Steam Heating Application

7/27/2019 Steam Heating Application

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TECHNICAL MANUALTES-375A

Bell & GossettDomestic PumpsHoffman SpecialtyMcDonnell & Miller

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Steam HeatingApplication Manual


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S T E A M H E A T I N G S Y S T E M S

CHAPTER 1 - - - BASICS OF STEAM HEATING

O p e r a t i n g PrinciplesThe thermodynamic propert ies of stearn make i t an excel lent medium

for the t ransfer of heat from a source to a point of use.Where stearn is used for space heating, a boi le r is used as a source

of heat . The boiler generates stearn which is del ivered to the heating units byappropria te piping sys tems. There are a number of piping sys tems in use andthe s imples t of these, a one-pipe sys tem, is shown in Figure 1. This sys temwil l be used to descr ibe the principles involved in the operat ion of stearn heatingsys tems.

,.......MAIN VENT

' r - - - - - - - - - . r ~ L ~ o ~ w ~ ~ ~ ~ - ~ - - - - - - - - - r - - - - , ~ ~ - - - - - - - - - - - - - - - riSA.FETYF A C T O ~

BOILER

r2 L 5 T A ' I C AfTOTALPRESSUREDROP_L____ _

~ I ~ E A OE_ J 1P R E S ~ U R . E D ~ O P _O F S Y 5 T E , . ,1=.-. _ ...l.___ _

~ S O \ L E R WA.TER LINE

. - - - -- -- ----- - -, ; . -. : - - - - - ~

Pre s s u re Drop in a One-Pipe Stearn SystemFigure 1.

Fig. 8

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Before being placed in operat ion, the system is fi l led with wate r tothe boi le r wate r l ine. This water level will be the same in the boiler and thever t ica l leg of the re turn l ine before the boiler begins s teaming. The stearnspace of the boi le r and the system will be fi l led with a ir and addit ional a ir willbe driven out of the boiler water when i t is heated. This a ir in te r fe res with theflow of stearn to the radiators .

of thetern.them.

Thermosta t ic a ir vent valves are placed at each radiator and the endsupply main to allow the a ir to be purged by the stearn as i t fills the sys -These vents a re normally open and close of f as the hot stearn reaches

Stearn enters the radiators and condenses as i t gives up i ts hea t tothe spaces in which they are insta l led. This condensate re turns to the supplymain by means of the same pipe supplying stearn to the rad ia tors . In the sys -tem being descr ibed , stearn and accumulated condensate flow in the same direc-t ion down the supply main to i ts end. Here i t drains into the ver t ica l leg of there turn main .

The point of highest pressu re in a stearn system is a t the boiler ,where stearn is being generated. The pressure in the sys tem rad ia tors tendsto drop as the stearn they contain condenses . It is this pressu re differentialwhich causes the stearn to flow from the boi le r to the rad ia tors .

Stearn will flow through the system a t a ra te depending upon the press -ure differential exis t ing between the boi le r and the end of the stearn piping. Thisavailable pressu re difference wil l be used up in overcoming the friction of thestearn moving through the piping. This is cal led the sys tem pressu re drop.

The condensate moving through the re turn piping toward the boiler a l-so encounters piping pressu re drop and energy mus t be made available to movethis l iquid.

The energy requi red to overcome these pressu re drops i s providedby the stearn pressu re generated by the boiler . The pressu re in the stearn spacewil l be higher than that a t the end of the stearn piping by an amount equal to thetotal sys tem pressu re drop.

Reference to Figure 1 will show how this affects the re la t ive waterlevels in the boiler and in the ver t ica l leg of the sys tem re turn piping. Thehigher pressure in the boi le r causes the water to r ise in this pipe, which isexposed to the lower pre ssure exist ing a t the end of the sys tem. The wate rcolumn will r i se unti l i ts weight jus t offsets the exist ing pre ssure dif ferencebetween the s e tw o points .

2

As the drawing shows, the head provided by the height of this columnconsis ts of the stearn system pressure drop and the sta t ic head needed to over -come the pressu re drop in the condensate re turn l ine.


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Header .

Stearn SupplyMain

Risers

Heating Units

4

valve protec ts the boi ler f rom damage should exces s -ive pressu res occur . The burner is operated f rom apressu res t a t se t to open i ts contacts at a specifiedpressu re .A low water cut-off wired in ser ies with the burnercontrol shuts down the burner should the boi ler wate rlevel drop to i ts cut-out sett ing.Stearn heat ing boi lers are usual ly of the lo w pres suretype, with maximum working pressu res to 15 psig .They are selected on the bas is of the i r net rat ings, int e rms of thousands of Brit ish Therm al Units per hour .Larger boilers a re somet imes ra ted in t e r ms of horse -power, with 33,475 BTUH being equal to one horse -power.I t has also been common pract ice to rate stearn boi lersin t e rms of the amount of radiation which they willse rve . Stearn radiation is ra ted on the bas is of squarefeet of equivalent radia t ion (abbreviated EDR), with 1sq. ft. being equal to 240 BTUH.

Boi lers , depending upon the i r size, have one o r moreoutlet tappings. The ver t ica l stearn piping f rom thetapped outlet joins a horizonta l pipe called a "Header" .The stearn supply mains are connected to this header .

The stearn supply main car r ie s stearn f rom the headerto the radiators connected along i ts length. In the caseof one-pipe sys tems , it also car r ies the condensatef rom these units back to the dr ip connection. When thecondensate flow in the supply main is in the same di r -ection as the stearn flow, as i l lustrated, the system iscalled a para l le l flow sys tem .

The ver t ica l pipe carrying stearn to the radiator f romthe supply main i s called a r i se r . In the case of theone-pipe sys tem in the i l lustrat ion, the r i se r alsodrains condensate f rom the radiator back to the supplymain. In one-pipe sys tems , the horizonta l run-outsconnecting the main to the r i s e r m ust be pi tched up tothe radia tor to make this drainage possible .

As shown in Figure 4, stearn sys tems use convectors ,cas t i ron rad ia tors , wal l fin tube and s imi lar heat output units .


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Drip Connections

Dry Return

Wet Return

Hart ford Loop

A ir Vents

Radiator Valves

Where piping car r ies both s team and condensate, i tis often desirable to drain off the condensate at var -ious points to expedite s team flow. This condensateis drained off to a re turn l ine by a connection calleda "drip". F o r example, in Figure 2, the s team supplymain is dripped into the dry re turn, which in turn isdr ipped into the wet re turn.

The dry re turn is that port ion of the re turn main locat-ed above the boi ler water level .

The wet re turn is that por t ion of the re turn main located below the boi ler water level . It is always completely fi l led with water and does not car ry a i r or steam asdoes the dry re turn.

This is a plplng arrangement de signed to prevent complete drainage of the boiler should a leak develop inthe wet re turn . The wet re turn is connected to anequalizing l ine between the supply and re turn opening ofthe boi ler . This connection is made about 2" below thenormal water level of the boi ler .Should a leak develop in the wet re turn, the boi ler waterlevel wil l drop a maximum of 2". This keeps the heatt ransfer surfaces of the boi ler immer sed in water , pre-venting the damage that could occur with the f ir ing of adry boi le r . (Refer to Figure 2.)

Steam cannot circulate or radiators heat unti l a ir hasbeen vented f rom the sys tem. Thermostat ic a ir vents ,some of which a re pictured in Figure 5, mus t be in s ta l led on each radia tor and at the end of each s teammain .

The s team supply to the sys tem radiators is control ledby a radiator valve. Each radiator mus t be equippedwith an angle pat te rn radia tor supply valve of the typeshown in Figure 6.

The t ,erms discus sed in this sect ion a re those needed in or de r tounderstand the operat ion of simple, one-pipe s team heating sys tems. Theset e rms will be elaborated upon in the sections dealing with other system types.

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SUPPLY VALVE _ /'THERMOSTATIC

SUPPLY M A I ~ } TRAPHEADER_______ r - - - - - ~ ~ - - - - - - - - ~ ! - - - - - - - - - - - - ~

JMAIN V E N T ~ F& T TRAP--

6

-rr - L DRY RETU;NA I---+--4---* * Iof : -WATER LINEOILER'}-CLOSE I

I NIPPLEIL __ ,j

~ " - - WET RETURNHARTFORD LOOPOne-Pipe Para l le l Return System

Figure 2.

---:7"""----+- R'e.L\EP VA\'VE

L..OWWATER.CuT-OFF

Stearn Boiler ControlsFigure 3.


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RadiationtearnFigure 4 .

. t r Ventsadla O I . L _ ~ __

Typical

Figure 5.

ly Valvetearn SuppFigure 6.

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CHAPTER 2 - - - STEAM SYSTEM TYPESSteam. heating piping system.s a re classified by the m.anner in which

the steam. and condensate i s handled. One-pipe system.s use com.m.on pipingfor both. Two-pipe system.s use separate piping fo r the steam. and condensate.There are varia t ions of each of these system. types which will be explained inthis section.

ONE - P I P E SYSTEMSOne-pipe system.s of the type jus t discussed which re turn condensate

direct ly to the boiler are called Gravi ty Return System.s. Where the re is in sufficient height tom.aintain dim.ension "A" at i ts prescr ibed m.inim.um., m.echanical m.eans m.ust be provided to return the condensate. In the l a t ter event, acondensate pum.p is used for this purpose.

An im.portant factor in the operat ion of one-pipe system.s is the pitchof the steam. supply and dry return m.ains. They m.ust be pitched a t l eas t oneinch in 20 feet in the direct ion of condensate flow. No pitch is required for wetre turns . The following exam.ples describe the various one-pipe system. types.

Cou n t e r - F l ow Sy s t em .This system. is shown in Figure 7. The condensate flows in a direct ion

opposite to that of the steam.. Because of this , the m.ain m.ust have a pi tch upwards and away from. the boiler of a t l eas t one inch in 10 feet .

One-Pipe Counter-Flow System.Figure 7.

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The stearn main must be one size l a rger than that which would beused for other types of one-pipe sys tems . Dimension IIAI! mus t be of sufficient height to return condensate to the boiler as previously discussed. Theuse of this system type is usually confined to small res identia l sys tems .

P a r a I l e 1 F 1 ow S y s t e mThis is the system discussed in Chapter 1. Stearn and condensate

flow in the same direct ion in the horizontal stearn and return mains . Figure8 shows this system with a wet re turn from the end of the stearn main andFigure 9 shows a dry re turn from this point. In ei ther case , dimension IIAIImus t be sufficient to provide for gravity re turn of the condensate. This systemis used in l a rge r buildings of single level construction.

PITCH liNCH IN 20 FEEl AI- ~ - - . - . - . - - - - - 4 -ATER LINE I _HARTFORD LOOP I

L . e _ E ~ ~ N _ . _____ --1

One-Pipe Para l l e l Flow SystemWet Return

Figure 8.

