Hopkinsons Product Support

HopkinsonsINDEX

2 Weir Valves & Controls First choice for process protection WVC-HOP001-R0

Weir Valves & Controls 4

The Hopkinson Story 6 - 17

Company Milestones 18

Boiler Mountings & Valves 18

Parallel Slide Gate Valves(a) Operating & Design Features 19 - 20(b) Product Application 20(c) Hopkinsons Product Range & Features 20(d) Valve Construction 20

(i) Back Seating(ii) Packing Under Pressure(iii) Seats & Discs

(e) Comparison of Parallel Slide Valve with Wedge Gate 22 - 25(i) Seating Principles(ii) Thermal Binding(iii) Ease of Maintenance

(f) Optional End Connections 26(g) Bolted Bonnets 26(h) Stuffing Box Design 26 - 28

(i) Exfoliated Graphite Packing(ii) Upgrading of Conventional Glands & Pressure Seal Bonnets(iii) Water Sealed Glands

(i) High pressure Parallel Slide Gate Valves 28 - 33(i) Pressure Seal Bonnets(ii) Venturi Bore Design(iii) Follower Eye(iv) Seat Velocities(v) Product Ratings(vi) Relationship Between Nom. Pipe Size & Valve Seat Diameter (vii) Vee Port Outlet Seats(viii)Steam Purging with Venturi Valve Design(ix) Process, Petrochemical & Nuclear Market

Bypass Valves(a) Application 33(b) Method of Operating 34

Equalising Bypass Valves & Devices(a) Hydraulic Lock 35(b) Balanced Spindle Valves 35 - 36(c) Equalising Pipes & Applications 36(d) Over Pressure 36 - 37(e) Alternative Equalising Devices 37(f) Equalising Bypass 37 - 38

Types of Main Valve Operation 38 - 42

Check & Non-Return Valves(a) Swing Check Valves 43(b) Low & High Pressure Variants 44(c) Feedwater Check Valves 44(d) Vertical Lift Check Valves 45(e) Comparitive Disc Movements (Vertical Lift & Swing Check) 45(f) Stop Check Valves (Stop & Non-Return Valves) 45(g) Tilting Disc Check Valves 46 - 47(h) Bled Steam (Extraction Steam) Non-Return Valves 48 - 53

(i) Features of Hopkinson Design(ii) Valve Application(iii) Competition

3Weir Valves & Controls First choice for process protection

Hopkinsons INDEX

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Reheater Isolation Devices 53 - 56

Drain & Blowdown Valves(a) Comparison of Types 56 - 58

(i) Wedge Gate Valve(ii) Globe Valve(iii) Ball Valve(iv) Parallel Slide Gate Valve

(b) Rack & Pinion Blowdown Valves 58 - 59(c) Uniflow Drain Valves 59(d) High Performance Parallel Slide Gate Valves 60

Water Gauges (Water Level Indicators)(a) Absolute Type 60 - 61(b) Plate Glass Type 61(c) Bulls Eye Type 62(d) Try Valves 62

ASME Section 1 Safety Valves(a) Definition of Safety Valve Types & Terms 63

(i) Safety Valve(ii) Relief valve(iii) Safety Relief Valve(iv) Set Pressure(v) Simmer(vi) Lift(vii) Rated Capacity(viii)Accumulation(ix) Overpressure(x) Blowdown

(b) Hopkinsons Product Range & Ratings 64 - 66(i) Features & Benefits(ii) Principal Competitors

(c) Hopkinsons Steam Test Facility 67(d) Safety Valve Mounting 67(e) Hydrostatic Testing 68 - 69

(i) Hopkinsons Products(ii) Competitors

(f) Servo Loaded Direct Acting Safety Valves 69(g) Anti Simmer Devices 69 - 70

Feed Water Heaters 71

Feed Water Heater Bypass Systems(a) Electrically Operated Gate Valves 72(b) Spring Loaded Bypass Valves 72 - 73(c) Competitors 73(d) Atwood & Morrill 3-Way Valves 73 - 74(e) Medium operated 2-Way Changeover Valves 75

Combined Cycle Power Plant System

Fossil Fuel Power Plant System


HopkinsonsPRODUCT SUPPORT MANUAL

3-way valvesCheck valvesGate valvesGlobe valves

Control butterfly valvesIsolation butterfly valvesHigh performancebutterfly valvesTriple offset butterfly valves

Globe control valvesTurbine bypass valvesChoke valvesDesuperheatersSevere service valvesControl valve actuators

Pipeline surge absorbersPulsation dampersThermal expansioncompensators

Check valvesGate valvesGlobe valvesReheat isolation devicesSafety valves

Side entry ball valvesTop entry ball valvesSubsea ball valvesRotary gate valvesIntegrated systems

Spring-loaded safetyrelief valvesPilot operated safetyrelief valvesTwo-way change-over valvesThermal relief valvesTank blanketing system

Pilot operated nuclearsafety valves

Triple offset butterfly valves

Weir Valves & Controls The key to the success of Weir Valves & Controls isour capability to deliver engineering solutions thatadd value to the customers process. We offer a totalpackage of products to meet end-to-end projectrequirements. Using our own analysis andconfiguration system, we will design and deliver theoptimum valves and controls solution to protect thevalue of the production process.

A rigorous programme of information managementmeans that the division is able to take a moreanticipatory role in defining the future needs andexpectations of the market by fully utilising theorganisation's critical resources to provide wholeprocess isolation and control valve solutions for theglobal Energy sector.

With a comprehensive range of engineered valveproducts Weir Valves & Controls have developed anextensive global installed base and expertise acrossa wide range of industry sectors:

Power Generation General Industrial Oil & Gas Production Refining Petrochemical Chemical Pulp & Paper Desalination


Hopkinsons PRODUCT SUPPORT MANUAL

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Quality assuranceWeir Valves & Controls operates qualityprogrammes to cover the full scope of theiractivities. Comprehensive quality systems havebeen developed to serve the power, oil and gas andindustrial markets which they serve.

The company holds approvals to:

ASME Section III N, NPT, NV

ASME Section I V

ASME Section VIII code UV

BS EN ISO 9001:1994

NF EN ISO 9001

API Q1 TO API LICENCES API 6D (6D-0182) and API 6A (6A-0445)

API 526

TUV - AD MERKBLATT WRD HP 0

The Quality systems have been approved for thesupply of products to meet the requirements of thePressure Equipment Directive (PED) andcompliance modules A,D1,H,B&D have beenapplied in categories I through IV respectively.

The company is committed to compliance withlegislation and has an established environment andhealth and safety policy.

An ongoing commitment to customer care is metthrough the process of continuous improvementand the further development of our systems andprocesses towards meeting ISO 9001:2000.

Valve testing facilitiesAll pressure containing items are hydrostaticallytested, seat leakage tested and functionally tested.In addition, gas, packing emission, cryogenic andadvanced functional testing can be arranged.

Material testing facilities Non-destructive examination by radiography,

ultrasonics, magnetic particle and liquid penetrant.

Chemical analysis by computer controlled directreading emission spectrometer.

Mechanical testing for tensile properties at ambientand elevated temperatures, bend and hardnesstesting. Charpy testing at ambient, elevated andsub-zero temperatures.

Further technical information can be obtained fromour Web site: http://www.weirvalve.com

HopkinsonsWeir Valves and Controls manufacture HopkinsonsValves and Boiler Mountings for use on steamraising plant of any size and type.

Hopkinsons brand products, renowned for longand dependable service life, can be seen oninstallations ranging from shell boilers for heatingand process steam up to the highest capacity unitson electricity generating stations.

In the nuclear power industry, the Hopkinsonname is synonymous with expertise in the designand production of safety related items such as fastoperating main steam and main feed isolationvalves.

The Hopkinson range of products also includesvalves for isolation, regulation, pressure relief,instrumentation and drain and specific plantprotection duties on the new generation ofCombined Cycle Gas Turbine Power Stations.

6A-04456D-0182


HopkinsonsTHE HOPKINSON STORY

Britannia Works, Huddersfield, UK, the headquarters and mainfactory of Hopkinsons Limited.

The Early History of ValvesThe history of the development of valves containsvery little recorded information, and cannot besaid to have shown much progress beyond themost primitive stages until the beginning of the19th century.

As far back as about 230 B.C., Philon of Byzantiumdescribed arrangements for drawing wine fromcasks, corresponding to present-day faucets forremoving beer from barrels, and even mentioned asimple design of a two-way-cock. The Romansmade use of the elementary types of valves,probably for controlling water in pipes, andamong those preserved is a bronze plug cockdiscovered in the Palace of Tiberius in Capri (builtA.D. 39). This type of valve continued to be usedwith little variation until the advent of steam as amotive power, when the screw-down stop valveand weight-loaded safety valve were developed.

The apparent absence of progress in valve designfor two thousand years is obviously due to the factthat man had not yet appreciated the uses ofsteam as a source of power, and such valves aswere required called for no particular technicalskill in design and construction. The crudewooden plug valve (illustrated), dating from thelate 17th century, was probably quite adequate forthe very unexacting duties which it had toperform.

With the development of steam power, however,the importance of valves as a means of promotingefficiency and safety began to be appreciated byengineers. It is at this stage, in the early decades ofthe 19th century, that the Hopkinsons story began.

