Flow of S team —R. D . Napier w as one

of the first experimenters to secure resu lts o f value on the flow o f

steam .He publ i shed data in 1 866 to Show that when steam flows

through a cyl indrical nozzle having a rounded inlet the weight dis

charged in a given time depends only on the initial absolute pres

sure , so long as the absolute pressure against which the nozzle dis

charges does not exceed 71 0 o f that pressure . Thus , i f steam

flows from a pressure of 1 00 p ounds absolute to a pres sure of 60

pounds absolute , the w eight dis charged in a given time wil l be

practical ly the same as though, the nozzle were discharging at some

lower pressure,as into the atmosphere, or into a partial vacuum .

I f,however

,the final pressure is more than 60 pounds

,the

weight discharged wi ll be less than before and wil l become very

much less as the difference of pressures decreases .In the London Engineer for November 26 and December 3 ,1869, Professor Rankine reviews Napier’ s work and presents one

Of the best theoretical discuss ions of the flow of steam that has been

publi shedHe concludes that the formu las given bel ow ,cOmmzonly

known as Napier’ s Ru les,wil l give a rough approximat ion of the

weight of steam discharged through a conoidal converging nozzle .

The ru les also app ly in the case of sho rt , cyl indrical tubes with

rounded inlet s .

Let W: : flow in pounds p er second .

p l z higher pressure and pzz low er pressure , both in

pounds per square inch absolute , and

az area of orifice in square inches .

CaseI.—Lower absolute pressure equal to or l ess than (71 0 o f

higher absolute pressure

218 STEAM TURBINESCase I I .

-Lower absolute pressure more than

absolute pressure :

W2 (P2+ 42)XV (PI—P2 ) 3P2

E.rample.—p 1 : 100 ; az l .

Case I .

70p ounds per second .

Let p2 : 80. Then,

XV ( 1 00—80) i" X80

pounds p er second .

Napier’ s ru l es give better resu lts in cas es where appl icable than

the more compl icated rules based on the laws of thermodynamics .

Brow nlee’s Safety-Valve Exper iments—The next important

tests to be recorded are des cribed in a“Repo rt on Safety Valves ,

”

by James Brownlee , in the“Transactions Of Engineers and Sh ip

bu i lders in Scotland ,

”Vo l . XV I I I . (Al so contained in London

Engineering,December 4 and 1 1

,Tabl e I . i s made up

from the data of two sets of tests,in the first of which the higher

pressure w as constant and the l ow er pressure vari ed ; while in the

second the l ower pressure w as constant and the higher p ressure

vari ed .

These tes ts are quoted here because the resu l ts i l lus trate Napier’

s

ru les for the flow of steam .In making the tests the weight offlow w as measured and the veloc i ty of flow w as calcu lated by

theoretical formu las . I t wi ll b e noted from column 4 , of the first

group , that the weight of steam discharged increases unti l the lower

pressure drops to 58 p er cent"< of the higher pressure , after which

the weight remains constant . This is as i t shoul d be from Napier’ 3

exp eriments , which showed that the flow i s proport ional to the

higher pressure , when the lower pressure i s not over ‘71 0 of thehigher .

*The value, 58 p er cent , quo ted in the table w as firs t used by Weisbach , and is

frequently given instead of 6-10, as the l imiting po int at w hich Napier ’ s ru les ho ld. Bothfigures are only approximate, how ever, and vary considerably w i th the cond i tions, as

w i l l b e show n . See reference t o this in the first chapter,in connection w i th the dis

cu ssion of the fl ow of steam .


220 S TEAM TURBINESof steam through tubes or mou thpieces inch in diameter. There

w ere three mouthp ieces tested having inl ets rounded with a radius

o f 1 inch and straight sections of , V2 and 1 72 inches , respec

tively .The experiments were conducted to find the weight of

steam discharged for different differences of pressure. The flow

w as then calcu lated by a theoretical formu la based on the principleso f thermodynamics , and the results compared , which gave the

probable coeffi cient o f flow for the three mouthpieces . The flow

w as als o calcu lated by Napier’ s formu la.

When under tes t the mouthp ieces were screwed into a brass

part it ion between two castiron reservoirs , in the first one of which

the steam Was maintained at a constant ini tial pressure, and in the

second the pressure w as vari ed . The pressure in the tube w as

found by dri l l ing into the tube at the middle of the straight section

o f each mouthpiece .

TABLE I I .

FLOW THROUGHSHORT T UBES WITHROUNDEDINLETS .

S team p ressu res F low in p o und s

(gau ge), 1b . sq . m . p er hou r .

E0 a w

.Q A o o y-Q A a >3

e st s: s e e 0 .o .o +4«a t"

a v a w a8 03 0 0

a fi " v-t ‘" vcr r T3 0 33 9 “

fl v-4 u -n a

$3 O i ; q,u p

,” a)+3 Q O E h v—c

v—4 0 N aas 8 E Q 8 8 0 o o “3 0o8

.

Q a) a)3 a) o r

am$3 v

s at “ oa)

d

fi t’

fa

.

“ s c‘

o ..4"

La v e , E4 5 3 m Q u a) O Z CL oHl

3

if J

:

CT

C3

qI0

EXPERIMENTS ON THE FLOW OF S TEAM 221

It is to be observed that the actual flow is larger than that cal

culated by the theo retical equati on . This equation i s based on the

assumption that no heat i s lost to or given up by the tube . But i ti s evident that some heat must have been conducted through thewal ls o f the nozzle from the hot steam in the upper chamber to thesteam pass ing through the tube , and this may explain why the co

efficient of flow i s greater than uni ty in each case . The resu lts in

dicate that this transmiss i on of the heat w as more than enough toovercome any l oss from friction in the tube .

For the longest tube Nap -ier’

s ru l e gives results greater than the

actual weight of steam pass ing through the nozzle , and for the

short tubes the resu lts calcu lated by Napier’ s ru l e fal l b elow the

actual . Thi s shows the greater effect of friction in the longesttube . The largest discrepancy between the actual resu lts and thos egiven by Napi er’ s formu la i s about 3 p er cent .The pressure in the tub e ranges from . 5 8 to .64 of the upp er abso

lute pressure and ' is more for the long tube than for the shorter

ones, and i s als o sl ightly more fo r the high p ressure tests with

the Short nozzle than for the low p ressure tests . The question ofthe pressure of steam at or near the throat of the nozzle has an im

portant bearing on the design of a nozzle . These tests and ot hers

yet tobe quot ed Show that the throat pres sure does not vary widely ,and that i t l ies between . 5 and .7 of the upper absolute pressure, orat a mean o f about .6 . Theoretical ly it shou ld be .58 of the upp erpressure .

Exp eriments on the D ischarge of Steam Through Orifi ces , by Strickland L . Kneas sfi‘

These experiments were completed in 1 890 at the works ofWi l l iamSellers Co .

,Inc . ,

Philadelphia,in connection with their

steam inj ector work . Their obj ect w as to determine the behavior

of steam within a discharging nozzle , and the extent to which theterminal veloci ty is affected by changes in the proportion of thetube . The nozzles tested were 8mm . inch) internaldiameter at the throat

,and 34mm . inches) long. The other

dimens ions of the nozzles,however

,were vari ed . The tubes were

connected to the steam supply by a 2- inch pipe and care w as taken“Proceed ings of the Engineers ’ Club Of Philadelphia, Ju ly, 189 1 , from w hich the

fol low ing abstract w as prepared .

222 S TEAM TURBINESto secure dry steam. In

‘

order to determine the pressures wi thinthe nozzle seven smal l hol es were dri l led equal d istances apart in

the wal ls Of the nozzle , commencing at the point where the curve

of app roach becomes tangent to the cyl indri cal barrel Of the tube .

Each of these apertures had gauge connections at the outer end ,

and the holes not in use were closed by plugs . ( See F ig. A

smal l searching tube w as used for finding the internal pressure of

the j et at points beyond the end of the nozzl e . The tube w as closed

at one end and had holes dri l l ed in one s ide near the end. TheSYPHON AND GAUGE

F ig . 1 . Method of Measuring Pressures .

other end of the tube w as connected -with a gauge, and by placing

the tube concentri c with the ax i s Of the nozzle and sl i ding it to

different pos it ions the pressures could be determined . S ince the

tube changed the relati on of the areas Of 'the different sections of

the nozzle in which it w as inserted , the nozzle w as made of p ro

port ionately larger diameter to comp ensate for this , when the tube

w as used .

M r. Kneass w as the first in this country to make systemat ic in

vest igationo f steam discharge through nozzles . The questions of

internal pressures,the relat ion between l ength and terminal

veloci ty , and the taper and shape of nozzles were carefu l ly goneinto .

Exp lanation of Diagram .

— The diagram,Fig . 2 , shows

tudinal cross section of each of the five nozzles tested .

l ines,I, 2 , 3 , 4, etc .

, cutting each nozzle pass throuat wh i ch the pressures w ere measured .

are plotted pressure curves pass ing th


224 S TEAM TURBINESto the Observed pressures , while abo ve the nozzle sections are

velocity curves . The points for these latter were calcu lated by first

plotting the Observed pressures and volumes of a unit weight o f

steam , and drawing a curve through the po ints . The area under

the curve represents the energy in foo t pounds producing the

velocity of the steam ,just as an indicator card represents work

done . The veloci ty corresponding to th i s area w as then found bythe formula

taken from Rankine ’ s The Steam Engine , page 298, the U in

the formu la represent ing the work done by uni t weight of steam if

admitted to a cyl inder at the init ial pressure,expanded adiabatic

al lv,and expelled at the terminal pressure . Theoretical ly , at l east ,

the work done by steam in giving itsel f veloc ity in a non-conduct

ing nozzl e Shou ld be equal to the work done by steam in an engine

cyl inder under l ike pressure ranges .

Tes ts upon Nozz le No .I.— The cyl indri cal nozzle w as first

tested and the pressure curves show a gradual ly decreas ing pres

su re , steeper at high pressures than at low . The pressure at the

first hole bears nearly a constant relation to the initial pressure ,while the ratio of terminal to ini tial pressure fal l s sl ightly as the

init ial.pressure decreases . These points are shown in the fol

lowingRatio of Ratio of

Throat Pressure Terminal PressuretoInitial Pressure. toIni tial Pressu re .

p1 p”I) p

120

90

60

30

20

The action of the steam and cause of ineffi ciency are apparent.Taking ,

for examp le, the 1 20—pound l ine , we find that , while

travers ing the nozzle the pressure is reduced only from 80 to 64

pounds and i s discharged at that pressure into the atmosphere ,los ing nearly 66 per cent of i ts veloc i ty-producing power. At 60

pounds in i t ial pressure the velocity l ine i s a l ittle higher than at

1 20 pounds .


Tes ts w ith Nozz le No. 2 .

—In this nozzle,diverging with a

straight taper of 1 in 1 0 in diameter ,‘

the throat pressure fal ls to

about 910 of the ini tial and i s very nearly the same as the terminalpressure in the cyl indrical tube . W ith high initial pressure the ex

pansion l ine approaches the hyperbolic curve and discharges veryclose to the atmospheri c l ine , while the 60—pound curve fal ls even

into the vacuum lines and i ssues from the tube in a j et that contracts to a smal ler diameter than that Of the orifice . This phenome

non occurs with the 30-p ound and 20-pound l ines within the confines Of the nozzle and the pressure at the

.

mouth is greater than

that at the fi fth or ifice . This shows that for these lower pressuresthere is a loss in efficiency in going beyond this point of max imum

expans ion, and that the discharging j et w ou ld have higher terminalvelocity i f the tube were made short er. When the j et expandswithin the nozzle to a pressure lower t han 1 5 pounds absolute,there wil l be a cont raction of the jet after leaving the tube , dueto the pressure o f the atmosphere . These important facts wereprobably first noted in thi s series o f experiments .

An experiment with the 1 in 1 0 tube , before and after reaming

the discharge end with steeper tapers , showed that such change in

the angle Of divergence produc ed no effect upon the steam discharge Oi the inlet hal f of the tube , as the curves of veloci ty and

pressure are identical for the inlet end of the tube under bothconditions . The experiment has also been tri ed .of gradual ly

shortening the tube by cu tting sections Off the ou tlet end , and i tw as found that the pressures nearer the inlet were not affected -bythe alteration.

Design ofNozz le No. 35.—In all the straight nozzles there is loss

of energy ,due to flu id fri ct ion ,

ow ing to changes in velocity .

Mr. Kneass reasoned that these changes in velocity Should cause

less loss and internal friction i f the acceleration of the jet weremade uni form . Nozzle No . 5 w as designed to give constant acceleration. The pressure at the throat w as assumed at i ts lowesttheoretical value and the terminal velocity at the highest attainablein expanding from 1 20 pounds to the atmosphere . The tube w as

divided into seven part s and the acceleration calcu lated . Then, in

order to divide the work evenly,the expans ion w as made uni form

and from these data the area of the tube at each given secti on w as

226 STEAM TURBINESdetermined . As shown by the diagram , this tube gives superior

resu lts .

Deductions from the Velocity L ines—It will be noticed that,

notwithstanding the marked differences in ini tial pressure , ranging

from 30 to 1 20 pounds , gauge , the velocity curves for the several

nozzles , and particu larly for nozzle 5 , fal l very close together.Inthe latter nozzle the velociti es at any g iven po int are practical ly the

same for all the pressures u sed . M r . Kn eass finds by analyz ing

formu las of Rankine for the flow of steam that i f the ratio of the

throat to the initial pressure were the same under al l conditions ,there wou ld be a lower velocity for 30 than for 1 20 pounds ini tial

pres sure at any given point in the nozzl e . I t wil l be seen from

Tabl e I I I . ,however

,where this ratio is given for the different noz

z les and for the different ini tial pressures , that its value decreases

with the ini tial pressure .In other w ords , the throat pressure i s a

smal ler percentage of the ini t ial p res sure w hen steam is be ing used

at a low ini tial p ressure than when u s ed at a h igh init ial pressure .

This condition, apparently , affects the velocity at any po int in the

nozzle in a w ay partial ly to neu tral i ze the effect Of the ini tial pres

sure upon the velocity. This i s shown bo th by the formu las andthe tests . For example , in nozzle 5 , taking the actual throat pres

sures as found by the tests , the veloc i ti es at po int 4 for the different

ini tial pressures are found by cal cu lation to vary only by 4 p er cent .In TableIV . are the velociti es of the steam for the d ifferent

points in the several tubes as cal cu lated from the experimental results . The variation of the velocity from a cons tant value for all

the pressures in the table i s smal l . M r. Kneass states that for

practical purposes the veloc ity may be cons idered constant and a

s imple formu la derived for the weight of steam discharged throughan orifice

P

in a given time which i s more conveni ent to apply than

the thermodynamic equation . It i s based on the assumption of

constant velocity of discharge and i s to be appl i ed where the ratio

o f final to initial absolute pressures does not exceed

Let Wz w eight in pounds discharged p er second ,az area o f orifice in square inches

,

d z w etght of 1 cubic foot Of steam in i ts initial condiThen, W: 6 .1 9 ad .


228 S TEAM TURBINESExamp le— az l init ial pressure : 1 00 pounds absolu te ;

d : .2271 ( from steam table) . Then,

pounds p er second . This i s to be comp ared with the same example

solved by equation th i s chapter, according to Napier’

s ru le .

Exp erim ents on Steam Jets by Wal ter Rosenhain.

*

Descrip tion of Apparatus —In thi s seri es of experiments bo thcylindrical and diverging nozzles were used , and the veloc ity of dis

charge w as measured by the ingenious plan Of weighing the re

act ion of the j et upon the nozz l e by means of a special apparatus .

Knowing the reaction of the j et in pounds and the weight of steam

discharged in a given time , the veloci ty cou ld be accurately deter

m inedrjIn Fig . 3 i s a diagram of the apparatus . A vert ical tube , F, i s

j oined to a steam pip e , D ,and suppo rts at i ts lower end a cylindri cal

chamberH,which has a circu lar Opening for the noz zle . The

tube , F,IS Of bicycle tubing ,

which has sufficient fl ex ibi l ity to al l ow

the cyl indrical chamber to swing freely about the p oint of sup

po rt at D . The reaction Of the j et i s measured by weights placed

in the scal e pan , S ,carri ed by a cord pass ing over the pu l ley , P,

and attached to the hori zontal arm at K . A po inter indicates the

movement Of the arm and chamber,H, on the scale Shown above

the arm . Pu l ley P i s a finelv fini shed steel disk,with bal l bearings .

A gauge regi sters the pres sure o f the steam inH.In the tests thepressure of the steam supplied the apparatus w as control led , ei ther

by varying the boil er pressure or by throttl ing the steam after i t

left the bo i ler. After the Observations of reaction w ere made , the

di scharge w as measured in po unds p er second under as nearly thesame conditions as poss ible , the steam being condu ct ed to a surfacecondenser and weighed .

The formu la for the veloc ity of di scharge is bas ed on the Old

*Proceed ings of TheInst itu tion of Civi l Engineer s, London, V ol . CXL. , 1900.

+A ser ies o f articles in London Engineer ing ,1872 , u pon “

Exper iments and Researches Of the Efliux Of Elastic Flu ids ,” by W i lson, descr ibes a s imilar method for

measur ing the velocity o f a j et . Wi lson ’s apparatu s w as e laborate and his tests w ere

exhau stive, b u t the resu lts are no t o f value for the present purpo se. Ano ther methodhas been u sed by Strickland L . Kneass , w h o arranged the nozz le t o d ischarge againsta del icately balanced parabo l ic target . The target tu rned the jet through an angle Of

90 degrees and the pressure against the target shou ld give a resu l t equ ivalent t o the

reaction of a sw inging no zz le.


principle that action and reaction are equal ,—the accelerating forceof the j et i s equal to the reaction of the j et up on the nozzle and i tschamber,H, —and may be derived thus : Suppose a force , F ,

act

ing as a constant pu l l or push on a free body,to give the body a

velocity Of V feet p er second at the end o f one second . Then,s ince

3 . Method of Measuring Veloci ty of

F low .

we that gravity, acting on the same body with a constant

force of W pounds , equal to the weight of the body , would producea velocity of feet p er second at the end of one second , we have ,

F : W: V : g,or

,

Rs

W

S TEAMIn applying th is formu la to the steam jet , we

l'=veloc ity in feet per second ,F=rcac tion in pounds ,

g=acceleration of gravity

W=pounds steam discharged per second .

TABLE V .

No zzu cs.

O rna te

The Noss les Used in the Tes ts are represented in F ig 4 , and

their dimens ions are tabulated in Table V . The nozzles were all

made with a throat d iameter as nearly as po ss ibl e 3-1 6 inch in

diameter, the exact dimensions being g iven in the tab le. Th i s i s the

diameter Of the nozzles of a De Laval 5-horse power turbine. The

dimensions of De Laval nozzles of thi s s ize for several d ifferent

pressures are given in Tabl e VI. , wh i ch shows the tapers to varyfrom about 1 in 1 7 to 1 in 27 . Gu ided by th i s , the tapers o f the ex

perimental nozzl es were made 1 in 12 , 1 in 20, and 1 in 30, wh ich

gave wide enough latitude for the tests and yet kept reasonablyclose to proportions that had proved sati s factory in practice .

T ABLE VI.DR LAVAI. No zzw s FUR 5-H. P. TURBINE.

Length . Tap er.


232 S TEAM TURBINESthe quanti ty of steam passed by a nozzle depends very cons iderablyon the shape of the inlet , the velocity on leaving the nozzle depends

more on the shap e of the outlet port ion. This po ints to the con

elusion that the dens i ty of the steam at the throat of the nozzle de

pends upon the shape of th e inl et and that this dens ity is greater

with a well-rounded inlet than with a nozzl e having a sharp inner

edge .

This accounts for themos t conspicuous featu re of this set of

velocity curves , viz ., that up to a p ressure of abou t 80 pounds perINITIAL PREBSURE, LE8. 80 .IN. , GAUGE.

square inch the greatest vel ocity is attained by a j et from an orifice

in a thin plate and that above 1 00 pounds p er square inch ,II. B,

having a sharp inlet , gives a greater velocity thanIIw hich hasa rounded inl et and the sam e out let. Apparently the round ed inlet

admits a greater weight of steam to the narrowest sec tion than the

nozzl e can deal w ith effici ently .

The reason , of course , w hy the diverging nozzles give great er

velocities at the higher pressures than the thin plate or the con

verging nozzl e is that expans ion i s not complete in the two latter

at the higher p ressures and there i s wasted energy .

Comparing the dim ens ions of noz zl eII. B with the d imens ionsof the De Laval nozzles , i t i s found to l i e midway between the ex


tremes , and hence two other nozzles were designed ,III. andIVhaving tapers , respectively , of 1 in 1 2 and 1 in 30, as previou slystated . These

,however, were made with inl et rounded sl ightly ,

with smal l radius , instead of with a large radius , as in nozzleII.this in view of the fact that the preliminary tests had shown that

w hen the inlet w as cons iderably rounded the velocity of flowwould not be as -great .

w ith Nozz leIII—In order to secure information upon

the best ratio of out let to throat diameters of a steam nozzle . testsINIT IAL PRESSURE, LBS . SQ .IN. , GAUGE.

F ig. 6 .

were run with nozzleIII. at i ts original lengt h of inches and

then i t w as cut down ,first to .79 inches and final ly to .64 inches

long. NozzleIII. B discharged the greatest quantity of steam ,

nozzleIII. s lightly less andIII. A the least . The discharge curveskeep very close together

,how ever, and it i s not thought necessarv

to rep roduce them herewith , as their mean values very nearly co

incide with curveII. A,Fig . 5 , for the converging nozzl e . The

velocity curves are given in Fig . 7 , which shows nozzleIII. A tobe the most efficient . Comparing the curves in Fig 7 , i t seems

probable that in nozzleIII. B expans ion w as insufficient and that

234 S TEAM TURBINESin nozzleIII. i t w as too great . I t may be suppos ed that in the lat

ter the steam expanded down to atmospheri c pressure and then

flowed through the remain ing p ort ion of the noz zle much as an

incompress ible flu id wou l d do , the steam increas ing in section at

the expense of the velocity . ( See veloc i ty diagrams , al so,in

Fig .

NozzleIII. A,with 1

.

in 1 2 tap er, i s rough ly comparabl e with

nozzl eII. B , w hich showed up the best of the 1 in 20 tapers , and

from their veloc ity curves there app ears to be a sma l l d ifference

in favor of the 1 in 1 2 tap er.

INITIAL PRESSURE, LBS . SQ .IN. , GAUGE.

Fig . 7.

Tes ts w ith Nozz leIV—It will be noted from Table V . thatnozzleIV. i s so des igned as to be directly comparabl e with nozzlesIII. andIII. A. It has the same lengt h as nozzl eIII. , but a

smal ler outl et diameter, s ince i ts taper i s 1 in 30 instead of 1 in 1 2 .

Its outlet diam eter i s the same , however, as of nozzl eIII. A,bu t

i ts length , of cours e , is greater. The velocity curves for these threenozzles are plotted in F ig . 8. NozzleIII. gives the poorest resu lts,as before , in diagram in Fig . 7

, andIII. A gives the best resu lts , asbefore , while nozzl eIV. fal l s between. The conclus i on has already


236 STEAM TURBINESproper rati o of greates t and leas t diameters i s given, according to

present resu lts , in the fol low ing table

Steam p ressure in pounds p er square inch 80

Rat io of diamet ers

Rateau’

s Exp eriments .

*

Professor A. Rateau , of Pari s , the inventor of the Rateau steam

turb ine , has made experiments upon the escape of steam through

circular orifices .He experimented with the nozzles and the orifice

shown in Fig . 9, the diameters of w hich are as fol lows :

Nozz le. M i l limeters.Inches .

A .412

B .598

C .954

.793

F ig. Nozz les Used by Rateau.

Tes ts w ith Final Pressure Less than .58Initial Pressure—Inthis seri es a large number of tests were made , and a few data and

resu lts for each of the nozzles have been sel ected from the tables

publ i shed by Rateau and grouped in Tabl e VII. herewith . The

original metric uni ts and their English equ ival ents are given.Inthe cas e of the three converging nozzl es the weight of steam dis

charged depends only on the ini tial pressure and i s not affected by“Paper by A. Rateau u pon “

L’Ecou lement de la Vapeur D

’

Eau par Des Tuy ers

et des Orifi ces”in the

“Annales des M ines ,

”Par is , January , 1902 . S ince this abstract

w as made this paper has been trans lated and is now pub lished by the D . Van Nos trandCompany , New Yo rk.

EXPERIMENTS ON THE FLOIV OF S TEAM 237

TABLE VII.FLOW THROUGHCONVERGING No zzu zs AND ORIFICEIN FLAT PLATE .

Ab so l ute p res su res .

Ra t io o fIto P .Ini t ia l P . F ina l p .

No zz le .

the final pressure . This is shown bv the last two c olumns of thetable , which g ive the di scharge p er kilogram , o r pound

,init ial

pressure , according as metric or Engl i sh units are taken . Thesecolumns express the rati o,IW t . discharged p er second p er uni t area

P Initial pressure p er uni t area

It wil l be noted that this ratio is very nearly a constant quantityexcept for the orifice , D ,

in the thin plate , showing that flowthrough the latter does not follow the same law .

238 S TEAM TURBINESRateau plotted the resu lts of these tests , us ing as ordinates the

ratiosI/P and as abscissas the discharge p er second p er uni t area.He then plotted the theoretical discharge l ine , us ing a formu la de

rived by the principles o i thermodynamics , in order to compare re

sults . The differences do not usual ly exceed two p er cent . The

actual discharge w as sl ightly in excess of the theoretical , the meandeviation for nozzle A being .01 2 of the actual dis charge ; for noz

zle B, .007, and for nozzle C,

.003 o f the actual . The difference in

the s izes of the nozzles apparently had no marked effect on the results .

Formula for Weight Discharged .—From the foregoing it i s evi

dent that a s ingle formula may be employed to calcu late app roxi

mately the weight di scharged for al l pressures within the l imits of

the tests , provided the fina l pressure i s not more than .58 of the

ini tial . The following is proposed , the form of which is derived

by theory , but the constants of which are taken from the tests :I—P ( 1 5 2 6—9 6 log P ) ,inwhichIi s the flow in grammes p er square centimeter p er second ,and P i s the ini tial pressure in kilograms p er square cent imeter.

This may be cal led the formu la of max imum discharge , s ince it

gives the greatest quantity that wil l flow through the nozzle for agiven pressure .In English units i t reduces toI: .001P ( log P—l—logwhereIi s the flow in pounds p er square inch per second and Pinit ial pressure in p ounds per square inch .

Examp le—Given,P 2 6 68

,met ri c ; 95 , English .In met ric units ,

grams per square cent imeter per second .In English uni ts ,Iz .001 ><95

O95X 1 4 .4 7

p ounds p er square l l‘

l Ch p er second .


240 S TEAM TURBINESstantly as p low ers .In the diagram ,

Fig . 1 0,are the relative resu l ts

up to

p/PZ OA.

By taking the ratio between the ordinates of th is curve and those

of the experimental curve for the converging mouthpieces,the

points fal l on a straight l ine CD, tangent to the thin plate curve atpoint D

,which is on the ordinate of the point where the curve AB

j oins the horizontal .Examp le— Initial pressure absolute : 10 kg . sq . cm . Ratio of

final to ini tial pressure : .8. From the diagram we find ,for a con

NOZZLE No . 3 NOZZLE No . 4

No . 1 WITHDIVERGENT No . 2 WITHDIVERGENTMOUTHPIECE ADDED MOUTHPIECE ADDED

TAPE-ZR 1IN 23 TAPER 1IN 23

F ig . 1 1 . Nozz les Used b y Gu termu th .

verging nozzl e,that the ordinate .8 cuts the curve at a

,and th i s

point proj ected to the left gives .82 for the ratio of d ischarge .

Now calcu lateIfor P 2 10,and mult iply the resu lt by .82,which

wil l give the flow through the converging nozzl e . The discharge

through the thin plate can be calcu lated in the same manner , by

means of the other curve .