A --- ~ - - ------~ W A T E R L I N EIf HARTFORD LOOPWET RETURN

One-Pipe Paral le l Flow SystemD ry Return

Figure 9.9


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Parallel F l o w U p f e e d Sys te IT lThis systeITl type is insta l led in ITlulti- s tory buildings. SteaITl is

distr ibuted upwards froITl a baseITlent supply ITlain. This ITlain pitches downfroITl the boiler and i ts end is dr ipped to the wet re turn. See Figure 10 .

HARTFORDRETURNCONNECTION

DRAIN COCK

SUPPLY VALVE

One-Pipe Paral le l Flow Upfeed SysteITlFigure 10 .

SteaITl is led to the radia tors by upfeed r i se r s , which also drain offcondensate. Note that the heel of each r i se r is dripped into the w et re turn,which re l ieves the supply ITlain of the condensate froITl the radiat ion suppliedby the r i ser .

The upfeed branch connections to the f i r s t f loor rad ia tors are notindividually dr ipped, discharging the i r condensate direct ly into the steaITlsupply ITlain. This condensate is dUITlped into the wet return by the drip connection a t the end of the supply ITlain.

Parallel F l o w D o w n f e e d Sys te IT lWhen a one-pipe systeITl distribution ITlain is overhead, such as in a

ceil ing or attic space, i t is known as a downfeed systeITl. The downfeed r i se r shave steaITl and condensate flowing in the saITle direct ion, as shown in Figure 11.

To insure good condensate drainage, all downfeed r i sers should betaken off the bottoITl of the supply ITlain. The ITlain vent ITlay be insta l led at theend of the supply ITlain or on the downfeed r i se r s below the f i r s t f loor as anoptional location. When installed on the r i se r s , the vents ITlust be insta l led sothat diITlension "A" is sufficient to prevent water froITl enter ing theITl. Thesevents have integral f loats which will close off the vent should water en te r theITl.

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SUPPLY MAIN AIR VENT

One-Pipe Paral le l Flow Downfeed SystemFigure 11.

M e c h a n ic a l C o n d e n s a t e R e t u r n S y s te m sWhere the re is insufficient available height to maintain dimension

"A" at the proper level, the use of a condensate pump becomes necessary .This device consis ts of a reservoi r open to a tmosphere into which

the re turn line discharges i ts condensate. A centr i fugal pump is a lso a par tof this device. This pump discharges condensate from the rece iver into theboiler . A float operated switch in the rece iver cycles the pump to re turn thewater to the boiler as it accumula tes at this point .

Figure 12 shows a condensate pump during the operating cycle. Thefloat has tr ipped the pump switch and the pump is discharging through a checkvalve into the boiler . When the condensate level in the rece iver drops to thecut-off level of the float switch, the pump s tops . Boi ler pressure causes thecheck valve to close, prevent ing backing up of boiler water into the rece iver ,as shown in Figure 13. A gate valve is provided in the condensate pump dis -charge line to pe r mi t servicing the pump without draining the boi le r .

Condensate Pump - - Pump onFigure 12.

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ECEIVER

Condensate Pump - - Pump OffFigure 13.

A one-pipe pumped return system appears in Figure 14. Note thatthe end of the stearn supply main is fitted with a float and thermosta t ic t rap .This t rap allows a ir and condensate to leave the main at this point but preventsthe loss of stearn. The outlet of this !IF" and IITII t rap is connected to the re -ceiver to permi t gravity drainage of condensate to take place. The connectingpipe is called a Ilno pressu re return ll because of this gravity flow.

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HOFFMAN VENT VALVE

_____ --I - -LBOILER WATER LINE i

~ ~ S _ ~ ~ ~ ~ ~ N ~ iCONDENSATE PUMP ""1

One -Pipe System with Condensate PumpFigure 14.


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The ITlanner in which an "F" and "T " t rap perforITls its function isi l lustrated in Figure 15. Air , steaITl and water enter the body of the t r ap .The norITlally open therITlostatic a ir vent allows a ir to pass but, closes offwhen hot steaITl reaches i t . The f loat-operated valve ITlodulates to allow condensate to dra in off as i t ente r s the t rap body. In this ITlanner, both a ir andcondensate froITl the systeITl a re discharged to the rece iver

\N.\.&.T

OU"L.I.T

Float and TherITlostatic TrapFigure 15.

T W O - P I P E S Y S T E M STwo-pipe systeITls differ froITl one-pipe systeITls in that the steaITl

and condensate are ca r r i ed in separate l ines. The steaITl l ines supply steaITlto the radiators , which discharge the i r a ir and condensate to the re turn l ines.Traps a re used a t each radiator and a t the end of each supply ITlain to preventthe entry of steaITl to the re turn l ines .

G r a v i t y R e t u rn S ys t e I T l sA two-pipe gravity re turn systeITl is pictured in Figure 16. SteaITl

enters the radiator froITl the supply r i se r , pushing a ir out the re turn openingthrough a therITlostatic t r ap . These t raps differ frOITl the "F " and "T " typein that they are s tr ic t ly therITlostatic in their operat ion. These t raps a renorITlally open as shown in Figure 17 . A ir o r condensate can pass throughthe t rap f reely . Should steaITl begin passing through i t , the operat ing bellowsor diaphragITl asseITlbly expands , closing off the t r ap . The t rap at the top ofthe i l lustrat ion is a bellows type. The other is a balanced pressu re diaphragITltype. Its therITlal eleITlent consis ts of diaphragITls arranged to forITl connectingcel ls which expand in the saITle ITlanner as does a bellows.

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SUPPLY VALVE _ /~ T H E R M O S T A T I C

SUPPLY M A I ~ l TRAPHEADER_______ r - - - - - ~ ~ - - - - - - - - ~ ! ~ - - - - - - - - - - ~jMAIN V E N T ~ F& T TRAP--

14

-rr -L DRYRETU;NA f_ _-+_ _4 - __ - * Iof : -WATER LINEOILER

~ C L O S E I: N IPPLE IL--,j~ " - - WET RETURNHARTFORD LOOP

Two -Pipe G ravi ty Return Syste:mFigure 16.

Typical Ther:mostatic TrapsFigure 17.


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During norma l system operation, condensate f rom the system drainsf rom the var ious t raps to the wet re turn, while the main vent discharges accumulated ai r . Dimension "A" mus t be grea t enough to provide the gravi ty headneeded to re turn condensate to the boiler . A water column 28" in height is re quired to re turn condensate agains t a boiler pressure of 1 psi , which l imi t sgravity re turn sys tems to operat ing pressu res between 1/2 to 1 psig in mos tcases .

M e c h a n ic a l C o n d e n s a t e R e t u r n S y s te m sInstal lat ions having insufficient elevation of the dry re turn over the

boiler water l ine to provide gravity condensate re turn mus t be equipped with acondensate re turn pump.

A two-pipe upfeed sys tem of this type is i l lustrated in Figure 19.Thermostat ic t r aps a t each radiator and the IIF" & "T" t rap a t the end o f thestearn supply main discharge a ir and condensate to the rece iver through the nopressure re turn .

~~ - " ,

IIIIIII,II

I

""__ III- - - - - - - - - - -----J

Two-Pipe, Upfeed System with Condensate PumpFigure 19.

Where two-pipe downfeed sys tems are used, i t is necessary to dripthe ends of the supply r i se r s to the no pressu re re turn as shown in F igure 20.Condensate accumula tes a t these points and m u s t be drained off. A ir m u s t bevented to insure stearn flow. "F " & "T " t r aps a re recommended for this appl i cat ion because of the i r abil i ty to quickly discharge a ir and condensate.

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-nCHI"'lllQfE(T

OIIITPOCUT

Two-Pipe, Downfeed System. with Condensate Pum.pFigure 20.

Vacuum. Sy s t em . sWhen two-pipe system.s becom.e la rge and involve the use of long

plplng runs, la rge vo1um.es of air a re presen t . I f this air is not quickly expelled, i t interferes with steam. flow to the radiators . The resul t is slowwarm.-up and sluggish re turn of the condensate to the boiler .

The boi ler water level will fal l due to lack of condensate return,causing the m.ake-up water feeder to begin supplying addit ional water . As thesystem. warm.s up, the norm.a1 ra te of condensate return will be establ ishedand this can cause flooding of the boi ler steam. space.

One m.ethod used to overcom.e this steam. distribution problem. andi t s adverse condensate return effect is to use a vacuum. pum.p for the quickelim.ination of a ir from. the system.. These pum.ps are de signed specificallyfor steam. heating system.s. They a re ra ted to handle a definite quanti ty of a i rat an average vacuum. of 5-1/2" Hg with a condensate tem.perature of 1600 F .prevailing. The pum.p is norm.ally controlled to cut in a t 3" Hg and a t out a t8" Hg

Figure 21 shows a vacuum. pum.p installed on a two-pipe downfeedsystem.. The pum.p acts to keep a vacuum. on the system. re turn l ines and alsoto return accum.u1ated condensate to the boiler . During the steam.ing cycle,the pressure in the steam. m.ains and radia tors will be higher than that in thereturn m.ains, allowing good condensate drainage.

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IIIIIIIIh

BREAKER IiI~ = = = = ~ I IJ

- THERMOSTATIC TRAP

STR'I'ERf ' T TRAP

Typical Two-Pipe Vacuum SystemFigure 21.

On the boiler off cycle, the stearn condensing in the supply side ofthe system can cause a vacuum to fo rm. This vacuum can be higher than the

re turn l ine vacuum, prevent ing condensate f rom flowing to the pump. Anequalizing l ine between the vacuum pump and the stearn supply l ine allows thesys tem pre s sure to equalize should this take place .

As shown in Figure 21, this equalizing l ine is taken off the overflowstand pipe of the vacuum pump. A check valve in the dra in from this l ine pre-vents loss of vacuum during the operating cycle. A check valve in the vacuumpump equal izer l ine is closed as long as the stearn side pres sure is greaterthan the return pressure . Should the stearn side pressu re drop below the re -turn l ine pressu re , this valve will open and allow these pressu res to equalize.

The vacuum switch which actuates the pump senses the pressu re a tthe end of the vacuum re turn as shown in the drawing. The operation of thepump will be adversely affected i f the induced vacuum is pulled to too I o w alevel. A vacuum breaker , usual ly se t to open at about 15 11 Hg , is ins ta l led a tthe inlet of the vacuum pump. This will open and admit a ir should the vacuumdrop below i ts sett ing.

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CHAPTER 3 - - - STEAM SYSTEM COMPONENTSSOITle of the cOITlponents used in steaITl heating systeITls have already

been discussed in explaining systeITl types . A ITlore detai led explanation ofthese and other systeITl cOITlponents wil l be given in this Chapter .

Ra d i a t o r Su p p l y Va l v e sThe choice of radia tor supply valves for a systeITl is governed by the

systeITl type involved.