Elm wood stop valve

Bronze plug cock

Roman stop cock

opposition to the introduction of machinery in thetextile industry.

However, Joseph Hopkinson believed inengineering and in the future of steam. Hisengineering interest obviously knew no bounds,he even patented an improved design of steelstiffener for ladies corsets!

Despite the hostile climate he started business in1843 in an upstairs room in Huddersfield. But evenas early as 1835 he was involved in tests toestablish the relative strength of the copper tubesin a boiler. From this evidence it can be assumedthat he was one of those engineers earnestlyinvolved with the early introduction of steampower to the textile mills of Huddersfield anddistrict.

By 1845 the business was firmly established inlarger premises, two converted cottages, inLockwood, Huddersfield. So, HopkinsonsHuddersfield seen on valves in virtually everycountry in the world, was born.

Identifying the Market

Right from the outset Joseph Hopkinson identifiedhis market. Indeed he left a hair-raising account ofwhat many boilers and boiler mountings were likewhen he began to design and manufacture valves.

The crude equipment installed, and the light-hearted manner in which boilers were looked aftercaused numerous serious accidents. Frequentcases arose where boiler attendants, ignorant ofthe consequences, tied-down the weight lever ofthe safety valve in order to gain an increase insteam pressure - often with disastrous results.

In fact it was not until there was an increasedsense of responsibility, fostered by the variousSteam Users Associations, and backed by reliableboiler mountings, that the boilerhouse explosionbecame a rarity.


Hopkinsons THE HOPKINSON STORY

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Views of Hopkinsons Cottage Workshop.

Typical of the devastation caused by a boiler explosion

The Hopkinson StoryToday Hopkinsons Limited is located in a 16 acre(7 hectare) factory and office complex inHuddersfield employing approx. 500 people. Itsbusiness is that of a world leader in themanufacture of valves, for power generation, theOil & Gas industries and process andpetrochemical applications. Behind these facts is aremarkable story of inventive genius, enterpriseand dedication to quality that has earned the firmits unique international reputation over the yearssince 1843.

That story began at a time when there were stillmen in the prime of life who had fought at theBattle of Waterloo and before Huddersfield had arailway link with the commercial world.

Opposition to Mechanisation

Huddersfield and its neighbourhood were stillaffected by the Plug Riots of 1842 (so-calledbecause men drew the plugs from factory boilers)that showed the continuing bitter



A Haystack boiler of the 1840sNote the crude repair patches (right)

Hopkinsons Compound Safety ValveSafety Indicator & Alarm

Early Mountings

Those were the days of the Haystack and WagonBoilers, simple, crude designs which remained ingeneral use in industry until nearly the middle ofthe century. Arrangements for safety and controlwere likewise crude - where in fact they existed.

The earliest method of ascertaining the level ofwater in a boiler was by holes through the boilershell each containing a wooden bung which couldbe withdrawn by the attendant to check if thewater or steam issued from the hole. A morerefined method followed in the form of twopetcocks or taps situated one above and onebelow the normal water level. Here again theattendant had to physically open the taps to checkfor the presence of fluid.

The breakthrough came with the addition of aglass tube to connect the outlets of the taps, soproviding a continuous indication of the waterlevel. This formed the basis of todays tubularwater gauge.

A means of boiler pressure indication wasintroduced by adapting the mercurial U tube ormanometer gauge with a wooden rod resting onthe mercury and moving over a scale.

Better Designs

Subsequently the primitive boiler designs werereplaced by other and better types, such as thesingle-flued, or Cornish boiler, designed to sustainrelatively high pressures, and originally introducedby Richard Trevethick in 1812. In due course thatwas succeeded by the Yorkshire and then the well-known Lancashire boiler, while the locomotivetype of boiler was also instrumental in affectingthe trend of design of boiler equipment,particularly in regard to spring safety valves, asopposed to lever or weight controlled valves.

Creating the Business - and its Symbol

It follows that when J. Hopkinson & Co. beganoperations in 1843 there was a genuine need forthe design and construction of safety boilermountings. In this regard the company adoptedas its trademark the stool, or saddle, which wasriveted to the boiler shell, and on which the safetyboiler mountings were mounted.

One of the first major successes of the companywas the Compound Safety Valve, which proved tobe an outstanding invention for preventing boilerexplosions. Moreover its later development, theDuad Safety Valve, became a standard fitting forLancashire boilers and can still be seen in servicetoday. The Compound design was among theproducts exhibited by the company at the GreatInternational Exhibition in 1851 when it received amedal and certificate signed by H.R.H. Albert, thePrince Consort.



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A 60 horse-power balanced horizontal condensing steam engine

Challenging Words

Not frightened to put his money where his mouthwas Mr. Hopkinson published an advertisement in1852 headlined Important Invention! Steamboiler explosions rendered impossible. The copyexplained the features of Hopkinsons New PatentCompound Safety Valve and at the end carried thebold statement:

200 REWARD is hereby offered, and will be paidby the Inventor, to any person who shalldemonstrate the possibility of exploding a boilerfrom pressure of steam or deficiency of water, iffitted with the New Patent Compound SafetyValve, provided that the Boiler operated upon isequal to its ordinary working pressure.

Needless to say 200 in those days of goldenguineas was no mean sum and clearly confirmedthe firms confidence in its product just as indeedit does today.

Moreover the early Steam Users Association -which were later to become the boiler insurancecompanies we know today - offered a 10 per centreduction in premium if a boiler was fitted with aHopkinsons Compound Safety Valve.

With these early developments, and the expansionof the firm to new premises in Leeds Road, thepattern was set whereby the history ofHopkinsons was to become that of the wholeprogress of valve design and manufacture.

In 1854 the Hopkinsons type water gauge madeits appearance, together with a mercurial typesteam pressure gauge. Similarly, the companyintroduced a patented Economical Self-CleansingBoiler which was claimed to work with perfectsafety at a pressure of 100 Ib/in2 - a remarkableinnovation in a decade in which anything inexcess of 40 Ib/in2 was considered a highpressure.

Three years later - in 1857 - the companyscatalogue stated the patent transverse boiler maybe used at 200 Ib/in2 or 250 Ib/in2 with greatersafety than the best of the ordinary boilers at 70Ib/in2. Actually there was considerablecorrespondence in the Manchester Guardian onthe definition of high pressure, which closed withthe view that it was 50 Ib/in2!



Mr. Hopkinson with his steam engine indicator.

Scale model beam engine

Hopkinsons on the Indicator

At about this time - and with more than ten yearsresearch and development behind it - thecompany introduced the Hopkinsons SteamEngine Indicator, which was an improvement onJames Watts invention. Put in Joseph Hopkinsonsown words:

What the Stethoscope is to the Physician, theIndicator is to the Engineer - revealing the secretworking of the inner system, and detecting minutederangements in parts obscurely situated.

His method of selling his Indicator is interesting initself. Very simple he used his own Indicator toimprove the efficiency of the engine by re-settingthe valve timings. If he did not improve thehorsepower by 10 per cent, then no fee wascharged. If he succeeded, he was paid sevenshillings and sixpence per horse plus 25 per centof the cost of the coal saved over two years.

This development of the Indicator was followed bythe publication of a book Hopkinsons on theIndicator, which contained a great deal ofadditional information on the management ofsteam engines and boilers. At once this book wasrecognised as making an important practicalcontribution to the existing knowledge on thesubject, and it ran into many editions.

It was not, however, entirely well received. Therewas apparently a critical review of it in TheEngineer and as the Editor failed to publish JosephHopkinsons reply, he wrote again to the Editorstating:

You publish a scurrilous article, which you call areview of my book - the third edition - from whichit is quite evident that the subject is one withwhich you are altogether at sea, and undoubtedlyhave a less knowledge than most operativeengineers.

Your cowardly conduct in this matter, refusingme a reply, and then withholding my property,deserves the highest censure, nay, more, such achastisement as I shall take the liberty of givingyou for your cowardice, viz., a horse whipping.

There is no record of whether he carried out histhreat, but it is indicative of the blunt andforthright manner of the man. Certainly he wasnot backward in coming forward and - like Brunel- was a first-class publicist. There is a reproductionof him with his new design in valve setting withthe copy which stated:

The prosperity of England depends upon thesuccess of her manufacturers, and the amount ofsuccess that is accomplished in all practicalsciences depends solely upon having the rightman in the right place to arrange and conductthem.



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Taking to the Waves

The earliest mention of Hopkinsons involvement inmarine engineering appears at this time in the 2ndedition of Hopkinsons on the Indicator dated1857. Joseph Hopkinson gives an account of testsusing his Indicator instrument on the engines ofthe S.S. Great Britain, the first ocean going ship tobe built of iron and to have screw propulsion.Hopkinson gives an account of some length inwhich he firstly proves the inefficiency of theoriginal engines, then goes on to show howmodifications to the engines resulted in increasingthe total output from 686 to 1,663 horse power.Holding nothing back he severely raps theknuckles of the original engine constructor forperpetrating such a glaring blunder as he didcommit in turning out such inefficient machines.

From that day on the name of Hopkinsons was tobe associated with the best of British Shipbuilding.Through the years of the great ocean goingpassenger vessels - to the latest and probably thelast - the Queen Elizabeth 2. The Royal YachtBritannia was also fitted with Hopkinsons valves.