Other Exp erim ent s .

Gu ternzuth’

s Experiments on the Ou tflow of S team—An ac

count of experiments by Pro fessor M . F . Gutermuth of the TechnicalHigh School , Darmstadt , l s g 1ven in the Journal of the

EXPERIMENTS ON THE FLOW OFS TEAM 24 1

American S ociety of Naval Engineers for May , 1 904 .

‘

NOzzles ,

orifices and passages o f various forms were tested , the shapes

shown in Fig . 1 1 being those best adapted to turb ine work . The

tests were conducted in groups , in each Of which the init ial pressu re w as kept constant and the final pressure varied .to give thedes ired pressure differences . This

,i t shou ld be said , i s the

correct w ay in which to Obtain comparat ive resu lts and i t i s

unfortunate that more experimenters have not adopted the sameplan. The weight and velocity Of steam flowing from a nozzle

depend more upon the ini tial pressure than upon the final pressure,

TABLE V I I I .

COMPARISON OF FLOW THROUGHNOZZLES SHOWNIN FIG . 1 1 .

F low in k i logram s p er hou r- actu a l . Ra t io o f fl ow .

Ab so lu te Ab so lu tein i t ia l fina lpres su re p res su rein a tmos in a tmo s

p h eres . p h eres .

l 2 l 3 l

242 S TEAM TURBINESand tests in which ,

the final pressure i s kept constant and the

ini tial pressure vari ed are not as satis factory .

The two tables herewith were compiled from the resu lts Of

about 300 tests recorded in the article mentioned . Table V I I I

i s arranged to show the weights Of steam discharged by each

nozzle for different ini t ial pressures and pressure differences .

The first six columns are from the original data and the last two

TABLE IX .

COMPARISON OF FLOW THROUGHCONVERGING AND DIVERGING NozzLEs .

F low in l b . p er ho u r .

A ct ua lRa t io o f F low in 1h .

Ra t 1o Of fl ow thro ’

p er hourIni t ia l fina l t o d iverg ing p er sq . inchp res su re F ina l p res 1n1t ial no z z le t o area a t

l b . p er s ure 1b .p ressu re fl ow thr o ’ throa t Of

sq . in. p er sq . in. (Item 2 converging d ivergingab so lu te . a b so lu te. i tem no zz le . noz z le .I2I3I4I5II

79

.944

.907

.77685 .4 66674 . o f im t ial p r essure .

. 555

. 1 1 1

.972

. 928857714 172 . 9

57 . o f im t ia l p r es su re.

. 57

. 1437

.960

. 9 10800

42 . 7 59941 . o f im t ia l p r es su re.

.200


244 S TEAM TURBINESinto kinetic energy in a nozzle may be less effi cient than supposed,and that the commonly-accepted theory Of the flow Of steam

through orifices does not conform to practice .In any case the

tests show_that further investigation i s needed before We can

assert that the passages of a steam turbine have been designed

along the most success fu l l ines poss ible .In F ig . 1 3 i s a sketch giving the dimens ions Of the nozzle .

The pressures at the different points with in the nozzle were

determined in the usual manner by means Of searching tubes .These were made in three different ways—one having an opening

Opposed to the current , one with the orifice Opening in the

d irection Of the current,and the th ird with the Opening in the

s ide Of the tube . As a matter Of course these three tubes gave

widely different resu l ts,and i t seems better, for the sake Of

compari son with other experiments,i f for no other reason

,to use

the resul ts Obtained with the latter for m Of tube . s ince th is i s

the type employed by other experimenters .In the diagram,F ig . 1 2 ,

are four curves showing the variation

Of pressure at different points within the tube , start ing at init ial

pressures Of and pounds absolu te , resp ec

tively . The nozzl e discharged against atmospheri c pressure and

w as evidently des igned for a greater pressure range Of steam than

w as used . It wi l l be noted that in each case the steam reaches at

mospheric pressure midway between the inl et and outl et sections Of

the diverging portions Of the nozzle,after which the effect is to

cause What we have previously cal led“over-expans ion” Of the

steam,the pressure dropping to 1 0 pounds absolute and then

ri s ing again to atmospher ic pressure as the outl et Of the nozzle is

reached .

The theoretical crit ical point Of 58 p er cent Of the initial pres

sure is not reached unti l a point about .1 2 inch from the throat

is reached , represented by the l ine xv. The points in the different

curves at which the pressure is 58 p er cent Of the ini tial pressure

fal l very nearly in the same vertical l ine . The actual throat pres

sures at A,B

,C,

and D are much higher than this .

Temperature Determinations —In Fig . 1 3 i s a diagram rep re

senting temperatures at different points in the nozzle for steamhaving an initial pressure Of pounds . The measured temper


atures are represented by l ine A. The temperatures were determined by means Of a thermo couple Of thin nickel copper wirewhich w as stretched through the nozzle . I t wil l be seen from thediagram and al so from Table X . that the steam w as superheated

F ig. 1 3 .

throughout the entire length Of the nozzle . Because Of throt

tl ing at the point Of approach,the steam w as superheated sl ightly

at the start and remained so unti l i t discharged . Line B showsthe amount Of superheating at different points , and indicatesthat the superheat increased to about the middl e Of the divergingpart Of the nozzl e and then gradual ly decreased .In the last column Of Table X . i s given the number Of thermalunits in the steam just before it enters the nozzl e and at the point

246 S TEAM TURBINESTABLE X .

T EMPERATURESIN AN EXPANDING NOZZLE.

c ome ” B . T . U . inDifs

r

t

o

a

lplc e

Ab so lu te M ea s ured Degrees S t eam z x

T hre a teen

s;T e

ase S

iesInche s .

q .

Sa tu ra ted( t s—t)b t eani

18

Of di scharge . These were cal culated by taking the total heat

from a steam table and adding the amount Of h eat due to the

superheat , found by mu l tiplying the number Of degrees Of super

heat by the specific heat at atmospheri c pressure,which is .48.

The difference between the heat present at the beginning and

end represents the heat energy Of the steam converted into work ,as equal to thermal uni ts .

I f the steam had been saturated at the start , however, and , as

i s general ly assumed , the expans ion had been adiabatic , about 1 0

per cent Of the steam wou ld have been condensed and its heat

converted into work ; and furthermore , the heat represented by

the convers ion wou ld be nearly five times as much as w as actual lyconverted into kinetic energy.

The questions to be answered are : Why w as so l ittl e heatconverted into work ? and

, Why did the steam superheat insteadOf condense within the nozzle ? Further experiments are to be

conducted,along these l ines , which shou ld be productive Of much

valuable information.


248 STEAM TURBINESTO convert Fahrenheit to centigrade , subtract 32 and mul tiply

Example—1 40° F . Again,5° F . (or

27° below —1 5 ° C . ,

or 1 5°

below zero, C.

Absolu te Temperature.—The absolute zero Of temperature , at

which heat i s supposed.

to be entirely absent , i s theoretical lydegrees F. below the freezing point Of water. The demon

strat ion Of this given in treati ses upon heat i s based upon the law

Of the heat expans ion Of gases,under the assumption that the law

holds at the extremely low temperatures . Th i s assumption i s in

error, but to what extent is not known. Letting T : absolute tem

perature and tz temp erature on the ord inary scal e ,

T: t+460.7 Fahrenheit, and

T : t+273 .7 centigrade .In steam calcu lations absolute temperatures are not to be used

unl ess it i s so stated . The temperatures Of the steam table are the

ordinary temperatures .

Pressure—The average atmospheric pressure i s taken in th is

country to be pounds p er square inch . On the continent Of

Europe pressures are usual ly measured in atmospheres,and one

atmosphere i s taken to be equal to a pressure Of one kilogram p er

square centimeter , which is equ ival ent to pounds p er square

inch , instead Of pounds .

Gauge pressure i s the pressure denoted by a steam gauge and i s

measured above the pressure Of the atmosphere ; that i s , i t doesnot include the pressure Of the atmosphere .

Abs o lu te pressure i s equal to gauge pressu re plus atmospheri c

pressure , usual ly taken at pounds p er square inch . The exactabsolute pressure can be determined only by the use Of the

barometer, which gives the pressure Of the atmosphere in inchesOf mercury . One cubic inch Of mercury weighs pound at

60 degrees F . and 30 inches Of mercury are therefore equ ival entto pounds pressure at thi s temperature .In steam cal cu lations absolute pressures are to be u sed insteadof gauge pressures

,unl ess otherwise stated .

Vacuum is measured in inches Of mercury or mil l imeters Of

S TEAM ANDITS PROPERTIES 249

mercury . The vacuum gauge used in commercial work shows the

height in inches Of a column Of mercury that the pressure Of the

atmosphere will support against the pressure that i s being

measured

Examp le.

—If a vacuum gauge attached to a condenser reads

26 inches , and the barometer stands at 30 inches , what i s the ab solute pressure in the condenser ? S ince the barometer stands at

30 inches , the atmospheric pressure i s pounds per

square inch . 30—26z 4 ; and the pressure in condenser:

pound p er square inch .Heat Unit, or Thermal Unit—In the Engl ish system heat i smeasured in Bri tish thermal units (B . T . A British thermal

uni t i s the amount Of heat necessary to rai s e one pound Of water

from 62 degrees F . to 63 degrees F .In the French system thecalori e i s the unit

,equal to B . T . U .

M echanical Equivalent ofHeat. —This is the number Of unitsOf mechanical work to which One unit Of heat i s equ ivalent .

1 B . T . foot-pounds .1 calori e : 426 .9 meter-kilograms .

SpecificHeat is the number Of thermal units requ ired to rai s eunit weight Of a substance one degree

,temperature . The specific

heat Of water i s unity at temperatures ranging from 59 t o 68 and

from 1 04 to 1 1 3 degrees F and app roximately unity at othertemperatures . The specific heat of nearly al l other substances isless than one.

The foregoing is properly the definition for true specific heat .Sometimes , when a substance is rai sed through several degrees

temperature , i t i s necessary to find the mean specific heat betweenthese l imits Of temperature . This is the average number Of

thermal uni ts p er degree requ ired to rai s e a unit weight Of a sub

stance from one temperature to any other given temperature .

Specific Volume.—In problems relating to the expansion Of

gases , it i s conveni ent to deal with unit weights Of the substanceand to consider the volume occupied by unit weight . This i s

cal led specific volume .In the English system it i s the cubic feetoccupied by one pound and in the metri c system the cubic metersoccupied by one kilogram .

250 STEAM TURBINESSpecific Pressure—Wh en specific volumes enter into an exam

ple we have to deal with cub ic feet instead Of cubic inches and

with cubic meters instead Of cubic centimeters . Pressures used

in carrying through the calcu lation mu st therefore be expressed in

pounds p er square foot or in kilograms p er square meter, accord

ing to which system i s being used . These are cal led specific

pressures . Errors frequently creep into cal cu lat ions by fai lure to

note when specific pressures shou ld be u sed .

Saturated S team i s steam generated in contact with water and

the temperature Of which always corresponds with the pressure .

Superheated S team i s steam heated to a temperature higher

than that corresp onding to the pressure , as in saturated steam .

The superheating is produced by applying heat directly to the

steam itsel f,instead Of to the water from which it i s generated ,

and i f the superheating is to be carri ed far , the steam must be in

a s eparate chamber,and not in contact with water.

S team Tables .

—Tables Of the properti es Of saturated steam ,

used to fac il itate steam cal cu lations , contain columns Of figures

giving certain important properties Of steam . The fol lowing are

the most important headings for steam turbine calcu lations .

Columns Of the table giving heat units re fer to the number Of heat

units in One pound Of water or steam,as the case may be .

1 . Absolute pressure , pounds p er square inch .

2 . Temperature Of the boil ing point corresponding to pressuresOf co lumn 1 .

3 .Heat Of the l iqu id,from 32

° F .

Latent heat Of vapor ization;Total heat in the steam and water

,from 32

° F .

Entropy Of water.

Entropy Of steam .

Specific volume—cubic feet p er pound .

9 . Dens ity—weight Of a cubic foot in pounds .

Of these , numbers 6 and 7 wil l be explained later,Whil e num

bers 3 ,4,and 5 can be best i l lustrated by cons idering the several

steps involved in the generat ion Of steam .

The Generation of S team—In the operation Of a steam boilerthe pressure is so nearly constant that i t may be assumed to be so

during the evaporation Of each individual pound Of water. When


252 STEAM TURBINESweight Of the mixture . One pound Of the mixture contains a p or

t ion x Of steam and ( 1 —.r ) Of water. The total heat Of the m ix

ture i s equal to the heat requ ired .to rai se one pound Of water to

the given pressure , plus the heat requ ired to evaporate the part x

Of the water into steam ; or, q—I—xr .Hence total heat Of one

pound Of wet steam : xr+q. ( 3 )

Specific Volume ofWet S team .

Let s : sp ec ific volume Of dry steam .

v : sp ecific volume Of wet steam .

c : sp ec ific volume Of s ince the

weight Of one cubic foot Of water i s pounds .

Then,

v : xs ( 1 ( 4 )

The last term , ( 1 i s so smal l that it can usual ly be

Omitted . At high pressures , say at 200 pounds , spec ific volumes

have low values and the effect of the term ( 1—x)a i s proportion

ately great . At 200 pounds pressure , however, i ts Omission would

cause an error Of l ess than a tenth Of one p er cent for each 1 0 p ercent Of moisture present , which i s l ess than probable errors in the

steam table . We may , therefore , use for specific volume Of wet

steam , v :.rs . 5 )

Total heat of Superheated S team—TO determine this , w e have,

Total ( t s—t), ( 6)

whereA: to tal heat Of dry saturated steam at the given pressure .

ts: temp erature Of the superheated steam .

t : temp erature Of saturated steam at the given pressure .

c : sp ecific heat Of superheated steam at constant pressure .

Values Of thi s wil l shortly be discussed .

Examp le.—F ind the total heat Of superheated steam at 4 50 de

grees F . and 1 00 pounds absolute pressure , assuming c : 0.5 5 .

From the steam tables,A and t : 327 .3 . Hence

,

Total heat : 1,1 81 .9 ( 4 50

Adiabatic Expansion.

-\Vhen steam expands without receivingor giving up heat it i s said to expand adiabatical ly . Steam flowing through a correctly proportioned nozzle flows adiabatical ly , or


nearly so , because its passage i s so rapid that l ittl e or no heat can

be transmitted to it from auv external source , nor can much heat

be lost through radiation or otherwise .

Temp erature-Entrop y D iagram .

The graphical method Of representing mechanical work is by

means Of the pressure-volume diagram , l ike the indicator card of

a steam engine .

‘In laying out such a diagram we. use two co

F ig. l . Pressure~V o lume Diagram .

ordinates , OX and OY,Fig . 1 , drawn t hrough point O, the zero

Of volume and pressure . Points on the diagram are determined

by measuring volumes from OX and pressures from OY. The

area Of the diagram represents mechanical work .Heat Diagram—S imi larly , heat energy may be represented by

the area Of a diagram constructed with vertical ordinates Of abso

lute temperature and hori zontal d imens ions Obtained by dividing

the number Of heat uni ts added or sub tracted'

during any changeby the absolute temperature during that change . The horizontal

distance Of any point from the vertical axis OX Of the heat dia

gramIS cal led its Entropy , just as this distance On the work diagram represents volume . This term “entropy” gives the nameTemperature-Entropy Diagram to the heat diagram .

The Analogy betw een the Work Diagram and theHeat Diagram may be further explained by selecting some one part of the

diagram , Fig . 1, as the expans ion l ine bc, which

“ i s reproduced in

Fig. 2 . The area abcd under thi s curve represents the work done

254 S TEAM TURBINESduring the change b rought about by the expansion from b to c.

The mean pressure during this change i s h . The volume at the

start i s represented by distance Oa ; the volume at the end by Odand the change in volume due to the expans ion by ad .

*

Now the area abcd : p roduct Of width by mean height , or ad

by h.

Hence, for the pressure-volume diagram

ork done in foot—p ounchange Pf

vo lumeInduring any change cub ic feet .In F ig. 3 i s the corresponding temperature-entrOpy diagram ,

in

which bc i s the expans ion curve showing a change , both in abso

lute temperature and entropy . The area abcd under thi s curve

represents the heat uni ts given up by the working flu i d during the

expans ion. The mean absolute temperature during the expans ion

i s h. The entrOpy

'

at the start i s shown by the distance Oa; the

entropy at the end by Od ,

’

and the change in entrOpy , due to the

expans ion, by ad. It i s to be noted that the entropy i s measured

from the ordinate OX and that ad i s not the entropy Of point d,but that i t i s the change in entropy during the change in the condi

tion Of the substance .

*In the English system the w ork is in foo t-pounds , the pressures are in pounds p ersquare foo t and the vo lumes in cubic feet . Thi s is real ly w hat is represented by the

ind icator d iagram , although the pres su res are alw ays measured in pounds p er squareinch instead of pounds p er square foo t. This is balanced , how ever , by taking the

area Of the pi ston in square inches instead o f square feet , so the final resu l t is the

same.


256 S TEAM TURBINES9 l

T: c O

9g

0It answers practical requ irements to take the specific heat , c, inthe above formu las equal to 1 .

Entropy of Saturated . S team—The total heat Of steam is con

sidered made up Of two parts , the heat q requ ired to rai se the tem

p erature Of the water from the freez ing point to the temperature

Of vapori zation, and the latent heat r requ ired to convert the water

into steam .In l ike manner the entropy Of steam cons i sts Of tw o

parts , the entropy Of water at the temperature Of vapori zation and

the change , or increase Of entropy that occurs when the water i s

changed into steam . The latter i s sometimes cal l ed the entropy ofvaporization

,bu t more properly it i s the change Of entropy due to

vaporizat ion.

During vapori zation the temperature remains constant and the

change Of entropy i s eas i ly cal culated by dividing the latent heat

r by the absolute temperature T,or

,

Change Of entropy—T

From this we have,for the entropy Of steam ,

introducing x to

make it general for either wet or dry steam ( see formu la

x r

z a lT “W

(1 3)c Og492 . 7 T

Examp le—TO find the entropy Of saturated steam at 1 00

pounds absolute pressure , we have , from the steam tables , p : l o0 ;

r : 884 ; t : 327 . 5 8,whence Assuming

steam to be dry ,

l og

884Hence,

47788. 3

STEAM ANDITS PROPERTIES 257

Entropy of Superheated S team— The entropy Of superheated

steam may be found by adding to the entropy Of saturated steamthe change in entropy due to superheating , which is expressed by

the equation,

T

S10

8

1 4a ct c g]

.

where cps— cl) i s the'

change in entropy , c i s the specific heat Of

superheated steam ,and T

s and T are the temperatures Of super

heated and saturated steam ,respectively , at the given pressure .

Examp le—Ii the steam in the last example were superheated

250 degrees , what wou ld be its entropy , assuming its specific heat

to be Here T : 788. 3 and Hence ,1 65

and p er -1 .

Temperature-Entropy Diagram for Water and S team—InFig . 4 the various heat

'

changes for water and steam are shown

graphical ly . Absolute temperatures are laid Off on OX and

values for entropy on OY.-The different steps in the process Of

plotting the diagram are as follows

( 1 ) Assume one pound Of water at 1 00 degrees F . to beheated unti l its temperature reaches 3 50 degrees F . Its entropyincreases and the change in temperature and entropy is rep re

sented by the water l ine ab . This curve starts on the ordinate

OX , at the freezing point , and other points on the curve are cal

cu lated by the aid Of equat io'

n ( 1 0) or they may be plotted fromvalues Of

“entropy Of the l iqu id given in steam tables . I f 191

is the entropy at point a and 0, at point b,then 02— 01 i s the

change in entropy while the temperature increases from 100 to350 degrees . The heat added during the change is representedby area al abb l .

( 2 ) I f the water,at 350 degrees , i s vapori zed , the temperature

will remain constant and the l ine be will represent the change inentropy . At point c the vaporization i s complete and i ts di stancefrom OX i s the entropy Of steam at 350 degrees temperature , calculated by equation The heat requ i red for this change isshown by the area b l bcc l .

258 S TEAM TURBINES( 3 )In the flow Of steam through nozzl es

,i t i s assumed that

the expans ion i s adiabatic , no heat being added or subtracted .

This condition can be represented only by the vert ical l ine cd,

which has no area under i t to indicate heat added or subtracted .

8

Sca le of Ent rop yF ig. 4 . Temp erature-Entrop y Diagram .

Th i s l ine shows that whil e the temperature drops the entropy t e

mains constant .

( 4 ) TO complete the cycle , assume the steam remaining at the

end Of adiabatic expans ion to condense at constant temperature ,as shown by the l ine do . The heat given up during con

densation i s represented by the area aladc l . Deducting this area

from areas alabb

l—I—b l bcc l , which show the heat appl ied

,l eaves


260 S TEAM TURBINESsteam

,say 80 per cent , then the change Of entropy due to vaporiza

t ion will be

xr 0 . 8r

T T

and the conditions will be represented by point n,which is 80 p er

cent Of the distance from m to 13 . By the princ iples Of percentage ,therefore , the ratio

mk

will give the percentage , x ,Of dry steam present .

The chief value Of the temperature- entropy diagram for steam

turbine work l i es in the fact that i t may be made to Show the

quant ity Of moisture presen t in steam by the method just indicated .

Thus , in the above case , suppose the steam to expand ad iabatic

al ly to temperature T1 . By drawing the adiabat i c l ine np, w e

find the percentage of dry steam present to be

of

OS

I f dry,saturated steam expands adiabatical ly from T

2to T, ,

we find,by drawing adiabatic l ine kd that there is

p er cent Of dry steam present .

I f superheated steam expands adiabatical ly from t emperatureTS to T1 , draw the adiabati c l ine fr . At pointI, where it intersects the steam line, the steam loses its superheat and becomessaturated ,

~

w hile at temperature TIi t i s only0 7

’

p er cent dry . I f it were des ired to know how far to continue

superheat ing to s ecure dry , saturated steam at the end Of ex

pansion, the superheat curve kf mu st be extended unti l point fcomes vertical ly over point s , which wou ld show the des ired tem *

p erature T8 .

STEAM ANDITS PROPERTIES 261

Charac teris tic Equations fo r Ad iabatic Exp ans ion.

During adiabatic expans ion heat is neither added nor abstracted

and , as seen above, the change is represented by a vertical l ine on

the temperature-entropy diagram . The entropy , therefore , remainsconstant during the adiabatic expans ion,

and by expressing this

relation in the form Of an equation the percentage Of dry steampresent at the end Of adiabatic expans ion may be eas i ly calcu lated .

This relation i s expressed in the three equations which follow ,in

which the letters with subscript 1 refer to the higher pressure and

those with subscript 2 to the lower pressure .

( 1 ) For saturated steam ,

1 52 1. 7 ;

( 2) Steam superheated sufficiently to remain superheatedthroughout expans ion

,

Tel 75 27 2 T

s2

+ 01 + 2 . 3 c l og + 02 + 2 . 3 c l og (1 6)7 1 7 }

( 3 ) Steam superheated at the start but saturated at the end Of

expans ion,

+ 01 + 2 . 3 c l ogTITIT2

The appl ication Of these formu las wil l be.

shown in the following chapter.

(17)

The Sp ecificHeat Of Sup erheated Steam .

Regnault’

s Resu lt.—Unti l recently the value universal lyadopted for the specific heat Of superheated steam at constantpressure has been derived in 1 840 from the results Of threeseri es Of experiments by Regnau l t .In steam calorimeter work ,where the temperatures came Within the l imits Of Regnau lt’ s ex

p eriments , the value Of i s practical ly correct , but with thehigh pressures and temperatures prevai l ing in power plants us ingsuperheated steam a higher value shou ld be taken.

TheImportance of a Correct Value.—In tests upon super

262 STEAM TURBINESheaters

,o r upon turbines and engines u s ing superheated steam , the

weight Of the steam u sed does n ot afford a fair bas is for est imat

ing the gain or l oss from superheating , because weight alone

gives no indication Of the amount Of heat in superheated steam Of

a given pressure . I f the specific heat Of superheated steam were

accurately known,however

,thi s would give us the means Of cal

cu lat ing the number o f heat units in the steam and the effic iency

Of the apparatus cou ld be determined on this bas i s , by the method

explained under “The Thermal Uni t Bas i s Of Performance” in

Chapter IX . The author has made cal cu lations upon tests Of a De

Laval turbine,run first with saturated and then with superheated

steam . By first taking the rate Of water consumption in pounds as

the bas is for calcu lating the gain from superheating , the gain w as

found to be p er cent . Then,by taking as the bas i s the heat

uni ts in the steam ,the gain w as found to be as fol lows : Assum

ing specific heat : 0.48, gain: 4 .8 p er cent ; specific heat : 0.6 ,

gain: 4 p er cent ; specific heat : 0.8 ; gain: 2 .7 p er cent . Theseresu l ts show that the gain from superheating on the bas i s Of heat

units ut i l i zed i s much less than when on the bas i s Of pounds Of

water p er horse-power p er hour ; and that the higher the value

assumed for specific heat the less the gain i s found to be . This

i l lustration Shows the importance Of a correct value for the spec ific heat Of superheated steam in calcu lating effici enc ies .

Resu lts of Tes ts to Determine SpecificHeat.*—Many exp eri

menters have attempted to derive values for the spec ific heat Of

superheated steam at constant pressure for other pressures and

temperatures than covered b y the tests Of Regnau l t . Among the

more important work in th is connection i s that Of Grindley in

England , o f Greissmann,Lorenz

,and M essrs . Knoblauch ,

Lindeand Klebe in Germany

,and Of Carpenter, Jones , Thomas , Bur

goon, and engineers Of the General Electric Company in America.

The resu lts Of the variou s experimenters are more or l ess contra

dictory and i t i s no t yet defini tely settl ed how the specific heat

vari es in relat ion to pressure and temperature changes .

*The reader w ho w ishes t o inves t igate the subject Of specific heat Of superheatedsteam is referred t o the J ou rnal of the Wor ces ter Po ly technicIns titu te, November ,1904 , containing an art icle by Pro f. S idney A. Reeve ; t o Pow er fo r Au gus t , 1904 ,

containing an ar ticle by Chas . A Ot rok ; t o the S tevensInsti tu teIndicator for October ,1 905 , contain ing an ar ticle by Pro f . J . E. Denton ; and t o the paper u pon the

“Steam

Plan t o f the White M o tor Car , by Carpen ter , in the proceed ings Of the A. S . M .

December , 1906 .


264 S TEAM TURBINESfor the incongru i ti es in the resu lts Of some Of the previou s re

searches . A table prepared by Professor D enton from their

formu la i s given bel ow ‘

MEAN SPECIFICHEAT AT CONSTANT PRESSURE .

(KNOBLAUCH, LINDE ,AND KLEBE . )

Bo i ler Bo i l ing Po in t Range Of Su p erhea t ing .

Pres su re Degrees 10° C . 50° C . 100° C .

Lb . Sq .In. A b so lu te . C . 50° F . 122° F . 212° F.

99 48 164

1 78 597 . 5 77 . 5 59

192 634 . 609 . 586

208 686 656 626

Resu lts at Cornell Univers ity—Experiments upon specific heat

Of superheated steam have been under w ay for over 1 0 years at

Cornel l Univers ity . The following table i s made up from a

chart giving resul ts Obtained by Prof . Carl C . Thomas and Mr.

C . E. Burgoon at this universi ty , and publ i shed by Prof . R. C .

Carpenter in a paper,

“Steam Plant Of the White Motor Car ,

”

read before the A . S . M . E. in December,1 906 .

S PECIFICHEAT AT CONSTANT PRESSURE.

(THOMAS AND B URGOON. )

Degrees F . S u p erhea t50 100

5 13 5 12

544 54

576 5 7

6 1 598

642 629

Sp ecific V o lume Of Sup erheated Steam .

Wh i l e the specific volumes Of saturated steam for different

pressures are to be found in the steam tables,i f cal culations are to

be made requ iring the specific volume of superheated steam,the

information i s not SO readily Obtained .