On e - P i p e Sys t e IT l sSteaITl ITlust ente r and condensate leave the radiator through a COITlITlon

por t . The valve ITlust therefore be installed at the bottoITl of the radiator andhave a por t la rge enough to accept both f lows. The valve cannot be throt t led asthis would r es t r i c t condensate drainage. I t ITlust either be wide open or closed.

A typical valve for one-pipe systeITls is shown in Figure 22. This isan angle type valve. Straightway pattern valves cannot be used for one-pipesysteITls because they do not perITlit adequate two-way flow of the steaITl and condensate. The steITl of the valve i l lus tra ted is of the packing type. These valvesare also furnished in the packles s type, seaied with a bellows or diaphragITl.

Two - P i p e Sys t e IT l s

Radiator Supply ValvePacked SteITl Type

Figure 22.

Radiator supply valves for two-pipe systeITls ITlay be angle type ors t raightway. They a re available as ITlodulating valves as well as the ord inaryshut-off type. 19


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20

Figure 23 i l lus tra tes a packless type valve, applicable to ei therone or two-pipe sys tems . This type is especial ly desirable on vacuum re turnsys tems , since there is no possibili ty of a ir leakage pas t the s tem. Thisvalve uses a diaphragm s tem sea l . The valve i l lus tra ted in Figure 22 may a lso be used on two-pipe sys tems .

V E N T V A L V E S

HANDLE - - - - : : __-=t:w--

DIAPHRAGM

LEVERS; PLUI\.GERS,AND ~ i t - - - ; : : : i : t : L J J L ,STEM ASSEMBLy

Radiator Supply ValvePackless Type

Figure 23.

CJ

These valves , used for the el iminat ion of a ir from one-pipe s teamsys tems , are classif ied into two genera l types as follows.

R a d i a t o r V e n t V a l v e sThese valves are available in a wide range of a ir venting capaci t ies .

They are furnished in special construct ions depending upon whether they willbe used in non-vacuum sys tems .

F o r non-vacuum sys tems , the valves are of the "open" type. Theirventing ports are open to atmosphere unless e i ther wate r o r s team ente r the i rbodies, in which case the vents wil l close off. A typical open vent is shown inFigure 24. This vent operates in the same manner as the end of the main ventdiscussed in Chapter 2 and pictured in Figure 18. These vents are furnishedwith either non-adjus table or adjustable venting ra tes . The vent in Figure 24is of the adjus table type.

Large one-pipe sys tems often heat a t a very uneven ra te on s tar t -up .The f i r s t radiators off the main wil l vent the i r ai r f i r s t and hea t quickly, withthose a t the fa r end being the l as t to vent and heat . I f adjus table vents are us ed, the venting ra te of the f i r s t radiators can be se t lower than that of the fa rend radiators resulting in better heat dis t r ibut ion. Smal l sys tems , where thisis not a problem, m ay use vents with non-adjus table a ir ports .


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Adjustable Type Radiator VentFigure 24.

Vacuum type sys tems requi re vents which will not admit a ir if theradiator is under vacuum. They a re essential ly the same as the non-vacuumtype with one exception; they have a check valve in the vent port . Figure 25shows a vent of this type.

Adjustable Type Radiator VentF or Vacuum Systems

Figure 25.

The vent i l lus tra ted is of the adjustable type. Anyone of six ventingra tes is made available by rotating the disc containing the venting por ts unti lthe des i red por t is over the vent opening. A check valve in the vent por t closesoff i f a vacuum occurs in the radia tor . This prevents the entry of ai r . Thesevents a re also furnished without the adjustable venting feature.

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22

End o f Ma i n Ve n t sThe :major difference between these and radia tor vents is the vent-

ing ra te . End of :main vents have a :much la rger venting ra te than radia torvents .End of :main vents are furnished for either open or vacuu:m opera-

tion, the dif ference being in the check valve furnished with the vacuu:m vent.The construct ion of an open type vent was shown in Figure 18 and a vacuu:mtype is shown in Figure 26. This vent e:mploys a bellows to close off the porton stea:m entry but in other respects i ts operation is si:milar to that of thevent in Figure 18.

TRAPS

The r :mo s t a t i c T r a p s

CHECK

End of Main V enVacuu:m Type

Figure 26.

Ther:mostatic t raps are the :most co:m:mon of a ll types used in two-pipe stea:m heating syste:ms. The operating principle of this t rap was discus s -ed in Chapter 2 and two types a re pictured in Figure 17. Other ther:mal ele-:ments, such as a ser ies of diaphrag:ms or specia l ce l ls .:made for diaphrag:msare also used.

The te:mperature a t which a ther:mostat ic t rap will open is variablebut is always the required nu:mber of degrees below the sa tura ted te:mperaturefor the exist ing stea:m pressu re . In addit ion to being ins ta l led on radiators ,they a re used as dr ip t r aps and to handle condensate fro:m unit hea te r s .


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I t is necessary to use a cooling leg between the equipITlent or dripand the therITlostatic t rap . This is siITlply an adequate length of pipe to coolthe condensate sufficient ly to open the t rap and discharge the condensate.

TherITlostatic t r aps are provided in angle, straightway, swivel andver t ical patterns and ITlay be used on applicat ions froITl vaCUUITl to high press -ure steaITl.

F l o a t T r a p sFloat t raps a re used to discharge condensate at points where a ir is

not a probleITl. They are the saITle as an "F " & "T " t rap except that the ther -ITlostatic eleITlent is not provided. For exaITlple, i f the cover of the "F I & "T"t rap in Figure 15 were reITloved and replaced with a plain cover , the resu l twould be a float t r ap . The discharge froITl a float t rap is continuous as thefloat tends to throt t le the pin or valve in the seat por t .

In sOITle cas e s , a the rITlOstatic vent is instal led in a bypas s linearound the inlet and outlet of the valve body for venting air .

F l o a t and The r IT l o s t a t i c T r a p sThis t rap cOITlbines the features o f both types jus t discussed. The

operation of the valve was explained in Chapter 2. Since the condensate dis -charge of float and float and therITlostatic t raps depends entirely on float ac-t ion, a cooling leg is not requi red where they are used.

ifF" & "T" t raps a re widely used for dripping the end of steaITl ITlains,the heels of upfeed steaITl r i sers and the bottoITl of downfeed steaITl r i se r s . Theyare also excellent choices for handling the condensate froITl unit heaters , unitventi lators and coils which a re a par t of a ir handling systeITls.

I n v e r t e d Bu c k e t T r a p sThis t rap type is able to handle condensate at any teITlperature up to

the saturated teITlperature corresponding to the steaITl pressu re a t the t rap in -let. I t is used for cOITlITlercial applicat ions in the ITlediuITl to high pressu rerange. Typical applicat ions a re clearing steaITl distribution l ines of condensateand draining heat exchangers , unit heaters , cooking kett les , etc.

Figure 26 shows the operating principle involved. A bucket t rap ITlustbe priITled with water before being placed into operat ion. The bucket wi l l bedropped because of the a ir vent hole in i ts upper portion. With the bucket inthis posi t ion, the discharge por t of the valve is open and i t vents the a ir and con-densate entering the t rap . The a ir passes through the vent in the bucket on i tspath through the t rap .

23


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24

Inver ted Bucket TrapFigure 26.

VALVE. 5(ATVALVE PINLEvER

When the condensate has been cleared, stearn now enters the bucket .The stearn fi l ls the bucket , causing i t to r ise and close off the t rap dischargeport . The t rap will open again when condensate ente r s and condenses thestearn in the bucket .

The bucket now becomes buoyant and r ises , closing off the dischargeport of .the valve. Additional condensate entering the body of the t rap will nowcondense the stearn in the bucket, causing i t to drop and discharge the conden-sate . The bucket continues to r i se and fall in this fashion, discharging the con-densate as i t accumulates .

Since the discharge port of the bucket t rap is wide open during i tsventing cycle, i ts capacity for a given port size is greater than that of f loattype t raps which modulate the i r discharges.

Up r i g h t Bu c k e t T r a p sThese t raps have an upr ight bucket as shown in Figure 27. The

bucket f loats as condensate enters the valve body, closing the discharge port .As condensate continues to enter , i t wil l spi l l over the top of the f loat andcause i t to drop. The condensate then r ises up the discharge tube and is ex-pelled through the outlet . A ir a t the top of the t rap is expelled through thevent hole in the discharge tube.

The bucket regains i ts buoyancy when the condensate is dischargedand r ises , closing off the discharge port . This cycle continues as long as con-densate continues to enter the t r ap . Inverted bucket t raps do not require pr im-ing, as the bucket will r ise and close off the discharge por t a s soon as conden-sate enters the t rap.


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Upright Bucket TrapFigure 27.

T h e rm o d y n am i c T r a p sThe principle of this t rap is shown in Figure 28. Should a ir and

condensate be pas sing through the t rap, i t will flow to the t rap outlet in a pathdescr ibed by the direct ional ar rows . The flow f irs t passes through the outerheating chamber , then through a centra l por t and out passageways around thisport . A disc check valve, called the l lcontrolled disc lI , is opened as th is takesplace.

HEATING CHAMBER OUTLET PASSAGES

Thermodynamic TrapFigure 28.

Steam enters the t rap through the heating chamber, rais ing thetempera ture of the control chamber as i t does so. Steam leaving the orif iceat high velocity tends to lower the pressu re existing a t that point. Steam a l-so enters the control chamber behind the controlled disc. The area of the discon the control chamber side is greater than the disc area which covers the in -le t orif ice , causing the disc to close off due to the pressu re differential .

25


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26

Heat fro:m the stea:m a t the t rap inlet :maintains control cha:mberte:mperature and pressu re , keeping the control led disc in the closed postion.Should condensate enter the t r ap , the control cha:mber will be cooled and thepres sure of the stea:m holding the control led disc c losed wi ll now be lowerthan that at the inlet orifice and the control led disc wii1 be pushed open. Thet rap will continue discharging condensate unti l stea:m again reaches the inletorifice and causes the cycle to repeat .

C o n d e n s a t e P u : m p sThe construct ion and operat ional pr inciples of condensate re turn

pu:mps were d iscussed in Chapter 2. Figures 12 and 13 i l lus tra te this dis -cussion. The const ruct ion of these pu:mps is :modified for spec ia l applicat ionswhere needed. So:me of these applicat ions wil l be discussed here .

U n d e r g ro u n d C o n d e n s a t e P u :m psWhen the re turn :mains fro:m a stea:m syste:m a re below the equip:ment

roo:m H o o r o r lower than the inlet of a conventional horizontal condensate pu:mp,underground type pu:mps are used. The construct ion of such a pu:mp is shown inFigure 29.

