instr 12207 control valves, actuators and positioners

8/13/2019 Instr 12207 Control Valves, Actuators and Positioners

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Module 12207

Control Valves, Actuators

and Positioners


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Instrument Trainee Task Module 12207

CONTROL VALVES, ACTUATORS,AND-POSITIONERS--------------------

Objectives

Upon completion of this module, the trainee will be able to:

1. Define and discuss principles of operation and construction ofvarious control valves.

2. Define and discuss the principles of operation and construction ofvarious actuators.

3. Define and discuss principles of operation of various positioners.4. Define and discuss variables measured and used as inputs tovarious types of positioners.

. Discuss valve selection criteria! and identify various control valves!actuators! and positioners usin" specification sheets! pictures! orsamples.

#rere$uisites

%uccessful completion of the follo&in" 'as( Module)s* is re$uired beforebe"innin" study of this 'as( Module+ ,--/ -ore -urricula ,--/ 'as(Module 12201! Craft-Related Mathematics; ,--/ 'as( Module 12202!Instrumentation Drawings and Documents II; ,--/ 'as( Module 12203!Principles of Welding; ,--/ 'as( Module 12204! ProcessControl Theory.

/e$uired %tudent Materials

1. %tudent Module2. /e$uired %afety $uipment

nstrument 'rainee 'as( Module 12207 2


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-ourse Map nformation

'his course map sho&s all of the Wheels of earning tas( modulesin the second level of the nstrument curricula. 'he su""ested trainin"order be"ins at the bottom and proceeds up. %(ill levels increase as atrainee advances on the course map. 'he trainin" order may be adjustedby the local 'rainin" #ro"ram %ponsor.

-ourse Map+ nstrument! evel 2

2 -OM#'

-ontrol alves! ctuators! and #ositioners 5 Module 12207 3


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TABLE OF CONTENTS

Section Topic Page

1.0.0 Introduction to Control Valves, Actuators, and Positioners 62.0.0 Principles of Operation and Construction of Various Control Valves 72.1.0 Gloe Valves ..72.1.1 Gate Valves 122.1.2 !nife Valves 222.1." #all Valves ..262.1.$ Plu% Valves .2&2.1.' #utterfl( Valves .."'2.1.6 )eedle Valves $1".0.0 Principles of Operation and Construction of Various Actuators .$$".1.0 Valve Actuator *er+s ...$$".1.1 ail Open $$

".1.2 ail Closed . $$".1." ail As Positioned . $'".1.$ ail -afe . $'".1.' -prin% to Open . $'".1.6 -prin% to Close . $'".1.7 Air to Open $6".1. Air to Close $6".1.& /pstrea+ $7".1.10 onstrea+ .. $".2.0 e%ulators and educers $$.0.0 Principles of Operation and Construction of Various Positioners ..''$.1.0 Valve Operators and Positioners ''

$.1.1 3(draulic Operators . ''$.1.2 Pneu+atic Operators .. '6$.1." 4otor Operators '&$.1.$ -olenoid Operators .. 60$.1.' 4anual Operators . 60'.0.0 Valve -election, *(pes, and Applications . 62'.1.0 Valve -election . 62'.2.0 Valve *(pes and Applications .6$'.".0 Valve 4ar5in%s and )a+eplate Infor+ation .6$'.".1 atin% esi%nation 6''.".2 *ri+ Identification ..66'."." -ie esi%nation 66'.".$ *read 4ar5in%s 67'.".' Valve -ce+atic -(+ols 6



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'rade 'erms ntroduced n 'his Module

Actuator:'he part of a re"ulatin" valve that converts electrical or

fluid ener"y to mechanical ener"y to position the valve.

Angle valve: type of "lobe valve in &hich the pipe openin"sare at ri"ht an"les.

ANSI:merican ,ational %tandards nstitute.

ASTM:merican %ociety for 'estin" Materials.

Ball valve: type of plu" valve havin" a spherical disc.

Bellows: fle6ible! thin&alled! corru"ated cylinder &hich e6pandsand contracts under differential pressure situations.

Bonnet:'he part of a valve containin" the valve stem and pac(in".