Z enner’

s Formu la—The formu la usual ly employed is that OfZeuner, based upon the experiments ofHim . I t is as fol lows

93 .5T 971P i

PIn th i s P i s pressure in pounds p er square foot , or p .


Examp le—Superheated steam ,having a pressure Of 100 pounds

absolute and a temperature Of 400 degrees F . ,or degrees

absolute,has a specific volume Of

93 .5X860.7

1 44x100

cubic feet .

Schmidt’

s Formu la.

—Another formu la that has been proposed

is that Of Schmidt , given below,which closely approximatesHirn’ s

results,though not as closely as Zenner’ s formu la . The differ

ence between the resu lts Obtained with the two formulas i s sl ight ,however.

t

v : 0. 5 9276

Examp le—Taking the same data as above,we have ,

—I—400100

cubic feet.

CHAPTER X I I I

CALCULATIONS ON THE FLOW OF STEAM .

The Ad iabatic F low Of Steam .In calcu lat ions on the flow Of steam it i s assumed that the

flow is adiabati c and afterwards al lowances are made , i f necessary ,based upon the resu lts Of actual tests . Under thi s condit ion al l the

avai lable heat energy Of the steam is assumed to be converted into

kinetic energy,withou t gain or loss Of heat through conduction,

radiation,friction or otherwise , and the energy Of the steam will

remain the same in amount at al l steps in the process , though it

may differ in form .

’

Equation for the F low of Saturated S team—In F ig . 1 i s a

cyl inder having a diaphragm which separates i t into two cham

Fig . 1 .

bers A and B . A nozzle N is inserted in the diaphragm and

steam in chamber A,at absolute pressure p flows through the

nozzl e into chamber B . Steam expands within the nozzle to the

pressure p2 .\

Let V : velocity Of steam in feet p er second as i t l eaves thenozzl e . Al so, l et x l , r 1 and q1 apply to steam at the pressure p l ,in chamber A

,and x

2 , r2 and q2 to steam at pressure pz , with in

the nozzl e . (Notation at beginning Of Chap . XII . )Now ,

S ince the energy remains constant during the flow , w e

write expressions for the energy Of one pound Of steam as i tapproaches the nozzle

,and for one pound Of steam as i t l eaves the

nozzl e , and place one equal to the other.


268 S TEAM TURBINEScharacteri stic equation ( 1 5 ) Chap . XII . ,

which,when transposed ,

becomes«7 17 1

Q

T2

I f steam tables containing values Of 6 are not obtainable , i t will

be necessary to use theapprox imate equati on ( 1 0) Chap . XII . ,

for finding the entropy Of water in the above equation.

Examp leI-Given, dry saturated steam flowing from a pres

sure Of 1 3 5 pounds absolute to a pressure Of 4 5 pounds absolute .

Cal cu late the energy Of the j et and the velocity Of flow ,assuming

complete expans ion in the nozzl e .

The following values are either known or taken from the steam

tableP1 : 1 35

TIr 1

q1

6, 5027

x,

1

F irst , calcu late the percentage Of dry steam at the end Of the

expans ion,from equation

. 5027

922

NOW sub stituting for x,in equation w e have , for energy Of

the j et,

778 ( 1X867 .3 X 922—Ift . lb .

veloci ty Of di scharge i s

V: V 64 .4X 66 ,032

ft . p er sec .

CALCULATIONS ON THE FLOW OF STEAM 269

When Expans ion is no t Comp lete in the Nozzle.

—In'

working

out the above example it w as assumed that the expansion Of the

steam w as carri ed to the terminal pressure Of 4 5.

pounds within

the nozzle itsel f and there w as no waste energy due to drop Of

pressure as the steam left the nozzle . TO accompl ish this with the

pressures given requ ires a diverging nozzle,as already explained

in Chapter I . under “Steam Nozzl es ,

”and in Chapter XI . Sup

pose,however

,that instead O

’

i a diverging nozzle a straight nozzle

with converging inlet were used . We have learned that in such a

nozzle expans ion may be carri ed to a certain point—usual ly about

60 p er cent Of the higher absolute pressure— and no further,and

in this case steam wou ld expand within the nozzle to about 80

pounds,which shou ld be used for the lower pressure p 2 in the cal

culat ions .In any case w here expansion is not comp let e w ithin

the nozz le, care should be taken to assume for p 2 the pressure to

w hich s team expands w i thin the nozz le its elf ins tead of the low er

ou tside pressure.

Examp leII-Assuming a straight nozzl e , we have for values

corresponding to p2 : 80 pounds, r2 : 895 .6 ,

T2 : 772 .5 .

Values corresponding to p 1 are given under Example I .

From we find x2 : 0.966 .

From

ft. p er sec .

Chart Giving Values of x.—TO ass ist the reader in determining

the percentage Of dry steam at the end Of adiabatic expans ion,the

chart in Fig. 2 has been prepared , which enables the value Of x2

to be read directly , without calculation. This quanti ty may al sobe eas i ly determined by the aid Of the temperature-entropy diagram , as explained in connection with the subj ect in Chapter XII .

Simp lified Formu la for the F low of S team .

—In the steam tablein the appendix values Of the entropy

,ct , of steam are given,

in

which


272 S TEAM TURBINESLet W: weight d ischarged p er second in pounds .

v : sp ec ificvolume Of the flu id in the orifice .

A : area Of orifice in square feet .

V : veloc ity Of discharge in feet p er second .

WXv Z AXV

AV

71( 9)

This formu la i s perfectly general and appl ies either to saturated

or superheated steam , or to any gas or l iqu id .

I f it i s to be appl ied to saturated steam,then

,by Chap . XII .

,

we have,v : xs

,where x 15 the qual ity and s i s the spec ific volume

Of the steam in the orifice . Al so ,

where a i s area in square inches .

aVHence , ( 1 0)l 44xs

Examp leIV. .

—What i s the weight Of steam discharged in

Example I I . ,assuming the area Of nozzle to be square inch ?Here we have , ini tial pressure 1 3 5 pounds , and pressure in noz

zle f71 0 Of th is , or approximately 80 pounds . The qual ity x at this

lower pressure w as found to be"

and th e velocity V

feet p er second . The specific volume s corresponding to 80

pounds isHence , from ( 1 0)5x1 ,

4 5 1

pounds p er second .

Napier’ s ru l e gives as the resu l t .

Calculations Up on Sup erheated Steam .

Equations for the F low of Superheateo

d S team—There are twocases according as the steam is superheated or saturated when

expansion i s completed , its condition at that point depending upon

the degree Of superheat at the start and the degree Of expans ion

that takes place . The cal cu lation Of the velocity or energy'

of

CALCULATIONS ON THE FLOW OF S TEAM 273

flow Of superheated Steam is a long and ted ious process , and unti lthe resu lts Of more tests are avai lable we are not sure that the

calcu lated resu lts agree even approx imately with experimental

results . Nearly al l tests have SO far been upon saturated steam .

The formulas for the flow Of superheated steam are derived by

the same method as the one for saturated steam .

The heat energy Of one pound Of superheated steam is

A c (t 8 1) (6) Chap . XII .

Placing the energy of discharge equal to the energy of ap

proach , and us ing letters with subscripts 1 and 2 to represent initial and final conditions

,respectively

,we have :

CaseI. , when steam is superheated at the'

end,

V2

c (t sz c (t sl t 1)]

V 2

C (t sl 11)—c (182 -t2)]2g

Case when steam is saturat ed at the end,

V 2

2g

+ f (xzrg 92) 2 ] [A1 c ( t 81 t 1)]

V2

5 (481 fl ) “ 4727 2 92]2g

To find the Pressure at w hich Superheated S team Loses its

Superheat During Adiabatic Expansion—B efore one can proceed

to calcu late the velocity Of flow Of superheated steam it must bedetermined whether the example comes under Case I . or Cas e I I . ;

that is , whether the steam is superheated or saturated at the end Of

the flow . This is done by making x2 : 1 in characteri stic equationChap . XII . ,

for superheated steam . The second member Ofthis equation will then be

which is the entropy Of dry , saturated steam ,and the equation will

express the relation that the entropy Of superheated steam at a

274 S TEAM TURBINEScertain pressure and temperature equal s the entropy Of dry ,

saturated steam at acertain pressure , which latter pressure is to be

determ ined . After making x2: 1 ,_ find the value Of the l eft-hand

member Of the equation, al l the quantit i es Of which have knownvalues . The resu l t wi l l b e the entropy Of saturated steam for a

certain corresponding pressure , to be Obtained from the steam

tables . This pressure wil l be that at which the steam gives up i ts

superheat for the example in question and will indicate whether

the steami s superheated or saturated at the end Of the flow . I f

the p ressure i s greater than the final pressure against which the

steam is flowing ,i t Shows that the steam becomes saturated before

the final pressure is reached,and hence wil l be saturated at the

end . I f the pressure determined i s l ess than the final pressure , the

steam Wil l be superheated at the end .

Chart Show ing Press ures at w hich Superheated S team Gives

UpIts Superheat — TO facil itate calcu lations the chart in Fig. 3

has been calculated by which the pressure at wh ich superheated

steam gives up i ts superheat in adiabatic expans ion can be read Offdirectly and the cond ition Of the steam at the end Of the expans ion

determined . Each curved l ine i s for a different init ial pressure .

The pressures at the left are those at which steam superheated a

given amount gives up i ts superheat and becomes saturated . The

vertical l ines correspond to d ifferent degrees Of superheat .

Calcu lation of the Velocity of F low of Superheated S team .Having found whether the given problem must be solved byequation ( 1 1 ) under Case I . or equation ( 1 2) under Case I I .

, p ro

ceed as follows

CaseI. —The steam in thi s instance is superheated at the end

Of the flow . All the quant iti es o f equation ( 1 1 ) will be known or

can be Obtained from the steam table except tsz, the final tempera

ture Of the superheated steam . This mu st be cal culated by the aidOf characteri stic equation Chap . XII .

,for superheated

steam .

Case I I .

—Here the steam is saturated at the end Of i ts flow and

equation ( 1 2) wil l be used . All the quanti ties Of this equation are

known except x_which is to be Obtained from characteri stic equa

tion Chap . XII .,for superheated steam .

Examp le V.

— Steam ,superheated 1 00 degrees F .

,flows adiabat


276 S TEAM TURBINESical ly from a pressure Of 1 3 5 pounds absolute to a pressure Of 4 5

pounds absolute . What i s its velocity Of discharge ? Assume spe

cific heat , c, to be

From the diagram ,

‘

F ig . 3 , we fi nd that steam superheated 1 00

degrees and flowing from a pressure Of 1 3 5 pounds to a pressure

Of 4 5 pounds wi ll give up its superheat at 5 6 degrees and hence

be saturated at the end o f the flow , making the example come

under Case I I . We find x2 from equation ( 1 7 Chap . XII . , as

fol lows :

7 2

734 . 99x x l og

922

From equation ( 1 2) the veloc ity becomes ,

2 166 f t . p er see.

Th i s velocity i s only Sl ightly greater than cal cu lated for saturated

steam flowing between the same pressures in Example I . The

s l ight increase i s due to the additional heat in the superheat , butto partial ly Offset thi s there is more heat carri ed away at the end,in the form Of latent heat , s ince in thi s example the steam is morenearly dry at the end than in the previous example .

STEAM NOZZLE DESIGN.

The fundamental (and sel f-evident) principle upon which the

des ign Of steam nozzles i s based is that the different cross-secti onalareas Of the nozzle mu st be sufficient to al low a given weight Of

the flu id to pass in a given space Of time .In other words , thesame weight Of flu id must pass different sections Of the nozzl e inthe same time .

This relation i s expressed by formula ( 9) for the we ight Of

flow ,

CALCULATIONS ON THE FLOW OF S TEAM 277

The Reason for Converging and Diverging Nozz les .—Let us

examine this formu la,and assume

,first

,that a .liquid i s flowing

through the nozzle . The specific volume v Of a l iqu id i s constant

and hence , as the velocity V increases , owing to drop in pressure ,the area A must decrease ; or in other words , the nozzle wil l con

verge,as in Fig . 4 .

CONVERGING CONVERGING AND DIVERGINGF ig . 5 .

Again,suppose

]

s team to flow through the nozzle .In this casethe specific volume , as well as the velocity, wil l increase with thedrop in

'

p ressure. I t i s a characteri stic Of steam that at first the

velocity increases more rapidly than the specific volume and laterthe specific volume increases more rapidly than the velocity ; andto conform to these conditions the nozzle shou ld first converge andthen diverge , as in F ig . 5 .

Critical Pressure.

-The point where the ratio

V

7}

changes from an increas ing to a decreas ing quantity is cal led thecri tical point , and theoretical ly is at a pressure Of Of the 1mtial pressure .

* The pressure at the throat i s therefore 58 p er centOf the higher pressure , theoretical ly , al though tests in Chapter XI .

Show that i t may vary material ly from this in certain nozzles .

“Pro fessor Rateau of Paris , in F low of S team Through Nozz les , states that he hascalcu lated the po ints at w hich the ratio

V

‘U

becomes a maximum for a number o f d ifferent initial pressu res and finds they varysl ightly w i th the pressure around the value 0. 58p .It is a very pecu l iar fact that thisrelation exists SO closely for d ifferent pressures . M r. Joseph C.

’

Riley , Mas sachusettsInstitute Of Techno logy , Bo ston, has show n that t he value is affected somew hat bymo isture in the steam . For 100 pounds initial pressure and 20 p er cent priming the

pressure at w hich the ratio changes is O.S4 —no t a w ide variation .

278 STEAM TURBINESConverging Nozzle for S team —In case expans ion i s no t car

ri ed far enough to pass the critical point , where

begins to decrease , the diverging sect ion Of the nozzle is not re

qu ired , a condition that ex ists when the d ischarge pressure is

58 p er cent or more than 58 p er cent Of the ini tial pressure , as w as

fu l ly explained in Chapter I .Inthi s case the nozzle Of F ig . 4

answers al l requ irements .

M ethod of Procedure in Nozz le Design—Cal culations for

superheated steam are SO compl icated that the method and cal

cu lat ions for saturated steam only wil l be presented here .In designing for superheated steam the same Obj ects are to be attained ,

but we have to use the superheated steam formu las for specific

volume,velocity

,etc . ,

in so far as such formu las have been de

velop ed and are avai labl e .In steam turbine design we know in advance how many foot

pounds Of energy p er second we wish to have del ivered to the

wheel by the steam , and what drop in pressure there is to be in

flowing through the nozzle . Equation ( 2) gives the energy develop ed p er pound Of steam for a given drop Of pressure , and the

total energy requ ired divided by the energy p er pound will give thenumber Of pounds Of steam p er second , or the fraction Of a pound ,as the cas e may be , that the nozzl e must be able to del iver.

From this , the area Of the nozzl e can be determined by the aidOf equation T hi s equation may be written

1 44Wv

V

I f the nozzl e i s Of c ircu lar cross—section its diameter in inches isgiven by

( 14 )


280 S TEAM TURBINESThe nozzl e discharges against atmospher ic pressure , but the di

vergence Of the nozzle is so great that the steam reaches a pressure

c orresponding to that Of the atmosphere Shortly after the throat i s

passed ; and beyond th is point the steam expands to cons iderablybelow atmospheri c pressure , reaching the lowest point at x. Then,

as i t discharges to the atmosphere,the pressure r i ses

,and

,Of

course,the velocity decreases . This shows the importance Of se

curing a correct relation between the throat and outlet areas Of a

d iverging nozzle . The method to be fol lowed can best be shownbv an example .

Examp leIllus trating the Design of a Diverging Nozzle.—Re

qu ired,the throat and outlet areas for a nozzle to del iver one

pound Of steam p er second , flowing from a pressure Of 1 3 5 pounds

absolute to a pressure Of 4 5 pounds absolute .

First , cons ider the throat area On l ine ao ,Fig . 7 . The steam , in

flowing through the converging inl et Of the nozzle , wil l expand toabout Of the absolute ini tial pressure , or to a pressure Of 80

Fig . 7.

pounds , app roximately .In Example I I . ; where the steam

panded from 1 35 to 80 pounds , as in the present case , the veloc i ty

V w as found to be feet p er second .In examples wheresteam is known to expand to 671 0 Of the higher pressure , however,i t i s not necessary to calcu late the velocity

,s ince for all ordinary

initial pressures the : velocity wil l be practical ly constant and range

close to feet p er second . ( See Tabl eI. , Chapter XI . ) FromExample I I .

,al so

,for pressure 80 pounds

,x : 0.966 , while s , from

steam tabl e : 5 .4 3 .

CALCULATIONS ON THE FLOW OF STEAM 281Hence , for section ao Of the nozzle ,

p : 80, V: 1 ,4 5 1 , W: 1, and

From1 44X 1X 5 .245

square inch .

Second , cons ider the outl et area on l ine bb .Here the absolutepressure i s 4 5 pounds and in ExampleI. , where steam expanded

from 1 35 pounds to 4 5 pounds , as in thi s case, we found V: 2,OG2

feet p er second and x : 0.933 . From the steam tables , s for 80

pounds : 9 .29.Hence,for section bb Of the nozzle ,

p : 4 5, V : 2

,OG2

, W: 1, and

144X 1X8.667

square inch .

It will be evident from the above that the two areas are directlyas the specific volumes and inversely as the velocities .

Prac tical Considerations .

AS stated at the outset , the calcu lations in this chapter are

based upon the assumption Of adiabatic flow . It is a pecu l iar

fact, however, that while such calcu lations approx imate closely

to t he results Of tests , i t is qu ite certain that the flow throughnozzles i s not adiabatic , or at best it i s only approximately SO.

This is indicated by the tests Of Pro fessor Lucke in Chapter XI .,

and i s further shown by the fact , which any one can veri fy , thatthe steam discharging from a nozzle does not contain the amountOf moisture cal l ed for by adiabatic expans ion. It i s the exp eri

ence Of experimenters that the discharge i s either blue , indicating dry steam , or dry and white , indicating not over two p ercent Of moisture .

Frictional Losses .-Nozzles Of different shapes and propor

tions have different coefficients Of flow and the best the designercan do in al lowing for frictional losses i s to select his ow n cO

282 S TEAM TURBINESefficients from tests upon nozzles as nearly as poss ible l ike those

he contemplates us ing . I t i s apparent from the tests Of Chapter

XI . that a converging nozzle can b e des igned to g1ve a velocity

Of discharge within two p er cent Of the theoretical velocity . Thediverging nozzles Show a wider variation ,

and in some cases a

very wide variation,depending upon their proportions .In cal

cu lat ing the weight Of steam discharged Napier ’ s ru l es can be

used , as already explained , but a proper coefficient mu st be selected

in each case from tests upon s imilar nozzles .

Diverging Nozz les .—Rosenhain concludes from his exp eri

ments that the taper Of diverging nozzles shou ld not be far from

1 in 1 2 and that the inner edge Of the nozzl e shou ld be Only

sl ightly rounded . De Laval nozzles are made with tapers rang

ing from about 1 in 1 0 to 1 in 20,with inl et only sl ightly

rounded . The experiments Of M r. Strickland L . Kneass , engineer

Of the inj ector department OfW i l l iam Sel lers Co . , Ph i ladelphia,

indicate that bett er resu lts are Obtained from nozzles with wellrounded inl ets and a taper Of about 1 in 6 ; and that i f properly

proport ioned it i s poss ibl e to‘

secure a velocity Of flow within two

p er cent Of theoretical . One Of several seri es Of experiments ,records Of which have been furni shed the author by M r. Kneass ,w as upon five different nozzles having a divergent tap er of

1 in 6,but with a ratio Of discharge to throat areas careful ly cal

cu lated for different ini tial pressures . The nozzles discharged at

atmospheri c pressure against a parabol ic target , wh i ch deflected

the steam through an angle Of 90 degrees . The target w as con

nected with a del icate . weighing device by which the impact ofthe steam cou ld be accuratelv determined .

Of the several nozzles , one des igned for 30 pounds init ial

pressure, gauge , and having a throat diameter Of mm and

discharge diameter Of mm,gave the best average resul ts

throughout‘

the whol e range Of pressures . as p er table belowImp ac t Pres s u res We i gh t Discharged .Ini t ia l P res sure , in l b . p er sq . l b p er sq . mmGauge . mm o f No zz le . Of No zz le .

120

90

60

30

15


CHAPTER XIVTURBINE VANES .

The Vanes OfIm pul se Turb ines .In preceding chapters ‘we have studied the principles Of the flow

Of steam and the convers ion Of the heat energy Of steam into the

mechanical kinetic energy of the escaping j et . The subj ect now to

be cons idered is the trans ference Of this mechanical energy Of the

j et to the vanes Of the turbine wheel .

At the beginning of Chapter I . the meaning Of»absolute and

relat ive motion w as explained,as related to the action Of a flu id

upon a moving vane, and the treatment there given wil l furni sh

sufficient introduction for what i s to fol low .

Diagram for a

.

M oving Vane.

—In Fig . 1 herewith a turbine

vane moves in the d irection Of the horizontal arrow and i s actedupon by a j et Of steam flowing in the direction Of the incl ined

F ig. 1 .

arrow . The paral l elograms Of motion show the velocity and

direction Of motion Of the steam in entering upon and leaving the

vane ; and the velocity and direction Of motion Of the vane itsel f .The lengths Of the several l ines represent velociti es in feet p er

second , drawn to any conveni ent scal e .In the diagram,

V i s the initial and v the final absolu te veloc i ty and direction Of

the steam ;

TURBINE VANES 285

R i s the initial and r the final velocity Of the steam relative to

the vane .

w i s the velocity and direction Of motion Of the vane .

I f there were no loss through fri ction or eddy ing , the relativevelocities R and r wou ld be equal , and th is will be assumed thecase in what follows , unless otherwise stated .

A is the angle made by V with the direction Of motion Of thevane ; C,

the angle made by R ; and D and B,the corresponding

angles made by the steam when l eaving the vane.In what follows A and D will be designated as the “initial” and final” angles ,and C and B the entrance” and

“exit” angles .

For tangential action upon the vane , allow mg the steam toenter upon i t without impact and to leave it without commotion,

the vane Should be tangent to R at the entrance and tangent to r

at the exit . The Shape Of the vane between the entranc e and ex iti s not very important , SO long as the curve is gradual and smoo th .In hydrau l ic turbines the water usual ly flows either outward or

inward,in a direction general ly radial ; and as the vanes are large

it is necessary to take into account the difference in velocity Of

their inner and outer circumferences when proportioning theangles , etc .

-In steam turbine work this i s not necessary , S ince thesteam usual ly flows 111 an axial direction and i t i s sufficientlyaccurate to assume that the vane

.

moves forward in a straight l ineat a speed equal to that Of the mean circum ferential speed Of thevanes .

F ig. 2 .

Calculating the Parts of the Diagram—Fig. 2 shows a con

venient arrangement Of the velocity diagram for finding the valuesOf the different elements

,either by graphical construction or by

286 S TEAM TURBINEScalcu lation. The several l ines are l ette

‘

red to correspond with

Fig . 1 and the several parts can be cal cu lated by the S imple

formu las Of trigonometry . The most important formu la used is

the one stating that “In any triangle the square Of any s ide is

equal to the sum Of the squares Of the other tw o s ides minus

twice their product into the cosine Of their included angle .

For example , i f there are given values Of V, w ,and angles A

and B ; and i t i s requ ired to find R : r) , v and angl es C and D,

then R2: w

2+ V2— 2 w V cos A ( 1 )v2: r

2

+w2— 2 r w cos B ( 2)

Also , i t can be shown that

V cOs A— w

COS CR

r eos B—w0

COS D (when l ine vIS 1nc l1ned to the r1ght as 111

v

( 4 )w—r cos B .

(when l ine v i s incl ined to the l eft) . ( 5 )v

Turbine Efficiency—The energy of one pound Of steam imping

ing against the turbine vanes is

V2

2g

and Of one pound Of steam as i t l eaves the vanes is

02

2g

The energy absorbed by,

the vane i s therefore

V2_ .

U2

By the principle Of machines ,

ener ab sorbed b vanesEffic iency _

gy y

total energy del ivered to vanes

[ 7 2— 712

the 2 0 cancel ing in each case soV2

that veloc iti es Only need be cons idered .


288 S TEAM TURBINESThe value Of w ,

and hence Of R,will then be calculated by

V

2 cos A

The final absolute veloc ity i s cal cu lated by

v : w \/2 ( 1—cos B ) ( 1 1 )

Whil e these proport ions do not give qu ite the max imum effi

ciency , they produce a S imple construction and are sati s factory i f it

i s poss ibl e to use them . Steam velociti es are so h igh , however,that the wheel velocity w must usually be selected from cons idera

tions Of safety and uti l ity rather than Of theory .

The question Of efficiency can be made clear, without difficult

calculations , by reference to the graphical constructions Of F igs .

3,4, and 5 .

Efficiency as Show n by D iagrams .

Examp leI.—Let A and B : 20 degrees and V: 3,OGO feet per

second .In accordanc e with the last art icl e , l et C: 2A: 4O degrees ;

Vfeet p er second . Th i s 18 al so the

2 cos A 2X .94

value Of R.In F ig . 3 draw w to any su i table scale , to represent and

V at an angle Of 20 degrees with w to represent Then drawR: w at an angle Of 40 degrees with the latter. Complete theparal lelogram .

Now construct the paral lelogram for the discharge in t he same

manner, making r : w and angle B : 2 0 degrees .

v i s the absolute velocity Of discharge and the vane curve i s

drawn with the entrance and exi t surfaces tangent respectively toR and r.

It wi ll be evident that a wheel with vanes lai d out as in F ig . 3

wil l have a h igh efficiency .

Examp le 2 .

—Fig . 4 has been constructed to Show the influenceOf the ini tial angle A upon the valu e Of v . AS in the previous

diagram C : 2A, w : R and B : 20 degrees . But angl e A has been

made 4 5 instead Of 20 degrees and C 90 instead Of 40 degrees .

TURBINE VANES 289

The resul t i s that w and R and hence r are much greater than

b efore and v in consequence is greater and the wheel wil l b e less

efficient. I t .will be noted , however, that whil e the size Of angle A

in Fig . 4 i s more than double its s ize in Fig . 3 , the value Of v is

Fig . 4 .

increased only a few p er cent . There can thus be a cons iderabl elatitude in the selection Of the initial angle . The chie f disadvan

tage Of a large angle in steam turbine work is that it necessitates

a high value for the speed w Of the wheel c ircumference ; and i fwe attempt to reduce the wheel velocity and stil l maintain a large

initial angle,the resu l t i s not good , as the next example wil l

show .

Examp le 3 .

—In Fig . 5 the angle A w as made 4 5 degrees as

in the last example, and the angle B 20 degrees , as in both Exam

ples 1 and 2 . Instead Of selecting C : 2A,however

,the speed w

of the wheel w as kept the same as in Example 1 , or l ess than in

Fig . 5 .

Example 2 , and the angle C w as then determined by drawing theparal lelogram . The final resul t i s a value for v greater than ineither Of the previous cases , indicating that the construction i s notso good as where C : 2A and w : R

,as

'

in Figs . 3 and 4 .

290 STEAM TURBINESWhil e the foregoing examples are not Of the nature Of demon

strations , they indicate why it i s des irabl e to have angle B as

smal l as poss ible and A reasonably smal l ; while the s ides Of both

paral l elograms shou ld be equal , making C : 2A.

Vanes w ith Entrance’

and Exit Angles Equal—An important

case for impu l se steam turbines i s that Of symmetri cal vanes having entrance and ex i t angles equal . W i th vanes so proport ionedthere is no thrust to be taken care Of

,due to the reaction Of the

steam leaving the vanes,s ince the reaction i s balanced by the im

pu l se Oi the j et striking the vanes .

F ig . 6 .In F ig . 6 is the diagram for this construction. Let us assume

V feet p er second , A : 2O degrees, C: 2A: 40 degrees

( the condition Of high efficiency) , and B ,wh i ch i s equal to C to

make the vane symmetrical , i s also 40 deg rees .