I" AIR VENT TAPGREASE. cup - - - - - - - - - , CUSHION SPIDER

COLLARS (2)J.. FLOAT ~ S W I T C H TRIPSWITCH" ~ i ~ ~ ; i ~ ~(OOPLEX U"'ITSONLY)

FLEXIBLE COUPLING

SWITCH BRACKET--./THRUST BALL BEARING WITHSINGLE SEAL AND PROVISION

: : = ( ; $ } . , ~ FOR RELU8RICATION, / ~ M O T O R SUPPORT

VAPOR SEALS (2,) - - - ~ I ....... ~ - DII'SCHARGE FLANGEP I P E ~ I YrPACK INGCOOTROL 8 A S E ~ I P P L E \ GLAND "0" RING,~ ==/ DISCHARGE FLANGE~ ~ ~ ~ ~ ~ = - GASKET.COVER PLATE /'" =1FISCHARGE FLANGEGA:::KET ~ 'F-- EXPANSION JOINTRECEIVER SLINGER ORIFICE [I GASKET,I I II MOTOR SUPPORT::::::R IIV r r l = ~ ' f , . , ~ ~ t g s ~ ~ ~ ~ .IFETIME CAST IRON

~ ~ 6 ! : ;RSTOP II II INLETORlfICv-\)q:W INTERMEDIATEFLOAT ROD I ",1 / I I 8 E ~ ~ ~ ~ ~ ~ S I N G

INTERMEDIATE

1ft"' I I B E A r ~ ~ u ~ 1 , i L E S SL " " T - - - ~ ...Cl ORIFICE - ~ - - DISCHARGE PIPEI . PUMP SUPPORTFLOAT ROD G U I D E ~ I I COLUMN. PILOTEDY [[ . OWER BEARING.Oil-lESS/ I LOWER BEARINGC O l l A R . ~ I l HEADFLOAT STOP ~ ~ DISCHARGE ELBOW

GASKET. C A S E - i I ~ 1 1 ~ 3 f i f T I ~ 1 1 1 / ~ CASEU . ~ C A S E _ R ~ N G . BRASS~ 1 H ~ . DRAIN PLUGI M P E L L E R . - - - - T , - - - - - ~ / .BRONZE - ENCLOSED \ \ : , ~ \ " " \ S " " \ S " " \ S " ' S \ = = = = = = = = ~

Underground Type Condensate Pu:mpFigure 29.


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The pum.p assembly consis ts of a cas t i ron rece iver which is ins ta l led below grade. The sys tem condensate re turn empt ies into this rece iver . Thefloat switch cycles the pump to re turn condensate to the boi le r . These units a refurnished in both open and vacuum-t ight cons t ruct ion, the la t te r being used withvacuum sys t ems . A separa te vacuum pump is required where underground condensate pumps are used .

V a c uu m P u m p sVacuum pumps m ay be used for the single purpose of producing a

vacuum on the sys tem, o r they m ay be dual purpose types , producing vacuumand returning condensate to the boiler .

A vacuum pump is shown in cross - sec t ion in Figure 30. The pumpIS off and condensate is drain ing into the rece iver , or lower tank.

A I R ~WATER - -

_-- - - - . . .1

,- OPEN VENT 6- PUMP2- PI LOT VALVE 7- CH ECK VAL.:,IE

--'

3-DISCHARGE VALVE 8-INLET TO PUMP FROM RETURNS4-TO BOILER 9-STRAINER5-VACUUM JETS ID-FLO.T SWITCH FOR STARTING PUMP MOTOR

Je t Type Vacuum PumpPump OffFigure 30.

When the rece iver l eve l r i se r to the cut - in setting of the float switch,the pump is s tar ted. As shown in Figure 31, this c i rcu la tes water f rom theupper tank through the vacuum je ts and back to the upper tank. With the inducedpressure a t the j e t , water and a ir f rom the lower tank are drawn into the uppertank. Air is discharged through the upper tank vent . The upper tank wate r c ir culated to produce vacuum is called T1hurling water l l .

While the pump is operat ing in this mode, i ts discharge to the boi le ris held closed by a bellows type valve, actuated by the pressure of the pump asshown in the drawing. This valve wil l keep the pump discharge closed until thepres sure in the bellows i s rel ieved by opening the pilot valve. The pilot valveopens when the wate r l eve l in the upper tank r i ses sufficiently to act ivate thefloat which controls it .

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28

A I R ~WA T E R -

6

Je t Type VaCUUITl PUITlPTransfer of Condensate to Upper Tank

VacuuITl Being DrawnFigure 31.

When the wate r level reaches this point, the pilot valve opens asshown in Figure 32. The pressure on the discharge valve bleeds off and con-densate i s del ivered to the boiler . The pUITlP continues to run until the lowertank is scavenged and i ts float drops to the off posit ion. As the pUITlP s tops ,the check valve at the lower tank closes due to the vaCUUITl in the lower tank.

A I R ~WATER -

6

Je t Type VacuuITl PUITlPCondensate Discharges to BoilerVacuuITl Being Drawn

Figure 32.

While the pUITlP is operating to discharge condensate to the boiler ,i t is a lso drawing a vaCUUITl on the systeITl. I t is possible for this vaCUUITl todrop to a level that would cause pUITlping probleITls. F or this reason , a vaCUUITlbreaker se t to open before this takes place is usual ly installed at the vaCUUITlpUITlP inlet .


31/108

The pUITlP ITlay be called upon to operate by the systeITl vaCUUITlswitch, even though the re is no need to re turn condensate. Should the sys-teITl vaCUUITl r i se to the cut- in sett ing of the vaCUUITl switch, the pUITlP wil lrecirculate upper tank water , drawing a ir froITl the lower tank through thevaCUUITl jets until the vaCUUITl switch is sa t isf ied.

The vaCUUITl switch and float switch a re electr ically connected inparalle l to provide for controll ing the condensate and systeITl vaCUUITl independently as descr ibed.

Other vaCUUITl pUITlP const ruct ions using the je t vaCUUITl producer a reavai lable. One of these i s shown in Figure 33. Notice that separate condensatere turn and vaCUUITl producer pUITlpS are eITlployed. COITlbinations of this typeare used in l arger systeITls requir ing higher vaCUUITl, la rge a ir capaci ty orwhere the condensate ITlust be discharged to high pressu re boilers .

FLOATSWlfCH

FLOAT SWITCH FOR HURLING WATERLEVEL CONTROL------,

CONDENSATE RECEIVER

CONDENSATE --"DISCHARGE

Je t Type VaCUUITl PUITlPTwo PUITlP Type

Figure 33.

AIRPUMP

VACUUMSWITCH

WATERPUMP

29


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30

The hur l ing water supply is separa ted from the condensate and ismaintained by a solenoid valve actuated by a f loat switch. Where high vacuumis to be maintained, the hurling water is somet imes maintained a t some pre-determined maximum l imit . This is done by using a the rmos ta t in the separa-t ion chamber to admi t cooling water as needed through the solenoid valve. Anoverflow connection maintains the hur l ing water a t the proper level .

The hurling water pump is cycled by an electr ic switch actuated bysystem vacuum. This vacuum is drawn through a connection to the condensatereceiver . A check valve a t the vacuum connection outlet closes off when thehur l ing water pump shuts down, maintaining the system pressu re differential .

Condensate drains into the rece iver , with the water pump dischargingf rom this point to the boiler . A float switch in the rece iver actuates the waterpump.

Bo i l e r AccessoriesSteam sys tems lose some water dur ing operat ion due to venting,

blow-down and possible leakage. As a result , provis ion must be made for theaddition of make-up water . The boi le r mus t also be protected f rom damageshould a lo w water condition occur while the boiler is being f i red.

The accessor ies used to automat ical ly per form those functions areboiler water feeders , low water cut-offs o r a combination of both in one control .

Some sys tems add make-up water to the condensate rece iver and usea water level sens ing switch on the boiler to actuate the boiler feed pump to br ingthat water to the boiler . This switch is known as a pump control . Both lo w andhigh pres sure s team systems incorporate this type of make -up arrangement.

Figure 34.A s team boiler with a water feeder and pump control is shown in

CITY WAT(R SUPPLY ,SAFETY F(EDER j ~ U M P CO:ROLrCHECK VALVE

;; \ -!-~ Q I L . E ~ ~ T E R !.,IN' _ IJ _ ~ -~ - f - - _ ~ ~~ CONTROLLEVEL fl) -EEDER CLOSING LEVEL ....

BY P A s S " ~ .;r;DIR(eT FEED TO BOILER\ H

ill 1,...0"1 ----ISteam Bo i ler Controls

Typical Instal lat ionFigure 34.

~

J


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Bo i l e r W a te r F e e d e r sA combination water feeder and low w ate r cut-off is shown in Figure

35. This is installed in an equalizing l ine on the boi ler so that the float cansense the boiler w a te r level.

Large, accessible, built-instrainer protects feed valve.

Dependable low watercut-off switch.

All working parts isolatedfrom heat of float chamber.

Ingenious toggle multipliesfloat power at instant ofclosing or opening.

Slot and roller constructionassures straight thrust of.valve stem.

Heavy duty hydraulic bellows, built for higher pressures, eliminate packing.Special spring-cushionedbellows fo r higher steampressure service.

Combination Water Feeder and Low Water Cut-offFigure 35.

A make-up water feeder does not act to mainta in the normal boilerw a te r l ine, which should be a t the center of the gauge glass. On initial firing,the water level tends to drop somewhat below normal unti l the condensate begins to re turn and provis ion mus t be made for this in establishing the feederoperating level . A marke r on the float bowl casting indicates the feeder closinglevel. Feeders a re usual ly instal led with the closing level 2" to 2 -1 /2" belownormal water l ine, but not lower than 111 of w ate r in the gauge glass .

Should the boi ler water level drop below this point, the float of thefeeder will drop and open the valve. Water enters through the s t ra iner , stoppin g when the feeder closing level is reached. The valve as jus t descr ibedwould comprise a make-up water feeder .

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32

A low water cut-off switch can be added to such a water feeder tomake i t a combination control. A l inkage from the float lever operates thisswitch so as to open i ts contacts on a drop in boiler water level. A drop inboi ler water level to 3/4" below the feeder operat ing level causes this switchto open and shut down the burner unti l the water feeder re-es tab l i shes a safeoperating level . A r i se in water level of 1/2" over the cut-off level causesthis switch to make its contacts and r es ta r t the burner .

L ow W a t e r C u t - o f f sSome boilers require separate lo w water cut-offs. One of these is

shown in Figure 36. The control should be ins ta l led so as to have the cut-offlevel ma r k e r on the float bowl about 1/2" higher than the lowest visible pointin the sight glass. The control wil l shut down the burner when the boiler waterreaches this level and r es ta r t it on a 1/2!! inc rease in boiler water level overthis point.

Low Wate r Cut-offFigure 36.