Butterfly valve: $uarterturn valve havin" a plateli(e disc &hichstops flo& by the outside area of the disc sealin" a"ainst the inside ofthe valve body.

Check valve: valve that allo&s flo& in one direction only.

CWP:-old &or(in" pressure.

Deformaton: chan"e in the shape of a material or component dueto an applied force.

Da!hragm actuator: valve actuator in &hich pressure e6erted onthe diaphra"m is used to position the valve stem.

Dsc: #art of a valve used to control the flo& of system fluid.

"ate valve: valve havin" a strai"htthrou"h flo& desi"n &hich

e6hibits very little resistance to flo&+ normally used for open8shutapplications.

"lo#e valve: valve in &hich flo& is al&ays parallel to the stem as it"oes past the seat.

I$entfcaton !late: metal plate or disc located on a valve!sho&in" the manufacturer9s name and the desi"n information for thevalve.

%a!!ng:'he removal of matin" surface defects usin" an abrasivecompound.

%ft:'he actual travel of the disc a&ay from the closed position &hen a



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valve is relievin".

Packng: Material used to ma(e a dynamic seal! preventin" systemfluid lea(a"e around a valve stem.

Plug valve: $uarterturn valve havin" a ported disc.

Safety&'elef valve: type of pressure relief valve that can be used as asafety valve or a relief valve.

Seat:'he part of a valve a"ainst &hich the disc presses to stop flo&throu"h the valve.

Throttlng:'he re"ulation of flo& throu"h a valve.

Tor(ue: t&istin" force used to apply a clampin" force to a mechanicaljoint.

)alve #o$y:'he part of a valve containin" the passa"es for fluid flo&!valve seat! and inletand outlet connections.

)alve stem:'he part of a valve &hich raises! lo&ers! or turns the valvedisc.

)alve trm:'he internal components of a valve &hich are e6posed to theflo&in" fluid.

We$ge: term for the disc in a "ate valve.

*oke #ushng:'he bearin" bet&een the valve stem and the valve yo(e.

1.0.0 ,'/OD:-'O, 'O -O,'/O %! -':'O/%! ,D#O%'O,/%

s an instrument trainee! you &ill encounter many different types of fluidtransport systems. 'hese9 systems may be as simple as potable &aterplumbin" or as comple6 as petrochemical process pipin" systems./e"ardless of the desi"n! they &ill all have at least one thin" in common

there &ill be some type of control valve! valve actuator, or positionerin the system.

alves are necessary in these systems to start! stop! and control orthrottle flo&. 'hey are essential to isolate hi"h ener"y or ha;ardous fluidsfrom the atmosphere. ctuators for these valves provide a means ofautomatic operation as a result of some type of system input! i.e.!pressure! flo&! or temperature.

ny discussion of valves and actuators &ould be incomplete &ithoutconsiderin" the use and operation of valve positioners. 'hese devices areessential in cases &hen remote operability of a valve is re$uired due to

inaccessibility for manual operation. 'hey also provide a means ofoperatin" e6tremely lar"e valves a"ainst hi"h differential pressures usin"



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pneumatics or hydraulics as an ener"y source.

2.0.0 #/,-#% O< O#/'O, ,D -O,%'/:-'O,

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valve is a controlled restriction )in a pipe system* &ith some means ofoperatin" it. 6amples of its basic principles of operation include &hen asurface is pressed a"ainst an openin"! as one closes a door or &hen asurface moves across an openin"! as one closes a &indo&. =ith one of thesurfaces overlappin" the other! a ti"ht seal is formed. alves! as sho&n in!igure "# are used for three principles+

'o control the volume or amount of flo&

'o control the direction of flo&

'o control the pressure at &hich a system operates.


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dama"e trim and stem packing, and actuators! as &ell as causetroublesome noise. n addition! lar"e si;es re$uire considerable po&er tooperate! thus necessitatin" "earin"! levers! etc.

nother dra&bac( is the lar"e openin" needed for assemblyof the disc.

>lobe valves areoften

heavier than other valves of the same flo& ratin".'hen! too! the cantilever mountin" of the disc on its stem is a potentialtrouble source. ach of these shortcomin"s yields to analysis andin"enuity! but only at a price in dollars! space! and &ei"ht.