By formu la

1 28 feet p er second . This i s al so the v alue Of2X .94

R and r .

By formu la

feet p er second .

The efficiency may be calcu lated by either the first or second

parts Of formu la ( 9) as most conveni ent . T aking the first part,we have ,

Effic 1ency per cent .

Obviously nO such wheel velocitv as the above wou ld be possi


292 S TEAM TURBINESvelocity Of the wheel . I f the wheel traveled with hal f the velocityOf the j et the effici ency wou ld be 1 00 p er cent , and as the velocityOf the wheel decreased the efficiencv wou ld grow less .

F ig . 7.

Th i s i s an impossibl e condition, of course , and the buckets must

be designed to al low the flu id to depart at a sl ight angle from the

path Of the bucket, as indicated by r in Fig. 7 .

Let w ,F ig. 7 , be the wheel velocity . I f VIS the velocity Of the

j et,then r, the relative velocity Of the flui d on the bucket, i s V—w

The final absolute velocity v i s cal culated by formu la

v2: r

2

+w2 —2 r w cos B

,

where B is the angl e Of di scharge .Having found thi s the effic iencv i s eas i ly calculated by the firstpart Of the formu la ( 9) or the second part Of the formu la may be

used remembering that angle C i s zero and that cos

Examp le.

—Let V feet p er second ; w : 400 feet ; and

B : 1 5 degrees . Then r : V—w : 600 feet p er second andv2

_—2X 600X400X .966

Effic 1ency p er cent .

This , l ike other calcu lations for effi ciency in thi s chapter , is

purely theoretical and i s higher than can be real i zed in actual con

ditions .

Diagrams for CampouudImpu lse Turbines—In F ig . 8 the ini

tial velocity VIOf the steam is assumed to be four t imes the wheelvelocity w , and angl e A1

: 20 degrees . The steam ,having acqu ired

its velocity , flows Of i ts ow n momentum through two sets Of mov

TURBINE VANES 293

ing vanes and one set Of gu ide vanes between them , and final lyissues at an absolute velocity TO avoid end thrust the movingvanes must be symmetrical and hence C,

: B, and C2 : E2 . I f thereI

lIFirst Guide VanesI1IF irst Moving Vanes

Second

F ig . 8 .

F ig . 9 .

were no loss through friction,etc . ,

then the entrance velocity R,

relative to the vane would equal relative velocity r,at exit ; the

294 S TEAM TURBINESabsolu te veloc ity v , Of steam leaving the first set Of moving vanes

would equal the absolute velocity V2 in pass ing through the inter

mediate set Of gu ide vanes ; and relative veloc ities R2 and r2 wou ld

be equal . The dotted arcs indicate which velocities are to be

drawn equal in this construction.

Case Where There is Loss Through Friction—If i t i s des ired

to take account Of fri ctional loss thi s may be done as in F ig . 9 ,

where relative veloc ity r, i s made less than relative velocity R,

absolute velocity V2l ess than v , ; and relative velocity r2 l ess than

R, . The diminution Of the veloc iti es may be made either an

arbitrary amount in each case or a certain percentage Of the

velocity,as desired .

It wil l be noted that in F igs . 8 and 9 the vane angles are differ

ent for the two wheels . I f des ired to make them the same for

conveni ence in manufacture , a plan must be fol lowed similar to

that now to be described in connection with reaction blades .

The Vanes Of Reac tion Turbines .In F ig . 1 0 i s a diagram by which the action Of the steam in

reaction turbines may be studied . For convenience in manu

facture the gu ide and moving vanes in any one step or seri es Of

the turbine are usual ly made al ike . The upper paral lelogram

shows the absolute velocity and direction V Of steam leaving the

gu ide vanes , i ts velocity and direction R relative to the moving

vanes at the point Of entrance,and the velocity and direction w Of

the moving vanes .

The lower paral l elogram shows the absolute velocity and direc

tion v Of the steam leaving the moving vanes,i ts velocity and

direction r relative to the moving vanes at the point Of exit, and

the velocity and direction w Of the moving vanes .

Characteris tics of the Reac tion Diagram—The essential di fference between this diagram and those for impu l s e turbines is

that the relative velocity r i s greater than R.In the reaction turbine steam first expands and acqu ires a velocity in the gu ide passages

,as in the impu l se turbine . Then

,in flowing through the

wheel passages i t cont inues to expand and acqu ires a greater

velocity relative to the moving vanes than it had at the entrance.

The abso lu te velocity Of the steam ,Of cou rse

,dimini shes .


296 S TEAM TURBINESF ig . 1 1 .

s ides are proportional to the s ines of the opposite angles, as

fol lows

( 19)

The efficiency of the reaction turbine must be studied by taking

the machine as a whole , s ince the action i s continuous from the

first to the last row of vanes and the losses through l eakage , fric

tion, etc . , are such that no estimate of efficiency can be made by

calculating the effi ciency of any one set o f gu ide and moving vanes .

The efficiency can only be determined by experiment .

t o sin ( 1 80 -C)

sin (C—A)

w sinA

s in ( C—A)

w sin B

sin (D—B )

t o sinD

sin (D—B )

TURBINE VANES 297

TESTS UPON BUCKE’f‘S AND CHANNELS .

Tes ts of S trickland L . Kneass , C. E.

'

-l n 1 894 a smal l , exp erimental turbine w as bui lt and tested in the inj ector department of

Wi l l iam Sel lers Co .,Inc . , Philadelphia. The machine w as so

designed that it cou ld be assembled to operate on the plans of

several types of turbines , including the Parsons , what later became

known as the Curtis , and the De Laval ; and when under the latter

arrangement i t cou ld be run either as a compound or a s imple tur

bine.Prel iminary to the turbine tests an investigation w as undertaken

o f the action o f steam j ets upon vanes and in flowing through

Taper 1 in 6 ‘ Taper 1 in 6

F ig. 1 2 . F lat and Parabo l ic Targets fo r M easuringImpu lse .

curved tubes .

f

These, as well as the turbine tests , were at the in

cep tion of Mr. Kneass,whose experimental work has several

times before been re ferred to, and who has al lowed the author to

make selections from the records of tests on buckets and tubes .In the prel iminary tests a del icately balanced target w as em

ployed , against wh ich a steam j et from a nozzle w as directed . Thetarget w as provided with a sensitive weighing device and w as so

manipulated in taking readings as to el iminate the effect of fri c

tion in the final results .In order to measure the impul se o f thej et , the target w as made with a parabol ic surface coming to a

point at the center,so as to deflect the stream through an angle of

ninety degrees,with as l ittle loss as possible . When vanes or

passages of any particu lar shape were to be tested , the piece com

298 S TEAM TURBINESpri s ing these w as bolted to the target , by which means the im

pu l se o r reaction co u ld be measured .Impac t 71s . Tangential Ac tion—In theoretical d iscu ss ions ofturbine vanes

,i t i s assumed that the flu id must gl ide upon them

tangential ly in order to avoid losses from impact .In operation,

however, hydrau l i c turbines seldom run at exactly the speed re

qu ired to produce tangent ial action ; and in fact , tests have not in

frequently shown that the best resu lts are obtained by running

at sl ightly faster o r slower speeds .In elucidation o f this subj ect are tests by M r . Kneass,in which

j ets were al lowed to discharge against flat and parabol ic targets,

as in Fig. 1 2 , and the pressu re measured in each case , with results

as in Tabl e I .

TABLE I .

FLAT TARGET . PARABOLIC TARGET .

Average ,

These tests show,that by ad ju sting the distance of the nozzle

from the target it w as possible to secu re as great a pressure with

the flat as with the parabol ic target and point to the conclus ion

that perfect tangential action o f a j et upon a vane is not essential

to h igh economy.

Another test i l lu strating the same fact w as made with two di f

ferent vanes,Fig . 1 3 ,

one with an entrance angl e of 60 de

grees and one with an entrance angle o f 20 degrees . The

angle o f the nozzle and the exit angle o f the vanes were the same

in both tests . The steam pressure w as 1 5 pounds , gauge , and

the pressures upon the target were , fo r the GO-degree angle


300 S TEAM TURBINESExperiments w ith Curved Tubes—A seri es of experiments w as

made with curved tubing arranged as at A and B in Fig . 1 5

No . 1 No . 2 NO. 3

No s . 4 & 5

No zzle 4 mm .di9m .

F ig . 1 4 . Exp erimental Buckets .

which shows what large losses may resu l t from fri ction. Copper

tub ing w as u sed,

inch diameter , bent on an inner radius of

inch . The nozzle used w as 1 in 6 taper, mm . diameter at the

throat and mm . diameter at the mou th . Tests were first made

with a s ingle tube mounted on the target and bent through an

angle of 1 80 degrees . Three S imilar bends were next used with the

first two stationary and their ends s eparated inch , as at B ,

and the third one mounted on the target . The resu l ts with this ar

rangement,when compared with the first set o f resu lts , show the

losses in pressure due to fri ction in the tubes and disturbance

caused by the spaces between the ends of the tubes . F inal ly , test s

were made with a s ingle tube mounted on the target , ( this tube

not shown) making 1 % turns , or the same number of turns all

TURBINE VANES 301

T ABLE I I .

+3 Nc"d‘

0 8 2 x,

o fis .

o w a) w ow “?33a u

'"a) o 9 Hk a) s R k

0 0 a v“ :S o 5a

N emar s .

.Q v 8 (3 0 aa: M m 0 8 c

8o aN

: a Cl as m gm 23022 2

a ? “3: ”H”as ggfi+3

fl OZ E Q 5. UML L'J Ch i-4 2 c

No 2I6 j 333 125 .MQO A l l s team enter ing channe l .

Apparentl y no res is tance in s tr ik ing kn ifeed ge .

as No . 4 , b u t end s o f bu cke t w ere eu

ed , thu s confining t h e s team s idew ay s .

arged al l in to B .

told as the three tubes at B in the diagram . The pressures upon

the target in the three cases , p er square mil l imeter o f nozzle area,are givenIIITable I I I .

No zzle Nozzle

op p er Tub ing

TangetTarget

Fig . 1 5 . Exp erignent s w i th Curved T ub ing.

Experiments w ith Rectangu lar Tnbcs .

—Instead of continu ingexperiments with the round tubing

, a curved rectangular tube w as

made with three hal f turns , as at B,Fig . 1 6 . The dimens ions o f

302 S TEAM TURBINESTABLE I I I .

PRESSURESIN POUNDS PER SQ UARE MILLIMETER OF NOZZLE, WITHg-INCHT UBING , ARR

‘

ANGED AsIN FIG . 1 5 .

the tube increased from by mill imeters at the inl et to

by 1 2 mill imeters at the outlet .

The nozzle u sed in thi s seri es w as of 1 in 6 taper,

mm .

diameter at the throat and mm . at the mouth . I t i s the same

nozzle used in the tests in Table I . with the parabol ic target. Four

arrangements were tri ed as i llustrated at A,B

,C, and D in Fig. 16

Nozzle

Fig . 1 6 . Experiments w i th Rectangu lar Curved T ubing .


304 S TEAM TURBINESchanges were al so made in the nozzl e . W ith a continuou s tube al lthe steam entered

‘

from the nozzle nicely ; but when the three hal f

turns were separated by - inch . spaces all the steamwou ld not

enter and there wvas some waste at the mouth . Th ere were also

TABLE V .

PER CENT DROPIN PRESSURE, DUE TO OPENINGSIN T UBE.

leaks at each opening ,but not as much as in the previous tests . At

90 pounds there w as very l ittle waste at the Openings and none at

the mouth . At 60 pounds a sl ight leak from second opening onlyand at 30 pounds no waste at all . The effect w as then tri ed of

increas ing the width of Openings from to inch and the pres

sures measured in each case . The readings were first taken with

a continuous tube.

and then the tube having Openings of 15 3 ,and inch , the resu lts being as in Table V .

CHAPTER XV

BODIES ROTATING ATHIGHSPEED .

Critical Speed of Rotating Bodies .

—In the description of theDe Laval turbine , Chapter I I I . , reference w as made to the so

cal led crit ical'

sp eed of the wheel and flexible Shaft when rotating

at high velocity . This phenomenon may be explained by the aid

of the accompanying diagrams :In Fig. 1 is a disk l l’ mounted on a shaft A B turning in bal l

and-socket bearings , as . indicated . One s ide o f thi s d isk is sup

posed'

to have a dense section atH,making it heavier than the

Fig . 1 . Disk and F lexib le Shaft.

opposite s ide . The center of gravity of the wheel,therefore

,will

l ie to one s ide of the Shaft A B,say on the ax i s C D . Now i f th is

shaft and disk be rotated,the centri fugal force generated by the

heavier s ide wi ll be greater than that generated by the l ighter s ide

diametrical ly opposite to it,and the shaft wil l deflect toward the

heavy side , as in Fig . 2 , caus ing the center of the disk to describ ea smal l c ircle, indicated by the dotted l ine at a. To locate the

point at which a weight shou ld be added , or on the other hand , at

which metal shou ld be dri l led out in order to bring the piece into

balance , a piece of chalk i s held so that the high s ide o f the diskwill just touch it as it comes around . The weight necessary to balance , to be told by trial , i s then added opposite to the high side

where the mark appears ; or else , i f the balancing is to be done bydrill ing, metal i s removed on the same side with the mark .In themost accurate balancing it i s advisable to use a steel point heldrigidly , but which can be fed up gradual ly unti l the point makes a

faint scratch on the edge o f the disk .

306 S TEAM TURBINESThe foregoing conditions hold unti l a comparat ively high speed

is reached , depending upon the weight o f the disk and flex ib i l ity

o f the shaft . A point wil l eventual ly be reached , however, at

F ig. 2 . Ro tat ion abou t Geometrical Axis .

several thousand revolutions a minute , when there wil l momen

tarily be excess ive vibrat ion, and then the parts wil l run qu i etlyagain. The speed at which thi s occurs i s cal l ed the critical speed

Of the wheel , and the phenomenon itsel f i s cal l ed the settl ing of

the wheel . The explanation i s that at this speed the ax i s of rota

tion changes and the wheel and shaft,instead of rotating about

their geometrical center, begin to rotat e about an ax i s through

Fig . 3 . Ro tation abou t Axis of Gravity .

their center of gravity,or about the ax i s C D in F ig . 1 . Th i s

i l lustrated in F ig . 3 , where the wheel and shaft have tak

position i n which the ax i s C D ,i f extended

,would

the centers o f the tw o bearings , wh i l e the shaft i s deflected

it traces a c ircle shown by the dotted line b in Fig . 3 . I t i s tonoted , however , that this c ircl e is now on theH, or heavy , s ide

the disk instead of on the other s ide as before , so that now i f 0

were trying to locate the point where weight shou ld be added

order to balance the disk , he wou ld find that the chalk markon the l ight s ide of the disk

, and that the weight shou ldOn the same side .


308 S TEAM TURBINESready for balanc ing . The machine is placed under a dri l l press

and by its aid the heavy side of the casting is located and enough

metal dr il led ou t to br ing the flang e into balance . On top o f the

stand are kni fe edges w hich carry a table C with a movable cross

sl ide B . This cross sl ide is fitted with a pendu lum in the form of

F ig . 4 . Apparatus for S tat ic Balancing.

a screw which runs down into the base and has a weight at its

lower end .Hal f w ay up there i s a pointer and a graduated scalefo r indicating the posit ion of the pendu lum . The arbor for sup

porting the piece to be balanced is at the top of the s l ide B . By

adjusting the Sl ide one w ay or the other the indicator i s brought

exactly at the center o f the scal e and then the coupl ing is turned

BODIES ROTATING ATHIGHSPEED 309

around hal f w ay by hand without moving the sl ide .If the ind icator does not move , i t shows that the coupl ing is in balance at this

point ; i f it does move , the coupling must be out o f balance and

the necessary dri l l ing is done . From eight to a dozen points

around the circum ference o f the coupl ing are tested in this manner.In order to steady the tabl e and avoid wear o f the kni feedges when dri l l ing , there are pins D w hich are raised against thebottom of the table by a cam and thus take the strain.

Balancing Cy linders—In attempting to balance a cyl inder, l ikeFig. 5 , a heavy portion might come at one end , as atH, and p erhaps at the other end , also , but at a different point o f the circumference , as atH1 , so that a cons iderable twisting moment wou ld

Fig. 5 .

be introduced . It is desirable,i f poss ible

,to divide the cyl inder

into a number of disks , as A,B

, C , D ,and balance each one

separately. But this cannot always be done , as in the case of turbine drums and the rotors o f electric generators . The only w ay

with such parts is to mount them in loose bearings supported bysprings and then run them by motor or other means up to therequ ired speed .

Locating theHeavy S ide—It i s ,not always easy to tel l by this

means where the heavy spot i s located,s ince

,as explained in con

nection with the flexibl e shaft and critical speed,i t may under cer

tain conditions be on the same S ide with the high spot and underother conditions on the opposite s ide ; and frequently , i f thecyl inder i s approaching the crit ical point the heavy spot wil l l iesomewhere between these two extremes .In the American

Machinist for February 22 , 1 906 , E. R. Doug las gi ve s sugges

tions for finding the position of the heavy spot . After rotatingthe cyl inder up to speed and marking the high spot on each end

3 10 S TEAM TURBINESwith chalk , run i t in the opposite direction and make similar marks .

I f they are in a different position from the first ones the heavy

spot wi l l l i e hal f w ay between the tw o marks , but on which“s ide

can be told only by . trial . Attach heavy balance weights at each

end o f the cyl inder midway between the first and second marks .

The weights Shou ld be heavy enough’

to completely outweigh the

heavy spots . Now i t wi l l be evident that i f the weights are in a

position coinc iding with the heavy Spots,chalk marks made on

the circumference as the cyl inder i s rotated wil l agree with the

marks previ ously made when the cyl inder w as rotated in that

d irection ; but i f the weights are oppos ite the heavy spots , and are

heavy enough to overpower the latter, then the new chalk marks .

wil l be Opposite to the original ones , indicating that the balance

weights Shou ld be attached in the pos ition that the heavy onesnow occupy .

Stres ses in Ro tating Bod ies .

The cal cu lation o f the stresses in rotating bodies i s Often a com

plex problem . Fortunately the excel lence of material now avai l

abl e makes well constructed turbine parts safe against bursting at

the speeds that compound turbines usual ly r un.In practice a factorof safety i s needed , so that approximate methods may be us ed in

cal culations , i f the factor i s on the safe s ide . I f we are deal ing

with a disk in which there are both tangential and radial stress es

(Fig . we might neglect the considerabl e effect of the radial

tens ion and suppose the disk to be made up of a seri es of concen

tr i c r ings,in which the tangential or hoop tension only wou ld be

cons idered . Such a method,al though only roughly approx imate ,

wou ld be safe , s ince there would actual ly be the additional radial

tens ion to help . This method woul d be preferabl e to calculating

the average tens i l e stress across the whole cross section of a disk ,

as i s sometimes done , S ince the strength of a disk i s at i ts

weakest part and i t wou ld give w ay at the point where the tens ion

w as the greatest . - ( See Weisbach’s Theoretical M echanics, page

61 8,for method of cal cu lating the average stress . )

S tresses in a Rotating Ring—When a cyl indrical ring that i s

comparatively thin radial ly , l ike the rim of a flywheel,i s rotated


312 S TEAM TURBINESthickness the e quations reduce to comparat ively s imple forms .

W ithout any attempt at derivation w e give the final resu lts .

Let w z w eigh t o f mater ial p er cub i c inch .

s p e e d , R . , P . M .

r lz inner radiu s in inche s .

r zz ou ter rad iu s in inch e s .

h z a cons tan t (Poi s son’ s rat i o) u sual l y taken as for

iron or s t e e l .r z rad iu s o f any p oint at wh i ch s tre s s is d e s ire d .

S t z tangent ial s tre s s , lb . p er s q . inch .

Srz rad ial s tre s s (See Fig . )

T hen

5 ,=o.0000035 5 w N 2

5,

w N 2

(s+e) rH—rfiFor r z rz, that i s , at the ou ter c ircum ferenc e ,

S t=0 .0000035 5 (27 32

4 4 22

) (1+3h)r 22

] .wh i l e at th e inner circum ference where r z r b

S , : 0 .0000035 5 (r 12

+2r22

) (1+3I)I t wil l be observed that the thickness of the disk has no in

fluence on the stress . The factor outs ide the brackets depends

only in the material of the disk and the speed : that ins ide the

brackets upon the d imensions o f the wheel . Evidently the stresses

increase as the square of the speed .

Examp le—Take a‘

flat—

disk 40 inches outs ide and 4 inches

ins ide diam eter, material weighing pound per cubic inch and

running at R . P . M . Taking the tens i l e stress at theinner circumference is

( 2x202

+22

)pounds p er sq . in. approx . ,

and at the outer circumference it i s

( 202

+2x22

)—1 .9x205]

580 pounds p er sq . in. nearly .

BODIES ROTATING ATHIGHSPEED 313

Of course , the larger stress is taken as determining thestrength

of the disk . From the form o f the general equation it i s seen thatthe maximum tangential stress wil l always be at the inner c ir

cumference.

The Circum ferential speed in the example above is about 1 75feet per second . I f the disk were run at five times this speed

,

which is something l ike that of a De Laval turbine disk o f thisdiameter, the stresses wil l be twenty-five t imes as largepounds p er square inch for the inner circum ference and

pounds p er square inch at the ou ter circumference .In the DeLaval turbine , however, the disk is not made of uni form thick

ness , and the design i s such that the tangential stresses are the

same at all radi i .

CHAPTER XVINOTES ON EFFICIENCY AND DESIGN.

Efficiency of a Turbine—On page 1 81 i s an explanation of thethermal efficiency of turbines , u se fu l in comparing the perform

ance of d ifferent turbines .In estimating the losses in a turbine

another method for computing effi ciency i s us ed , which gives

entirely d ifl erent and much higher resu lts . It consi sts in cal

cu lating the rate Of steam consumption for an ideal turbine , in

which there are assumed to be no losses Of any kind ,and then

finding the ratio of this to the rate of steam consumption for an

actual turbine .In an ideal turbine steam wou ld expand adiabatical ly from the

initial to the final pressure and the energy can be cal cu lated by

any one of formu las ( 7) or ( 8) for saturated steam ; or

( 1 1 ) and ( 1 2 ) for superheated steam , Chapter XII I .

For example,in ( 8) the foot pounds of energy p er pound of

steam are represented by

T2 (¢I—92)—92]One horse-power i s equ ival ent to foo t pounds p er m in

ute, or X 60 foot pounds p er hour.Hence,the number of

pounds of steam p er horse-power p er hour requ ired by the ideal

tu rbine,in which steam expands adiabatical ly

,i s

60

m .—9z)—ezl

'

KI~ T2(¢1—92)—92 (2)

Example—Steam expands adiabat icallv in a turbine from 1 65

pounds absolute to 1 pound absolute . The rate o f steam consump

tion i s

— 70


316 STEAM TURBINESso

,at al l loads , while another class Of losses , such as l eakage,

nozzl e losses , etc . ,i s d irectly proportional to the load . At no

load , or where the power del ivered by the turbine becomes zero ,the variable losses disappear while the constant losses become the

load of the turbine .

*Hence 0D on the diagram represents the power absorbed by the

constant losses at zero load and therefore at al l loads . B0, drawn

E lec tr i calHorse Pow er

F ig . 1 . Diagram of To tal S team Consumption Curves .

through‘ O

,paral l el with AD,

i s the total steam consumption l ine

for the turbine , with the constant losses deducted , and the in

c linat ion of C0 to B0 shows how the variable losses increase with

the load .

The power represented by the losses in the turb ine can be esti

mated from the diagram . Suppose w e wish to find what it i s at

‘As a matter o f fact the lo sses due to leakage. friction in the nozz les , et c do not

entirely d isappear at no load , w hen a turb ine is running l ight , b u t they are verysmal l in amount and in our analys is mus t b e classed w ith ' the constant los ses .

EFFICIENCY AND DESIGN 317

640 horse—power. From this point on the base l ine, Fig. 1 , trace

vertical ly to A,and then horizontal ly to C. Distance x shows the

power that could theoretical ly be developed by the steam if there

were no losses ; y the part of this power that goes into use fu l

work ; 2 the part that is wasted ; w the part absorbed by the

variable losses{and u the part absorbed by the constant losses .

Variable Losses .

—Having separated the constant from the

variable losses , the latter can be divided into their elements onlyby a study of the conditions and of such tests upon nozzles

,vanes

,

etc . , as are avai lable .

The variable losses are due chiefly to

1 . Leakage .

2 . Radiation.

3 . Residual veloc ity o f the steam leaving the last row of

buckets .

4 . Imperfect action of the steam in the nozzles and bladechannels , due to friction,

eddying, etc .

The latter (No . 4 ) may be placed under two heads , one cal led

thermal and the other “hydrau l i c .

” The thermal losses are

caused by the fai lure o f the nozzles and blade channels to properlyexpand the steam and convert its heat energy into mechanical

energy, while the hydrau l i c losses are caused by the fai lure of the

moving vanes to convert al l the mechani cal energy of the steaminto work at the spindle .

Losses in Kw . Turbine—To illustrate what has preceded ,take the second test on the Kw . Westinghouse-Parsonsturbine, page 1 90. This test w as with saturated steam ,

with a

mean initial pressure of 1 43 pounds and a condenser pressure ofone pound absolute .

The theoretical steam rate,calcu lated by formu la ( 1 ) i s

pounds p er horse-power hour.

The results of the test are given in terms of electrical horse

power, and it wi ll s impl i fy the analys is to el iminate the generator

efficiency from the resul ts and plot the diagram in terms of

brake horse-power . On page 1 78 the efficiencies o f the generator

of this turbine are given as follows : Fu l l load , hal f load ,quarter load , and by using these the brake horse

318 STEAM TURBINESpower may be calcu lated from the electri cal horse—power. The

second column below gives the brake horse-power for different

loads and the first column, taken from the resu l ts of the test,the

total steam consumption. Us ing these values , the total steam con

sumption curve for the turbine i s then plotted .

S team perHour. BrakeHorse-Pow er .

Full load ,Half load,Quarter load ,In Fig . 2 AD i s the total steam consumption curve , and BO i s

the curve with constant l osses deducted .

B rakeHorse Pow er

F ig . 2 . Diagram for Kw . T urbine.

To locate C0, the curve for the ideal turbine, we have , steam

used p er hour by the ideal turbine at normal load 2 7 .928X

( from tabl e above) : 1 5,095 pounds

,from which the point cor

responding to normal load can be located ; and this point , together

with the zero point,will locate the l ine .

To obtain the efficiency , p er cent .

The brake horse-power at normal load is approx imatelyThis is p er cent of the total power represented by the avai l


326 S TEAM TURBINESbe more sat i s factori ly handled by aid of the temperature—entropy

diagram .

Temperature-Entropy D iagram for S tage Turbine.—Assume

the ini tial and final pressures to be 1 6 5 pounds and one pound ,respectively

,the turbine to have three stages and the steam to

expand adiabat ical ly . By formula Chapter XII I . , the

kinetic energy acqu ired p er pound of steam i s found to be

foot pounds , requ iring an expenditure of heat

uni ts . For the construction of the temperature-entropy diagram

we have the fol lowing data

Temperature saturated steam at 1 6 5 lb .

Entropy of water at 1 65 lb .

Entropy of steam at 1 65 lb . abs :

Temperature saturated steam at 1 lb .

Entropy dry saturated steam at 1 lb .

Points b and c,F ig . 3

,represent the entropy of water and

steam respectively for the higher temperature . Through b draw

the straight l ine ba intersecting the 3 2—degree point on the vertical

coordinate . This i s the water l ine of the diagram and closelyapprox imates the true water l ine , which i s a logarithmic curve .