P u m p C o n t r o l sPump controls are usually furnished with auxil iary switches which

also enable them to function as low water cut-offs . An example of such a cont rol is shown in Figure 37. The control has two mercury switches each ofwhich operates independently. One s tar ts and stops the boi ler feed pump, theother serves as lo w water cut-off and alarm switch.


35/108

Pump Control and Low Water Cut-offFigure 37.

A marke r on the f loat bowl cas t ing indicates the low water cut-off level.When used as a pump control , the marke r should be about 1_1/2 11 to 211 belowthe normal boiler water level but never lower than 3 /4 11 of water in the gaugeglass . The boiler feed Ilcut-offll level will be 1-1/2!! above the marke r andthe Ilpump_on ll level wil l be 3/4 11 lower than th is . Where the boiler feed pumpis operated by a pump switch, a make-up water feeder is insta l led in the re -ceiver.

With this arrangement , the pump switch and low wate r cut-off actto control condensate re turn to the boiler and also to shut down the burnershould a low water condition occur. As the need for make-up water appears ,this wil l show up as a drop in the water level in the rece iver . The make-upwater feeder located a t this point will then add water as needed to insure thatthe re will always be a reservoir of water for the pump.

33


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34

Electric W a t e r FeedersIn addit ion to str ict ly mechanical water feeders , electr ically opera t -

ed water valves are used to supply make-up water d i rec t ly to low pressu restearn boi lers under 5, 000 sq. ft. of radiation. These valves are actuated bya low wate r cut-off switch.

The construct ion of an electr ic water feeder is shown in Figure 38.A solenoid coil , available for 24 or 115 vol t operation, opens the valve in themanner shown when i t is energized, causing w ate r to be added to the boi ler .Any low water cut-off with the proper auxil iary switch can be used to operatethe valve .

Button for Compoundmanual leverage,feeding spring loaded,for powerful

Removableopeningan d closing

en d plate foreasy wiringMcDonnellself-centeringPowerful roller providesiron-encased stra ight-thrust

coil valve action

Pack less Stainless(bellows) steotl valveconstruction

Large Largeintegral streamlinedstrainer waterways

Electr ic Water Feede r ValveFigure 38.

The low w ate r cut-off level ma r k e r on a proper ly instal led lowwate r cut-off wil l be about 1/2" above the lowest visible point in the sight glass .Should the wate r level fall to within 1/2 I to 3/4" of the marker , the auxil iaryswitch will close i ts contacts . The electr ic wate r feeder will open adding waterto the boi ler . The cut-off level of the switch is 1/2" to 3 / 4" higher than thecut- in level and the electr ic w ate r feeder wil l close when this boiler water levelis reached.


37/108

Strainers

Boiler wate r contains a grea t am.ount of sedim.ent. It is im.portantthat l a rger par t ic les be kept out of the working par ts of boiler controls .Strainers , ei ther in tegra l o r external , are extensively used for this pu rpose.A good exam.ple of an in tegra l s t ra iner is given in the com.bination control pictured in Figure 35.

External s t ra iners are available in m.any shapes and sizes to fitvarious applications. One thing they m.ust all have in com.m.on is acces sibil i tyof the s t ra iner fo r cleaning and provision for blow-down of accum.ulated sedi m.ent. The m.ost com.m.only used steam. s t ra iner is the "Y" type, pictured inFigure 39. These s t ra iners are furnished with ei ther m.esh type or perforatedm.etal screens in a wide var ie ty of openings.

Typical Steam. StrainerFigure 39.

The tapping in the s t ra iner cover perm.its installation of a blow-downvalve. The s t ra iner screen m.ay be rem.oved for inspection or replacem.ent bytaking off the screen cover . In sm.al ler s t ra iners , the access cover is sc rew-ed into place . Stra iners a re identified by line size and the m.esh or perforat ionsize required.

Pressure R e g u l a t i n g V a l v e sSteam. heating system.s do not always rece ive steam. from. a boiler

installed on the prem.ises . Often the boilers are in a rem.ote area , generatingsteam. at a higher pressure than can be used in the heating system..

Where this is done, the pressu re of the steam. m.ust be reduced before i t is introduced to the heating system.. Pressure reducing valves are u s -ed for this purpose . These valves have the capabil i ty to reduce the pressureof f luids from. a high ini t ial pressu re to a controlled lower pressu re . The fluidsm.ay be of any type, such as steam., ai r , w ate r or fuel gases . 35


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36

Pressure reducing valves operate on the principle of balancing thecontrolled pressure against a known, adjustable pressu re . This is usual lyaccom.plished through the flexing action of a diaphragm., which controls flowthrough the valve por t through an appropriate l inkage. The construct ion ofthese valves follows a num.ber of pat terns , depending upon the resu l ts to beaccom.plished.

Figure 40 i l lus tra tes the operating principle involved. Controlledlo w pressu re is sensed by the diaphragm. through a flfeeler pipe fl A needlevalve in this l ine acts as a dam.per to prevent rapid pressu re fluctuations.The controlled pressu re acts to close the valve while the spring tends to openi t . I t therefore follows that the controlled pres sure can be regula ted by vary -ing the spring pressure and a m.eans is provided fo r doing this . A bypass isusual ly instal led around the valve to perm.it m.anually controlled flow shouldthe valve requi re se rv ice .

BONNET

BRACKET NUT - - A ~ ~ ~ ~STUFFINGBOX NUT - - t - - t+ - l

STEM -+-++--1

FEELER PIPE

GLOBE. VALVE

....EDLEIVALVE

BYPASS

Typical Diaphragm. Type Reducing Valve Com.position DiscFigure 40.

Valves are always installed so as to perm.i t the disc to close againstthe higher inlet pres sure . Flow in the reverse direct ion causes "valve slam.fIor flchatter" on closing. The valve disc in Figure 40 is a s ing le - sea ted com.posit ion disc type. Com.position disc valves a re lim.ited to the control of inleto r ini t ial pressures not to exceed 50 psig.


39/108

Where higher pressu res a re to be control led, ITletal to meta l valvesare eITlployed. Figure 41 shows this cons t ruct ion.

METAL VALVEBONNET

Single Seated Valve Construct ionMetal Seat and Disc

Figure 41.

Valves are also furnished in double seated const ruct ion. Two por tsand two discs a re used to provide balanced hydraul ic pressu res on the valvesteITl. As shown in Figure 42, water entering the valve body provides a c los-in g force on one disc and an opening force on the other . The lower disc is abit sITlaller than the upper to provide clearance for inser t ing i t into the valvebody. The difference in disc areas resu l t s in a very sITlall pressure unbalancewhen the valve i s c losed.

"BODY~ P O S T

STEM

Double Seated ValveFigure 42.

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38

Ful ly balanced va lves can be const ructed by using the principlei l lustrated in Figure 43. This is a single seated valve with an in te rna l pilotoperat ing the main disc. A drop in control led pr e s su r e causes the pilot valveto open i t s por t . Fluid enter ing the por t pushes the piston upward, openingthe main va lve . The areas of the main valve disc and the piston a re the s ame ,resul t ing in balanced valve act ion.

PISTON TYPE, ~ - VALVE

~ : : r - - - m ___- SEA TPILor VALVE

Internal Pi lot Opera ted ValveFigure 43.

Anothe r commonly used single seated valve is the bal l type withspring re turn shown in F igure 44. The bal l valve is held closed by its re turnspring and pushed open by the valve stern on a drop in the control led pr e s su r e .The valve shown in the i l lus t rat ion is of the sel f contained type, with the con-t rol led pr e s su r e acting on the bot tom of the diaphragm agains t the spr ing p r e s s -ure a t i ts top.

The requi red opening and clos ing of the valve has an effec t on theforces acting on the diaphragm. The spr ing pr e s su r e va r i e s as the diaphragmf lexes and this effec ts va lve regula t ion. The in te rna l pi lot por t a r ea is smal l .This pe rmi t s r easonably low spr ing ra tes which do not vary the control ledpr e s su r e as much as those r equi red for direc t acting valves .

Anothe r approach to c loser pressure regulat ion is the use of aweight and l eve r to provide the needed operat ing force . Figure 45 shows al ever type pi lot opera ted valve. The control led pr e s su r e is adjus ted by movingthe weight as needed on the l ever . The relat ively constant pr e s su r e exer ted bythe weight and l ever coupled with the sens i t ivi ty of the pilot va lve providesclose cont rol . Weight and l ever valves a re usual ly l imi ted to appl ica t ions withreduced pr e s su r e s under 15 psig. F o r higher reduced pr e s su r e on the diaphragm,the weight and l ever r equi red becomes imprac t ica l . Regulat ion also suffers be-cause of the heavy f r ict ion load on the fulcrum pins.


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REGULATINGSCREW A N D ~ - - < ! aLOCI-


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40

TO P B O N N E T - - ~ ~ m : s m ; ; ~MA lN VA LV E - - - - - - t ~ .

B O D Y - - - - ~ ~ ~

MA IN S EA T - l J ! f I I f I J - h I ~ ~ ~PI LO T V A L : . . . : E = - - - ~ c 3 1 - t ; . 3 ; l ' - - - l P " lAND STEM

DIAPHRAGM

Internal Pi lot Operated Weight and Lever ValveFigure 45.


43/108


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42

Gross Boi le r OutputThe gross bo i le r output s ignif ies the t o t a l hea t avai lable f rom aboi ler operat ing under the l imi tat ions of rat ing code for which i t iss t amped . The gros s output is neve r refer red to as a ra t ing, s incei t inc ludes an a l lowance for pick-up and piping tax in addit ion to theac tua l rad ia t ion load .The piping tax i s an a rb i t r a ry al lowance to compensate for the hea tlosses imposed on a sys tem by a norma l amount of insulated piping.The pick-up al lowance is an a rb i t r a ry al lowance to compensate forthe addi t ional load imposed during warming up per iods . This al lowance var ies with the rat ing agency involved.

Net Boi le r RatingThe net boi l e r ra t ing is the actual heat ing load that a boi ler is cap-able of handling. I t inc ludes :

1. All connected rad ia t ion at design tempera tu re , asdetermined by accepted prac t ice .

2. The est imated hea t requ i red by a connected wate rhea te r o r other connected appar t aus .

Adding the piping tax and pick-up load al lowance to ' the net rat ing p ro -vides a t o t a l which is the Gross Boi le r Output.Net ra t ings a re derived by applying a div i sor to the Gross Boi l e r Output. The Gross Boi le r Output i s der ived by tes t ing the boi le r underthe conditions required by the ra t ing assoc ia t ion .F o r example , boi lers ra ted by the SBI ar r ive a t the ne t rat ing bydividing the Gross Output by 1. 333. A boi le r with a Gross Output of1,800 ,000 BTUH i s de t e rmined by t e s t , would have a net ra t ing of:

1,800 ,000 -;- 1.333 = 1,350 ,000 BTUHConver t ing to EDR, we have a neting rat ing of:

1,350 ,000 240 = 5,625 Sq. Ft. EDRSBI cata log rat ings a re based on the ne t load. These ra t ings a re obta ined f rom the manufacturer1s ca ta logs , f rom publ ished SBI ra t ingso r f rom recommendat ions of the Mechanica l Cont rac tors Associa t ionof Amer ica . Unless the sys tem conta ins an unusual amount of barepipe o r the nature of the connected load in such t ha t the norma l al lowances fo r pick-up a re inadequate, the net load ra t ing is used forse l ec t ing the boi ler .