With the Royal Navy too, the company has a longreputation for technical expertise and productreliability. Standard and special purpose valveshave been supplied for a variety of ships from theaircraft carriers and battleships of the SecondWorld War to the smaller frigates and nuclearpowered submarines of today.

Indeed it was from the companys experience indesigning and supplying rapid operatingemergency closing parallel slide valves - astandard requirement on all RN steam driven shipssince the 1930s - that has enabled Hopkinsons togain substantial orders over recent years for quickclosing steam and feedwater isolation valves onnuclear power stations worldwide.

Emergency closingvalves suppliedfor the cunard

passenger liner.

An ocean going containership.

The great S.S. Great Britain



Original Patent

Hopkinsons premises at Viaduct Street

In their Fathers Footsteps

In 1867 Joseph Hopkinson was followed in thebusiness by his two sons, John Addy and Joseph,the firm then becoming J. Hopkinson & Co. butthe polices of good design and high-qualitymanufacture remained the same. So, too, did theinventive and entrepreneurial spirit.

Thus three years later, in 1870, the HopkinsonsDeadweight Safety Valve was introduced and, withits weights contained within a lockable cover,provided a valve which overcame the problems ofinterference by irresponsible or incompetentoperatives.

By this time the increasing reputation ofHopkinsons products meant production had to bestepped up. As a result the company moved to arelatively large factory in Viaduct street, nearer thecentre of Huddersfield, in 1871. It was there overthe following thirty-three years that the firmsteadily advanced to become recognised as theforemost valve manufacturer in the world. It was areputation not only for being the best, but equallyfor constantly producing new designs and newinventions.

These included a pressure gauge operated on theBourdon principle, an automatic isolating valve,and a steam separator.

The Parallel Slide Valve

Most important, in 1881 the company patentedthe Hopkinsons Parallel Slide Valve, an inventionthat greatly influenced the trend in stop valvedesign. So effective was the design that it remainsbasically unchanged even today where it accountsfor the major share of the firms production.

Its great merit was, and is, that fluid-tightness ismaintained without the aid of wedging action. Nomechanical stress is exerted between the discs,and the valve is not subjected to dangerous strainsin opening and closing.



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A drawing of theHopkinsons PSV

Deadweight SV

Accessible Check Feed Valve

Originally the valves were made in cast iron andgunmetal, and were designed for pressure up to200 Ib/in2. By the late 1890s they were beingoffered in cast steel - capable of with-standinggreater mechanical stresses in the pipeline thancast iron - and suitable for steam pressures up to250 Ib/in2. Today however, they may cope withsuperheated steam at pressures of 4,350 Ib/in2 attemperatures of 1085F (300 bar at 585C), or,boiler feed water at 6,250 Ib/in2 at 500F (431 barat 260C).

1889 saw the production of the Accessible CheckFeed Valve, which was designed to enable thevalve and seat to be examined while the boiler wasunder steam. That was followed by the AbsoluteWater Gauge, which was fully automatic in bothgauge arms, thus preventing the escape of steamand water in the event of breakage of the gaugeglass.

With these new products and sustained growth, inMarch 1894 the firm was converted into a privatelimited company with a capital of 40,000 andtrading under the name of J. Hopkinson & Co Ltd.

The next milestone came in 1903 when - stillinnovating - the firm introduced the HopkinsonsCentre-Pressure Valve, primarily designed as aturbine stop valve. This unit comprised two mainvalves and a leak-off-device - all automaticallycontrolled in sequence. Advantages of the design -mainly that the master valve never had to close oropen against full pressure - were quickly realisedin the power industry, and soon added new lustreto Hopkinsons reputation.

Even more significant, 1903 was the year when thesite was prepared for the present Britannia Worksin Birkby as, despite extensions, the Viaduct Streetworks was too small to handle the constantlyexpanding volume of orders. The reason Birkbywas chosen was because at that time the site wasin a designated Industrial area and the companywas to have had a railway line, but in the event itdid not materialise.

In this regard it is interesting to note that while in1890 the number of employees totalled about 120,the new works employed some 600, a figurepractically trebled before the Second World War.



A Hopkinsons venturi parallel slide valve.

The venturi parallel slide valve.

Hopkinson & Ferranti

Back to 1904 and a association betweenHopkinsons and another Great British innovator,Dr. Sebastian Z. de Ferranti, the pioneer of electricpower. It was he who, looking at the drawings ofthe Hopkinsons Parallel Slide Valve and also at thedrawing of a Venturi flow meter, had the idea ofcombining the features of one with the other. Hetherefore adapted the design of a Hopkinsonsvalve to incorporate a converging inlet and adiverging outlet flow passage similar to that of aVenturi meter. This concept was developed andthe result was the Hopkinsons-Ferranti Stop Valve,which made one more significant advance in thevalve industry.

The general features, still as valid today as then,were similar to those of the parallel slide valve butembodied the Venturi principle. Owing to thereduced bore, the valve travel and fittings areproportionately smaller, the load area is less thancorresponding sizes of full-bore valves andoperation of the valve is therefore easier.

Underlying this development is the story thatFerranti originally offered his idea to theHopkinson then running the business for a lumpsum of 10,000. However he was told that theidea had no particular future, but that Hopkinsonswas prepared to take up the patent on a royaltybasis.

In the course of further negotiations the pricedropped from 10,000 to 5,000 to 2,000, butstill Mr. Hopkinson insisted on an agreement on aroyalty basis only. Ultimately Ferranti agreed - andcollected some 64,000 over the course of the lifeof that patent.

But hindsight is of little use, and as it was, thesustained overall progress of Hopkinsons meantthat its interests soon extended internationally.

By 1910 the firm had depots and showrooms inthirty cities around the world and, to catch the eyeof the relaxed industrialist, there was even ashowroom on the pier at the North of Englandsmost popular seaside resort, Blackpool!

Naturally the First World War years 1914-18 hadprofound effect on the firm insofar as manyemployees joined the services and production wasconcentrated on essential war materials.

A year later in 1920, a new private company wasformed with a capital of 600, 000.



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Throughout its history the company has produced valves to meetthe highest pressure and temperature requirements of the powerindustry.

This graph illustrates the upward trend in water tube boilerpressures to the middle of this Century. Since then, however, UKelectricity generating station practice has remained virtually levelat 2,400lb/in2 (165.5 bar).

Stateside Testimonial

Hopkinsons technical excellence was still beingrecognised far from home as indicated by a notefrom the American Prime Movers CommitteeReport given at the National Electric LightAssociation convention in Chicago in 1921.

The Hopkinsons English valve has been used inthis country on high pressure superheated steamwork with marked success...The success of thesevalves is due to the very careful design of body,grade of materials used throughout, and goodworkmanship.

Proud of its success and anxious to increasebusiness even more the private company exhibitedat the British Empire Exhibition at Wembley in1924. This event coincided with the firmcelebrating eighty years in business so a MonsterExcursion - as the paper dubbed it - wasorganised by the company. In brief, 1,300employees and their relatives were taken fromHuddersfield to London on a free, all expensespaid, visit to the Exhibition.

In 1926 the firm became public company, with acapital of 700,000 and with the title, HopkinsonsLimited.

Other examples of the success achieved byHopkinsons designers and engineers on the shopfloor are numerous. To take one example in 1930Hopkinsons were asked to supply a 10 in. centre -pressure turbine stop valve for an experimentalturbine installation at the Delray No. 3 PowerStation of the Detroit Edison Company, USA.

This valve was required to operate at 415 Ib/in2

maximum pressure and 1,000F, a temperaturepreviously unapproached in power stationoperation. The arduous operating conditionsnecessitated the use of special steels for the bodyand lid. As a result the order gave Hopkinsons yetanother first and heralded the company as amanufacturer of alloy steel valves.

Six years later, in 1936, Hopkinsons producedvalves for Brimsdown A Power Station North ofLondon. Here the safety valves had pressure of2130 Ib/in2, and pressure at the turbine stop valvewas 1950 Ib/in2 with a working temperature of930F.

Year of Installation

Op

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Pre

ssu

re L

b/I

n2

Bar

War Work

A few years later Britain was involved in theSecond World War when the efficiency andcontinuous operation of the power stations andvital industrial plants were essential. Since these inturn depended on the reliability of boilermountings and valves, Hopkinsons products weregiven the highest priority. Actually for some timeprior to September 1939 the firm had substantialorders for equipment for the new power andprocess installations in Government factoriesthroughout the country, in addition to extensionsto electricity generating stations which thenacquired a new urgency.

Furthermore there was the extra production forthe war effort in the form of components forarmaments, aircraft, tanks and even assemblies forAsdic submarine detection instruments.

Britain Rebuilds

Post war nationalisation of Britains electricityindustry brought in considerable orders forHopkinsons when the new authority commenceda national plan for the modernisation of existingplant and the construction of additional powerstations. Once more, the companys expertise wascalled upon to provide the best in the design andmanufacture of valves and associated products tomeet this challenge.

In fact, as the industrys expansion programcontinued, Hopkinsons supplied practically two-thirds of the valve requirements and over a third ofthe sootblower systems for the fifty 500 MWelectricity generating units built in the 1960s.



High investment in the machine shop.