The entropy of point a at a temperature degrees i s found

by measurement to be Through a draw the hori zontal l inead , and through c the adiabatic l ine cd . The l ine ce i s the sat

urated steam line and the entrOpy of point e :

The area abcd represents the number of avai lable heat uni ts

p er pound of steam and should equal but actual ly equal s

because the water l ine w as taken as a straight instead ofa curved line .

We now have the geometri cal figure abcd in the form of a

trapezoid ,‘

to be divided into three equal parts , each part rep re

senting the energy expended in one stage of the turbine . This

i s a geometri cal problem,merely

, and may be solved by the fol

lowing formu la, taking the values in terms of temperature and

entropy units .

*

Let A l eng th of top of trapezoid in entropy uni ts .

l ength of bottom in entropy uni ts .

*Fo rmu la propo sed by Ralph E. F landers .


C : height in degrees F.

P z p ercentage of whole area which is to be included between a l ine horizontal with the base and the base itsel f .

t eight o f hori zontal l ine above base in degrees F

Then

B— VBz— s —A?

)In the example above A Z 1 .5 58 B : 1 .5 58

C : 3G5 .88 P : % and

Substituting in ( 3 ) and solving ,Hwhen and

when P :

Taking these values o fH, the hori zontal l ines fg and hk are

drawn,dividing the diagram into three equal areas . The tem

perature represented by hk i s —l and by fgis —lIn Fig . 3 ceIS the saturated steam line of the diagram and the

amount Of dry steam present at the end of adiabatic expans ion i s

Diagram Show ing Reevaporation.

-Under actual conditions

there wou ld be friction and eddying of the steam which would re

tard the velocity of flow and part o f i ts kinetic energy would be

converted into heat,which wou ld reévaporate some o f the moist

ure, making the steam dri er than indicated by the above ratio .

Fig: 4 shows how this action may be represented by the heat

diagram . Taking the same pressures as before , assume that

steam flows from the higher to the lower pressure and that , after

discharging , its velocity is checked by eddying or otherwise , sothat 20 p er cent o f i ts kinetic energy is converted into heat energy .

The avai lable heat energy is represented by area abcd,con

taining heat uni ts as in Fig . 3 .

We wil l assume two different conditions o f discharge .

First , that it i s into a space so large or unconfined that thereevaporatiOn will have no tendencv to rai se the steam pressure.

322 STEAM TURBINESThe evaporation of the moisture wi l l then take place at constant

temperature and the change in entropy wil l be along the isother

mal l ine de. I f thi s change is dh, the area d’

dhh’

under dh will

represent the work of reévap orat ion, er —1-5 2 6 5 5 2 heat

units , the reévap oration being 20 p er cent .

The l ine dh i s at an absolute temperature

degrees and dh wil l therefore have a value of

5 626 9 2 0 1 1 6 entropy uni t . This added to the entropy of

point d,gives as the entropy of the steam at the compl etion

of the reévap orat ion. The dry steam present i s there fore

or 84 p er cent .In the diagram the area afgd i s equ ival ent to the area d’

dhh'

,

which,deducted from abcd l eaves fbcg as the net heat energy

converted into u se fu l work .

Second : Another w ay to regard the matter i s to assume the

steam to discharge from the nozzl e into a closely confined space so

that the reévap orat ion will rai se the pressure and temperature of

the steam . I f th is change is adiabati c and 20 per cent o f the

energy is expended in reévaporat ion ,i t i s obvious that the tem

p erature wil l ri se unti l i t reaches a point‘

g, where the percentage

of dry steam is 84,as before determined . TO find the qual ity of

the steam,first l ocate fg,

cutt ing Off 20 p er cent from the total

area of the diagram . By formula 3 ) i t i s found to be de

grees above ad,giving a temperature of

degrees . Entropy of dry , saturated steam at this temperature

( point 1, F ig . entropy of steam discharging from

nozzle remains constant at dryness of steam :

as found by the other method .

A curved l ine drawn from c to h wil l give approximatelythe qual ity o f the steam at any point .

F ig . 5 i s a reproduction of F ig . 3 , but with the dotted l i

f’

g'

,h

’

k'and ad , showing the net work and the temperature

each stage under the assumption that expans ion i s adiabati c ,evaporation i s 20 p er cent and that the latter action i sas above explained . Then


324 S TEAM TURBINESbe calculated ; and al so the pressure differences ex i sting ,

by wh ich

the velocity of flow may be calcu lated .

Examp le in Design—Requ ired , to proportion a 500 Kw . tur

bine , mu lt icel lu lar type , with one wheel in each compartment ;pressures 1 6 5 pounds and one pound absolute .

Tests on a 500 horse-power Rateau turbine of this type Show

a brake efficiency of 60 p er cent. Thirteen p er cent o f the power

at normal l oad is requ ired to turn the rotor, l eaving 27 p er centto be ‘ distributed among the other losses .

F ig . 5 . Diagram Show ing Re-evapo ration.

The turbine wil l b e governed by throttl ing the steam and we

wil l assume that the initial pressure is throttl ed to 100 pounds

absolute at normal load , l eaving a smal l margin for overloads

withou t resort to the secondary admiss ion valve .

There wil l be 1 0 stages,this being suffi cient to produce a mod

erate wheel velocity and to ensure that the drop in pressure from

stage to stage wil l not exceed 40 p er cent , so that d iverging nozzles

wil l not be necessary .

The energy avai lable i s found by formu la ( 1 ) to be heat

uni ts,or foot pounds ; and p er stage , giving a

velocity of discharge o f feet p er second . Tests with con

verging nozzles indicate that the actual velocity wil l be within


2 p er cent of the calculated ; and the actual velocity of dischargemay therefore be taken at feet p er second .

Making the wheel vanes symmetrical, , w e find

,formu la

Chapter XIV . , wheel velocity w : 628 feet p er second ; and byformula ( 1 1 ) res idual velocity of steam z 430 feet p er second .

To determine the area of the gu ide passages or nozzles three

additional items must be known ( 1 ) the weight of steam re

qu ired ; ( 2) the pressure at each stage ; ( 3 ) the dryness of thesteam at each stage .

1 . With a turbine efficiency o f and a generator efficiency

of the combined efficiency wi ll be To obtain weightof steam ,H. P . and

369 foot pounds that must be provided for p er s econd. The

avai lable energy p er pound o f steam w as found to be foot

pounds .Hence , weight o f steampounds p er second .

2 . The pressure in each stage i s to be determined by the aid

of formu la following the approximation o f either Fig . 3 or

Fig. 5 , and carrying through the calcu lation for the 1 0 stages .

This wil l give the temperatures for each stage,from which the

pressures can be obtained .

3 . The dryness Of the steam at the different stages is to be

Obtained from the diagram by estimating the evaporation as

already explained ; either doing this at the end of expansion and

sketching in .the temperature-entropy line for the mixture o f the

steam and vapor ( ch in Fig . or by calculating the entropy at

different points and plotting the curve .

To arrive at the probable reévap orat ion,let u s assume the losses

as follows :

Constant ( to turn rotor)Radiation and l eakageResidual velocity ( last stage)Friction in nozzles .

Friction and eddying in channels , etc

326 STEAM TURBINESOf these , a part of due to fri ction of the rotating disks in

the steam ,represents convers ion of mechanical work into heat .

I f the turbine i s designed so that steam blow s directly from one

stage into the next,only a part o f ( 5 ) will cause reévaporat ion ;

but i f the steam is brought to a standsti l l in each stage , the whole

1 8 p er cent will act in thi s w ay . I t probably wil l not be far wrong

to take the reévap oration at 20 p er cent ..It '

wi ll be real ized that calcu lations based on normal load become

nu l l and void at other loads and that the turbine problem is one

of compromise between di fferent running conditions . The final

and most important determination of proport ions must be em

p irical , based on tests of the completed machine .


328 S TEAM TURBINESwhich this i s not true i s that of the M etropol itan stat ion in Pari s ,which is being completed by the instal lation of one large engine

driven unit . I t i s rather interesting to note that in interviews

with leading engineers no question w as ever rai sed as to the

comparat ive meri ts o f engines and turbines for electri c l ight

plants .

”

Whil e the turbine in al l s izes i s very success fu l for electri c

generating ,the distinct field that it has w on for i tsel f i s that of

large units , in central stations . Large steam engines , with their

heavy frames,ponderous moving parts and large generators , are

in marked contrast to the smal l and compact turbine uni ts o f

corresponding power.

The Field of the Reciprocating Engine—The power for roll ing

mills,blast furnaces , waterworks , mine hoist ing , air and ammonia

compress ing,etc . ,

will be furni shed by the piston engine for a

long time to come . Roll ing mills have been driven by electric i tyto a l imited extent

,and centri fugal air compressors , turbine

driven, have been success fu l ly u sed . But in.

general the turbine

must wait upon the development of such apparatus before it can

enter the above fields . I t i s al so safe to say that the Corl i ss or

s imilar type o f engine wil l continue to be used for mill work ,where driving by bel t or ropes i s in vogue .

The competition to be met in electri c generating wil l depend

upon the future development Of the turb ine . The des ign of Par

sons turbines i s not wel l adapted to smal l-s ized uni ts , and turbines

o f thi s type are not now bu i lt in this country in powers of less than400 Kw . ,

o r about 600 horse-power. As long as these turbinesare not made in the smal l er s izes

,the only competition with re

c ip rocat ing engines of less than 600 horse-power will be turbines

of the impu l se type , such as the De Laval and the Curt is , and

there -i s thus a comparatively clear field for the several types Of

engines made in these s izes . Their real competitor at the present

t ime is the gas engine rather than the turbine .

The poss ibi l ity of engines of intermediate s izes,say from 600 to

horse-power, meeting turbines on an equal footing in com

petition depends mainly upon whether land values and space avai lable are at a premium . I f such i s the case the turbine wou ldnatural ly be selected ; but i f not , many engineers wou ld sel ect in

COMMERCIAL ASPECT OF THE TURBINE 329

preference compound engines o f medium speed,which are

economical and rel iable and reasonably compact .

Turbine Advantages , as usual ly claimed ,are about as fol lOWS ’High economy under variable loads ; smal l floor space ; uni form

angular velocity and close speed regu lation ; freedom from vibration ; inexpensive foundations ; ease o f erection and qu ickness instarting ; steam economy not seriously impaired by wear or lack

of adjustment ; smal l cost for maintenance and attendance ; butl ittle danger from water entrained in the steam ; adapted for highsuperheat ; water o f condensation free from Oil .

Reciprocating Engine Advantages—Rather than cal l attentionto special features , engine bu i lders point to the proven rel iabil ityo f the reciprocating engine ; to the fact that i t i s in no sense an

experimental o r undeveloped device ; that its condens ing systemis simple

,requ iring only a smal l quantity Of ~

coo ling water ; andthat high economy is obtained withou t the use of superheatedsteam .

Several o f these cla ims for the turbine and engine wil l beardiscussion.

Comparative Economy—This has been cons idered in its di fferent phases in Chapters IX . and X . A point in this connection.

not as general ly appreciated as i t'

shou ld be , is that a compound

engine will not show up creditably under variable loads unl essproperly designed and ad jus ted . It i s held by some authorities thatunder variable loads the best resu lts cannot be obtained with thedrop cut-off gear o f a Corl iss engine . W i th thi s gear the initialpressure in the cyl inder approximates the steam pipe pressure at

al l points of cut—off, and i t is held that better economy is to be

obtained by throttl ing the steam in the high-pressure cyl inder at

short cut—offs . This is easi ly accompl ished by the use of shi ftingeccentrics and a Shaft governor .In the matter of ad justment . tests on one o f the horse

power engines Of the 59th Street station of the InterboroughRapid Transit Company , New York

,show what effect this may

have . When running with a load equal ly divided between tw o

cylinders the steam rate at Kw . w as pounds and at

Kw . 1 9 pounds . Afterwards , by adjusting the low—pressure

gear the receiver pressure w as changed ,with results at these tw o

330 S TEAM TURBINESloads o f 1 7 and pounds p er Kw . hour.

* I t is reasonable to

suppose that a large proportion of compound engines,even i f

designed along the l ines of best economy , are not running under

proper adjustment , and this fact must be cons idered in connec

tion with the comparative economy of turbines and engines ; for

there are no adjustments to be made on the turbine that can

seriously affect its rate of steam consumption.

F ig . 1 . Relative F loor Space fo r Kw . Engines and Turb ines .

E lec tric Generating—In running direct—connected al ternatorsin paral l el

,the turbine has the advantage o f a uni form turning

moment and i ts high speed produces a powerfu l regu lating force

without the use of a flywheel . There i s no reciprocating motion

to be converted into synchronou s rotary motion. The regu lation

Of turbines i s so close that it has been found possibl e to run rai l

w ay , power and l ighting circu i ts from the same machine . Wherea tu rbine i s instal led in a plant with piston engines or water

Wheels , i t t ends to have a steadyingInfluence on the whole system ,

owing to its inertia effect .

The Use of Oil—No cyl inder oi l i s requ ired for the

so that the exhaust may be condensed and used over

again in the boi l ers,provided precau tions are

*See d iagram in paper byHenry G . S tott on Pow er PlantInst . E. E . , January, 1 906 .


S TEAM TURBINESF ig. 3 . P lan and Elevation of 5 00 KW . West inghouse Turbine.

Elevation and Plan o f 5 00 Kw .High-Speed Engine.


Relat ive Sp ace Occup ied by Engines and Turb ines .

Comparison of 5 0 0 Kw . Units .—Fig . 1 i s a graphic comparison

of the floor space requ ired for horizontal turbines, and vertical

and horizontal cross-compound Corl i ss engines , the basi s of com .

Scale of Feet

Fig . 5 . P lan and Elevation of 5 00 Kw . Corl iss Engine.

parison being a Kw . uni t , including the direct-connected

generator , the engine cyl inders being 28 and 5 6 by 48 inches , 95

“In pamphlet by Edw .H. Sniffin ,issued by The Westinghouse Machine Company.

334 S TEAM TURBINESFig . 2 i s a

,

compari son of the famous Reynolds vert ical

horizontal engine of Kw .,and a Curti s turbine of the same

power.

The most favorable case for the steam engine i s to be had byselecting high and medium- speed engines for comparison with

10 Sca le of Feet

S ca le of Fee t

F ig. 6 . P lan and Elevation of 5 00 Kw . Vertical Engine. F ig . 7. Curtis Turbine, c

500 Kw .

turb ines of corresponding power.In Figs 4, 5 and 6 are

different styles of engines of 500 Kw . capacity, two of w hichorizontal mach ines and are to be compared with the 500West inghouse

b Parsons turbine , F ig . 3, while the th ird is a ve

machine comparable with the 500 Kw . Curti s turbine,Fig

. 7 .


‘

336 S TEAM TURBINESworked out by first estimating the indicated horse-power by theru l e—of—thumb method Of squaring the diameter of the low

pressure cyl inder and dividing,by two ; and then estimating the

TABLE I I .

DIMENSIONS OFHORIZONTAL CROSS-COM POUND CORLISS ENGINES.


net kilowatt capacity as two thirds of the indicated horse-power.

The above ru l e for indicated horse-power i s on the bas is of 600feet piston speed .In the table the same values have in some instances been given to engines of different s izes .In such casesthe value ascribed to the smal ler engine is on the basis o f about

feet piston Speed .

Space Necessary for Condensing Appara tus . Comparative

MULATORAND PUMP

Arrangement Condens ing Apparatus Cur t l s Turbine.

figures of space requ ired for power units are of but l i ttle value ,unless the room occupied by the condens ing apparatus i s alsotaken into cons ideration.In the engine plant , which is usual ly

equipped with j et or barometri c condensers , the percentage of

room is very smal l and can be easily estimated , because of the

simplicity of the apparatus .

The condensing apparatus for turbine plants i s ful ly describedin Chapter XIX. I f a surface condenser i s used , it must be at

least double the S ize requ ired for a reciprocating engine and a

338 S TEAM TURBINEScorresponding increase in the capacity o f the circu lating pump ;

and p iping .In order to maintain a high vacuum the air pump

employed in engine practice i s usual ly replaced by two pieces of

apparatu s : the hot-well pump , which removes the water of con

densation,and the dry—air pump , which exhausts the air and vapor

from the condenser . The dry-air pump is frequently made in the

form Of a two-stage air pump driven by a steam cyl inder with

Corl i s s valve gear , making a large and compl icated piece of

apparatus .

F ig . 9 . Condenser Arrangem ent'

fo r Parsons T urbine.

I t i s difficu lt to est imate offhand the space requ ired for turbine

condens ing ou tfits,becau se cons iderations of conveni ence in pipe

connections often make it advisable to widely separate the parts of

the equ ipment . Several d iagrams are shown,however

,indicating

the relat ive floor space occupied by turb ines and their condens ing

plants , where the condenser and aux iliari es are compactly ar

ranged .

Condensers for Curtis Turbines —In F ig . 8 i s a layou t of con

denser and aux i l iari es for a Curti s turbine , sketched roughlyfrom a blue pr int furni shed by the Alberger Condenser Company.

The accumu lator and pump in the upper right-hand corner

‘

are

for the step bearing Of the turbine and have nothing to do with


340 S TEAM TURBINESat A,

B and C,as indicated by the dotted sections . An arch

wou ld be sprung between B and C andI-beams running fromA to B wou ld be used to stiffen the baseplate at this point . I f

the condenser i s of the downward-flow type , receiving steam at

the top,i t wou ld be placed directly under the exhaust nozzl e of

the turbine , as indicated , and the various pumps”

could be group ed

as Shown.

I f a counter-current condenser i s used , receiving steam at the

bottom,i t wou ld be necessary to locate it to the left , next to pier

A,Fig . 9 , u s ing an elbow in the exhau st pipe . The locat ion and

Turb ine

F ig . 1 1 . T w o T urbines served by one Condenser.

arrangement are indicated in Fig . 1 0. A S imilar arrangement of

piping wou ld be adopted i f i t were desired to set the condenser

paral l el with the turbine and alongside of the turbine foundation,

as i s often done . F ig . 8, Chapter XIX . ,shows a turbine with

condenser located underneath .

Frequently space i s economized,as wel l as first cost of ap

paratus,by having one condenser serve tw o turbines , placing the

condenser between them,as in F ig . 1 1 . This makes one of the

most compact arrangements and i s sati s factory for smal l and

medium - s ized units .


From the foregoing it appears feas ible to arrange the con

densing apparatus to come into an area equal to tw o to threetimes the space occupied by the turbine and generator, in the

case of horizontal turbines ; and an area of four to five times thespace requ ired for the foundation of vertical turbines

,with due

regard for the removal o f condenser tubes .

Enlargement of P lant—The poss ibil ities of the turbine as a

means for the enlargement of an existing plant,i s wel l i llustrated

by the turbine instal lation of the B . F . Goodri ch Company,Akron

,

O. The plan of the engine room is as in the accompanying illus

0 4 8 1 2 16

Scale of k‘

eet

GeneratorAir Comp ressor

Sw it chboard

200 K-W . Ro t ary Convert ers

Fig . 1 2 . Engine Room w ith Turbine Add i tions .

trat ion.

* There were original ly the cros s-compound engines and

generators Shown,and i t w as found imposs ible by any arrange

ment of the machinery toIncrease the capacity of the plant byany more than 500 Kw . ,

without extending the bu i lding , i f the

same type Of units w as adhered to . Instead , i t Was decided toinstal l two turbines

,as indicated in the plan,

which doubled thecapacity of the plant without disturbing the old arrangement . Itwill be evident that another increase in the capacity may be madeby replacing the 1 50 Kw . engine unit by tw o 400 Kw . turbo

*Or i gm al ly appeared in Engineering New s .

342 STEAM TURBINESuni ts .

The power house w as original ly laid out for kilo

watts , but without enlarging the bu i lding or replacing the large

engines it cou ld be made - to accommodate kilowatts , an in

crease of 80 p er cent . The present engine plant Of Kw .

occupies square feet , or 44 p er cent of the‘

total . The tur

bine plant of Kw . occupi es 980 square feet or 1 6 p er cent of

the total . The balance of the space i s occupied by other apparatus .

Com p arative Co s t o f Tu rb ine Outfi ts and Their Maintenance.

The cost o f complete turbine and engine outfits i s practical lythe same ( exclus ive of land and bu i ldings), and such differences

as ex ist wil l be found to be no greater than often met with in

the cost of different engine equ ipments of the same power. The

sel l ing price of turbine outfits i s governed by the price of engine

ou tfits rather than by the cost to manufacture .

It wi ll be Of interest to compare cost figures for the apparatus

of tw o plants o f equal S i ze , one engine-driven and one turbine

driven. Such an i temi zed statement wil l Show the distribution ofexpense

,i l lu strating how certain factors entering into the engine

costs,such as the foundations and generator, are offset by other

i tems,such as the turbine condens ing system . The data will

al so assi st the reader in making his ow n prel iminary estimates .

Examp le for Comparison—Assume the case of a 750 Kw .

turb ine and generator Operating with 1 50 pounds steam pressureand 1 00 degrees superheat . The generator to be 60-cycle

,3-phase ,

volts .

As the equ ival ent of thi s a firm of engine bu i lders have p roposed to supply a cross- compound 24 and 50 by 42 engine

,1 00

revolutions , operating with 1 50 pounds pressure , saturated steam .

The engine i s rated at horse-power, or about 1 % times the

Kw . capacity of the turb ine . This is ample to al low for the

losses in the engine and generator when comparing the indicated

horse—power of an engine with the net output in kilowatts o f aturbo-generator . The proportions of the engine are generous ,giving ample power for overloads . The generator i s to be 60»

cy cl e , 72-pole , 3-phase , volts .


344 S TEAM TURBINESAn ordinary j et condenser cou ld be instal l ed for

Foundat ion.

—Concrete , feet deep ; 276 cubic yards , $6 p eryard . Price

,

Erecting and Freight on outfit complete,

Apparatus in Common— The feed pumps,switchboard , stack

and boi lers , superheater excepted , wou ld be the same for eithertype o f plant . Water tube boi lers

,del ivered and erected

,cost

p er boiler horse-power. The piping,exclus ive of exhaust ,

wou ld cost practical ly the same in either case,and may be esti

mated at $8 p er boil er horse-power. The expense of exhaust

pip ing wi ll depend upon the location of condenser , wh i ch , in the

case of the turbine i s o ften connected d irectly to the turbine .

Smal l er water piping is requ ired for the condenser with an

engine than with a turbine .

Summary—Assuming the surface condenser for each type of

apparatus and tabu lating the items that differ in the two types,

we have

Tu rb ine. Engine.

Turbine and Generator, Engine,Su r face Condenser , Generator ,Erecting Condenser , Su r face Condenser,

Foundations , Foundation,

Superheater , Erecting,

Ordinari ly the sur face type of condenser wou ld not be instal l ed

with the engine,thus reducing the cost somewhat .

General Figures—Taking the above figures

,with the omission

of the superheater cost,we have

,for a 750 Kw . turbo-generator,

surface condenser, foundation and instal lation, or $37 p er

Kw . The engine figures are $40 p er Kw . To compare with this ,the actual cost of two larger uni ts wil l be given. One w as a

Kw . turbo—generator,which

,with surface condenser ,

foundation and instal lation, cost p er Kw . The other w as

an Kw . cross-compound engine,j et condenser

,foundation,

and instal lation,cos ting p er Kw .

The cost Of turbo-generators p er Kw . ( 60 cycles) is app roxi

mately as follows : Kw . , $20 ; Kw . , $24 ; 750 Kw

$30 ; 500 Kw . , $32 .


Surface condensers for high vacuum cost , with necessary aux

iliaries , from $7 to $10 per Kw . ; and barometri c j et condensersfrom $5 to $6 p er Kw . Two additional examples o f condenser

costs will be c ited .

A square foot surface condenser for a 750 Kw . engine ;26- inch vacuum ( 2 square feet p er direct-acting pump

underneath condenser and centri fugal c irculating pump and en

gine at end o f condenser . Price , f . o . b . factory , or,say

p er Kw .

A square foot surface condenser for a 5 00 Kw . turbine

28- inch vacuum ( 4 square feet p er Edwards air pump ;centri fugal circulating pump and engine . Price

,f . o . b . factory ,

or, say p er Kw .

Cos t of Land and Buildings .—NO estimate of turbine costs is

o f any value whatever without taking into consideration the costof land and bu i ldings .

-In comparing turbine and engine costs

the important item to be cons idered is the investment for realestate in the two cases . Ou ts ide of the operating room the space

requ ired for the plant wil l not be material ly different , whichever

type o f apparatus i s instal led . The turbine room o f the turbineplant , however, need be only about one hal f the size o f the sameroom in an engine plant , and knowing the cost of bu i lding and

the value of land p er square foot in any community f the savingcan be very qu i ckly arrived at in the rough . Thus , take the caseo f a plant with four 750 Kw . units . By the aid of Tables I . and I I .

and a l i ttle figuring with pencil and paper,it wil l be found that

an engine room o f square feet and a turbine room of hal fthis , or square feet wil l be ample for al l the power—generating machinery . At $5 p er square foot the land saving would

be and the saving in the bu i lding might easi ly be as

great, depending entirely upon the style adopted .

Cos t of Maintenance and Operation—In a paper be fore theAmeri can Institute o f Electrical Engineers

,January , 1 896 ,Henry

G. Stott , superintendent Of motive power, Interborough RapidTransi t Company, New York

,gives a carefu l analysis of power

plant economics .He cons iders different types of prime movers ,including gas engines and combinations of gas engines and tur

bines and o f reciprocating engines and turbines .

346 S TEAM TURBINESIn the paper i s a tabu lation of the relative values of thevarious items necessary in the maintenance and Operation of

powe r plants,and two columns of. the tabl e are reproduced here

with . The first column covers a plant with compound condensing

reciprocating engines without superheat and i s derived from a

year’ s record of actual costs in a plant with horse-power

Al l i s vert ical-horizontal engines . The turb ine compared with thisIS a Kw . uni t , which i s bel i eved by M r. Stott to have the

TABLE I I I .

DISTRIBUTION OF MAINTENANCE AND OPERATION.

CHARGES PER Kw .HOUR.

Rec ip ro

Ma intenance . ca t ingTif

e

lfil

fil

e sEng ine s .

Engine room mechani ca l .Bo i ler ro om .

Coa l and ash hand l ing app ara tu sE lectr i ca l ap p ara tu s .

Op era t ion .

Coa l and a sh hand l ing la bo rRemova l o f ashes .

Dock renta lBo i ler room labo r .

Bo i ler room O il, w as te , et c .

Coa lWa terEngine ro om m echani ca l la borLu b r i ca t ionWa s te

,et c

El ec t r l ea l labo r

Re la t ive co s t o f m a intenance and Op era t ion .

Re la t i veInves tmentIn p er centbest record for economy up to date .It has a flatter steam rate

curve than the engine , shows practical ly as goo d economy at

normal load with saturated steam and a thermal economy p er

cent better with superheated steam . The variou s turbine items

are derived from actual costs .

Turb ine T roub les .In beginning the construction of steam turbines,i t w as inevita

bl e there should be difficu lt i es which cou ld no t be foreseen and

which cou l d be overcome only by observing the machines in


348 S TEAM TURBINESways , which stopped the flow o f oi l , and w as overcome by the

use of special oil , carefu l ly fil tered .

One company , operating Curti s turbines , reported“

a Shut

down caused by a worn bearing on the tachometer connected with

the latch of the emergency stop valve ; al so s l ight trouble from

loose laminations in the armature of the generator. On another

Curti s turbine the needle valves and the main nozzle valves were

warped by the high degree of superheat employed . On sti ll

another turbine of this typ e there w as air l eakage in the turb ine

and al so troubl e from water mixing with the oi l lubri cating the

step bearing .

Several companies having Parsons turbines reported difficul ties .

One experienced trouble from the oil sol idi fying into a j el ly in

some of the bearings . Another reported the repeated cutting

out of the throttl e valve seat , which w as attributed to the pecu l iar

water used in the local i ty ; al so excess ive vibration caused by the

expans ion of the exhau st p iping , throwing the turbine out of l ine .