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Where unusual c i rcumstances apply, the load should be calculatedtaking all fac tors into considerat ion and the select ion based on thegros s output .Like s teel boi le r s , cas t i ron boiler net rat ings a re avai lable f rommanufac ture r ' s catalogs. They m ay also be obtained f rom publishedtables of the IBR or Mechanical Contrac tors Associat ion of America .These published net rat ings may be used for select ing the boi ler unless the system has more than the average amount of bare pipe orthe nature of the connected load is such that norma l al lowances forpackage load and piping tax do not apply. In such a case , the se lec-tion i s bes t made on the basis of the gross output .Packaged Fire tube Boiler rat ings as published by the American BoilerManufacturers Associat ion a re Gross Output ra t ings . The ent i re connected load should be calculated, including the Radiation Load, HotWater Supply Load, Pick-up Load and Piping Tax. The total of theseloads is then used to select the boiler based on the Gross Output .

B o i l e r ConstructionAlthough there are a grea t number of individual boi ler types in use,

they can be classif ied into three general categories:1. Fi re Tube Boiler s2. Water Tube Boilers3. Cas t I ron BoilersThis discussion will be confined to these principal t ypes .

Firetube Boilers

One of the m o s t widely used boi le rs of this type is the hor izontal re turntube type shown in Figure 46. The combust ion gases move along the bottom ofthe boi ler on the fir.st pass and re turn through the f iretube on the second.

Horizontal Fire tube BoilerFigure 46. 43


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44

The wate r ci rculat ion pat terns in two types of hor izontal re turn tubeboi le rs is shown in Figure 47.

Staggered TubeArrangement

Baffled Para l le lTube Arrangement

Water Circulat ion in Horizonta l ReturnTubular Boiler

Figure 47.

During World War II, the need for a compact sh ipboard boiler resu l t -ed in the development of the Scotch Marine Boiler in Scotland. The bas ic con-struct ion consis ts of a l a rge f iretube in which the combust ion takes place, su r -rounded by sma l le r f i retubes through which the combust ion gases t rave l .F igure 48 shows the bas ic principle involved.

0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 0000000000000 0 0 0 0 0 0 00 0 0 0 0 00 0 0 0

~ &Basic Const ruct ion

Scotch Marine BoilerFigure 48.


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Many variat ions of the Scotch Marine Boiler have been developed.Typica l construct ions are shown in Figure 49. In the th ree pass category, anUITlber of designs are used that are basical ly f i rebox types as dist inguishedfroITl the internal furnace type. One of these is shown in Figure 50. Thisboi ler has a flat bottoITl and ver t ica l sides going into an arched crown shee tthat forITls the top .

concept.pUITlP andboi le rs .

ITlethods.

WET-BACK, TWO-PASS, OIL-OR GAS-FIRED

WET-BACK TOP, TWO-PASS, Oil-OR GAS-riRED

D R Y - B ' \ C ~ , THREE-PASS, OIl.OR GAS-FIRED

DRY-BACK, TWO-PASS, Oil-OR GAS-fiREDCORRUGATED FURNACE

DRY-BACK, TWO-PASS, COAL-FIRED

DRY-BACK, THREE-PASS, Oil-OR GAS-FIRED

Marine Scotch Boiler TypesFigure 49.

The Scotch Marine Boiler is par t icular ly adaptable to the packageThis is furnished com_plete with fuel burner , draf t fan, feed waterother needed accessor ies . Figure 50 is typical of such packaged

Scotch Marine Boilers are rated according to s tandard SBI rating

45


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46

Scotch Marine BoilerThree Pass Const ruct ion

Figure 50.

Anothe r boi ler type cornrnonly used in heating ins tal lat ions i s theshor t f i rebox boiler i l lustrated in Figure 51. The f ront port ion of the she l ls i t s over the furnace. Combust ion gases pass through the sho r t tubes of thef i r s t pass and exi t v ia the second pas s above the f i r s t pas s . These a re furni shed as e i ther br ick-se t o r water l eg types. The boi ler shown is br ick - se twith a s tee l j acket f i t ted over the boiler .

The water l eg type has water l egs on each side of the f i rebox as shownin Figure 52. in place of the br ick l ining.

Anothe r boi ler popular for l a rge apar tment and inst i tut ional heatingis the compact f i rebox type i l lus t rated in Figure 53. This is a th ree passboi ler including the f i r s t pass through the combust ion chamber . The boi leri l lustrated is a water l eg type wi th a re f rac tory combust ion chamber for oilf i r ing. These boilers a re also furnished as br ick - se t types.


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Short Firebox BoilerBrick-Set - Steel Encased

Figure 51.

Waterleg TypeShor t Firebox Boi ler

Figure 52.47


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48

Compact Firebox BoilerFigure 53.

W a t e r T u b e B o i l e r sWater tube boilers are used pr imar i ly as large, high pressu re

boilers . Some s tee l wate r tube boilers a re found in the low pressu re (l5 psi)heating field in smal le r s izes .

A l imited discuss ion of this boi ler type is in order because of thesmal l number of these installations in the heating f i e l d ~Figure 54 shows a cross section of a horizonta l s tra ight tube boiler ,

detai l ing the circula t ion. Combustion gases pas s over the s tee l boiler tubes,heat ing the water within them. The heated water and stearn flow to a header o rdrum, f rom which the stearn is drawn. This boi ler type i s somet imes furnish-ed as a packaged type. One is i l lus tra ted in Figure 55.

Horizontal St raight Tube Water Tube BoilerFigure 54.


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Packaged Water Tube BoilerFigure 55.

Larger stearn genera tors are furnished wi th water wal l constructionas shown in Figure 56. The boiler shown has two headers . Water flow isf rom the lower to the upper drum, with stearn being generated in the tubes asthe water r i ses through them. The stearn is then taken off the upper drum orheader . These l a rger stearn genera tors are often furnished as packaged units.

Water Wall Type Water Tube BoilerFigure 56.

49


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50

C a s t I r o n BoilersCast i ron boi le r s a re const ructed in two genera l types :1. The round boi le r , used pr imar i ly for resident ia l

appl ica t ions .2. Sect ional boi le rs , used for a ll appl ica t ions .Cast i ron boi le r s a re used pr imar i ly for low pr e s su r e sys tems ; up

to 15 psig for s team and 30 psig for water . A sect ional boi l e r of the push-nipple type is shown in F igure 57. The ver t ica l sec t ions a re connected at thebot tom water legs and a t top center by push-nipples . The sect ions a re drawntoge ther by t ie rods . The t ie rod ends and one of the tie rods can be seen inthe i l lustrat ion.

Cas t I ron Boi lerVer t i ca l Section Pus h Nipple Type

Figure 57.


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Lar ge cas t i ron boi le rs a re often of the externa l header or drum type .One of these is shown in Figure 58. The cas t i ron sect ions a re individually con-nected to the header dr ums with screwed nipples . This pe rmi t s quick rep lace-m ent of a damaged sect ion without dismant l ing the boi le r . The appearance ofthis boi ler type when comple te ly assembled is shown in Figure 59.

Cas t I ron Boi lerVer t ica l Section Exte r na l Header Type

Par t ly As sembledFigure 58.

Cas t I ron Boi lerVer t ica l Sect ion Externa l Header Type

Comple te ly AssembledFigure 59.

51


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52

CHAPTER 5 - - - THE APPLICATION AND INSTALLATION OF STEAMCONTROLS

The selection of the prope r s team control for a given applicat ion r e qui res the considerat ion of a number of var iab les . The control type involvedalso deserves separa te consideration. These factors wil l be expla ined in thischapter , taking the controls in the same or de r in which they appeared inChapter 3.

R a d i a t o r S u p p l y V a l v e sFour factors should be considered in the select ion of a rad ia tor

supply valve :1. System Type2. Opera t ing Pressure3. Pipe Size4. Body Type

O n e - P ip e S y s t em sAny angle pat tern , non-modula t ing valve may be used . The valve

should be full r i se r size and installed as shown in Figure 60. I f the sys tem isfitted with vacuum type rad ia tor vents , the valve should be of the spring loaded packing or packless type to prevent loss of vacuum pas t the valve s tem.Conventional packing type valves may be used where non-vacuum sys tems a reinvolved.

I()ffi1ANPACKlESSRADIATORVAlVE\

~ ' M A N A m ~ ~ ~ /[

...--PITCH DOWN fROM HERf.r SUPPLY MAIN

~ ~ ; ; ; ; i ; ; ; ; ; ; ; _

UPfEED CONNECTION TO RADIATOR.

One -P ipe Steam SystemUpfeed Radiator Connection Detai l

Figure 60 .


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T w o - P i p e S y s t e m sThe supply valve m u s t be full r i s e r size. Vacuum sys tems should

be fi t ted with spr ing- loaded packing or packless type valves . The s tandardpacked type construct ion m ay be used on non-vacuum sys t ems .

The valve body configurat ion m ay be of the type which bes t fits thejob piping requi rements . F igure 61. shows an angle type valve installation.Modulating type valves may be used where control of the rad ia tor output isdes i red . These open ful ly with one turn o r less and a re equipped with a dialand pointer for visual regulat ion.

tOO=MAH SUPPlYV A l V E " ' ~ ~ ~ ~ ~ ~

SUPPlYMAIN RETURN MAIN.)UPFEED CONNECTIONS TO RADIATOR.

Two-Pipe Steam SystemUpfeed Radiator Connection Detai l

Figure 61.

V e n t V a l v e sThe choice of vent valves requi res that the following factors be con-

sidered:1. Type of Equipment to be Vented2. Operat ing Pressure3. Maximum Working Pressu re4. Venting Rate Required5. Vacuum or Non-Vacuum System

53


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54

Radiator V e n t sVents used with convent ional free standing cas t i ron rad ia tors a re

of the angle type, being screwed into a side tapping of the rad ia tor as shownin Figure 60. The vent ll1ust be r a ted a t an opera t ing pr e s su r e equal to orgrea te r than that of the systell1. Radiator vents have two pres su re rat ings :

1. Opera t ing P r e s s u r e The ll1axill1ull1 pr e s su r e a twhich the vent wil l perforll1 i ts function.2. Maxill1ull1 P r e s s u r e The ll1axill1ull1 pr e s su r e that

can be applied to the valve.The venting rate ll1a y be adjus table or non-adjustable . The non

adjus table type a re used where the steall1 distr ibution on s ta r t -up is no pr oblell1. Adjustable vents should be used on systell1s where var i a t ions in c i rcu i tlengths resu l t in sill1ilar var iat ions in venting of systell1 a i r . Under the se cir-CUll1stance s, the rad ia tors ll10re rell10te froll1 the boi le r wil l be the las t to heat .The instal lat ion and proper adjustll1ent of adjustable vent va lves resu l t s in abet te r balanced systell1.