The internationally recognised N code

Going Nuclear

Perhaps the most notable innovation in the powerindustrys history has been the introduction ofnuclear power, and beginning with the worlds firstindustrial scale nuclear power station opened atCalder Hall England in 1956. Hopkinsons hassupplied both conventional and purpose designedvalves for all the UKs commercial andexperimental nuclear reactors.

On the international scene too, Hopkinsons isrecognised as an authority on valves essential tothe safe operation of nuclear power stations. Themain steam safety valves, main steam and mainfeedwater isolation valves made for PWR(pressurised water reactor) type nuclear powerstations in the USA, Europe and Asia are notableexamples. Valves for controlling heavy water havebeen supplied for the primary heat transfersystems of Canadian CANDU type reactors.

Drilling valve bodies in F bay.



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A main steam isolation valve

Butterfly valves molded in GRP material

X-Stream TrimControl Valve

Referring again to the Venturi parallel slide typemain steam and main feedwater valves for nuclearpower stations, at which they fulfil a requirementfor the safe shutdown of the nuclear reactor in anemergency situation. The incredible fast closingspeed of these 30in. (750mm) valves - a mere twoseconds for full operation - contrasts sharply withthe five minutes or more which would be neededfor the manual operation of a much smaller valveat the beginning of the century.

The above and other examples quoted throughoutthis publication indicate the results of the constantresearch and development work by the companyand, in parallel the capital investment in newbuildings, plant and equipment.

Continuing Development

The Weir Group vigorously encourages andsupports product innovation by membercompanies, of Weir Valves & Controls.

Hopkinsons products continue their leadership ofthe high integrity valve industry by constantresearch and development. The use of highlydeveloped materials - ceramics, plastics, carbonand graphite and new metallic alloys - arecontributing to improvements in valve design. Themain aims are valves having lower weight, higherstrength, smaller components and longer servicelife, all advantageous to the valve user in reducingpower plant construction and running costs.



Company MilestonesCompound Safety Valve patented 1852

Steam Engine Indicator improvements patented 1857

Deadweight Safety Valve introduced 1870

Parallel Slide Gate Valve patented 1881

Steel valves introduced 1890s

Hopkinsons-Ferranti (Venturi Flow) Stop Valve patented 1904

Steel foundry opened 1912

Electrically operated valves introduced 1920s

Public company floated, Hopkinsons Ltd 1926

Alloy Steel valves for 1,000F duty produced 1930

Sootblowers added to product range 1938

Valves for worlds first industrial scale nuclearpower station, UK 1956

Supplied two-thirds of valves etc. for UKs 25 newpower stations 1960s

Main Steam Isolation Valves for PWR nuclearpower stations 1970

Repair & Servicing subsidiary opens in Cardiff 1981

Autotork Electric Actuator/Controls subsidiary launched 1987

Blakeborough Controls Valves incorporated inHopkinsons range 1988

Hopkinsons Ltd bought by Weir Group 1989

Oil & Gas Industry pipeline valves range announced 1993

Acquisition of Batley Valve 1996

Acquisition of Sebim Group 1998

Acquisition of Flowguard 1999

Formation of Weir Valves & Controls 2002

IntroductionMost valves on a power station can beconveniently listed in two groups,

1. For safety

2. For control (A few belong to both groups)

Group 1. Includes Safety Valves, Water Gauges, Non-return Valves and automatic Isolating Valves.

Group 2. Includes Feed Valves, Blown Down Valves, Drain Valves and all the various kinds of Stop Valves.

The following pages are intended to helpnewcomers to steam engineering to becomefamiliar with the many types of Hopkinsons Valvesand Boiler Mountings they are likely to comeacross in the course of their work.

Weir Valves and Controls Salesmen, Agents andRepresentatives will also benefit from a greaterunderstanding of the various products and theirapplications, enabling them to provide a betterservice to their customers.

Boiler Mountings & ValvesIn the complex equipment of a modern steam,generating plant, the boiler mountings andauxiliary valves rank among the most importantitems, as the safety and smooth working of thewhole plant depends to a great extent on theirsuitability and correct design.

The casual observer would hardly notice themountings and valves, as they are usually almostindistinguishable under a thick covering oflagging. Many of them - such as Re-heaterIsolation Devices - are placed in remote positions,well away from the firing floor. Some are soinsignificant in size that one might easily assumethat their design, construction and duties werematters of little consequence.

The power plant engineer however quickly findsout the value of these fittings. He appreciates thenecessity of obtaining first class equipment,installing it correctly and maintaining it properly.He soon learns that one faulty valve can cause themost exasperating and costly shutdowns, and thata leaky valve can waste an extraordinary amountof expensive steam.

When it is remembered that in a large steamgenerating plant there are hundreds of items ofequipment that come within the category ofmountings and valves, the responsibility placed onthese fittings will be fully appreciated.


Hopkinsons PARALLEL SLIDE GATE VALVES

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Parallel Slide Gate ValvesThe Parallel Slide Gate Valve (PSGV) in its variousforms, accounts for some 65% of the total numberof valves manufactured annually under theHopkinson name.

First introduced in 1881 the basic design principleon which the valve operates has remainedunchanged to the present day.

Before examining this important design of valveand its various applications, we should firstconsider basic valve construction and operation.

TYPICAL HOPKINSONS PARALLEL SLIDE GATE VALVES FORA WIDE RANGE OF APPLICATIONS.

Figure 1

600# Bolted Bonnet Valvewith Flanged End Connections.

Small BoreForged Steel Valve

1000# Class Valve incorporatingPressure Seal Bonnet

with Butt Weld End Connections.

(a) obturating(direct thrust)

rotating

sliding

(b) pinching

There are only two ways of controlling the flow ofliquids and gases and all valves, whatever theircomplexity might be are based on one of thesefundamental principles.

Fig1. Shows a simple tank from which water isflowing from an outlet near the bottom. In orderto control the flow, one can either place a fingeragainst the pipe (diagram a) or alternatively, if thepipe is flexible it can be pinched (diagram b).

These illustrations represent the two basicprinciples of valve construction, although the firstprinciple is developed in three ways, representingthe different means by which the stopper can bepresented to the pipe end, or seating.

If you can think of another practical way you willhave invented a new type of valve!!

Advantages Disadvantages

Globe Smaller sizes have best shut-off Very high pressure drop ( p) through valve and rapidand regulating characteristics. wear of seating faces. Larger High Pressure sizes require

massive actuators.

Conical Quick acting, straight through Difficult to combine tight shut-off with ease of operation.Plug flow.

Ball Quick acting, straight through Unsuitable for regulating duties whichflow, easy operation. can cause damage to the ball surface.

Butterfly Quick acting, good regulating Unsuitable for very high pressures andcharacteristics. temperatures.Compact.

Gate Straight through flow, Wedge gate type unsuitable for varying temperature low p. applications. Parallel slide design unsuitable for low p

conditions.

Pinch Glandless, positive shut off Pressure and temperature limited by diaphragmon dirty fluids. material.Lends itself to linings such asglass, rubber etc.


HopkinsonsPARALLEL SLIDE GATE VALVES

Figure 2

How does it operate?

Nominally parallel seat faces

Self aligning discs

Closure takes place atoutlet only

Inlet disc lifts fromseat face

FLOW

Figure 3

Larger sizes &higher pressuresfitted with gearssometimes need asmany turns of thehandwheel, as agate valve.

The first & simplest way of moving the stopper isby a direct thrust on to the seating. This we call theobturating movement and is the basis of the globevalve. The word globe being based on the shapeof the first valves of this type which were like asphere or globe.

The second method of motivation is to rotate thestopper, which is the basis of the plug cock, aprinciple dating back to early Roman Times.

The third way is to move the stopper across theface of the seating which is the basis of the gatevalve (Both Parallel Slide & Wedge Type).

All diaphragm valves are based on thepinching/squeezing action.

To summarise, here then we have the fourprincipal methods of valve closure:-

1. OBTURATING - Globe Valve

2. ROTATING - Ball Valve, Plug Cock Butterfly Valve.

3. SLIDING - Wedge Gate, through Conduit Gate,

Parallel Slide Line Blind.

4. PINCHING - Diaphragm Valve

Each has its own particular characteristics,advantages and disadvantages.

The Hopkinsons Parallel Slide Gate Valve bydefinition falls into category 3.



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1. Low Pressure Valves i.e. 150 & 300 Class Ratings having a Full Bore and incorporating a Bolted Bonnet.

2. High Pressure valves i.e. 600 - 3100 Class Ratings having a Full Bore and incorporating a Pressure Seal Bonnet. [NB Exception is the 600 Class Valve in WCB, WC6 & WC9, which has a Bolted Bonnet].

3. High Pressure valves i.e. 600 - 3100 Class Ratings having a Venturi Bore and incorporating a Pressure Seal Bonnet. [NB Exception is the 600 Class valve in WCB, WC6 &WC9, which has a bolted Bonnet].

The range of valves listed above are essentially insizes 5 - 30 but there is also a complementaryrange of smaller sizes of valves manufactured byHopkinsons in ASTM A105 Forged Carbon Steeland ASTM A182-F22 Forged Alloy Steel.

This range of Parallel Slide Valves is utilised onPipeline Isolation duties and in a modified form, asa Bypass or Equalising Bypass for the larger sizeHopkinsons Parallel Slide Valves.