This latter w as corrected by instal l ing an expans ion j oint in the

exhaust p ipe . The field coils of the generator of two Parsons

turbines burned out at les s than normal load , indicating some

error in design. There w as al so a breakage of one or more of the

brass sl eeves of the main bearings of these turbines and Special

attention w as requ ired to keep the lubricating system in good

order.

Three compani es reported breakages of blades in Parsons turb ines .In one case where superheated steam w as used

,suffic ient

t ime w as not al lowed in starting to warm up the mach ine and

maintain the proper cl earance between the blade tips and thecasmg .In another case , where there w as said to have been no

rubbing of the blades against the cas ing,many of the blades of

the rotor were broken while running . Whatever the cause ofthi s may have been, such accidents are now guarded against by

the use of steel lacing to stiffen the blades . The third companyhad a few blades broken by some foreign substance carri ed into

the turb ine through the steam pipe . This did not affect the

operation of the turbine , which continued to run . until it w as

conveni ent to repair i t .

I t wil l be seen from the above that the accidents reported are


al l Of a minor character, with the exception of the blade fai lures .

Even when making al lowance for the reticence of the firms in

terrogated , the difli cu lties experi enced must be admitted to be veryfew and comparatively ins ignificant.Danger from Water.

—It i s claimed for the turbine that i t i snot injured by water coming over from the boiler in case of excess ive priming.Instances are on record where a -slug of water has

suddenly efitered a turbine, bringing the rotating member almost

to a standsti l l , without injury to the machine . Destruction of theblading has al so occurred from this cause in some cases , but thisis practical ly imposs ible except in machines l ike the Rateau or

certain types o f Parsons turbines in which the outer ends of the

blades are unsupported ; and even in these machines the highpressure blades are so Short that damage from water mingled with

the incoming steam seldom resu lts . Breakage would be more

l ikely to occur i f water shou ld set back from the condenser

through some difficu lty with the pumps . At the low-pressure

end of the turbine the blades are l ong and slender, and running as

they do at very high speed , sudden contact with the Water mightstrip Off the last row .

' Further damage seems to be prevented ,

however, by the next row of fixed gu ide vanes,which divide the

water into smal l streams and thus protect the other rotating mem

bers . Compared with the breakages that so Often occur from

water in a steam engine cyl inder, turbine troubles from waterseem ins ignificant .

Dis tortion of Cas ing—In Parsons turbines there has been

trouble from the distortion of the cas ing, resul ting in the movingand stationary parts coming in contact , tearing out some of theblading . Troubl e has been experi enced from the cas ing archingupward under the effect of superheated steam

, on account ofthe top of the cyl inder expanding more than the bottom

,this

being due to the fact that the Shell w as not made symmetrical ,sometimes having ribs or heavier parts at the bottom than at thetop . This has been remedied in later machines by more care inthe design.

Another cause for distort ion has been the pul l of the con

denser at the low-pressure end , due to the vacuum . Inasmuch as

a high vacuum is carri ed , at which pressure steam has a high

STEAM TURBINESSpecific volume , the opening to the condenser i s necessari ly of

unusual ly large d imens ions and atmospheri c pressure distributed

Over thi s opening produces a heavy stress . Under the most approved form of construction the exhaust nozzle leading from the

turbine passes down through the pedestal at the low -pressure end

of the turbine , thus placing this stress directly upon the founda

tion in so far as possible .

A corrugated copper expans ion j om t i s also placed in the ex

haust p ip ing jus t below the turbine outlet , to compensate for

unequal expans ion and for any change in the relative posi

tions o f condenser and turbine , due to settl ing of foundations .

Another method that has been tri ed cons i sts in bolting the con

denser flange rigidly to the cas ing , with the condenser under the

cas ing . The base of the condenser rests on a flex ibl e foundat ion

o f springs,sufficient to rel ieve the turbine of the weight of the

condenser,but al lowing it to go and come with the turbine . The

condenser i s thus to al l intents and purposes a part o f the tur

bine,supported by the turbine foundation,

and i t wil l be evident

that the “pu l l” of the vacuum wil l have no more tendency to dis

tort the casing than will the pressure at any other part of the

cas ing.

S tripping the B lades .

—The most serious accident that can

be fal l a turbine i s that mentioned under the last heading,of the

rotating and stationary part s coming together and the stripp ing

of the blades . This trouble has been experi enced to a greater or

l ess extent in turbines in which the blades have no protect ion or

support at their outer ends .In the early days of theParsons turbine there w as an endless amount o f trouble from blade fai lures .

The blades broke , not only when the rotating and stationary parts

came in contact,but from no visibl e cause, one theory being that

rapid vibration of the rotating member produced repeated stressesin the blades

,l eading to their rupture .

Lately a great deal o f attention has been given to the blade

quest ion . Where the material i s an al loy,the composition is

sel ected with due regard to strength and ductib il ity as well asres istance to erosion.

*Several manu facturers have adopted steel

o f high grade .In turbines patterned after the original Parsons

type , in which the outer ends of the blades have no support , a


S TEAM TURBINESB lade Ero s ion.

~

During the l i fetime of a reciprocating engine , thereIS con

tinually increas ing steam leakage ,~

because of the wear of the

valves , p iston rings and cyl inder .

* At best this loss i s considerable ,

and in order to maintain the economy of the engine the valves

must occasional ly be scraped to their seats , the cyl inder rebored ,and the piston rings refitted .In the turbine there are no corresponding wearing parts and

practical ly the only deterioration that can affect the steam con

sumption comes from the cutting action of the steam or water

upon the blades . Experi ence thu s far indicates that blade erosion

wil l not prove a serious matter ; but the turbine must pass through

a longer trying-out period than i t vet has to demonstrate whether

a drop in steam economy is to be expected from this cause , when

a mach ine has had a long period Of service.

’

l‘

Erosion Caused byHigh Velocity and M ois ture.—TO test the

tendency of steam flowing at different velociti es to erode the

surfaces of buckets , Franc is Hodgkinson experimented at the

Westinghouse Machine Company ’s plant with hard-drawn delta

metal blades exposed to two steam j ets . The velocity of one j et

w as abou t feet p er second and of the other about 600 feet

per second . The blades were continuously exposed to the j etsfor 1 28 hours . Those subj ected to the higher velocity were

stripped and eroded,while those subj ected to the lower velocity

were not injuredi‘In 1 904-05 the S team Research Committee of theIns titu tion of Mechanical Eu

gineer s , England , investigated the leakage of valves and pis tons of a smal l s l idevalve compound engine . The tests w ere carried ou t under al l manner o f cond itions,and the resu lts show that w i th w e l l-fi t ted valves the leakage m ay amount to over 20 yer

cent and is rarely less than 4 p er cent, depend ing upon the s team pressure, speed , lapof valves, etc . Other types of valves might be ei ther better or w orse.

1-A 500 Kw . Parsons tu rbine w as instal led at the plant o f the Cambr idge Electrical

Su ppl y Company, England . A fter i t had Operated abou t a year, i t w as tested byPro fessor Ew ing and show ed a resu l t of 25 pound s p er Kw . hou r , normal load ; and

at a s l ight overload . The factory test of thi s machine show ed a resu l t of

pounds p er Kw . hour .In the later tests , how ever, bes ides running w i th w et steam,

the turbine w as dr iv ing it s ow n air and circu lating pumps , and the steam for thesew as charged to the turbine.In the tes t at the bu i lder ’ s w orks the turbine did not

dr ive it s ow n pumps. There have al so been some o ther tests of turbines after com

parat ively shor t per iods of operation, bu t as yet no resu l ts have been publ ished of testsmade after tu rbines have been in longer operation, say for a per iod of 10 years .

i Pap er by FrancisHodgkinson before t he A. S. M . E. in 1904 .


It al so appears to be well establ ished that erosion i s greatlyincreased by the presence o f moisture in steam , especial ly when

flowing at high velocities , and th is may account for the rapidwear in the case o f the high-velocity steam in theHodgkinsonexperiment . Such action i s corroborated by the manner in whichsteam inj ectors invariably wear . The steam nozzles of inj ectors

are seldom eroded , although steam flows through them at velocities exceeding feet p er second ; but the combining nozzles ,through which the feed water and condensed steam pass at a

more moderate rate , are Often so badly scored that they must berenewed .

_

Inqu iry o f several manu facturers of inj ectors has

brought repl ies showing that but l ittle trouble is experi enced withthe steam nozzles .

Erosion in De Laval Turbines .

-In the De Laval turbine,Inwhich enormous steam velocities are real ized

,thereIs occas ional

cutting of the blades , when the condi tions o f water or steam are

not favorable . This w as commented upon in a paper before theA. S . M . E. in 1 904

,by E. S . Lea,

then o f the De Laval SteamTurbine Company, who stated t hat there have been a few in

stances where buckets have worn ou t in a year,necess itating re

placement .In other cases the wear has been very .

sl ight,even in

a run of four or five years . The w ear affects only the steam inl etside o f the buckets and hence does not impair the efficiency to a

great extent .In tests upon a turbine o f 1 00 horse-power,where

the edge o f the buckets had been worn away about one s ixteenthinch , the steam consumption w as abou t five p er cent higher thanwith new buckets .

Erosion in Pars ons Turbines .

—In the Parsons turbine,where

steam velocities are low , the trouble from erosion appears to bealmost entirely absent , such cutting

‘

as occurs being sl ight and

mostly in the low-pressure end,where the steam is moist. Some

time ago articles were publ ished in certain technical journals ; inwhich were il lustrations of badly scored Parsons buckets

,and

the impression w as conveyed that they were samples of the condition that turbine buckets might be expected to get into . Theauthor succeeded in running down the source of the informationand found that the blades i l lustrated had been taken from a tur

bine which had become injured by contact o f the moving vanes

S TEAM TURBINESwith the cas ing , and that the cutting had undoubtedly been done

by partic les of steel broken Off and blown through with thesteam .

TO further investigate this important subj ect letters‘

w ere wri tten to American engine bu i lders and to a number of engineers mEngland , where the turbine has been used longer than in th i s

F ig . 1 3 . Appearance of T urbine Ro tor after five years ’ Service.

country , asking for defini te information in regard to blade

erosIOn. It w as expected that the engine bu i lders , at l east ,would b e wel l informed upon turbine d ifficu l ti es ; but no in

formation w as secured from them , nor from any other source , to

indicate that the question of eros ion need cause apprehens ion.

Some erosion does occur when the conditions are right for it,

even in the Parsons type o f turbine , with its low steam velociti es ;


356 S TEAM TURBINESF ig . 1 4 . B lad ing in upp er half of Cas ing .

Fig . 1 5 . O ld B lades compared w i th new B lades .


in the appearance o f any part o f the turbine with which thesteam came in contact Nor wou ld thi s be a matter ofserious moment i f conditions were different , for the reason thati f i t were necessary to replace every part of a Curti s turbine withwhich the steam comes in contact the machine i s so constructedthat this cou ld be accompl ished without serious inconvenience and

at an expense not exceeding 1 0 p er cent o f the first cost .”

Compos ition of B lades .

—There is no doubt that the breakage

and erosion o f blades depends to a cons iderable extent upon theii'

compos ition, which , as before stated , has received a great deal of

attention. Ordinary bronzes containing t in have their properties

too much affected at the temperatures of superheated steam to

make them rel iabl e, one o f the reasons being that t in melts at 4 50

degrees F . Brass also weakens at high temperatures , to a less

extent, but has been extens ively used for blades , the al loy varying

from 72 parts copper and 28 parts z inc,to 63 Copper and 3 7 zinc .

I ts tens il e strength,anneal ed

,i s about pounds p er square

inch ; but by cold drawing this can be increased .

An al loy of abou t pounds tens i l e strength,which with

stands erosion well,consi sts o f 80 parts Copper and 20 parts

nickel ; and i t is only sl ightly affected by temperatures coming

within the range of steam temperatures in practice . Steel forgings

,which are

-

u sed more or less for blades , also retain their

properties sati sfactori ly at the temperatures of steam .

One manu facturer u ses a nickel bronze,which is sai d to be a

Copper-zinc al loy containing a smal l percentage o f nickel and iron,

the latter to increase its strength and wearing qual ities . Thisbronze is the resu l t o f much experimenting and its makers do not

care to give the exact composition.

CHAPTER XV I I I

CARE AND MANAGEMENT .

The duties of the engineer of a turbine plant are in most re

spects l ike those of the engineer of a plant equ ipped with recip ro

cating engines . There are, however, special things to be attended

to in order to keep a turbine in good running condition.

F irst of al l i t must be remembered that the turbine is a high

speed machine and that i f anything is to happen to it i t wil l

happen suddenly and almost without warning . A turbine that

has frequent inspection and regu lar care wil l run day in and dayou t . But i f the oil c ircu lation i s al lowed to fai l , or the step

bearing pump al lowed to balk , or other vital part to get out of

order through lack Of attention, a shutdown i s the inevitable

resu lt . An engineer must not deceive himsel f by th inking he can

coax a turbine along which he has not kept up in condition.

There i s no possib il ity , for example , of nurs ing a hot bearing on a

turbine as SO o ftendone with a reciprocating engine .

It i s general ly held that turbines requ ire less care than re

c ip rocat ing engines,which is true i f by “care” i s meant the

actual labor expended upon the turbine itsel f . But i f the high

vacuum condens ing system be counted in,i t i s a fair question for

argument whether a“rotary engineer” may not be kept j ust as

busy as a“reciprocat ing It needs to be emphas ized

‘Upon this po in t C . J . Davidson , chief engineer o f pow er plants , the M i lw aukeeElectric Rai lw ay and L ight Company , w r i tes the au thor as fo l low s :

“In our

company there is no great d ifference in the extent and degree or qual i ty Of attendance ( requ ired by turbines and reciprocat ing engines ) , no tw i thstand ing the popu larOpinion t o the contrary . Our experience has been w ith turb ines of the Curtis type.

Whi le i t m ay b e po s s ib le t o real ize the claims o f s ome of the ad vo cates of turbinesrelative t o their abil ity t o b e p u t qu ickly in service, i t is bo th our experience andOb servation that i t requ ires some t ime after starting fo r the bucket w heels to find

their final running po s ition , due t o expans ion , and on this account w e exercise qu iteas much care as w e w ou ld do in w arming up a large engine .

“The s tep-bearing pump mu st b e kept in cons tant operation or ser ious resu lts w i l l

fo l low . T his means eternal vigi lance. Synchroniz ing tw o alternators driven byturbines is exceptional ly easy ; b u t great preci s ion and consequent care on the partof the attendant is neces sary , as a comparatively s l igh t Shock w i l l unbalance thesemachines .

“In generalIshou ld say that t he modern steam turb ine is more refined me

chanical ly and consequently a mo re del icate piece of apparatu s than the reciprocat ings team engine, and t o insure it s rel iabili ty of operat ion probably requ ires somew hatless labor b u t correspond ingly greater skil l than is neces sary in case o f the engine.

”


360 S TEAM TURBINESstart can be made more eas i ly with Curtis than with Parsons tur

bines and i f a Curtis turbine has been kept warm it Can be

brought up to speed in tw o o r three minutes in an emergency .In general , however, 10 to 15 m inu te s Shou l d b e taken in warming up and starting either a Curti s or Parsons turb ine , and i f

the auxil iar i es are put into operation at the same time it wil l

u sual ly requ ire about the same interval to get them running

regu larly .

S hu tting Dow n— Partly clos e the throttl e before reducing the

load on the generator, so the turbine can be brought under instant

control in case it should speed up when the load is thrown Off .

This cannot happen ,of course , i f the safety stopIS operative .

After clos ing the throttl e i t i s well to trip the stop motion to test

its action. After shutting off steam close the condenser valve or

i f the turb ineIS connected to an independent condenser, stop the

air pump ,hot-well pump and c irculating pump . I t i s not un

common for a turbine rotor, running in vacuum and with no load ,to continue to rotate for from 30 to 60 minutes after steam is

Shut off. The speed can be checked by opening the drains ,admitting air to the casing ,

and by leaving the current on the

generator fields . I f the turbine has an independent load,in

stead of running in paral l el with others , this can be u sed to

qu ickly check the speed .

Condens ing Apparatus .

—The turbine engineer,who has a high

vacuum surface condenser and connected apparatus under his

care , will find the turb ine itsel f to be the least source of hi s

troubles . A loss of an inch or two in vacuum in a reciprocating

engine plant , where 26 inches i s cons idered a good vacuum ,i s

not a serious matter . But in a turbine plant , where 27 or 28

inches or more are carri ed ,a drop of an inch or two in vacuum

means a large increase in steam consumption,as explained in

Chapter XIX . It i s there fore a much m ore important matter to

keep the condens ing system of a turbine plant up to a high state

o f effic iency than in the case of an engine plant , and i t i s al soa much more d ifficu lt matter to do so

,because of the greater

chance for air l eakage through glands,j oints and rel i ef valve .

It i s a temptation to let air l eaks go and cover up their existence

by pushing the air and c ircu lating pumps,with consequent addi

CARE AND MANAGEMENT 361

tion to Operating expenses . But the painstaking engineer will

not be satisfied to do bus iness in this w ay .

More or less troubl e is experi enced from the carboni zation ofthe Oil in the ports and valve chambers of the dry-air pump .

One plan for overcoming this i s to provide an additional oi l cupof the positive- feed type for the air cyl inder, and to use this to

feed in soap suds along with the oil . The trouble can also be re

duced by having the j acket cool ing water as cold as possible and

forcing a large quantity through the jacket . M ineral Oil Shou ld

be used of the grade des igned for gas engines and air compressors .

Changing from Condensing to Non-condensing .

—When run

ning condens ing ,the exhaust end and exhaust passages Of the

turbine are cool , but i f a change is made to non-condensing thetemperature of the steam in these passages will rise at once to

above 21 2 degrees and the quantity of steam flowing will al soincrease . I f the change is made suddenly, the turbine wil l besub j ected to wide temperature changes and care must be exer

c ised to shut off the condenser as gradual ly as possible to avoidthis . When changing from non-condensing to condens ing , theweight of steam flowing dimini shes and the cool ing effect wil lnot be as marked as w as the heating effect in the other case .

Op erating th e De Laval Turb ine.

*

S tarting—Upon first start ing ,

after erecting or after a longshutdown

,the bearings Shou ld be flooded with oil

,the amount

being gradual ly reduced to the normal quantity . The Oil reservoirs on the sel f-oil ing bearings Shou ld be fil led unti l the oil

stands between the red marks on the gauge glass . The smal loi l valves on the governor valve Shou ld be fil led with cyl inderoil , the valve stems then pressed down,

thus al lowing the oi l topass into the governor valve . Steam is then turned on, and thegovernor valve and wheel case al lowed to become thoroughly

heated . Before doing this,however

,the nozzle valves Shoul d be

Opened about a hal f turn ; otherwise they wil l stick when thewheel case becomes hot. The turbine shou l d be started gradual lySO as to give the bearings time to heat thoroughly . More time

*Abr idged from d irections fu rni shed by the De Laval Steam Turbine Company.

362 S TEAM TURBINESi s requ ired for thi s in the larger turbines than in the smal l er . As

soon as the turbine starts , the sel f-oil ing bearings must be ex

am ined to see i f the oi l rings run properly . I f the turbine is

running condens ing ,the condenser

‘ shou ld be started first . I f

starting with no load it i s wel l to start with a low . vacuum ,say

from 24 to 25 inches . AS soon as th e load i s p u t on, th e

vacuum shou l d b e rai s ed to i t s max imum .

Shutting Dow n—When a machine running non-condensing

is to be stopped,the throttle valve shou ld be closed and the

lubricator shu t off as soon as the machine has come to a stand

sti l l .If the turbine is running condens ing , and i f operating the

water and air pumps , either directly or indirectly , the air cock

on the exhaust end of the turbine wheel case Shou ld be Opened

before the throttl e valve is Shut off.

General Care of Turbine—The u sual precautions , with which

engineers are famil iar,Should be taken to keep the oil ing ar

rangements in working order. The S ight- feed lubricator must

be kept clean and the Oil in the sel f-oil ing bearings , and accumu

lating in the gear case , drawn Off and fi ltered as often as meces

sary . Particu lar attention shou ld be given to the oil ing of the

governor mechani sm,and especial ly the contact surfaces between

the governor p in and the plunger on the bellcrank . The h igh

speed bearings Shou ld be removed and examined at interval s .

Shou ld a bearing run hot , i t shou ld be taken out , the Oil-grooves

cleaned and i f any bright o r black spots appear, they Shou ld be

removed with a scraper .

The strainer above the governor valve , to prevent foreign

particles from entering the turbine , shou ld be removed and ex

am ined at least once a month .

I f the turbine speed is too high ,the brass nut holding the

governor Springs s hou ld be screwed out , or i f the speed i s too

low , the nut should be tightened . I t i s well,every time a tur

bine i s started , to press down the bellcrank, to ascertain t hat

these parts do not stick ; and when ful ly depressed , the governor

valve Shou ld shut off steam ent irely, or at l east with in a few

pounds .

To keep the gears in proper condition,the teeth shou ld be

cleaned occas ional ly when the machine i s not running . Kero


364 S TEAM TURBINESengineer o f the United L ighting Company of that city ,

has

wr i tten the au thor regarding t he care of Westinghouse-Parsons

turb ines as follows

We hav e th ree Kw . Westinghou se-Parsons turb ines connectedwith j et c ondenser. They have g iven us no troub le at al l , som etim es

running from Sunday t o Sunday w ithout stop p ing .In starting up w e w arm up t he turb ine, s tart t he d ry -air p um p , and

then t he inj ec tion p um p .

‘

T he tu rb ine is then s tarted s low ly , fo l low ed

b y the exc iter, w hich is steam -driven. The turb ine and exc iter are

b rought up t o sp eed at about the sam e tim e, tak ing from 10 t o 15 m in

utes t o get up to sp eed .If y ou s tart too fast there is to o great a

vib ration.

After the turbine is up to sp eed and the load on, al l the attention itneeds is to w atch the o il supp ly on the bearings and the gland w ater.

The auxiliaries need more care than the turbine. We have had some

trouble from the oil carboniz ing in the valve chambers of the dry-air

p ump , stop p ing up the p o rts and causing the valves to stick, but haveovercome this to a great extent. Otherw ise the care of the outfit is sim

p ly keep ing things clean, c leaning the o il strainers on the turb ine, keep ingthe governor from getting gummed and the p ilot valve in good condition.

The o iling sy stem should be given c lo se attention,being carefu l not to

pump any air into the system and hav ing p lenty of o il in the suction tank .In stopp ing c lose the throttle and Shut dow n the exc iter and con

densers, being sure to shut off the gland w ater as the w ater m ight otherw ise get into the Oil as the vacuum falls .

We use an auxiliary Oil pump to ensure a good sup p ly of o il on the

bearings w hen the turb ine'

is running at a slow sp eed .

Care of the Turbine.—In the Parsons turb ine the spindle

bearings support the weight of the drum and this w éight , in

connection with the high Speed of the j ournal s , cau ses the bear

ings to run so hot that the hand can scarcely be held on them .

Their high temperature makes necessary the cooling coi l for

the oi l and t his must be cleaned as Often as requ ired to keep the

coi l surfaces effective . This al ternate heating and cool ing of

the Oil makes some oi ls,which otherwise wou ld be good lub ri

cants , poorly adapted for turbine work . The heating tends to

decompose them and i f they contain p araffine thi s wil l b e de

pos ited on the surfaces of ‘ the coil and in the Oil passages dur

ing the cool ing process . Some oils , al so,have a tendency to

form an emu l s ion when they become mixed with water , which


might happen in case of leakage from the turbine glands . Thisemul s ion i s l ike j elly and chokes up the coil .In the general care o f the turbine , the governor parts and

connections with the primary and secondary admission valvesmust be regu larly inspected to see that they do not becomegummed , and i t must be seen that the pilot valves work freely

and are in good condition. Occas ional inspection of the bladingis advisable , at which times the blade channels may be cleaned ,i f requ ired . When the machine is running, give the oil ing systemclose attention,

making sure there is enough oil in the suction

tank to avoid air being drawn into the system . Try the pet cock

on each b earing frequent ly to se e that the Oil i s c ircu lat ingproperly .In the base of the turbine is an Oil strainer whichshou ld be removed and cleaned every few days and which can bedone while the turbine is in operation. The oil ing system and

the water supply to the glands and cool ing coi l are the threethings that requ ire regular attention when the turbine is running.

Op erating the Curtis Turbine.

Practical ly the only feature of a Curtis Turbine ( as ide fromthe condens ing apparatus) which requ ires care or attention di fferent from and in addition to that which wou ld be given a

steam engine is the high-pressure hydrau l ic system fer the step

bearing. Double-acting duplex pumps are used , usual ly in con

nec tion with an accumu lator, and so much depends upon themaintenance o f pressure in the step bearing

,and the pump is

working under such high pressure , that unusual care must betaken to keep the pumps packed and in good order and to seethat they are regularly inspected when in operation.

Direc tions for Care of Turbine—The author has talked and

corresponded with many turbine engineers in regard to the man

agement of their plants,and among the letters rece ived is one

from A. A. Leavitt, engineer o f the Gl oucester , Mass , ElectricCompany, in which are the following conc ise directions forhandling Curti s turbines

1 . The air and c irculating p ump s and al l p ip ing connections to the same

must receive frequent attention, as it is of the greatest imp ortance that thevacuum carried be as high as p oss ible.

366 S TEAM TURBINES2. The p ressure p ump s must be kep t in first-c lass condition and p ip ing

exam ined frequently to ensure it s being in good cond ition. As the p ressure

carried is h igh , usually about 500 p ounds p er square inch betw een p ump s

and accumulator, and about 200 pounds at the step bearing, and as thisstep bearing is w hat carries the w hole mach ine, the imp ortance of attentionto th is feature is evident.It requires great care in p acking the step -bearingp ump s to ensure a steady , uniform full stroke.

3 . The o iling system must be kep t tight, as a small leak w ill not onlymake a mach ine look unsightly , bu t w ill materi ally affect the op eration of

it by the o il drop p ing dow n onto the co llector rings and causing sp arking.

4 . The brushes and co llector rings must be kep t abso lutely c lean and

p erfectly adjusted , to ensure steady voltage ; for after they start to sparkthe voltage w ill be very unsteady .

5 . The governo r must be kep t in the best p ossible condition to ensure

steady sp eed . As the governors of these machines al l run at high sp eed

the p arts w ear quite rap idly and this w ear should be detected and remediedby making the necessary adj ustments .

6 .In starting , the turbine should be given time to w arm up and the

p arts exp and to w orking conditions, especially if a high degree of sup er

heat is used . The step -bearing p ump s are first started , to give the accumu

lator time to rise to its p osition, and then the c irculating pump is started,then the vacuum p ump and lastly the Oil p ump s. After these are al l w orking p rop erly the turbine is started . The exc iter set is started and the cur

rent put on the turb ine fields w hen the turb ine is up to about half Sp eed.

7.In Shutting dow n,shut steam off the turbine first

,then stop the air

p ump , the c irculating p ump , and last the o il pump s and step -bearing p ump s.

When the turbine has come to rest, it Should be carefully gone over and

scrupulously cleaned, the same as any dynamo , as there is nothing w hichw ill co llect dirt any faster than electric machinery and there is no

machinery to w hich dirt is any greater detriment.

Practice at a Large Turbine S tation.-At the L-Street station

of the Edison L ighting Company , S outh Boston,Mass

, are

four Kw . Curt is turbines , each with condenser in i ts base

and auxil iary apparatus ranged about the turb ine on the same

floor l evel as the turbine .In Fig . 5 , page 3 79 , i s a view of one

o f these uni ts , with its group o f auxil iari es . Cool ing water i s

suppl i ed to the condenser by a steam-driven centri fugal pump .

The wet o r hot-wel l pump is an electrical ly driven centri fugalpump placed in a pit below the floor l evel . The air pump has a

s ingle cyl inder,steam driven. There i s a boi ler feed pump for

each turbine unit , which discharges into a heater where the feed


368 STEAM TURBINESthe main bearings

,except the step bearing. Oil i s pumped from

a receiving tank to an elevated supply tank,from which it flows

to a smal l distr ibuting reservoir at the top of the turbine . The

system requ ires no special attention,therefore

,different from that

requ ired in engine work .