'he angle valve of !igure % is another and simpler modification of thebasic "lobe form. =ith the ends at ri"ht an"les! the diaphra"m can be asimple flat plate.


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valve stem, &hich is no& out of the fluid! contracts on coolin". 'his action

tends to lift the disc off the seat, causin" lea(s &hich eventually result in&ire dra&in" on seat and disc faces. 'herefore! in hi"htemperature steamservice! "lobe valves may be installed so that the pressure is above thedisc.

2.1.1 >ate alves

>ate valves are used to start or stop fluid flo&! but not to re"ulate orthrottle flo&. 'he name "ate is derived from the appearance of the disc inthe flo& stream! &hich is similar to a "ate. !igure * sho&s a "ate valve.

'he disc is completely removed from the flo& stream &hen a "ate valve isfully open. 'his characteristic offers virtually no resistance to flo& &henthe valve is open and! hence! there is little pressure drop across an open"ate valve. =hen the valve is fully closed! a disc to seal rin" contactsurface e6ists for 3C0 and "ood sealin" is provided. =ith proper matin"of disc to seal rin"! very little or no lea(a"e occurs across the disc &henthe "ate valve is closed. On openin" of the "ate valve! the flo& path isenlar"ed in a hi"hly nonlinear manner &ith respect to percent of openin".

'his means that flo& rate does not chan"e evenly &ith stem travel. lsothe partially open "ate disc tends to vibrate from the fluid flo&. Most ofthe flo& chan"e occurs near shutoff &ith a relatively hi"h fluid velocitycausin" disc and seat &ear and eventual lea(a"e if used to re"ulate flo&.


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%olid wedge


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&hich side is the hi"h pressure )relievin"* side. -are should be ta(en toensure these valves are not installed bac(&ards in the system.


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ate alve


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ate alve

>ate valves are classified as either risin" stem or nonrisin" stem valves.On the nonrisin" stem "ate valve sho&n in !igure "*# the stem isthreaded on the lo&er end into the "ate. s the hand&heel on the stem is

rotated the "ate travels up or do&n the stem on the threads &hile thestem remains vertically stationary. 'his type valve &ill almost al&ays



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have a pointer type indicator threaded onto the upper end of the stem toindicate valve position.

'he nonrisin" stem ),/%* confi"uration places the stem threads insidethe valve! out of contact &ith the environment! and also assures that thestem merely rotates in the pac(in"! &ithout much dan"er of carryin" dirt

into the pac(in" from outside or inside.

/isin" stem )/%* "ate valves! !igure "+# are desi"ned so that the stem israised out of the flo& path &hen the valve is open. /isin" stem "ate valvescome in t&o basic desi"ns. %ome have a stem that rise above )throu"h*the hand&heel &hile others have a stem that is threaded to the bonnet!!igure ",. n this case! the hand&heel rises &ith the stem.

%eats for "ate valves are either provided inte"ral &ith the valve body! orin a seat rin" type of construction. %eat rin" construction provides seats&hich are either threaded into position or pressed into position and seal&elded to the valve body. 'he latter form of construction is recommended

for hi"her temperature service.

nte"ral seats! !igure "+# provide a seat. of the same material ofconstruction as the valve body &hile the pressedin or scre&edin seatspermit variation. /in"s &ith hard facin"s may be supplied for theapplications &here they are re$uired.

%mall for"ed steel "ate valves may have hardfaced seats pressed into thebody. n some series! this +type .of valve!! in si;es from 182 to 2 inch israted for 200 psi" steam service. n lar"e "ate valves! discs are often of

the solid&ed"e type! &ith seat rin"s scre&ed in! &elded9 in! or pressed in

%cre&edin rin"s are considered replaceable since they may be removedand ne& seal rin"s installed.

2.1.2 Fnife alves

special type of "ate valve is the (nife "ate of !igure ". 'his valveserves in slurry and &aste+ lines and in other lo& pressure applications.

'he sharp ed"e of the disc bottom is easily.forced closed in contact &ith ametal or elastomer seat. Open! the disc is in the air! after passin" throu"ha full&idth pac(in" bo6.

Fnife valves have a disc able to cut throu"h deposits and flo&streamsolids such as resin slurry. 'hey! li(e most "ate valves! can be positionedby manual! electrical! pneumatic and hydraulic actuation.