Let us first consider the design features of the LowPressure Full Bore Valve; -

1. Complies with the design requirement of ASME B16.34 1998 In 150 & 300 Class Ratings.

2. Overall length in accordance with ASME B16.10

3. Flanges in accordance with ASME B16.5 with alternatives available if required.

4. Butt weld ends to ASME B16.25 with provision for alternative profiles should they be required.

5. Available in Nominal Bore sizes 212" to 30".

Valve Construction The valve has been designed with a boltedrectangular Body/Cover assembly incorporatingan exfoliated graphite gasket.

All valves operated with a direct mountedhandwheel are of the two pillar design with rollerthrust bearings fitted in the bridge to provide lowfriction operation.

When electric, pneumatic or hydraulic actuation isrequired, there is provision on the standard valvecover to fit a four-pillar arrangement to providethe necessary additional support.

In considering the operation of a Parallel SlideValve, an important fact to remember is that in itsbasic form i.e. without special seats or bypassarrangements, the valve is bi-directional.

Fig 3. Shows a typical Parallel Slide Valve sealingarrangement, incorporating a male and femaledisc held against their respective seat faces bymeans of an internal spring.

The purpose of the specially designed spring is toprovide initial sealing of the valve under no loadconditions.

When the valve is under pressure, the force of themedium (steam or water) on the inlet disks movesit away from its seat face and compresses thespring.

This action allows the medium to enter andpressurize the intergate space (i.e. that part of thevalve between the seat faces) and force the outletdisk against its seat face.

Once the pressure in the intergate space is equalto the inlet pressure, the inlet disk is returned to itsseat face by the action of the spring.

The intergate pressure continues to act against theback face of the outlet disk, maintaining isolationof the valve/pipeline.

THE GREATER THE LINE PRESSURE, THE TIGHTERTHE SEAL.

What is a Parallel Slide GateValve Used For?The application of a Parallel Slide Gate Valve isessentially that of providing positive isolation onthe following duties:-

1. Steam & Water services in the Power Generation Industry.

2. Process Steam & Water applications in the Petro-Chemical and PaperMaking Industries.

3. Fuel or Lubricating Oil distribution.

In certain circumstances, a parallel slide valve maybe used on regulating duties - such as Boiler FeedPump Start up - by the fitting of a Vee Portoutlet seat. This feature will be explained in detaillater on in the text.

Product FeaturesSo far, we have considered Parallel Slide GateValves only in the most general terms. However, itshould be appreciated that there are in fact, THREEspecific Hopkinson designs manufactured in Castand Forged Carbon and Alloy Steels i.e. ASTMA216-WCB, ASTM A217-WC6, ASTM A217-WC9,ASTM A105 & ASTM 182 Gr. F22. For special hightemperature applications, a select range of valvesis available in C-12A Modified 9% Cr.



A substantial stem stop (together with an indicatorplate on the valve pillars) provides positiveindication of the degree of opening/closure of thevalve and prevents rotation of the stem.

The valve is closed when the stem stop reachesthe lower shoulder of the pillars and open whenopposite the open mark at the opposite end of thepillars.

A Backseating facility is incorporated in the coverand is brought into effect by opening the valvebeyond the Open mark on the indicator plateuntil resistance is felt.

The sealing action is achieved through a seatingface on the end of the disc holder contacting aBackseat bush fitted into the cover below the baseof the stuffing box.

It is important to remember that irrespective ofwhat may be written in Contract/Tenderingspecifications, the purpose of backseating is NOTto allow repacking of the stuffing box when thevalve is under pressure.

The function of a backseating facility is to isolate aleaking stuffing box, thus preventing stemdamage, until the problem can be attended towhen the system is shut down and no longer live.

Failure to follow this ruling can result in seriousinjury to anyone attempting to re-pack a glandwhile the valve is under pressure.

As with all other Hopkinsons products, thestuffing box packing material in the Low PressureFull Bore Parallel Slide Valve is Exfoliated Graphite.

The seats and discs are the very heart of a ParallelSlide Valve. Sound design and selection of thecorrect materials are essential to its properfunctioning.

Over many years experience, Hopkinsons havedeveloped their own proprietary materialPLATNAM for use on the wide variety of seatingapplications across their extensive product range.

On the Low Pressure Parallel Slide Valves, the seatsare manufactured from No.12 Platinum (which is ahigh nickel content steel) and are a press fit intothe valve body.

Discs on the smaller sizes of valve are producedfrom solid No.12 Platinum castings while thelarger sizes (above size 4) are manufactured fromsteel with a No.6 Stellite facing.

Comparison of the ParallelSlide Gate Valve with theWedge Gate ValveWe learned earlier that a Parallel Slide Valve is aposition seating valve, utilising line pressure inorder to effect closure. Originally invented byHopkinsons, it is also manufactured by a numberof other Companies around the world i.e.

MANUFACTURER LOCATIONBailey - Birkett UKShaw Valves UKTaylor Valves Ltd UKPeter Smith UKDewrance - Tyco Germany & ItalySapag - Tyco FranceTOA JapanUTSUE JapanMalbranque FranceVelan CanadaAudco IndiaBabcock Borsig SpainCrane Pacific USA

There are also a number of other companiesworldwide who manufacture a Parallel seatingvalve but this design utilises a mechanicalspreading disc feature and cannot beconsidered a true parallel slide valve. In theintroduction to this manual, we examined thevarious types of valves and their applications. Eachtype has its own special capability but no oneparticular valve can satisfy a number of functionsadequately.

Such an example is a Globe Valve which hasexcellent regulating characteristics but at theexpense of the seating surfaces. These can quicklybecome eroded to the point that completeisolation of the valve is impossible.

Essentially a Parallel Slide Valve is an isolationvalve and performs best on systems with a highpressure differential across the seating surfaces.Where no such pressure differential exists, analternative solution is required. A Wedge GateValve, which mechanically seals on both inlet andoutlet seat faces without the assistance of linepressure is a suitable option.

Unfortunately Wedge Gate valves which are usedextensively in the Oil, Petro-Chemical and Refineryprocesses are also utilised in Power GenerationIndustry with less than satisfactory results.

To understand the reasons for this, we mustcompare the relative design features of both theParallel Slide and Wedge Gate Valve.


Hopkinsons PARALLEL SIDE GATE VALVES

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Wedge Gate Valve tries to seal on 2 seat faceswhich is difficult to achieve. MSS SP 61 spec.acknowledge this and gives a large leakage ratefor test.

Figure 4

The shortcomings of the traditional solid WedgeGate design as illustrated in Fig. 4 have long beenrecognised by manufacturers and various waysdeveloped as a means of overcoming the problem.

Positive Isolation of Seating Faces with ZeroLeak

The highly effective Hopkinsons flat disc closuremechanism is far superior to the wedging actionclosure used in a Wedge Gate design [Refer Fig.4]the line pressure alone causes a tight seal farsuperior to that of the Wedging action system.

In the Hopkinsons design it is SYSTEM PRESSUREnot mechanical force which achieves a tight seal.After moving the disc assembly to the isolationposition in a Parallel Slide Valve, no additionaltorque is required to isolate the line.

For this reason, torque spanners, or wheel keysshould never be used on a Parallel Slide Valve toeffect closure. Added force once the discs are inthe sealing position will result in bent stem stopsand damaged spindle threads.

Additional travel of the spindle due to a bent stemstop can in extreme circumstances cause the discholder to be forced against the bottom of the valvebody causing distortion of the disc holder. If thishappens, the discs will become jammed and theirsealing effect lost.

The use of torque switches instead of limitswitches to control the opening and closing of anelectrically operated Parallel Slide Valve can alsocause damage to the external and internalcomponents as previously described.

NEVER SET AN ELECTRICALLY OPERATED PARALLELSLIDE GATE VALVE TO OPEN/CLOSE ON TORQUE USE ONLY THE LIMIT SWITCHES.

Conversely, the design principle on which theWedge Gate Valve is based is that of driving awedge between two tapered seats and effectingclosure on both the inlet and outlet seat faces.

This is difficult to achieve and specification MSSSP61 acknowledges this fact by giving a leakageallowance on test of 10cc/inch bore/ hour. Toachieve isolation, the Wedge Gate Valve requiresextra torque to consolidate the Wedge in itssealing position, thereby placing additional stresson the valve yoke/pillars/stem/body and seatfaces. Larger actuators are therefore necessary andWedge Gate Valves are not suitable for use with airoperators. (i.e. 5 7 bar air supply usually foundin most plants would result in unacceptably sizedair actuators.)

Flow

Incorrect angle results in leakage



One such solution is the Flexi-Wedge in whichthe wedge has some means of permittingmovement of its opposing faces to enable them toalign themselves with their respective seat faces.On larger sizes of valves operating at highpressures, the extra torque required to achieve thisis considerable and in reality, the Flexi-Wedge GateValve is only providing a complicated solution to aseating problem which a Parallel Slide Valveaddresses succinctly.

A typical Flexi Wedge Gate Valve design is shownin Figure 5.