The lubri cant used for the step bearing is water. The step

bearing pumps operate against a pressure of pounds , which

i s reduced to 800 pounds at the step hearing by pass ing through

a pressure reducer of the baffle type . An accumu lator i s used

with each turbine to maintain a steady pressure and to act as a

pressure storage in case the pump fai l s , the capac ity being suffi

cient to hold the pressure for 1 0 minutes . I f a qu ick start i s

l ikely to be requ ired , the accumu lator i s shut Off from the system

when the turbine i s stopped , so that the step-bearing pressure will

be ready at a moment ’ s notice .

NO troubl e has been experi enced with the step hearings in th i s

stat ion. I f the water were gritty,however

,the bearings would

wear down and wou ld need occas ional adjustment to bring the

turbine rotor into proper position,as determined by clearance

indicators on each stage . Much of the foreign matter in the

water i s removed by the baffl e above mentioned,which should be

occas ional ly cleaned . It i s found that even with the large accumu

lators used at this station i t i s poss ibl e to pack them so tight that

the plunger wil l no t drop , and i t i s the practice to test each

accumulator dai ly for freedom of movement by caus ing the ram

to move through its whole range of travel .IVarm ing up and Synchronizing—Each of these machines is

warmed up by a special by-pass and three admiss ion valves which

are electrical ly and separately controlled and furnish the meces

sary amount of steam for warming up and al so start ing the tur

bine and bringing it up to speed, taking, in this case , only from

two to five minu tes . The exciter set i s started and the field given

excitation during the early period Of rai s ing the speed .In syn

chronizing great care i s taken to have the mach ine come into

phas e whil e its Speed i s accelerating instead of fal l ing off . It i s

common experi ence that turbines which were once in good al ign

ment and balance may be thrown out of balance by lack of care

on the part o f the operator in synchroniz ing . But by following


themethod advocatedabove , severe Shocks will be avoided and thebalance and ad justment o f the parts preserved .

Notes of Exper ience.

—C . E. Stanton,chief engineer o f the

Union Electri c Company , Dubuque ,Ia. , gives the resu lts of his

Operative experi ence with Curt is .four-stage 500 Kw . turbines *

The chief difficu lties have been in connection with the watersupply for the s tep b ear ings , the gravity oi l supp ly fo r lub r i cation, and the occas ional sticking o f the nozzle valves . The difficulty in lubrication arose through an air lock formed in thegravity oi l tank , al lowing air to come into the Oil feeder pipeline and interfere with the flow of oi l , and w as remedied byventing the top o f the tank .

All water for the step bearings in his plant passes through a

strainer after l eaving the pumps , to remove particles that mightclog up the passages of the step bearings or injure the latter.

The pumps for the service have fibrous packing and i f this isleft until it loses its elasticity and becomes soft , smal l particles

find their w ay into the strainer and soon choke the supply ofwater to the step bearings . Dirt or particles o f packing , when

once in the system ,may find their w ay into the strainers , even

after many days or weeks , and the strainers must therefore becleaned at interval s of twenty- four hours .

The hydrau l i c accumu lator fo r the s t ep-b ear ing system , ifal lowed to remain in one position for a cons iderable period oftime , w as found to rust fast and not drop , even i f al l the pressurew as removed from the system

,thus defeating the obj ect for which

the accumu lator i s intended . It therefore must be tested frequently by al lowing the ram to drop Sl owly and then return toits former position

, a test that w as made each day . One other

precaution that Shoul d be taken with accumulators for this workis to have some kind o f signal

, usual ly a steam whistle , whichwil l blow i f the accumu lator starts to come down, thus noti fyingthe engineer o f the fai lure of the oil Supply .In the 500 Kw . turbines there are eight main nozzle valves ,each with its individual p ilot valve , which is electr ical ly con

trolled . On any l oad with in the rated capacity of the turbine ,running condensing,

five valves are all that Open , leaving three“Paper presented at meet ing ofIo w a Electr ical As sociation,

Apr i l , 1906 .

370 S TEAM TURBINESvalves which might not open for days at a t ime . I f these are

l e ft long , they wi l l corrode and sti ck and i f a heavy overload

should come might not open at al l— or i f they did open they

might remain in this pos ition. To obviate these troubles al l

valves are opened and closed several times each day when starting the turbines . Some difficu l ty w as experi enced in securing

su itable packing for the main nozzle valves which wou l d stand a

high degree o f superheat . M etal l i c packing w as not success fu l

and asbestos ring packing is now employed,which i s satis

factory , except that the valve stems must be repacked more irequently than wou ld be the case i f metal l ic packing cou ld be used .


372 STEAM TURBINESthe pressure o f the steam wou ld not be suffici ent to overcome the

fri ctional res istances , to say nothing of doing u sefu l work,and the

expans ion of the steam beyond thi s point wou l d therefore be a

dead loss . The increased condensation in the low-pressure

cyl inder wou ld al so be a serious factor.

Below are given the volume of one pound of steam correspond

ing to different“vacuum” pressures

,indicating how imposs ibl e it

i s to uti l i ze these low'

pressures in the steam engine . To expand

steam from 1 50 pounds to 1 pound absolute,or to 28 inches

vacuum , wou ld mean that the volume must increase 1 1 1 times .

To carry the expans ion to this point in a compound engine , the

ratio o f the cyl inders wou ld have to be about 33 to 1 ; that i s , the

diameter of the low -pressure cyl inder woul d be 1 0% times that of

the high—pressure cyl inder—qu ite an impracticabl e figure .In the case of the turbine , however, the steam may eas i ly be ex

panded from 1 00 to 1 50 t imes without encountering any con

structive difficu lt i es .

Why a Turbine Derives more Benefit fromHigh Vacuum than

anEngine—Figf l i l lustrates the expansion of one pound of steam

from an ini tial pressure Of 1 00 pounds to the pressures indicated ,and i l lustrates the difference b etween the w ay in which an engineand a turbine benefit from a high vacuum . It shows the work

done both before and during expans ion, as in an indicator dia

gram . Th e section of the diagram marked a—b-c-d-e represents

that part of the energy of the steam that might be converted into

work by a condens ing engine operating against a back pressure of

four pounds , or a vacuum of about 22 inches . At point: c expan

s ion has been carri ed as far as the size of the engine cyl inderpermits and hence , when the exhaust valve Opens

,the pressure

drops from po int c to point d.

CONDENSING APPARATUS 373

Now assume the back pressure to be reduced to two pounds , andit i s evident that the gain in power for the engine wou ld be duesimply to the reduction in back pressure represented by the

b

0 l b . A b so lute

4-pound back -pressure line2—pound back -pressure l ine

of zero pressure

Fig. 1 . Diagram Show ingHow the Turbine Takes Advantage ofHigh Vacuum.

shaded portion having the length x on the diagram . This,i t will

be noticed , i s but a smal l percentage of the total area of the dia

g ram .In the turbine , however , it is different , s ince expans ion

can be cari ed to the lower back pressure l ine within the turbineitsel f. The turbine is able to uti l ize the toe of the diagram , in

dicated by the Shaded portion y,in addition to the shaded port ion

x, while the engine is unable to turn to any account the e nergyrepresented by the toe of the diagram .

Theoretical Gain fromHigh Vacuum—An idea of the theoretical gain can be Obtained by referring to a few calculations .

Konrad Anderson* compares power values for steam expandingfrom 60 and 200 pounds , respectively ,

and finds that the theoreticalgain in running condens ing

,with 25 inches vacuum , over run

ning non-condensing is nearly 1 00 p er cent with steam at 60

pounds pressure, and 5 0 p er cent with steam at 200 pounds

pressure . I f the vacuum be then increased to 28 inches , the gain

with the 60-pound . steam wil l be abou t 22 p er cent and with the200-pound steam about 1 8 p er cent . This shows that the p er

“TransactionsInstitu te of Engineers and Shipbu i lders of Sco tland , 1902 .



the water cannot pass back into the condenser. The condenser i s

fitted with an air cooler which is frequently appl ied when high

vacuums are to be maintained . This is s imply a smal l chamber

containing tubes l ike a surface condenser. The vapor and air

from the condenser pass through this air coo l er , where they are

cooled by circu lating water and their temperature and specific

volume thereby reduced . A rotative dry vacuum pump exhauststhe air and vapor from the air cooler and maintains a high vacuum .

The rotary circu lating pump driven by an engine is used for thecool ing water . I t is usual in instal lations of this kind to mainta inpractical ly a constant supply of coo l ing water, suffici ent to meetthe conditions under fu l l load .

Wheeler Condenser and Edw ards Air Pump—In Fig . 3 i s anelevation Showing one o f the 500 Kw . Curti s turbines at the New

port,R.I. , station of the Massachusetts El ectri c Company. This

turbine is equ ipped with a Wheeler condenser and an Edwardsair pump made by the Wheeler Condenser and Engineering Company , New York . The construction of this pump is such as tomake one of the s implest possibl e arangements of the condens ingapparatus . Fig. 4 i s a section Of the pump cyl inder} It has no

foot valves , which requ ire a pressure in the condenser somewhatabove that in the pump in order to l i ft them . The condensedsteam flows continuously by gravity from the condenser into thebase of the pump and i s there deal t with mechanical ly by theconical bucket working in connection with a base of s imilar shape .

Upon the descent of the bucket the water i s proj ected at a highvelocity through the ports into the working barrel ; the plunger

then rises , closing the ports , and sweeps the air and water beforei t, causing them to escape through the valve at the top o f thebarrel . The elimination of the foot valves in this pump enables ahigher vacuum to be Obtained than with the old style pump ,

80

that 27 or 28 inches can be maintained without the use of an aux

iliary air pump .

AS indicated in F ig . 3 the condenser i s located near the base ofthe turbine and in front o f it are the Edwards air pump and a

centri fugal c irculating pump , both driven by el ectri c motor.Inthis plant

, as in others arranged according to .modern ideas , thesuction sewer and discharge sewer for the circulating water are

378 STEAM TURBINESnearly on the same level . The system of p ip ing leading from the

suction sewer , through the circu lating pump and condenser, and

back to the discharge sewer,thu s c onstitutes a closed circu it , one

column of water balancing the other. The so l e work of the cir

F ig . 4 . Cro ss Section of Edw ards Air Pump .

cu lat ing pump , ther efore , i s to overcome the fri ctional res istance

of the water flowing through the piping and condenser tubes .

Cur tis Turbine w ith Condenser in Base.—In F ig . 5 i s one

of the Kw . Curti s turbine uni ts , with its condenser and

other aux i l iari es , instal l ed at the L-Street station of the Boston

(Mass ) Edison Company .In thi s case the condenser i s bu i ltinto the base of the turb ine and forms a part o f the unit ,while the auxil iari es are on the same floor l evel as the tur

bine itsel f , where they are more access ibl e . Th i s i l lustrationgives an excel l ent idea of the quant ity of apparatus requ iredto keep the plant in Operation , s ince the feed pumps , heater,hot-well , and accumu lator for supplying the hydraul i c pressure


380 S TEAM TURBINESthat must be maintained under the step bearing of the turbine

,

etc . , are all grouped abou t the turb ine , ih addition to the condenserauxil iari es . The lettered parts of the i l lustration are as fol lows

A,generator ; B ,

turbine ; C,condenser ; D ,

governor ; E, nozzles

F,circulating pump ; G,

accumu lator for step bearing ;H, engineto dr ive circu lating pump ;I, air pump ; K,

feed pump ; L ,heater ;

M ,hot-wel l ; N,

air-pump engine .

Fig . 6 . End View of Turbine and Condenser Show n on Oppo si te Page.

Wes tinghouse-Parsons Turbine and Alberger Condenser .

F ig . 6 18 an end view and Fig . 7 a plan of an Alberger surface

condenser and apparatu s appl ied to a Kw . WestinghouseParsons turbine . T he Alberger condenser i s a counter-current

condenser and does not requ ire the use of a separate air cooler.

The exhaust enters at the bottom and passes upward over the

tubes . The cool ing water enters at the top and ,passes downward ,


384 S TEAM TURBINESth is auxi l iary pipe i s

i

a steam nozzle which discharges a jet of

steam that acts similar to the j et o f an inj ector ; this j et draws

nearly al l the res idual air and vapor from the condenser and de

l ivers i t to the air pumps . The main pipe leading to the air pump

is so curved as to form an air seal wh ich prevents the air and

vapor from returning to the condenser. W i th thi s arrangementthere need be a vacuum in the air pumps of only about 26 inches ,whil e the vacuum augmenter wil l increase the vacuum in the con

denser to 27 or 28 inches . M r. Parsons states that the quanti tyof steam requ ired for the steam j et i s about p er cent of

Fig . 9 . Parsons Vacuum Augmenter.

Jet andInjec to r Condensers .

used by the turbine at fu l l load,and this

,together with the air

extracted , i s cooled by the aux i l iary condenser .

Surface vs . J et Condensers .

—The surface condenser has comeinto extens ive use with the steam turb ine b ecau se the steam dis

charging from a turbine i s entirely free from oil and i f col lectedand condensed can be used over and over in the boilers . The feed

water l eaves the hot well of a surface condenser operating at high

vacuum at nearly 1 00 degrees F. , and passes through a heater

where the temperature i s rai sed sti l l further by steam from theaux i l iari es .In j et and inj ector condensers the condensed steampasses off with the inj ection water , which is at a temperature of


80 or 90 degrees , and when part of this i s used for boiler feedthere is a loss of some 1 0 or 20 heat units p er pound , as comparedwith the surface condenser. This is so sl ight , however, that itdoes not pay to instal l a surface condenser and attending apparatus

on the score o f heat saved . The j et type is cheaper,simpler and

works as well or better .In local ities where the avai labl e water supply contains sulphateof l ime , acid , grease, or other harm ful impurities

,or where the

cost o f pure water i s high,the surface condenser shou ld probably

be given the preference,though i f it i s merely the cost o f the

water that i s at stake , the problem should be gone into very care

ful ly before deciding .

*Inj ector Condenser .

-A Bulkley inj ector condenser w as in

stal l ed by Geo . I . Rockwood in connection with a WestinghouseParsons turbine at Providence , R. I . The inj ection water i s el e

vated into a vert ical tank 30 inches square by 1 5 feet deep, in

which the water level i s maintained 6 inches below the water inl et

nozzle of the condenser. The inj ection pipe takes the water from

near the bottom o f the tank . The air entrained with the water

rises to the top o f the tank and i s largely el iminated from the

inj ection water entering the condenser . The flow of the inj ection

water through the throat of the condenser i s what constitutes the

air pump , and it i s found to be the only air pump needed since a

vacuum of 28% inches has been maintained,regardless of whether

steam is pass ing through the turbine or not .

l et Condenser.—A j et condenser

,which is a modification o f the

‘In a paper be fore the A . S . M . E. , December, 1904, Geo .I. Rockw ood contend s thatthe injector condenser w ou ld seem to bar ou t al l other condenser systems in s ituationsw here the w ater is pure.He gives figu res to show that i t does not p ay to instal l asur face condenser s imply to save paying city rates for bo i ler feed w ater.His estimate for the cost of a high ~vacuum sur face condenser ou tfi t is from $7 to $10 p er

kilow att and of a jet or barometric condenser sys tem from $5 to $6 p er kilow att.In a paper before the Amer ican Rai lw ay Mechanical and Electr ical Association, 1 905 ,Fred N. Bu shnel l w ri tes : “In cases w here the cost of feed w ater is a material factorin the cost of pow er , or w here i t contains a large percentage of calcium o r magnesiumcarbonate, or o ther scale-form ing mater ials, there w i l l be great advantage in u singa surface p ondenser on account of the pure d is ti l led w ater returned to the boi lers ,bu t w here these cond itions do no t exist i t w i l l frequently be found practicable to u se

some s impler form of condens ing apparatus su ch , fo r example, as the inj ector or

barometr ic type of j et condenser s . These types of condensers o ffer very great ad

vantages over the sur face condenser in the matter o f low er first co st , space occupied ,greater s impl icity, and less co st of maintenance . Up to th is time they have no t beenvery general ly u sed, bu t there seems t o be no good reason w hy they shou ld no t w orkas satis factori ly in connection w i th s team tu rbines as w ith reciprocating engines .

”

386 S TEAM TURBINESinj ector condenser , i s made by the Worth ington company . As in

the inj ector type, the condenser proper i s placed about 30 feet

above the hot well and the water fal l ing , through the action of

gravity , creates the vacuum . There i s no contracted throat to

th i s condenser,however

,and the water i s sprayed into the head ,

where it becomes intimately mingled with the steam before dis

charging through the vertical pipe . F ig. 1 0 shows a section of

the condenser head .

‘An air cooler and a dry vacuum pump are

HEELAIR COOLER

ENINGlNJECT t

OPEN ING TO TAIL P IPE

Fig . 1 0. Section of Worth ingtonJet Condenser.

employed,such as used with surface condensers , and any air that

accumu lates in the condenser head , where the steam is condensed

by the spray of the water, i s removed by the pump .

An interesting appl ication of a j et condenser to a Parsons tur

b ine i s shown in F ig . 1 1 . The plan i s here adopted of sub

stituting a centri fugal pump for the u sual barometri c column,

enabling the condenser to be placed under the turbine . The ex

haust steam is led through a pipe,A

,and a gate valve , B ,

into the

condens ing chamber, C ; and there , i t i s condensed by a j et and

flows into the Opening of a centri fugal pump , wh ich is driven by

a belt from the pu l l ey on the extended shaft of the turb ine .


388 S TEAM TURBINESpounds ) and wil l condense about 5 pounds of steam p er square

foot of cool ing surface . A common al lowance in turbine work

is 4 square feet o f cool ing surface p er kilowatt . I f the tempera

ture o f the cool ing water i s above 70 degrees the weight of

water wil l have to be increased , sometimes very largely . A l ess

quanti ty o f inj ection water i s requ ired for j et or barometri c con

densers than fo r surface condensers . One manu facturer of the

barometri c type has furnished the au thor with the following figures for a 28- inch vacuum :Inj ection at 40 deg. ,

26 lb . p er lb steam( t

50C‘

296

60 35

70 50

A common al lowance is 60 pounds p er pound of steam for

water at 70 degrees .

Tes ts on Condensers .

—There are no data yet avai labl e at

l east to the publ ic , in regard to the performance of h igh-vacuum

condensers , by which the relations between the several el ements

entering into the cal cu lation of the quantity of cool ing water,area

o f tube surface , etc . , can be establ i shed ,and resu lts for the present

must be more or l ess empirical .

Before cal cu lations o f condenser performance can be made,the

ini tial and final temperatures of the steam and cool ing water must

be known. The fol lowing figures were given to the author at

the works of the B . F . Goodrich Company , Akron, O. ,where

Westinghouse-Parsons turbines are instal l ed .

Test 1 . Barometer 30 inches ; vacuum temperature

steam in condenser temperature hot wel l init ial tem

perature inj ection water 5 4 degrees ; final temperature inj ectionwater 73 degrees .

Test 2 . Barometer 30 inches ; vacuum temperature

steam in condenser temperature hot well init ial tem

p erature inj ection water final temperature inj ection water7

The data in regard to the quantity of water used and the powerdeveloped by the turb ine during the tests were not sufficientlyaccurate to denote exact resu lts

,but they indicated abou t 60

pounds cool ing water p er pound of steam condensed .


The following resul ts are from tests upon a surface condenserwith Edwards air pump ,

in connection with a Curtis turbine which

w as running at a very l ight load

Test 1 . Test 2. Test 3 .

Vacuum , inches ,Area cooling surface, sq. ft ,

Temp eratures, degrees F

S team in condenser,Hot w ell,Coo ling w ater, initial,Cooling w ater, final,

Weight steam p er hour, lh. ,

Weight cooling w ater p er hour,Ratio, w ater to steam ,

These three tests show a condition that i s seldom met with in

practice ; viz . , a final temperature o f the cool ing water equal to or

higher than the hot-well temperature . This w as attained because

of the smal l quantity o f steam condensed p er square foot of coo l

ing surface . Under ordinary conditions the final temperature of

the cool ing water will be f rom 1 0 to 25 degrees below the hot

well temperature .In“ counter-current condensers the temperature will be higher than in the paral lel flow type . The final tem

perature i s also dependent upon the quantity o f cool ing water

forced through the condenser tubes and upon the area o f the tube

surface .

Condenser Calcu lations .

— The following simple example shows

the method o f cal cu lating the w eight of cooling or inj ection water

when the temperatures are known. No al l owance is here made

for the effic iency o f the condenser, which must be determined by

experiment,lzu t the example wil l explain why it is so diffi cu l t to

maintain a high vacuum .

Example —The temperature o f the steam in a condenser at

28 inches vacuum is about 1 00 degrees , and its total heat p er

pound is found from the steam tables to be uni ts . By the

use of a dry vacuum pump it is possible to secure a hot well tem

perature o f 98 degrees , and the heat in each pound of condensedsteam is there fore 98 32 66 uni ts .Hence there are

390 S TEAM TURBINES66 heat units given up to the cool ing water p er pound of

steam condensed .

W ith cool ing water at 70 degrees init ial and 100 degrees final

temperature ( the latter equal to the temperature of the condensed

steam) , the water will have ri sen 30 degrees and gained 30 heat

uni ts per pound .

But the heat lost by the steam w as heat units p er pound .

Hence,

for the ratio of cool ing water to con

densed steam .In practice no condenser can work with so high an effici ency as

in this case , where the cool ing water takes up all the heat of con

densation of the steam and l eaves the condenser with the tempera

ture o f the condensed steam . Under normal condit ionsO

the final

temperature of the cool ing water will range from 1 0 to 25 degrees

bel ow the temperature of the condensed steam , as previouslystated . Let us assume i t to be 1 5 degrees below . Then, with cooling water at 70 degrees initial and 85 degrees final temperature ,we haveHeat uni ts absorbed r

~

r pound of water: 85 and

for the ratio of cool ing water to condensed steam ,

or double what i t w as before .In winter t ime,when the ini tial temperature of the coo l ing

water wou ld be abou t 40 degrees , we shou ld have , assuming a

final temperature o f 85 degrees , 85 and -e

for the ratio . As a matter of fact it wou ld be more l ikely that the

plant would be operated with as much cooling water in winter as

in summer to derive the benefit of the higher vacuum that wou ld

be secured ; and in thi s case the final temperature woul d drop to ,say 25 degrees below the temperature of the condensed steam ,

as

w as the case in the tests upon the Goodri ch plant previously

quoted .

On the other hand,i f cool ing towers were employed and the

temperature of the cool ing water ros e to 80 degrees or more in

the summer time,i t i s evident that the

'

square feet of cool ing sur

face of the condenser shou ld be on a l ib eral bas i s , in order to

secure as h igh a final temperature of the cool ing water as poss ibl e ;otherwise the quantity of water to be c ircu lated might be almostprohibitive in amount . Even under favorabl e conditions the prob


392 S TEAM TURBINESquently 85 degrees , which made it difficu l t to obtain the high

vacuum desired .

*

The foll owing tests upon the auxil iari es of the Kw . uni t

of the Boston Edison Company , shown in Fig . 5,were reported in

the report of the turb ine committee of the National El ectri c LightAssociation for 1 905 '

Test 1 . Test 2. Test 3 .

Kilow atts on turb ine,Vacuum ,

Barometer, Horse-p ower Develop ed .

Boiler feed p ump ,

Circulat ing pump ,Dry vacuum p ump ,

S tep bearing p ump ,

Wet vacuum p ump ,

Totals ,

Per cent p ow er of auxiliaries to p ow er

of turbine,Per cent w ater used by auxiliaries to

that used by turbine,“American Street Rai lw ay Associat ion , 1904 .

CHAPTER XX

THE STATUS OF THE MARINE TURBINE.

EarlyHis tory —Most o f the turbines appl i ed to the p ropul

sion of vessels have been o f the Parsons type , al though some work

of this character has been done both by Rateau and Curt i s .In1 894 the Parsons Marine Steam Turbine Company , Ltd . ,

Wal l send-on-Tyne,England , w as formed and the experimental

boat Turbinio constructed .Her dimensions were 1 00 feet beam ,

3 feet draft and 44 tons displacement . There were three

separate turbines—a high an intermediate and a low -pressure ,each driving a screw shaft and on each shaft were keyed three

propellers of smal l d iameter. The turbines were rated at

horse-power and the boat attained a speed o f over 34 knots .

Various other high speed boats were bu i lt during the next five

or six years . Two of these,the Viper and Cobra, high speed

torpedo boat destroyers,were lost at sea and turbine propu ls ion

received a serious setback . An organi zation w as final ly effected ,however

,which included the shipbu i lding firm o f M essrs . Denny ,

theHon. Charles A. Parsons and Capt . John W i l l iamson, whichresulted in the first turbine steamer, King Edw ard, in 1 901

,for

service on the Clyde .

The Firs t Turbine S teamer.—The King Edw ard i s a boat 250

feet long ,30 feet beam with 6 feet draft . The arrangement of the

machinery is practical ly the same as has been used in al l the morerecent vessel s

,including the ocean l iners

, .fit ted with Parsons

turbines . There are three separate turbines driving three screwshafts . The high-pressure turbine i s placed on the center shaftand the two low-pressure turbines each drive one o f the ou tershafts . Ins ide the exhaust ends of each of the latter are placedthe tw o astern turbines which rotate as one piece with the low

pressure motors and when in operation reverse the direction ofrotation of the low-pressure motors and outs ide shafts .In ordinary going ahead steam from the bo i lers 1s admitted tothe high-pressure turbine and after expanding about 5 times

passes to the low-pressure turbines and is again expanded in

394 STEAM TURBINESthem about 25 times and then passes to the condensers , the total

expans ion ratio being abou t 1 25 as compared with from 8 to 1 6

usual in tripl e expans ion reciprocating engines of the marine type.

At 20 knots the speed of the center shaft is 700 and of the tw o

outer shafts p er minute .

When maneuvering in or out of harbor the outer shafts only

are u sed and the steam is‘

adm itted by su itabl e valves directly into

the low-pressure motors or into the revers ing motors , for going

ahead or astern. The high—pressure turbine under these c ircum

stances revolves idly,i ts steam admiss ion valve being closed and

its connection with the low-pressure turbines being al so closed by

non-return valves .

Later Turbine Boats—Foll owing the King Edw ard, and a later

boat fo r the same l ine , the Queen Alexandria, has come a long

l ist o f other turbine vessels , notably a fleet of 1 8 cross-Channel

boats bu i lt or bu i ld ing ,to ply between Dover and Calai s . Again,

on theHeysham line running between Great Bri tain and Ireland ,

tu rbine vessel s have been in success ful operation.In 1 904 the

thi rd -class turbine cru iser Amethys t w as bu il t for the Bri ti sh

Admiral ty . She i s 360 feet in l ength and of tons displace

ment . Three other engine-driven cru i sers o f the same size were

bu i l t s imu ltaneou sly , one of which ,the Topaz

,w as sel ected for a

seri es of competitive trial s with the Amethys t .

The contract speed of the vessel s w as 21 % knots , and the resultsshowed that at al l speeds above 1 4g. knots the turbine vessel w as

the more economical, at 1 8 knots the turbine w as 1 5 p er cent more

economical , at 20% knots 3 1 p er p ent , at knots 36 p er cent,and at fu l l power in each vessel the Amethys t showed 42 p er cent

more power than requ ired by contract on the coal al lowed ; while

the Amethys t reached knots on the specified coal and theTopaz only knots .In other words , the Amethys t has a radiu s

o f action at 20 knots speed of nautical mil es , while her si ster

vessels with ordinary engines can only steam miles at thesame speed .