One-pipe systell1s that opera te a t atl l10spheric pr e s su r e to pr e s su r e sof about 2 - 3 psig use open type vents . As the steall1 in the systell1 condenseson the off cycle , these vents allow a i r to be drawn into the systell1. This a i r isvented on the next f i r ing cycle .

One-pipe systell1s which opera te in the vaCUUll1 range during a por t ion of the i r heating cycle have been in use for ll1any years . These systell1s opera te well when coa l - f i red . When enough heat is presen t in the fuel bed, thesystell1 opera tes a t above atll10spheric pr e s su r e . As the f i re dill1inishes; therate of steall1 generat ion dec reases . Check valves in the rad ia tor vents preventa ir froll1 being aspi ra ted as the steall1 condenses and a gradua l vaCUUll1 forll1sin the systell1. The decreased pr e s su r e al lows the continued product ion ofsteall1 at a l ower te l l1perature. The rad ia tors rell1ain warll1 over a longe r pe r iod of till1e, resul t ing in good te l l1perature control .

The systell1, cOll1ll1only cal led a "vapor vaCUUll1 systell1" does notlend i tself wel l to gas o r oil f ired boi l e r operat ion. During ll1ild wea t he r thef ir ing cycles ll1ay be too shor t to allow the steall1 to cOll1pletely purge the sys tell1 of air. On the off cycle, this a i r wil l expand as the systell1 drops to avaCUUll1, often to the extent tha t i t wil l creep into the ll1ains. Repeated shor tcycling in this fashion wil l resu l t in an ai r-bound systell1 with poor heat d i s t r ibut ion.

F o r this r eason, the use of vaCUUll1 type rad ia tor vents with one-pipeoil or gas f i red systell1s is not usual ly recoll1ll1ended.


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Vents with convector rad ia tors are of the s t ra ight shank type , in -stalled as in Figure 62. The nature of this rad ia tor type makes i t necessaryto instal l the vent at i ts top. In order to provide quick vent ing, an a ir cham ber should be ins ta l led . The a ir collect ing in the chamber wil l pe r mi t cooling of the thermosta t ic e lement in the vent , necessary for proper ventingaction. This i l lustrat ion also points out the need for pitching the rad ia torsin one-pipe sys tems to the r i se r .

M a i n V e n t s

____ HOffMAN AIR VALVE

P I T C H D . O W N ~HOffMAN - = M ~

AIR VALVE 5UPPLY VALVE OR UNION

HOffMAN5UPPLY VALVE OR UNION

One-Pipe Stearn SystemUpfeed Convector Connection Deta i l

Figure 62.

Main vents are always of the non-adjustable type , as the i r functionis to remove a ir as quickly as possible . They are available in var ious venting capaci t ies to fit the requi rements of smal l , medium and l a rge size sys -t ems . As a rule , their venting capaci ty is so descr ibed in the catalog information.

These vents a re of the s t ra ight shank type . The shanks are bothtapped and threaded for ei ther male or female installation. The usual s ize is1/2" female by 3 / 4 11 male on the shank of the vent . Figure 63 shows a typicalinstal la t ion. The connecting nipple should be at leas t 6 11 to 1 0 1 1 long to providea cooling leg for the vent .

55


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56

Un i t He a t e r Ven t s

HOff MAN MAIN VENT'-

ATLE"STIZ'-p _( J i = - ~ = ~

! '.RIPPING ENDOF ONE PIPESTEAMMAIHWHERE SAMEE.XTENDS8fYONOWETRETURN.

WfT RTURH j

ATLEAST 18ABOVE W.L.- ~

Typical End of Main VentInstallation Detail

Figure 63.

Vents designed especial ly fo r use with uni t hea te r s are available.The se should be installed as shown in Figure 64, with the vent to p level withthe top of the unit hea te r . The 1211 drop leg on the return provides enoughwater head at this point tQ insure opening of the check valve and provide goodcondensate drainage.

UNITHEATER

SEDIMENTPOCKET

/T\-""""'-----='::SU PPLY LIN EHOFF MANUNIT HEATERVENT VALVE

LOW PRESSURE ClOSEDGRAVITY SYSTEM

Typical Unit Heater Connection DetailFigure 64.

Unit hea te r vent valves a re constructed for higher working press -ures than are conventional radiator vents . Unit heaters a re often installedon high pressu re systems, making this necessary . Figure 65 shows an in -stallation of this type. A bucket t rap is used here for rapid condensate re -moval , with a separa te a ir vent to insure quick venting.


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T r a p s

UNITHEATER

SEDIMENTPOCKET

SUPPLY LINE/TI-__ > - - ~HOFFMANUNiT HEATERVENT VALVE

HIGH PRESSURESYSTEM

HOFFMANBUCKET TRAPHOfFMAN ~ __ _S T I i l A I N E R ~

Typical Unit Heater Connection DetailFigure 65.

When determ.ining the proper t rap to be used for an applicat ion,consideration m.ust be given to a num.ber of fac tors . The t rap type whichbes t fits the applicat ion is determ.ined f i rst . Then considerat ion is given tothe pressure differential across the t rap, its working pressure and the am.ountof condensate to be rem.oved.

Th e rm . o s t a t i c T r a p sTherm.ostat ic t raps perform. well where they are used on equipm.ent

with la rge in ternal volum.e. Although they a re furnished for low, m.edium. andhigh pressu re applications, they are used prim.ari ly in the lo w pressu re range.Figure 60 shows the m.ost com.m.on applicat ion, at the radia tor outlet.

They a re also com.m.only used to drip r i se r s and re turn m.ains.Typical installations a re shown in Figure 66 . I t is im.portant that a cooling legbe used as shown in the i l lustrat ion where th is is done.

SUPPLYI'IAIII. ~ o ; M I N ; ; I I ' I ; ; U M ; ; ; ; C ; ; ; ; O O ; ; ; ; L 1 ; ; ; ; N G ; ; ; ; L E ; ; ; ; G S;;;;'_O;;;;\;O;ONG-;;;;ilD~ : A M E Silf A5 TRAP'T R A P _ ~ DRY '--- RETURN.DRIPPING END OF SUPPLY MAININTO DRY RETURN_

- PROP RI5E.R OR END OF MAINMINII'IUI'I (OOlIMGLEG SeOLOnG.5AMl31lE AS TI!AP.c- TRAP! ~ HOFFMANR E ~ ~ ~ H : : ING DROP RISER OR END OFMAIN INTO DRY RETURN.

Two -Pipe - - - Steam.Trap Installations

Figure 66.57


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58

Typica l t r ap selection tables are shown in Figure 67 . As a se lec-t ion example, assume a t r ap is to be used to drip the end of a downfeed supplyr i se r with a pressure different ia l of 2 psi and a connected radiation load of17 0 sq. ft . The char t te l ls us that a l7C 1/2!! t rap wil l handle 235 sq. f t. a tthis condition. We would use this t r ap with the proper body type to fit the r i se rsi tuat ion.

TRAPNO.

17C8C9C I

CAP4CITY T A ~ L E ~ FOR LOW'PRESSURETHERMOSTATIC RADIATOR TRAPSCAPACITY SQ. FT. !,DR

S I ~ EPATTERN (IN.) DIFFERENTIAL pRESSURE ACROSS TR,AP1,.2' 1 11,.2'*' 2 5 10Angle V2 " " " ' ,Swivel 112 85 1 120 :1.65 20Q 235 370 530Vertical 112 " . ~ \ ' : " " ' : ~ . : : < " ; ~ ' ; " ' s : ; ~ , \ : I'Angle 0/4 "165Straightway 0/4 ,230 330 400 .465 730 1'050Angle . 1 299 :,,419 q80 "lOC> '. 810 1289: 1fl1,0

~ ; ; i 5 ; " , ",";':'t/',!< 'C"," ' ," , ' ' , ~ , ' > ,

TRAPNO.898H9H

MEDIUM AND HIGH-PRESSURE TRAPSCapacity Table - Pounds of Condensate Per HourSIZE DIFFERENTIAL PRESSURE - PSIPATTERN (IN.) 5 15 25 50 100

Angle 112 125Straightway 112 225 300 490 .. . .Angle 0/4 225 350 450 650 ....Angle 1 325 500 625 850 . . . .Angle 112

Straightway 112 '" . .... 300 490 650Angle 0/4 '" . 450 650 875Angle 1 .... '" . 625 850 1125

'. '. ,,:::

Figure 67.

", ::

PSI15

640",1.300,,',.2300

125'" .

". ,. ...720950

1250,,:';, .


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Float a n d Thermostatic T r a p sThese t raps a re divided into two ca tegor ies fo r ra t ing purposes .

Low pr e s su r e t r aps , opera t ing a t pr e s su r e different ia ls up to 15 psi , a rer a ted a t the i r net rat ings . This net ra t ing make s the needed provis ion forw a r m - u p and no safe ty factor need be appl ied . On the other hand, mediumand high pressure t raps a re r a ted gross . A safety fac tor mus t be applied forpeak loads . I t is common prac t i ce to double the opera t ing load to ar r ive a t thepeak load fo r se lec t ion purposes . F igure 68 shows typica l ra t ing t ab les .