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ate alve



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ate alve



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ate alve G %tem 'hrou"h ?onnet


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2.1.3 ?all alves

Ball valves,-as the name implies! are stop valves that use a ball tostop or start the flo& of fluid. 'he ball performs 9the same function as thedisc in the "lobe valve. =hen the valve handle is operated to open the 9

valve! the ball rotates to a point &here the hole throu"h the ball is in line&ith the valve body inlet and outlet. =hen the valve is shut! &hichre$uires only a A0 rotation of the hand&heel for most valves! the ball isrotated so that the hole is perpendicular to the flo& openin"s of the valvebody and flo& is stopped.

Most ball valves are of the $uic(actin" type )re$uirin" only a A0 turn tooperate the valve either completely open or closed*! but many areplanetary "ear operated. 'his type of "earin" allo&s the use 9of arelatively small hand&heel and operatin" force to operate a fairly lar"evalve. 'he "earin" does! ho&ever! increase the operatin" time for the

valve. Figure 20 sho&s the major components of a ball valve. 'he ballvalve! in "eneral! is the least e6pensive of any valve confi"uration. nearly desi"ns havin" metaltometal seatin" the valves could not "ivebubbleti"ht sealin" and &ere not fire safe. =ith the development ofelastomeric materials and &ith advances in the plastics industries! theori"inal metallic seats have been replaced &ith materials such asfluorinated polymers! nylon! neoprene! and buna,. ?all valves also havelo& maintenance costs.



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patterns. 'he latter has a ball &ith a bore e$ual to the inside diameter ofthe pipe. ?alls are usually metallic in metallic bodies &ith trim )seats*produced from elastomeric materials. lso! allplastic desi"ns areavailable. %eats are replaceable! as are the balls.


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%eat Material Operatin"'emperatures

'


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intended to divert the flo& to one line &hile shuttin" off flo& from theother lines. f complete shutoff of flo& is a re$uirement! it is necessarythat a style of multiport valve be used &hich permits this! or a secondaryvalve should be installed on the main feed line ahead of the multiportvalve to permit complete shutoff of flo&.

t should also be noted that in some multiport confi"urations! flo& tomore than one port simultaneously is also possible. >reat care should beta(en in specifyin" the particular port arran"ement re$uired to"uarantee that proper operation &ill be possible.

#lu"s are either round or cylindrical &ith a taper. 'hey may have varioustypes of port openin"s!Figure 28, each &ith a varyin" de"ree of free arearelative to the correspondin" pipe si;e.


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sin(in" the taper plu" deeper into the body! actuation tor$ue &ill climbrapidly and "allin" can occur.

ubricationremedies this. !series of "rooves around the port openin"s! inthe plu" or body! issupplied &ith "rease prior to actuation! not only tolubricate the plu" motion but also to seatil_ the "ap! see !igure. $.>rease!injected into a fittin" at stem top travels do&n throu"h a check valve inthe passa"e&ay and then past the plu" top to the "rooves on the plu"and!!do&n to a &ell belo& the plu".

'he lubricant must be compatible &ith the temperature and nature of thefluid! of course. Te most common fluids controlled by plu" valves are "asesand li$uid hydrocarbons. %ome &ater lines have these valves too! iflubricant contamination is not a serious dan"er. 'his type can "o to24inch !si;e! &ith pressure capability of C000 psi". %teel or iron bodies areavailable. 'he plu" can be9 cylindrical or tapered.

'he correct choice of lubricant is e6tremely important for successfullubricated plu" valve performance. n addition to providin" ade$uatelubrication to the valve! the lubricant must not react chemically &ith theymaterial passin" throu"h the valve nor must the lubricant contaminate thematerial passin" throu"h the valve because of solubility. ll manufacturersof lubricated plu" valves have developed a series of lubricants &hich arecompatible &ith a &ide ran"e of media. 'heir recommendation should befollo&ed as to &hich lubricant is best suited for the service.

'o overcome the disadvanta"es of the lubricated plu" valves! in so far astheir need of lubrication! t&o basic types of nonlubricated plu" valves&ere developed. 'he nonlubricated valve may be either a lifttype or have

an elastomer sleeve or plu" coatin" that eliminates the need to lubricatethe space bet&een the plu" and seat.