Ease of Operation

Because a Parallel Slide gate Valve stem is notconstrained at both ends and the spring loadeddiscs are free to adjust themselves to temperaturefluctuations, the spindle/disc assembly will neverjam or seize up. [Refer Figure 6]

In a Wedge Gate valve, the stem is constrained intwo places i.e. In the yoke/bridge and at theconnection to the Wedge (since the wedge isforced into the tapered seating). Severe jamming,(Thermal Binding) of the Wedge can occur whenthe valve is isolated when hot and the systemsubsequently cools. In attempting to open WedgeGate Valves from such a situation, it is notunknown for the spindle-retaining portion of theWedge to shear [Refer Figure 7]. Acknowledgingthis problem, some large bore Wedge Gate Valvemanufacturers (particularly where valves arerequired an low-pressure waterworks installations)supply their products with a jacking point for theWedge in the bottom of the valve body. [ReferFigure 8]

Figure 6Because the Parallel Slide Valve stem is not constrained at both ends the discsare free to adjust themselves to temperature fluctuations andstem /disc assembly will not jam

Figure 7Severe jamming of wedge can occur when the valve is isolated when hot andthe system subsequently cools. Stem distortion can also occur due to basicdesign weakness, which prevents stem expansion relative to the valve body.

Figure 8

Figure 5

Sleeve nut is the onlystem constraint

Stem can expand andcontract freely withoutchanging shutoff tightness

Discs slide over seat faces

Stem constrainedin two places

Stem liable todistortion andjamming ofwedge will occur



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Figure 10

Illustrated are examples of in-situ lapping

Figure 9

Self Cleaning Seating Surfaces

Seat deposits wipedaway by sliding actionof the discs.

The wiping action of the disks as they slide overthe seat faces, removing dirt and scale deposits is aunique feature of the Parallel Slide Gate Valve.Stellite or Hopkinsons PLATNAM seat and discfacings prevent wear under the most arduous ofoperating conditions. [Refer Figure 9]

Should there be evidence of a Parallel Slide GateValve passing once it has been isolated, the correctprocedure to achieve tightness is not to reachimmediately for a wheel key [Refer Page 21] but toopen and close the valve a number of times toremove any possible entrapped debris betweenthe outlet seat and disc faces. Of course, there maybe damage to either the outlet seat or disc - oreven both, which prevents isolation taking place.In such circumstances, remedial action can only betaken during a shut down of the plant.

The non-wiping action of a Wedge Gate Valvetraps dirt and scale between the wedge and seatfaces preventing correct seating and resulting inleakage. Use of a wheel key to further force thewedge into the seat taper and squash anyentrapped debris is the traditional action of plantoperatives to solve the leakage problem. It can bean effective solution but if the entrapped debris ismetallic it will also ultimately damage the wedgeand seat sealing faces.

In Line Maintenance

If properly cared for, in a well run plant,Hopkinsons Parallel Slide Gate Valves require littlemaintenance. Should it be necessary to carry outlapping of the seat faces, the operation cangenerally be carried out while the valve is still inthe pipeline. With no angles to match as with aWedge Gate Valve, a smooth flat surface is all thatis required for the lapping process.

Discs are easily removed for re-lapping on alapping plate and as with the seats, a smooth flatsurface is the only requirement.



Gland Stud

Disk springs& retaining cup

Gland flange

Gland packing

Carbon sleeve

Figure 13

Stem

Gland nut

Gland Follower

Bonnet

Optional End ConnectionsIn the Power Generation Industry, the use of flangedconnection valves has diminished over the years withan increasing preference for Butt-Weld joints - evenon low-pressure applications. The reason for thistrend has been purely economic. Flangedconnections enable a valve to be removed relativelyeasily from a pipeline for maintenance, but theflange joints are in themselves a potential leakagepoint whilst a welded joint requires no maintenanceat all. Certainly in pressures above 900# it is virtuallyunknown to have a flanged valve in the PowerIndustry. Conversely, in the Process andPetrochemical Industries, flanged valves of up to5000# are quite common.

On the Hopkinsons range of products, flanged orbutt weld end connections are available in a varietyof options generally up to and including 900#.Above this pressure rating, it is usual to have buttweld end connections only.

Bolted Bonnet JointsAlthough the problems associated with conventionalbolting have long been recognised i.e. creep athigh temperatures and stretching at high pressures,correctly designed bolted bonnet joints on lowpressure valves are perfectly satisfactory.

Exceptional Gland PerformanceThe traditional material for the packing of glands onall types of valves, was, for many years, braidedasbestos covered in graphite and impregnated withmolybdenum disulphide as a cohesive agent. It wasmarketed under various trade names, the mostpopular being CRANE 1066.

This type of packing worked well under mostcircumstances but it had two fundamental flaws: -

(a) The use of asbestos was considered a health hazard to plant operatives.

(b) At high temperatures, the molybdenum disulphide burned off, the packing shrank and the stuffing box leaked.

The trend towards having automated plants withfewer operatives, inevitably, meant that less dailymaintenance - such as tightening gland bolts - wascarried out with the results as described. A possiblemeans of overcoming the lack of daily maintenancewas the use of live loaded packing, which imposeda pre-determined compression on the gland packingthrough the use of Belleville spring washers. [ReferFigure 13]

Unfortunately, this is an expensive means of curinggland leakage problems and in todays competitivemarkets does not find favour amongst original buildcontractors. It is more likely to be fitted to key valves- such as Main Steam Isolation Valves, by the plantoperatives, once they have taken over the running ofthe Power Station.

Figure 11a600# Bolted Bonnet Valvewith Flanged End Connections.

Figure 12

Small Bore Forged Steel Valve

with Bolted Bonnet.

Figure 11b1000# Class Valve incorporatingPressure Seal Bonnet with Butt Weld End Connections.



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Figure 14

Gland Packing Comparison

Figure 15

Conversion from Soft Iron to Grafoil Pressure Seal

Expandedgraphitepacking

Reduced length &volume

Typicalasbestospacking

Greatervolumeshrinkswith age

Section showingoriginal soft ironsealing ring

Seal

Graphite packing rings

Section showinggraphite sealing ring

& gland packing

Neck bush

Distancepiece

Sealing ring

Bonnet

An expansion of 80 - 200 times the originalthickness is preferred because this will produce acohesive material without the need for binders,leaving the product virtually pure graphite.

Graphite has excellent mechanical properties atelevated temperatures, good friction properties, isradiation resistant and chemically inert. It alsopossess the necessary basic properties of a goodcompression packing material for Nuclear Service.

Hopkinsons Parallel Slide Gate Valves have beendesigned to utilise the best characteristics ofexpanded graphite packing. [Refer Figure 14]

Expanded graphite provides a stable glandpacking material which due to its resistance to lossof volatiles at high temperatures minimises thefrequency of gland adjustment.

Packing rings on new valves are supplied wholeand are also available whole as replacements.Alternatively, replacements can be supplied in twohalves so they can be fitted to the stem anddropped in position without removing thehandwheel assembly. It is important however thatthe rings are arranged so that the split betweenthe halves of each ring are staggered as shown inFigure 14. Since less graphite is used in glandpacking than conventional types, the consequentsaving permits stocking of the parts at site forimmediate replacement/overhaul work.

Upgrading of Conventional Glands &Pressure Seal Bonnets

Older valves incorporating a gland based ontraditional packing may be upgraded to utiliseexpanded graphite. To do this it is necessary toreduce the depth of the stuffing box since lessexpanded graphite packing is quite critical to itseffectiveness and an excess of packing wouldresult in failure to compress the lower ringsproperly with the inevitable results. Figure 15shows the basic modification to an older type ofgland preparatory to changing to expandedgraphite packing.

Some designs of valve bonnet closure incorporatea soft iron sealing ring as shown on the left handside of Figure 15. The disadvantages with this typeof seal are its resistance to compression and thedamage it can cause to the internal valve bodywalls in effecting a seal under pressure.Subsequent fitting of replacement seals thenbecomes problematical. By modifying some of theinternal components of the valve, a grafoil seal canbe fitted which will accommodate at least 0.04"ovality in the body seal bore.

A more economical and practical solution to theproblem has been achieved through the use ofExpanded or Exfoliated graphite packing. Firstdeveloped by the American Company UnionCarbide and marketed under the name GRAFOIL itis manufactured by various companies throughoutthe world but almost usually referred to asGrafoil Packing.

Expanded graphite is produced by subjectingflake, powder or chip graphite particles with ahigh degree of atom orientation, to an oxidizingmedium such as sulphuric or nitric acid.

The oxidizing agent forms openings, the length ofthe carbon networks in the graphite. Whenremoved from the acid and then rapidly heated,the gas trapped within the graphite layersexpands, in turn expanding the graphite. Thisexpanded mass is then compacted to the desireddensity (i.e. Sg 1.6 - 1.7) by mechanical means tothe required thickness and shape.



Figure 19

Pressure Seal Bonnet

Water Sealed Glands

Occasionally, the requirement for valves to be fittedwith a water sealed gland is a feature of TenderSpecifications. It is little used in the PowerGeneration Industry these days but is still widelyaccepted practice in the Petroleum Industry. APIstandard 600 issued by the American PetroleumInstitute for the design of steel gate valves givesprecise requirements for a water sealed stuffing boxon such valves. In the Power Generation Industry,the function of a water-sealed gland is to preventthe ingress of air into a vacuum system such as existsduring turbine trips and boiler feed pump start-ups.