CAPACITIES LOW PRESSUREThe capacity ratings of these low pressure traps (max. 15 PSI) are NET RATINGS based on the code established by the Steam Heating Equipment ManufacturersAssociation (SHEMA) Code ratings provide for overload conditions such as warming up period No safety factor need be applied

LOW PRESSURE PRESSURE DIFFERENTIALS IN LBS. PER SO. IN. LOW, MEDIUM and HIGH PRESSURETYPES and NOS. CONN.Float & SIZES 'I. lb. 'I, lb. 'I. lb. 1 lb. 2 Ibs. Sibs. 10 Ibs. 15 Ibs. WEIGHTSThermostatic Float CAPACITIES IN POUNDS WATER PER HOUR NET SHIPPING53-FT 53-F %" 70 100 120 140 200 210 220 230 7 Ibs. 7lbs. 4 oz._.---- - 1 - - - -- 1 300 350 500 525 550 575 7lbs. 7lbs. 4 oz.4-FT 54-F 1 " 175 250--- -- - 1--- - -- - ----- 850 1200 1260 1320 1380 121bs. 10 oz. 131bs. 8 oz.6-FT 56-F 1),;;" 425 600 735~ - - -- -- ------- 1---- - ---- -- - -57-FT 57-F l ' /" 850 1200 1470 1700 2400 2520 2640 2760 191bs. 6 oz. 201bs. 10 oz.2----- --

t-- 58-F 5250 5500 5750 381bs. 12 oz. 391bs. 12 oz.8-FT 2" 1775 2500 3060 3550 5000MEDIUM & HIGH PRESSUREThe capacity ratings of these medium and high pressure traps are GROSS RATINGS. To provide for peak loads, such as warming up periods, a safety factor mustbe applied Peak loads frequently are twice the hourly condensate rateMED. and HIGH PRESSURE PRESSURE DIFFERENTIALS IN LBS. PER SO. IN.TYPES and NUMBERS MAX. CONN. 'I, lb. 1 lb. 2 5 10Float & PRESS. SIZES 15 20 25 30 40 50 GO 70 80 90 100Thermostatic Float CAPACITIES IN POUNDS OF WATER PER HOUR

540-FT 540-F 30 %"or1" 300 405 530 890 1210 1485 1705 1885 2010 - - - - - - -~ - - - - - - - - - 1-- -- 1----541-FT 541-F 60 %"or1" 195 265 360 580 770 990 1110 1210 1290 1430 1560 1680 - - - ---------- -------- I- - - %"or1" 110 145 200 320 430 520 605 650 690 755 835 880 950 1000 1035 108042-FT 542-F 125-- - ---- - or H-;;" 600 880 1205 1845 2560 3230 3715 4100 4405 -60-FT 560-F 30 - - - - - -------- -_ .. -- - -- -- ---

1"or1),;;" 360 485 660 1020 1430 1740 1980 2200 2420 2670 2910 3135 - - - -61-FT 561-F 60-------_ .. ------ -- ---- - 1 - 1 " o r 1 ~ " 310 455 635 775 915 1010 1150 1270 1380 1460 1575 1680 1760 186562-FT 562-F 125 200 250------- 1----- -- 1'/ " 2625 3660 5660 7890 9440 10590 11360 1209580-FT 580-F 30 /2 2045 - - - - - - ------ -- -- -- - - ---------- - - - - - - . - - - - ------ ---1 J;;" -581-FT 581-F 60 1075 1300 1700 2600 3750 4350 4750 5050 5400 5960 6500 6950 - - - ------------ - - - - - --1- 125- - 1--'1)"2" -- ----582-FT 582-F 550 750 1150 1650 2250 2800 3200 3440 3700 4000 4350 4800 5020 5380 5700 6000

Figure 68.

The tables show different ia l pr e s su r e s . What i s mean t by th is t e r mi s explained in the following examples :

1. Return Back Pr es su r e - Assuming a s tearn supply pr e s su r eof 50 p si and a re turn back pr e s su r e of 20 psi , the different ia l pr e s su r e would be 30 psi .

Stearn Supply P r e s s u r eRetu rn Back P r e s s u r eDifferent ia l P r e s sure

50 p si20 p si30 psi

125

--

1190--2110--- ----6600

59


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60

2. Vacuum Return - The differential pressu re of a t rap d ischarging into a vacuum return is the sum of the supplypressu re and the pressu re in the re turn .

Supply PressurePressure in Vacuum Return is

8" Mercury (8 c .49 psig) =Differential Pressure

6 psi4 psi

10 psi

3. Lift to Overhead RetlJ.rn - Float and Thermosta t ic t rapsare often applied to discharge condensate into overheadre turn l ines. The amount of available l if t depends upon thedifferential pressu re . 1 psi is equal to 2 .3 f t . , but it iscus tomary to two feet of water column for each psi to allowfor piping pressu re drop. F o r example:

Supply P re s sureBack P re s sureDifferential Pressure

The maximum lift will be 30 x 2

S e l e c t i o n E x a m p l e

50 psi20 psi30 psi

= 60 ft.

Select an IIF" & liT" t rap for a system with 10 psi supply pressure .The back pressure is 6" mer cu r y column. The condensate load is 1,000 1bs.per hour . Pressure differential:

Supply Pres sureVacuum Return (6 x .49 psi)Differential Pres sure

10 psi3 psi

13 psiA t rap is requi red for 1,000 1bs. /h r . at 13 psi differential pressu re .

This is a low pressure t rap (under 15 psi) and no safety factor is requi red . Reference to Figure 53 indicates that the closest select ion would be a 560-FT t rapwith a capacity of 1, 32 0 Ib s . /hr . at 10 ps i diffe rentia1.

Traps a re never selected by pipe s ize . They are selected for capacity and should be installed with piping at l eas t full size of the selected t rapopening. The 560-FT t rap has 1-1 /4" openings and should be so piped.

I n v e r t e d B u c k e t T r a p sThese t r aps are s ized using the sam e select ion procedure s outlined

for both Floa t and Floa t and Thermostat ic Traps . The sea t por t opening var ieswith the pressu re differential with which the valve wil l operate and the select ion tables ref lect this .


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I t is always good pract ice to instal l a s t ra iner ahead of t r aps . Somet raps a re provided with optional in te rna l s t ra iners which can be removed forc leaning. Another optional feature is a thermosta t ic e lement which holds thet r ap por t open a bit af te r i t discharges condensa te and the bucket drops . Thisal lows any a ir enter ing the t r ap to vent even though i t is in i t s normal ly closedposi t ion. Should stearn reach the thermal e lement , i t wil l allow the va lve por tto close. The t he rma l e l emen t and s t ra iner a re shown in Figure 69.

INTfRNAL STRAI NER

Inverted Bucket Trap with Internal Stra inerFigure 69.

A typical select ion table for inver ted bucket t raps is shown in Figure70. The cata log number s designate the const ruct ion features of the valve .

A typica l bucket t r ap appl ica t ion appea r s in Figure 65. Here thet rap i s used to rapidly discharge condensa te corning off a uni t hea te r . The ventvalve furnishes addi t ional a ir venting capaci ty for fast s ta r t -up . The vent valveis elevated to pr even t condensa te f rom clos ing off i ts f loa t should it back upf rom the t rap .

A safety factor should be applied to the calculated condensa te loadwhen se lec t ing an inver ted bucket t rap . The condensa te load should be ca r e fully calcula ted, since a grea t ly over s ized inver ted bucket t r ap tends to losei ts pr i me and wil l then continually blow s tearn. The safety factor usual lyapplied is 2 to 3 t imes the nor mal condensa te load, depending upon the appl ica-

61t ion.


64/108

62

CAPACITY TABLEPRESSURE DIFFERENTIALS - POUNDS PER SQUARE INCH

150 Lb. 200,Lb. 250 Lb.TRAp CONN. 30 Lb. Seat 75 Lb. Seat 125 Lb. Seat Seat Seat SeatSIZE 5 10 20 30 30 50 75 75 100 125 125 150 150 200 200

CAPACITIES IN POUNDS WATER PER HOURtS01A V2" and 3,4" 450 590 770 910 620 740 870 590 660 740 600 660 450 510 415tSOl AS lh" and 3,4" 450 590 770 910 620 740 870 590 660 740 600 660 450 510 415tS01AT 112" and 3,4" 450 590 770 910 620 740 870 590 660 740 600 660 450 510 415tS01AST 1/2" and 3,4" 450 590 770 910 620 740 870 590 660 740 600 660 450 510 415tSOOB 1/2". and 3/4" 720 900 1100 1260 760 1115 870 960 1050 740 800 800 880 760tSOOBS V2" and 3,4" 720 900 1100 1260 760 940 1115 870 960 1050 740 800 800 880 760t600BT 1/2" and 3/4" 720 900 1100 1260 760 940 1115 870 960 1050 740 800 800 880 760t600BST 1/2" and 3/4" 720 900 1100 1260 760 940 1115 870 960 1050 740 800 800 880 760tS02B 1/2" and 3/4" 1085 1670 2225 2665 1550 1885 2245 1635 1795 2035 1740 1890 1375 1520 1170tS02BS 112" and 3/4" 1085 1670 2225 2665 1550 1885 2245 1635 1795 2035 1740 1890 1375 1520 1170tS02BT 1/2" and 3/4" 1085 1670 2225 2665 1550 1885 2245 1635 1795 2035 1740 1890 1375 1520 1170t602BST V2" and 3/4" 1085 1670 2225 2665 1550 1885 2245 1635 1795 2035 1740 1890 1375 1520 1170tS03B 3/4" and ]" 2750 4600 6200 7150 3300 4320 5400 3055 3490 3845 3700 3950 2900 3225 2180t603BT 3/4" and 1" 2750 4600 6200 7150 3300 4320 5400 3055 3490 3845 3700 3950 2900 3225 2180tS04B 1" and ]W' 4750 7600 9900 11500 5950 7525 8950 5880 6440 7180 6230 6750 5250 6040 4550tS04BT 1" and Jl/4" 4750 7600 9900 moo 5950 7525 8950 5880 6440 7180 6230 6750 5250 6040 4550'SOD 1/2" and 3/4" 980 1250 1600 1850 990 1180 1350 1000 ]100 1200 1000 1050 880 975 680'SOD ]" 2800 3550 4500 5200 3500 4150 4800 3100 3400 3700 3100 3300 2600 2900 2100'SOD Jl/4" and 1W' 5200 6700 8600 10000 7400 9000 10500 7500 8300 9000 6]00 6600 5400 6000 4900"T " Thermal Element in Trap "S" Internal Strainer tStainless steel interiors 'Brass lever

Figure 70.

T h e r m o d y n a m i c T r a p sThese t r aps find wide use in the medium to high pr e s su r e application

range. They have a minimum operat ing pr e s su r e and a maximum operat ingback pr e s su r e . Since these pa rame te r s va ry with the var ious types avai lable ,the specif ica t ions for the t r ap should be checked when applying i t to a specificappl icat ion.

I t is possib le for a the rmodynamic t r ap to be closed due to "flashing"of the condensate pass ing through it . The t rap specif ica t ions should be check-ed to determine the number of degrees below sa tura ted s tearn t empera tu re r e quired for prope r t r ap operat ion . Should the condensate t empera tu re be toohigh, prema tu re closing of the t rap and flooding of the equipment on which thet r ap i s ins tal led can take place.

These t raps m ay be ins tal led in any posi t ion and when ins tal ledver t ica l ly , they a re f r eeze-proo ' As a rule , a safe ty f ac tor of twice the es t i mated maximum load is applied.

250

460460460460840840840840

12751275127512752380238049704970

74023005350


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C o n d e n s a t e H a n d l i n g E q u i p : m e n tThis product spec:iiication covers a broad var ie ty of condensate

pu:mping syste:ms. In general , they:may be clas sified as:1. Condensate Pu:mps2. Boiler Feed Pu:mps3. Vacuu:m Pu:mps

All

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