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i%ure "'. -eat in% esi%ns

?ody construction varies. 'he most economical is the &afer type &hichsimply fits bet&een t&o pipeline flan"es. nother type of lu" &afer valveis held in place bet&een t&o pipe flan"es by bolts that join the t&oflan"es and pass throu"h holes in the valveIs outer casin". alves arealso available &ith conventional flan"ed ends for boltin" to pipe flan"esand in a scre&ed end construction.


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and see( its center in 9 the seat. :niform sealin" is accomplished ande6ternal stem fasteners are eliminated. 'his is advanta"eous in the caseof covered discs and in corrosive applications.

n order for the disc to be held in the proper position! the stem must

e6tend beyond the bottom of the disc and be fitted into a bushin" in thebottom of the valve body. One or t&o similar bushin"s are also necessaryalon" the upper portion of the stem as &ell. 'hese bushin"s must eitherbe resistant to the media bein" handled or they must be sealed so thatthe corrosive media cannot come into contact &ith them. ?oth methodsare employed! dependin" upon the valve manufacturer.


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increment scale on housin" cover plate. 'his type of actuation isrecommended for hi"h tor$ue conditions and corrosive atmospheres. tshould be noted that this type of actuator is self loc(in" in any position.6tension handles and floor stand hand&heels may! also be used onthese hand&heel actuators.

-hain&heel actuators are modifications of the hand&heel actuators in&hich the chain&heel operator has been incorporated into the assemblyrather than usin" the hand&heel itself.

n addition to manual operation! butterfly valves may also be operated bymeans or air or fluid po&er and electricity. vailable for this type ofoperation are cylinder actuators! diaphragm actuators, piston actuatorsand electric actuators.


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3.1.3


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3.1.7 ir to Open

ir to open valve operators use air pressure to open the valve and sprin"force to shut the valve. !igure && sho&s a sprin" to close valve operator!but it is also an air to open operator. !igure &) is an air to open valve

operator that uses the sprin" force to e6ert an up&ard force to close thevalve. t could also be referred to as a spring to close valve operator.


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3.1.10 Do&nstream

Do&nstream is e6actly the opposite of upstream. t could be said that ado&nstream component is located in the direction of flo& &ith relation

to a "iven component.

3.2.0 />:'O/% ,D /D:-/%

f fluids are clean and if flo& is reasonably constant! &ithout sudden andfre$uent chan"es! then the small! automatic control system &hich is there"ulator can be an ine6pensive! simple! and reliable solution to acontrol problem. /e"ulators can control do&nstream pressure!temperature! or flo& rate &hile the upstream pressure varies &idely.-ontrol of upstream pressure is also possible. -ontrol by a re"ulator isnot as close as it &ould be in a more e6tensive system of control valve!

actuator! and controller! but the controlled variable can be remar(ably!constant over the full flo& ran"e! if necessary! and to a lesser accuracyover a ran"e of upstream pressure chan"e.

'he sin"lesta"e re"ulator balances do&nstream pressure a"ainstoutsideset sprin" force! on a metal diaphra"m to open or close the valvedisc! !igure &+. Diaphra"m motion is restricted so capacities are limited.%team flo& of 1000 1bm8hr is close to the ma6imum for this sin"lesta"ere"ulator. %ensitivity to upstream pressure and flo& is hi"her than for thet&osta"e re"ulator. n this! &hat amounts to a small sin"lesta"ere"ulator controls flo& 9to a piston that has enou"h area to operate a

lar"e main valve. very small movement of the pilot valve ma(es a lar"echan"e in mainvalve position. 'he error or droop of the sin"lesta"eelement is not as pronounced in the controlled valve of the main valve.

n other versions of t&osta"e re"ulators! the first sta"e is remote froma lar"e main valve &ith a capacity of several hundred thousand poundsan hour of steam. ery small t&osta"e re"ulators for air! on the otherhand! may have capacities of only a fe& cfm.

lar"e sin"lesta"e re"ulator resemblin" a ca"e control valve &ithdiaphra"m and sprin" actuator! !igure &,! can reduce pressure ormaintain bac(pressure. 'he pressuresensin" line runs from the main

line either do&nstream or upstream! to the top of the heavy&alldiaphra"m case. #ressures up to 20 psi" for smalldiameter actuatorsare common.