The success of the Amethys t l ed Bri ti sh naval constructors toadvocate the turbine for larger vessel s and the activity of theadmiralty following the Russo-Japanese w ar cu lminated in the

construction o f the powerfu l battl eship Dreadnought . This ship ,


396 S TEAM TURBINESwhich is not only larger and carri es a heavier armament than any

battl eship afloat , i s remarkabl e because it i s the first battlesh ip to

be driven by turbines . Under tr ial the turbines developed

horse-power and propelled the vessel at an average speed of 21 %knots during a trial o f eight hours

,acqu ir ing a maximum speed

o f 22% knots . The turbines are so free from vibrati on that the

sh ip makes the steadiest poss ible gun plat form for a floating

battery .

Atlantic L iners F it ted w ith Turb ines .

Des crip tion of the S teamer Victorian.—The Al lan l iners Vir

ginian and Victorian started to ply between Liverpool and

Canada in the summer of 1 905 .In Apri l , 1 905 , Commander A. D.

Canaga , United S tates Navy , w as detai l ed to make the trip to

Europe and return on the turbine steamer Vic torian and report

the resu l ts o f h is observation to the department.* There unfor

tunately i s no s imilar vessel of the same l ine propel led by rec ip ro

cating engines with which a direc t compar i s on can be made , but

certain points brought out by Commander Canaga will be of in

terest . Figs . 1 , 2 , and 3 are reproduced from his report show

ing the arrangement o f turbines in this vessel which is l ike that

usual ly adopted for the Parsons ’ apparatus , and i s practical ly the

same as already described in connection with the King Edw ard.

The steam from the boi lers i s l ed into the engine room through

two 1 2—inch pipes , uniting in the throttl e valve at the working

plat form . From the throttl e valve steam is led through tw o

1 2- inch pipes to the high-pressure turbine . When in free route

the steam is passed through the high-pressure turbine where it

spreads , hal f going to the starboard and hal f to. the port turbine

through the receiver pipes,and thence through exhaust pipes to

the main condensers .In maneuvering , the main throttl e i s closed

and steam admitted to the maneuvering valves , F ig. 3 , one for

each low—pressu re turbine . These are s imple sl ide valves which

when placed at the upper end of their stroke admit l ive steam to

the forward end of the low-pressure turbine , when at the bottom

o f their stroke admit l ive steam to the backing turbine , and when

*J ournal of the American S ociety of Naval Engineers , Augus t , 1905 .

398 STEAM TURBINESin mid-position shut the steam from both the ahead and backing

turbines .

To prevent the steam blowin‘

g off into the h igh-pressure tur

bine when maneuvering , non-return valves are fitted in the receiver

pipes between the high-pressure and low-pressure turbines , as

shown in F ig . 2 . These valves are automatic , Opening or clos ing ,

as the l ive steam is admitted to the high-pressure or low—pressure

turbines .

Comments on the Operation of the Vic torian.

—At the forward

end of each turbine shaft i s fitted a safety governor,which in case

of accident closes the main throttle valve . These governors serve

another purpose , al so , by indicating whether the turbines are at

rest or in motion, s ince from the working plat form they are the

onlv vis ibl e moving parts . The commander reports that the tur

bines are eas i ly and qu ickly handled and that the minor mishaps

and annoyances met with in reciprocating engines are absent . He

notes a pleasing absence of vibration and of racing in h igh seas .

Against th i s immunity from racing , however , must be s et the lack

of holding power of the smal l screws with which turbine vessels

must be equ ipped . I t w as observed that the influence of head

winds and heavy seas reduced the vessel ’ s speed cons iderably more

than would have been the case with the large propell ers used withreciprocating engines .Attention i s cal led to the fact that heating of bearings is a mor '

serious matter with turbine machinery than with recip rocatir

engines as any unusual wear woul d cause interference between

the rotating and stationary blades , and on one of the trips the

Victorian w as delayed about 29 hours owing to some gri t that got

into one of the bearings and necessitated overhaul ing , after which ,

how ever,~ there w as no troubl e . There w as al so cons iderable dith

cu lty from priming of the boil ers , but with consequences l ess

serious than in the caseof reciprocating engines .

Turb ine B oats of the Cunard L ine.

The Carmania”< w as bu il t and equ ipped by M essrs . John BrownCo . ,

Ltd . , Clydebank . This vessel i s one of the seven or eight*Taken in part from London Engineering, December 1 , 1 905 .


STATUS OF THE MARINE TURBINE 401

siderab le and in order to distribute this pressure as equal ly as

poss ible the rings are arranged in groups and the pressu re to each

group is graded by su i table connections (Fig .

As a resu lt o f experiment with special ly constructed apparatusi t w as found the regular construction wou ld not answer for glandsof the large diameter requ ired for the Carmania. The speeds andpressures were so high that the rings wore rapidly . Final ly radial

fins,as in Fig. 8, were used in connection with a row of rings and

grooves . The action of these fins i s to alternately wire-draw and

expand the steam,each pair constitu ting an expans ion stage , thus

reducing its pressure as i t travels ou tward . The actual gland w as

fitted at each end of both the high and low -pressure turbines , as

i l lustrated in Fig . 6 , with four rings,K ; at the outer end . The

smal l amount o f steam which is al lowed to leak past them for thepurpose of lubri cation collects in pocket G, whence it i s led by thepipeHto the auxil iary condenser

,

or exhaust tank .In the case ofthe high-pressure turbine , where the radial fins do not suffi cientlyreduce the pressure of the escaping steam

,the pocket 0 i s con

nected to an expansion row in the low-pressure turbine .

Comparison w ith the Coronia.

—The area occupied by the turbines and aux i l iari es is p ract ical lv the same as requ ired for thequadruple-expansion reciprocating engines Of the s ister ship

Coronia,bu ilt sometime previously . The requ ired head room is

less , but no advantage is taken of this,as the space above the en

gine room w as left Open for l ight and air. There i s a saving in

weight o f about five p er cent . The boi ler pressure in the Coronia

i s 21 0 pounds and in the Carmania 1 95 pounds p er square inch .

The turbines take steam at an initial pressure of 1 5 0 pounds as

against 200 pounds in the quadruple engines . The cool ing surfaceof the condensers i s increased in the Carmania about 20 p er cent ,the capacity o f the centri fugal pumps i s about double , and theweight of circulating water i s from 50 to 60 times the weight offeed water as compared with a ratio of 25 or 30 times in theCoronia

’

s instal lation.

The Lusitania and M auritania,of the Cunard L ine , which are

expected to become the queens o f the sea,are turbine vessels

designed to maintain a minimum speed o f 24 to 25 knots . The

dimensions o f the Lusitania,which is more nearly completed than


404 S TEAM TURBINESabove , and it i s doubtfu l i f such great power cou ld be successfu l lvgenerated in the hold o f a ship by means o f reciprocating engines .Both the machinery and hu ll o f the Lusitania are from the

Clydebank Works o f M essrs . John Brown Co .,Ltd .

Comp aris on Betw een Turb ines and Rec ip rocating Engines .

The best opportuni ty for comparing the performance of vessel s

fitted with turbines and engines has been afforded by the M idland

Rai lway Company’ s four boats of theHeysham L ine of Great

Britain. Of these , the Londonderry and M anxman have turbines

and the Antrim and Donegal reciprocating engines . The London

derry, Antrim and Donegal have the following dimens ions

Length 330 feet,breadth 42 feet

,depth 25 feet

, 6 inches . The

M anxman i s of the same length and depth ,but has a breadth of

43 feet . The turbine boat Londonderry carri es 1 5 0 pounds boi ler

pressure and the others 200 pounds pressure . The engines of the

Antrim and Donegal are of the tr ipl e-expans ion type , differing

only in detail s , and drive a s ingle,three-bladed propeller. The

turbines of the Manxman were designed for 25 p er cent more

power than those of the Londonderry, but are of s imilar const ruc

tion and drive three three-bladed screws after the usual manner.

All the boats have high-grade condens ing apparatus , but the

M d ur man has in addit ion a Parsons vacuum augmenter, for p ro

ducing a high vacuum .

Official Trials ofHeysham Line Boats .

-The resu lts of the

official trials showed the two boats with reciprocat ing engines .to

be on a par in economy and to use p ractical ly the same amount of

feed water under l ike conditions . At speeds of 1 9 to 20 knots ,however

,which is the working speed of al l the vessel s in service ,

the water consumption of the turbine steamer Londonderry w as

8 p er cent l ess and of the M anxman 1 4 p er cent l ess than o f the

Antrim and Donegal, whil e throughout a speed range from 1 to 20

knots the turbine boats showed superior economy . Speed trials

were run between the two turbine boats and the Antrim and the

Londonderry proved abou t one knot faster and the M anxman from

one to two knots faster than the Antrim,under l ike conditions .

S TATUS OF THE MARINE TURBINE 405

Resu lts based on the Log B oohs .

*—Later,compari sons were in

stituted between the turbine steamers and those with reciprocatingengines , based on the log books in which the dai ly records were

kept whil e the boats were in regu lar service . During a part o f thiscomparative period the Manxman w as not on the same route as

the other vessels , so that she cou ld not be cons istently comparedwith the Antrim and Donegal during the entire time. Also

,the

high-pressure turbine of the Londonderry w as partial ly wrecked,

owing to the blades of the rotating drum coming in contact withthe stationary blades , so that the records from this steamer wereinterrupted for three months . Valuable comparative figures weresecured , however, and are summari zed in table below . The regularroute w as betweenHeysham and Bel fast , one vessel plying each

w ay every night except Sunday . The comparisons are made ineach case between vessel s running in opposite directions on thesame days and the table gives the weight of coal each vessel consumed on a given number of trips , exclus ive of that burned whenin port , which o f course does not affect the performance of thepropell ing machinery .

TABLE SHOWING RESULT S OBTAINED BY STEAMERS RUNNING SIMULTANEOUSLY ,

BUTIN OPPOSITE DIRECTIONS .

0

Recipro ca t ingEngines T urb ines .

Number o f T r i p sAverage C oa l

cper T r i p , tons

Average S pee in kno tDonega l .

Num ber o f T r ip sAverage C oa l p er T r i p . tonsAverage S peed in kno t

Number o f T r i p s .

Average C oa l p er T r i p , tonsAverage S p eed in kno t

Number o f T r ips .

Averag e Coa l p er T r ip , tonsAverage S peed in kno t s

An economy in the turbine steamers i s the smal l amount of oilrequ ired

,only five gal lons being used p er trip , and the dispensing

“Reported in London Eng ineering .

406 STEAM TURBINESwith the services of two oil ers usual ly requ ired . There is the ab

sence of vibration,but there is al so the inferiori ty in maneuvering

from rest in narrow waters . Experiments made during the trial

trips of these turbine boats ind icate that they may be brought to

rest from ful l speed inabout 1 % minutes . This i s a good resu lt ,but experi ence has shown the inadequacy of the backing powerfrom rest , when the s ide propel lers are l ess efficient .

Advantages and D isadvantages of the M arine Turbine.

—The

chief advantages , on the evidence already given,appear to be

absence of vibration,making the turbine boat a much pleasanter

passenger craft ; greater speed with the same amount o f coal or

l ess coal at the same speed , when running at or near normal

speeds ; ease of manipu lation ; s l ight saving in weight ; l ess oil ;l ess attendance ; less l iabil i ty of racing .

The ch ief disadvantages are the lack of holding power of the

smal l screws ; the d imini shed power of the revers ing turbines ; and

the poorer economy at low Speeds .

Cavitation—The size of the propell ers on turbine vessel s i s

l imited by trouble experi enced through cavitation. When the

speed of a propell er blade exceeds a certain amount , depending

upon the type , the head‘o r pressure i s not suffi cient to keep up

the supply of water to the propel ler and a part ial vacuum is formed

back of the blade , in consequence of which the efficiency of the

propeller drops off . This action i s known as cavitation. Marine

turbines are made larger in diameter for a given power than land

turbines u sed to drive el ectri c generators , and in this w ay the

speed of rotation i s reduced somewhat . The speed stil l remains

so high,however

,that the s ize of propell er must be reduced to

avoid cavitation ; and then, to secure a suffi ciently low thrust p er

square inch of propel l er area the blades are made wide . A wide

bladed propell er has usual ly been cons idered inefficient, due,probably

,to the increased fri ction that such a propel ler would

have i f of the usual large diameter. This ob ject ion' is not so

serious with smal l turbine propellers , however, wh i ch show a

reasonably h igh effi ci ency .


210

k

8 8 s“

e.“

s“

s“

F oot-Pound s o f Energy

a s a s s s s,a

s s

F ig . 1 . Energy of 3 S team Jet in Foo t-pound s , w hen the S team Expand s Ad iabati ca l ly betw een d ifferentIn i tial and F inal Pressures .

b at ical ly betw een d ifferentIn i tial and Final Pressures .


412 APPENDIXTABLE OF THE PROPERTIES OF SATURATED STEAM .

Abr idged from the tab les o f Pro f. C .H. Peabody , w i th h is p erm is s ion.

V alu es of the entrop y o f s team taken , b y p erm iss ion ,fromHea t and

[ fea t -eng znes ,b y Prof. F . R .Hutton. Both of the forego ing are p ub

l ished b y John W i ley and Sons , New York .

INDEXAbso lute velocity

calcu lation of

Accumu lator , Rateau ’

s s teamcalcu lations for

tes ts on

Ad iabatic flow ; s ee flow of steam.

Air~p um p , Edw ards 377

Al l is-Chalmers turbine . 1 5 3

Angles of vanes 287, 290-292 , 295

experiments on 298

Area o f condenser su rface . . 387

floo r, for engines and turbines . . 332

steam nozz les 278

Arrangement o f condensers 3370 34 1

for Curtis turbine 337

for Parsons turbine 339

Balance pistons . 14 6 , 1 55

Balancing high-speed bod ies 307

cylinders 309

locating heavy s ide . 309

static 308

B lades , s ee vanes .

B low ers , turbine-dr iven .

Br itish-Wes tinghouse turbine,B row n-Doveri turbineBrow nlee ’ s exper iments on flow o f

s teamBuckets , s ee vanes .

By -pass 1 52

Care and management of turbines 3 58

condens ing apparatus . . 360, 363 , 369

Carmania , turbines of 398

compared w i th Coronia 400

Cavitation 405

Chart for pow er uni ts 193

ad iabatic expans ionvelocity o f flow

energy o f flow .

condensation dur inglo ss of superheat du ring

Commercial aspect o f the

Compar ison of tu rbines and enginesadvantages of 329 ,

209

cal cu lations for 1 76

care o f 358

cos t o f 342

economy o f 196 , 329

under variable loadsw ith overload s 209

field o f 327, 328

floor area fo r 3 32

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

O O O O O O O O O O O O O O O O O O O O

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

O O O O O O O O O O O O O O O O O O O O O O

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Comparison o f turbines and enginesmaintenance of

marineCompos i tion of bladesCompound turbine, principle of

Condens ing surface, area of

Coo l ing w ater, quantity of

Condensers and auxil iariesAlberger

arrangement o f

for Curtis turbinefor Parsons turbine

calcu lations on

care of

co s t of

inj ector and j et

l is t of auxiliar iesm ar inepow er for

space requ ired fo r

surfacev s . jet

underneath turbineWheelerWorthington

Convers ion of pow er unitsCo s t o f engines , turbines , etc

maintenance and operationCr i tical pressure

speed o f ro tating bod iesCurti s tu rbine

care and operat ion of 365-369

condensers fo r 337, 377, 378

description -128

governor 128

patents 58-6 1

pr inciple 1 7 58, 1 14

ro tat ive speed 1 1 5

sectional view 1 1 5 1 17

smal l s izes 124

steam pressu res and velocitiesin

stages of

s tep bearingtes ts on

valve gear , electric typehydrau l icmechanical ly Operated

vanes , constructiond iagram for

414 INDEXcurt is turb ine

vertical typeDe Laval

care of .

gearsgovernornozz leso i l ingp atents on

sectional viewspeedsspecial app lications of.

tes ts on

Des ign . no tes on

example 1n

temperature-entropy d iagram ap

plied to

o f s teamarea of

d ivergingfrict ional

of

Deterioration of

Dimens ions o f

of

Dow

Dreadnought , turbine bat tleship .

Economy o f engines ,bes tin commercialin s treet rai lw ayunder variablew i th varying

Economy of smal l engines and tu r

bines 197

Economy o f turb ines , 192

miscel laneous tables . . 183-192

under difi erent 2 16

under heavy 2 10

w i th d ifferentEffi ciency of engine-type gener

ators

hydrau l ics teamsteam O

thermal unit bas isturbinestu rbinevanes o o o o o o o o o o o o o o o o o o o o o

highElectr icEnergy o f a jet .

see charts in append ix .

Enlargement of

Entropyof saturatedof superheatedof

Ero s ion o f b ladescause of

in De Laval turbinesin Parsons turbines

exper ience w i th Westinghouseturb ines

in Curt i s turbines .

Exper iments w i th nozz les ; see flow

o f s team .

u pon vanesupon tubes and channels

F loor area fo r engines and tur

b inescomparison of 500 Kw . uni ts

F low of steam :

calcu lat ions on 266-276

saturated 266

superheated 272

condensation during 260 267 270

expans ion incomplete 269

carr ied t oo

exper iments on .

Napier ’ s ru les for 2 17

pressu re at w hich superheateds team lo ses superheat 273

principles o f 9-1 1 , 2 18, 2 19, 225

shape o f j ets 9

s imp lified formu la for 269

thro ugh cylindrical nozz les ,B row n lee

Kunhardt

KneassGu termu th

through converging nozz les ,Rateau

Gu termu ththrough d iverging n o z z l e s ,

KneassRo senhainGu termu thLucke

through orifice in flat p late,Rateau 236

Ro senhain 228

w eight o f steam flow ing, 2 17 238 27 1

Fr ict ion of s team engines 179

lo sses in nozz les 281

Gears , data upon De Laval 74

Generators , effi ciency of 1 77

encased 148 330

Glands , w ater-packed 140

Governors , turbineDe Laval 75Hamilton-Ho lzw arth 1 12

Zoel ly 107

Curtis 128

Greissm ann’

s tests on specific heat 263

Grind ley’s tests on specific heat . 263


416 INDEXOperation of turbines

condens ing apparatu s . . 360, 363 , 367

d irections by engineers 364 , 366

general care 362 , 364 , 365

d irections 359

no tes o f exper ience 369

o i l ing sys tem 368 365 , 362

Operating Curt is turbine 365

De Laval turbine 36 1

Parsons turbine 363

synchroniz ing 368, 369

w arming up 3 58, 3 59, 368

Or ifice in thin plate, effect uponjet 12

Orrok’

s formu las for specific 263

Overloads , effec t on turbine economy , 2 10Parsons turbines . 1 35-1 58

care and operat ion 3 59 , 3 63 , 364

condenser arrangements for339, 380, 382

co s t of 343

d imensions of 335

his tory 135

patents on 36 , 42 , 43 , 54 , 144

pr inciples o f 20, 136

tests on 185 , 189 , 190, 2 10-2 12

vanes , d iagrams for 294

Patents , ear ly s team turbine 22

Altham 4 5

Babbitt 4 1

B o l lmann 62

B reguet 48

Curtis 58-6 1

Cu t ler 39

De Ferrant i 5 5

De Laval 4 1 , 4 7

Delonchan t 3 1

Dow 4 6

Fo ster and Avery 24Hartman 34Hoehl , Brakel l and 36Imray 40

Kerr 93

Las t 42

Leroy 25

Levin 9 1

M cEl roy 5 1

35

M oorhouse 3 7

Parsons 36 , 42 , 4 3 , 54

Perrigau l t and Farco t 36

Pil b row 2 7

RateauReal and Pichon 23

Richards 90

Seger 49

Tou rnaire 32

\Vi lson 29

-102

96

81

187

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Patents , ear ly steam turbineVOn

Zoel ly

Pel ton type, turbines of 80-94

Kerr turbine 93

Levin ’

s experimental w heel 92

Rateau 81

Richards ’ des ign 90

Ried ler-S tumpf 8 1

Zoel ly 88

Performance, thermal uni t bas is of 181

of engines and turb ines ; see

economy of.

Plant , enlargement of

Pressure, atmo sphericabso lu tecr i tical

in throat of nozz les , 220 22 1 224 , 227

specific 250

Pumps , turbine-driven . 77

Reaction o f jets , how measured 228

Rateau tu rbinesmu l ticel lu larpatents on

s imple impu lsetes t on

Reaction turbinesd istingu ished from impu lseshape of vanes

Reduction of ro tat ive speedin Curtis turbine .

in reaction turbinein Riedler-Stump f systems ee also patents o f Pilb row , Wi l

son ,Hartmann , M oorhouse,B reguet and Ferrant i , Chapt erII.

Relative velocitycal cu lation o f

Ried ler-Stump f turbines129

patent s on 83

pr inciple o f 1 7

s imple impu lse 8 1

Ro senhain’

s tes ts on fl ow of s team 228

Ro tation at high speed . 305

balancing for 307

s tresses cau sed by . 3 10

Seger tu rbine 49

Space for condens ing apparatu s 337

Space o ccupied by engines and tur

binesSp ec inc heat

of superheated s teams ee tes ts on

Specific pressurevo lume

INDEXSpecific pressure

o f superheated steam . 265

o f w et steam 252

Speed o f tu rbines , effect on economy , 2 1 6Curtis turbines . 120 , 124

De Laval turbines 70

s ee reduction o f rotative.

Stage tu rbines , definition o f 19

Curtis 1 14

Steam , flow of 9 , 2 17-246 , 266-276

generation o f 250

saturated 250

superheated 250

specific vo lume o f 265

total heat o i . . 252

w et , heat in 2 5 1

specific vo lume of 252

Steam accumu lator system o f Rateau , 1 66

S team enginesadvantages o f .

compared w i th steam turbines7, 8, 1 76 196 , 205 , 206 , 209 , 329 , 342

co s t o f 343

d imens ions o f 336

field of 328

frict ion tes ts o f 1 79

leakage in . 3 52

mechanical efl‘ic iency of

perform ance of, average 194

best 194

how turbines improve upon . 209

in street rai lw ay plants 209

under var iable loads 204

w i th varying superheat 195

Steam tu rbinesadvantages of

co s tcommercial aspect o f

compared w ith s team engines ,7, 8, 1 76 , 196 , 205 , 206, 209 , 329 , 342

w ater turbines . 6

compound impu lse 1 6 , 95 , 1 13

compound reaction 2 1 , 135

description o f

1 32

Al l is -Chalmers 1 53

Avery 24

B ri tish-Wes tinghouse 160

B row n-Boveri 1 50

Curtis 17, 58, 1 1 3

De Laval 1 7 4 1 4 7 , 67Hamilton-Ho lzw arth 109

Kerr 93

Lindm ark 162

m u lticel lu lar 95

Parsons 20, 36 , 42 , 43 , 54 , 1 35

Rateau 81 , 95

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0

O O O O O O O O O O O O O O O O O O O O O O O

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0

O O O O O O O O O O O O O O O

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0

O O O O O O O O O O O O O O O O

O O O O O O O O O O O O O

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0

0 0 0 0 0 0 0

0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

O O O O O O O O O O O O O O O O O O O O O O O

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

4 17

S team turbinesRied ler-Stumpf 81 , 129

Seger 49

s tage 19 95 1 14

Su lzer B ro s 160

Wes tinghouse 13 7

Zoel ly 102

deter io ration o f 352

d imens ions of 335

electr ic generating , fo r 327, 330

field o f 327

l imitations o f 327

principles o f

s imple impu lse 16 , 6 7 , 80

troubles o f 346

danger from w ater 349

d istortion o f cas ing 349

eros ion of blades 3 52

minor d iffi cu l ties 34 7

str ipping the blades 3 50

S tep bear ing of Cu rti s turbine 123

Stresses in ro tat ing bod ies 3 10

in ro tating ring 3 1 1

in ro tating d isk 3 12

Su lzer B ro thers turbine 1 6 1

Superheated steam 250

engine operating w i th 195

specific heat o f 26 1

Specific vo lume of 26 5

velocity o f flow 273-275

to tal heat o f 252

S urface condens ing plants 375

Taper of De Laval no zz les 7 1, 230

mo s t efficient nozz lesTemperatu re-entropy d iagram 2 5 3

for finding condensation 260

show ing reévap orat ion 322

fo r stage tu rbine 320

fo r superheated steam 2 59

fo r w ater and s team 2 5 7

Temperature , reference po ints of 24 7

abso lu te 248

convers ion of Fahr . to Cent 248

of steam in expand ing nozz leTests on channels and tubes 302

condensers 388 392

generators 1 77

nozz les ; s ee flo w of s team .

specific heat o f superheatedsteam

Regnau l t 26 1

Greis smann 263

Grind ley 263

Knoblauch , Linde and Klebe , 26 3

turbine boats 393 400 403

vanes 297

Tests on enginesaverage resu lts

418 INDEXTes ts on engines

bestfrictionin commercialin s treet rai lw ay p lantsunder varIab le loadsw i th varying superheat

Tes ts on tu rbinesat d ifferent speeds 2 16

best 192

under heavy overload s 2 10

w i th d ifferent vacuums 2 1 1 2 12

Cu rt is , 500 Kw . at Cork 188

at 190

De Laval , at d ifferent 183

30H. P 183

300H. P 184

Parsons , miscel laneou s 185

non-condens ing 186

Rateau 187

West inghouse-Parsons , 400 Kw . 189

Kw 190

Zoel ly 187

Thermal uni t , defin ition o f 249

bas is o f performance 181

T hru st , end , in Parsons turbine . 137

in mu l ticel lu lar turb ines . 102

To tal heat . 2 5 1

of superheated s team 252

Tu rbine ves sel s i-405

Carmania 398

Dreadnought 394

King Edw ard 392

Lusi tania 400

Turbinia,etc 392

Vacuum :

effect on engine economy 37 1

on turbine economy . . 372 , 2 1 1 , 2 12

gain from high 373

how measured 248

Vacuum augmenter, Parsons 382

"alve, secondary admiss ion . . 14 3 , 1 50, 1 52

anes

angles of 287, 290-292 , 295

compo s i tion o f 3 5 7

Curti s tu rb ine 12 1

De Laval turb ine 72

d iagram s fo r 284

compound impu lse turbines . 283

fr ict ional al low ance 294

high effi ciency 287

Pel ton w heel . 29 1

react ion 294

symmetrical 290

ero s ion of . 352

exper imental 299

gu ide , s ee gu ide vanes .

Vanesimpu lse and reaction upon 4

Kerr ’ s 93

Rateau , Pel ton type 52

regu lar type . 97

Richards ’ des i gn . 88

shape of 1 5

tes ts upon . 297

Wes t inghouse 138

Z o el ly 89

Variab le loads , characteris tics under , 198

s team-rate cu rve for Parsons t urb ine

RateauCurtis turbineDe Laval turb ine

Veloci ty o f s team flow ingcal cu lat ion 266 , 269

fo r superheated s team 272-275

exper iments on, KneassRo senhain 233-235

s ee charts in append ix .

Vo lume , specific 249

o f superheated s team 26 5

o f w et 252

Westinghouse-Parsons turb ines . 1 3 7

bear ings 139

care and Operation of. . 3 59 , 363 , 364

condenser arrangement . . 339, 380, 382

governing arrangement 14 1

ind i cator d iagram 1 42

lubrication 1 4 1 365

secondary admission valve 1 43

separate high and low -pressurecyl inders 148

sectional view 146

tests on 189 , 190, 2 10-2 12, 2 16

w ater-packed glands . 140

w i th encased generator 148

vanes , constru ction of 1 38

d iagram fo r 294

Weigh t o f steam d ischargedNapier ’ s ru les for 2 1 7

calcu lat ion o f 71

o r ifice in flat plate 232, 239

cy hndrical nozz les . 220, 24 1

converging nozz les . . 232 237, 24 1 , 242

d ivergin g nozz les 232 , 24 1 , 242

W il lans and Robinson turbine 1 58

Zo el ly tu rbine :tes ts on

patents on

Pel ton type, vanes o f

mu l ticel lu largu ides and vanesw heels and d isksgovernor

sectional view


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