A metallic ring, with a recess running around itsoutside diameter is inserted into a speciallydeepened stuffing box. An external tapping point(traditionally 14" BSP) is made from the inside of thestuffing box to the outside of the valve bonnet towhich is connected a filling cup or piping to acentral water supply. Water passes through to thelantern ring and forms a seal over the lower packingrings in the stuffing box.

Maintenance on such a feature is obviously quitehigh and the use of expanded graphite with all itsbenefits has superseded water sealed glands in thePower Generation Industry. Figure 16 below shows atypical water sealed gland layout.

High Pressure Parallel SlideGate ValvesAlthough the high and low pressure designs ofParallel Slide Gate Valves manufactured byHopkinsons serve the same function, the essentialdifference is that the low pressure valve is a Full Borevalve incorporating a Bolted Bonnet while the HighPressure valve may be offered in Full or Venturi Boreconfiguration with a PRESSURE SEAL BONNET.Figures 17 & 18 illustrate the respective designs.

Let us first examine the features of the High PressureFull Bore Valve which apart from having welded inseats and a pressure seal closure is virtually identicalto its low pressure equivalent.

Pressure Seal Bonnet

The bonnet sealing in Hopkinsons Pressure SealValves is accomplished with a sealing ring of pureexpanded graphite of the same material used in thegland packing.

Used as a pressure seal gasket, the seal is made ontothe standard machined surface of the Body andBonnet. Unlike valves having a metal to metalpressure seal joint, no inlay or hardfacing of thesealing areas is necessary.

Hopkinsons valves with graphite pressure seals aretherefore much easier to maintain. Any minordamage caused to the sealing faces duringmaintenance only requires blending into thesurface. No expensive and time consumingmachining, re-depositing and lapping is required.

Figure 16

Figure 17

Full Bore Valve

Figure 18

Venturi Bore Valve



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Figure 20

Parallel Slide Valve

Flexi-Wedge Gate Valve

Figure 21

Seat Faces protected

Open PositionFlow path uninterruptedwith valve in openpositiondue to eyelet

Flow

Seat Faces exposed to system dirt and scale

Open PositionFlow path interrupteddue to turbulencecreated due to noeyelet resulting inincreased pressuredrop

Venturi Bore

We mentioned earlier that the Venturi Bore principlewas first developed in the early 1900s by Dr SebastianZ de Ferranti.

His experiments proved that within certainparameters, a reduced bore valve fitted with aFOLLOWER EYE or CONDUIT in the intergatespace when the valve was opened resulted in verylittle pressure drop (p) across the seats. Such adesign of valve has many advantages over its full-boreequivalent. Because of the reduced bore, the valvetravel (i.e. distance from OPEN-CLOSE) and fittingsare proportionally smaller. The disc load area is lessthan corresponding sizes of full bore valves andoperation of the valve is therefore easier. Whereelectrical operation of the valve is required it ispossible that a much smaller and less expensiveactuator may be selected. Figure 20 shows a Venturivalve in the closed position with the follower eyelocated in the closed position with the follower eyelocated in the bowl shaped lower portion of the valvebody which is a distinctive feature of the Venturidesign.

The disc springs and disc clip which preventsspreading of the discs when the valve is open areclearly seen.

Follower Eye

The advantages of the follower - eye are clearlyshown in Figure 21 which compares the Venturidesign product with a full bore wedge gate valve.

A comparison between the Venturi valve with afollower eye and a wedge gate valve has been quitedeliberate in that it demonstrates that the benefits ofa follower eye are impossible to apply to a wedgegate design - at least in economical and practicalterms.

However, a shrewd observer would quite rightlyreach the conclusion that the shortcomings of the fullbore wedge gate valve compared to a Venturi parallelslide valve, apply somewhat equally to a full boreparallel slide valve. This raises the question that if theVenturi valve is all that it is claimed to be, why do weneed a full bore equivalent?

The answer to this is purely down to customerknowledge and experience: - without question, theVenturi bore valve is an exceptional design with manyunique features and benefits which are recognisedand appreciated in the World Power Market. By thecareful selection of seat to end bore ratio, coupledwith the benefits of a follower eye, a venturi valve willequal the pressure drop characteristics of a full boregate valve - be it wedge gate or parallel slide.



These primary service ratings were the permissibleworking pressures at a particular temperature.

The first deviation from this practice was in 1964when the manufacturers Standardisation Society ofthe valve and fittings industry (MSS) publishedStandard Practice SP66 covering pressuretemperature ratings of steel butt-weld end valves.The ANSI B16 committee set up a sub-committee tostudy the general subject of pressure temperatureratings and to develop rational criteria for suchratings.

ANSI B16.34 standard was the outcome of thesestudies and the 1973 version was issued to cover steelbutt welding end valves only. The SP66 type ratingswere included as Special Class. Flanged valves werestill included in ANSI B16.5 along with flanges.

A revision was issued in 1977 and another, thecurrent one, in 1996 with amendments in 1998. Thislatest edition covers flanged and butt welding endvalves in steel, nickel alloy and other special alloys. Inorder to cover flanged valves, rating tables have to beincluded for 150, 300, 600, 900, 1500 and 2500.

Since butt-welding end valves are not constrained bythe flange ratings, provision was made forintermediate ratings, which can be any class withinthe limits of the standard.

Analysis of market requirements shows that thecustomary (flange) ratings are not always aneconomic solution to the pressure temperaturerequirements. For example a 2500 class valve oftenfalls short of the requirements for main steam designconditions associated with large utility boilers.

If a 2500 class will not satisfy the requirements ofpressure and temperature the next standard rating is4500 class. Except for small sizes, the adoption of4500 class is not practical or economic. This can beillustrated by taking an example of a valve having a16" end bore.

Minimum wall thickness tm for 2500 class isapprox. 5 12 ".

Minimum wall thickness tm for 4500 class isapprox. 12 12 ".

Not only would the 4500 class valve be very expensivebut also there would be the practical problems ofsupport, unacceptable thermal gradients across thethick sections and the associated stress etc.

Many feed water applications require valves in excessof 1500 class and yet the required pressure-temperature rating is well short of 2500 class.

As stated earlier, provision is made in ASME B16.34for intermediate ratings (referred to as interpolatedratings in earlier editions). To quote the standard: - Abutt welding end valve may be assigned anintermediate rating or class, either Standard or Special,providing all requirements of this standard are met.

However, whilst the Venturi design can represent asignificant market advantage, the product may onlybe offered under the following conditions: -

(a) Steam velocities through the seat area must not exceed 90m/sec (Saturated Steam) 180m/sec (Superheated Steam).

(b) Water velocities through the seat area must not exceed 15m/sec.

Full bore valves i.e. valves without a follower eye arerestricted to the following:-

(a) Steam velocities through the seat area must not exceed 66m/sec (Saturated Steam)130 m/sec (Superheated Steam)

(b) Water velocities through the seat area must not exceed 12m/sec.

The following formula should be used in determiningseat velocities and pressure drop.

Velocity in ft/sec = flow in Ib/hr x Sp Vol in cu.ft/Ib19.635 x (seat bore in inches)2

Pressure Drop = K x (pipe velocity in ft/sec)2

9274 x Sp vol.in cu.ft/Ib

It should also be remembered that although the seatbore can be adjusted to suit a given set of designconditions for a specific pipe size, the nominal endbore size of the Venturi valve remains unchanged andcompatible with the customers designated pipingand butt weld end size. Even so, the benefits of aVenturi style Parallel Slide Valve are not always readilyunderstood or accepted by customers - even after themost strenuous sales efforts coupled with technicalsupport. This occurs most often in areas of the world,which have been exposed to American PowerTechnology and Consultants. Similarly EuropeanContractors, particularly German and Italian havevery conservative attitudes towards seat velocities andin spite of our own reassurances have rejected theproduct.

In such circumstances, it is more sensible for theSalesperson not to pursue the issue but offer a fullbore Parallel Slide Valve. The sales effort can then bedirected towards the benefit of the Parallel Slide Valveover the Wedge Gate, keeping the Venturi issue out ofthe equation. There are non-so blind as those who donot wish to see!

Product Ratings

The current range of High Pressure Parallel SlideValves comply with the design requirements of ASMEB16.34 in 600# 1000# 1700# 2350# AND 3100#Class Ratings. With the exception of the 600# valve,the other high-pressure valve ratings do not fall intocustomary defined categories.

The customary valve ratings in ASME (formerly ANSI)standards have been 300, 400, 600, 900, 1500, 2500& 4500 classes. Up to 2500 class these have followedflange standards and were originally Primary ServiceRatings.



WVC-HOP001-R0

Figure 22

Outlet disc

Flow path

Outlet seat

On this basis Hopkinsons have adopted pressure-temperature ratings as standard, 1000 class, 1700class, 2350 class and 3100 class. These replace thecustomary 900 class, 1500 class and 2500 class.Higher ratings are available as required.

The main point to remember is that theseintermediate rated valves conform to therequirement of B16.34. Standard or Special asappropriate, without any qualification.

A valve designed to meet 1000 class would only berated as 900 class standard if it had 900 classflanges. All flanged valves would be limited to theflange rating and in WC6 and WC9 would have anupper temperature limit of 1000F.

When the required rating is 600 class or less, theadvantages of intermediate ratings become marginaland tend not to be adopted by any company.

Relationship Between Nominal Pipesize andValve Seat Diameter (ASME B.16.34)

One of the most frequently misunderstood aspectsof he ASME design code and its intent, is theconfusion some customers have in regard to theVenturi Parallel Slide Gate Valve not meetingminimum flow path criteria.

The paragraph in ASME B.16.34 to which they referis 6.1.2 and states:- For the purpose of determiningthe wall thickness tm, the inside diameter d is takenas the minimum diameter of the flow passage butnot less than 90% of the basic inside diameter at thevalve end . . .

It is not unusual for some customers to mistakenlyinterpret this paragraph as meaning a valve seatbore should not be less than 90% of the valve endbore.

Let us be quite clear on this matter. ASME B.16.34makes no restriction whatsoever on seat bore. Thepurpose of clause 6.1.2 when used in conjunctionwith table A1 of the said code is for determining theminimum valve wall thickness tm. In determiningthe minimum thickness tm, the diameter used mustnot be less than 90% of the end bore. This 90%valve only applies to the determination of tm nothing more.

Market ApplicationsPower Generation Industry

The many applications of both Low and HighPressure Parallel Slide Valves can be clearly seen inthe schematic layouts of the Combined Cycle andFossil Fuel Power Plants accompanying this text.These are purely isolation functions but there areoccasions during start up of the plant where it isnecessary to have a degree of regulation through thevalve.

Vee Port Outlet Seats

Parallel slide valves are essentially isolation valves tobe used either fully open or fully closed and are notdesigned for continuous flow regulation.

There are however applications, such as bled steamfrom turbine to feed water heaters, where the flowneeds to be restricted during startup to avoidoverloading drains. The amount of steam required ismore than can be supplied through a small bypassvalve and would probably require the valve in themain line to be, say, 13 open. For short-term useduring startup this is permissible but if the turn-down ratio is high, that is, the valve would onlyneed to be opened a small amount, then it is notpermissible.

For flow regulation and good isolation with bothsteam and water, a suitable valve can be producedwhich is essentially a standard parallel slide valvesuitable for the pressure and temperature, with amodified seat and disc on the outlet side, that is,suitable for unidirectional flow only.

The seat has V port in it as shown in Figure 22. Theshaded area and inside the port is deposited withStellite or its equivalent, and the face of the disc issimilarly deposited but over a larger area thanwould be the case for a straightforward isolatingvalve.

The port shape would normally be of a shape asshown in Figure 22 and would be such that it wouldfit inside a circle of the same size as one of thestandard seat bore for the particular class of valve.

In all cases the minimum width of Stellite depositaround the port area would be the same as astandard valve for the same conditions.

As will be seen from the port shape thecharacteristic is approximately linear but it is notintended to be a control valve with a knowncharacteristic such that a particular stem positionwill give a precise pressure drop.

Its application is when a preset valve is required tobalance a system rather than that where a truemodulating control valve would be required to copewith constantly varying conditions.

Globe valves are often usedfor this application butwould have a shorter lifethan the type described hereand would certainly notprovide the positive closureof the parallel slide valvewhen required.



Figure 23

Spring loaded discswith hard facingdeposits

Temporary seat used during steampurge

Fabricated follower eyeassembly

Steam Purging with the Venturi DesignMain Steam Isolation Valve

Common practice during the commissioning of anew boiler or after extensive repair to an existinginstallation, is to install a sacrificial valve in placeof the Main Steam Stop Valve before commencingsteam-purging operations. This procedure ensuresthat the main steam stop valve internals do notsuffer any damage from the inevitable debris inthe system but it is a time consuming andexpensive operation to change and replace thesetwo valves.

A unique advantage of the Venturi Parallel SlideValve is that it lends itself perfectly to SteamSurging Operations without having to be removedfrom the boiler. Instead the valve is fitted with atemporary set of internal components whichincorporate downstream seat protection, whilstthe eyelet in the follower eye ensures a smoothstream flow through the intergate space in theopen discharge position.

Modified spindle and actuator insert leads enablecritical operating times to be achieved duringsteam purge sequences. Following completion ofpurging operations, the temporary internals maybe removed and refurbished, ready for use on thenext unit or held in store for future purgingrequirements.

Process, Petrochemical & Nuclear Market

The current range of Parallel Slide Valves havebeen designed to satisfy the requirements ofmarkets for steam and associated water services.From time to time, we are asked to quote for valverequirements for other services such as oil and avariety of gases in the process and petrochemicalindustries. For applications where the fluid is fuelor lubricating oil there is no reason whyHopkinson Parallel Slide valves should not beoffered.

If valves are required for oxygen service, we mustdecline to offer due to the difficulty in obtaining agas tight seal between the seats and discs. Ifhowever gate valves are required for gas servicesother than CO2 services such as are employed onGas Cooled Nuclear Reactors, we should offer ourvalves but making it quite clear to the customerthat we are offering products: -

(a) Designed to ASME B.16.34(b) The seat faces are Stellite(c) The gland packing material is graphite

We are not in a position to guarantee to acustomer that a Stellite on Stellite seatingarrangement is suitable for any particular gas orcombination of gases.

Hopkinsons Parallel Slide Valves with Stellite andPlatnam seats and discs are not suitable formodification to other seat deposit materials orcombinations such as Universal Trim i.e. Stelliteseat and 13% Cr. Disc, since our design engineershave taken full advantage of the properties ofStellite in reducing the general valve bulk andobtaining overall economies of construction.

Valves for CO2 services on Advanced Gas CooledReactors need seats other than Stellite andcurrently the choice is Fontargen E715 with ahardness of 62 Rockwell C. Any valves for thisservice will need to be specially designed.

Enquiries for valves are often received in which thecustomer specifies API standard 600 when in factvalves to ASME B16.34 would be acceptable.There is no reason why we should not offer ourproducts but again, we must qualify our offerwith the statements given in a, b & c detailedpreviously. Anyone taking the trouble to read APIstandard 600 will understand the reasons fordoing this. API standard 600 specifies a number ofrequirements - peculiar to the Petroleum Industrywith which our products - designed to ASMEB16.34 do not comply. The following list detailssome of the more significant requirements: -

1) API 600 defines Gate Valves as either Wedge (Solid, one-piece flexible and two piece split) or Double-Disc. Paragraph 2.3.6 defines a double disc gate valve as one having parallel seats and an internal spreading device (for example, a wedging device or spring) that forces the two disks firmly against the body seats when the gate is in the closed position.Such a statement would permit the use of our Parallel Slide Valves except where the customer wanted to Block & Bleed i.e. Isolate Inlet and Outlet Seats and drain the intergate space. Our Parallel Slide Valves do not conform with this requirement.

2) API 600 requires internal guiding of the gate.

3) API 600 stem diameters are greater than ASME.

4) API 600 stuffing box specifications are based onthe former use of Asbestos as opposed to graphite packing, which results in a greater depth.

5) API 600 specifies a thicker body wall than ASMEfor certain designs of pressure seal bonnet valves.

6) For cleaning (pigging) purposes, the seat bore of an API 600 valve is required to be not less than the bore of the mating pipe.

Bypass Valves andEqualising DevicesBypass Valves

In a Hopkinsons Parallel SlideGate Valve, the pipelinepressure is utilised to achievevalve shut off.

When opening the valve it isnecessary to overcome theforces created by the systempressure acting against theoutlet disc. However it mustbe recognised that ineffecting closure of the valve, an operator has to overcome threedistinct loads, i.e.

(i) Disc Load

(ii) Packing Load

(iii) Unbalanced Spindle Load

The design of the Parallel Slide Valve is such that itis a simple calculation to accurately determine eachof the above loads and ultimately their sum, inorder to establish the effort required to close thevalve against the design conditions of the system inwhich the valve will be located.



WVC-HOP001-R0

Figure 24

Plain Bypass

Disc Load = Disc area x design pressure x .N.B. varies between .2 and .4 depending on the design conditions. It should also be remembered that since a Parallel Slide Gate Valve is position seating, no additional force is required to move the disc from the seat. Experiments have shown that with a Wedge Gate Valve, an additional 20% extra effort is required. This can result in the requirement for a much largermechanical or electrical actuator than would be necessary for a Parallel Slide Valve under the same conditions.

Packing Load = Area of packing in contact with spindle x e. N.B. e varies depending on the type of packing fitted and is based on the minimum load necessary to prevent gland leakage. Overtightening of the gland stud nuts will greatly increase the gland packing load to the point that it can be impossible to operate the valve.

Unbalanced Spindle Load = Cross sectional area of the spindle x design pressure.

The unbalanced load acting on the valve spindlehas a positive and negative effect during theoperation of a valve. In the opening mode, theunbalanced spindle load will assist the operatorwhilst the reverse occurs during closure where theoperator is required to overcome the effect of theunbalanced spindle load.

By far the greatest of the three loads is the disc loadand when opening the valve it is necessary toovercome the forces created by the system pressureacting against the outlet disc.

On small size valves, these forces are easilyovercome with our standard size handwheels oractuators.

On larger bore valves, some means of equalizingthe pressure differential across the discs is desirableand this is achieved by fitting a Bypass Valve asillustrated in Figure

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