'he flo& rate controller of !igure &operates on some&hat differentprinciples. (nob at top rotates a sleeve to reduce the si;e of a slotshaped meterin" orifice cut in the &all of a stationary ca"e surroundin"the outlet tube. =hen the supply pressure rises! the impeller moves toclose the outlet valve ports and decrease pressure do&nstream of theorifice. 'his action restores flo& rate to the set valve.


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'he control assembly consists of a sprin" loaded mechanical lin(a"e&hich connects the temperaturecontrol element to the valve stem. 'heforce produced by the coil sprin" in the control assembly balances theforce of the vapor pressure in the temperaturecontrol element. 'hus! thedo&n&ard force of the vapor pressure in the temperaturecontrol

element. 'hus! the do&n&ard force of the temperaturecontrol element isbalanced at any point by the up&ard force of the sprin". 'he valve canthen be set to hold the temperature of the coolin" &ater &ithin theallo&ed limits.

/educin" valves are automatic valves used to reduce some supplypressure to a specified lo&er dischar"e pressure. reducin" valve can beset for any desired dischar"e pressure &ithin a desi"n limits of the valve.fter the valve is set! the reduced pressure should be maintainedre"ardless of chan"es in the supply pressure! as lon" as the supplypressure is &ithin the desi"n limits of the valve! and the amount ofreduced pressure fluid re$uired! as lon" as the amount re$uired is &ithin

the capacity ratin" of the valve.

'he dischar"e pressure of a reducin" valve &ill al&ays vary to a certaine6tent! dependin" upon the particular valve desi"n. 'his variation occursin response to variations in inlet pressure and flo& demand. 'he ran"eover &hich the dischar"e pressure &ill vary is called the accuracyre"ulation of the valve.

'he sprin"loaded reducin" valve sho&n in !igure )"# is a type &hich iscommonly used for "eneral purpose steam service. 'he valve consists ofthe main reverse seated valve &ith a piston on stop of its. valve .stem! areverse seated controllin" or au6iliary! valve! a controllin" diaphra"m!and an adjustin" sprin".

@i"h pressure! steam enters9 the! valve on the inlet side and acts a"ainstthe main valve disc! tendin" to close the main. valve. @o&ever! hi"hpressure steam is also bled throu"h ports to he au6iliary! valve! &hich.controls the admission of hi"h pressure steam to the top of the mainvalve piston. 'he piston has a lar"er surface area than the main valvedisc therefore! a relatively small amount. of hi"h pressure steam actin"on the top of the main valve piston &ill+ tend to open the main valve! thusallo&in" steam at a reduced pressure to flo& out the dischar"e side.

'he (ey to operation of this reducin" valve is the openin" of the au6iliaryvalve to allo& the hi"h pressure steam to "et to the top of the main valvepiston. 'he controllin" diaphra"m transmits a !pressure do&n&ard uponthe au6iliary valve stem! and this tends to open the valve. @o&ever!reduced pressure steam is bled bac( to the chamber beneath thediaphra"m and this steam e6erts a pressure. up&ard on the diaphra"m!&hich tends to close the au6iliary valve. 'he position of the au6iliaryvalve is determined by the position of the controllin" diaphra"m. 'heposition of the diaphra"m at any "iven moment is determined by therelative stren"th of t&o opposin" forces+ )1* the do&n&ard force e6ertedby the adjustin" sprin"! and )2* the up&ard force e6erted on theunderside of the diaphra"m by the reduced pressure steam. 'hese t&o

forces are continually see(in" to reach a state of balance! and! because ofthis! the dischar"e pressure of the steam is constant! as lon" as the



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amount of steam used is &ithin the capacity of the valve.


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because of the amount of force available from a relatively small operator. hydraulic operator is sho&n in !igure )%.


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4.1.4 %olenoid Operators

%olenoidoperated valves use a remote electrical si"nal to position valves!but it is a fastactin" type motion. 'he solenoid is a device that useselectrical ener"y to create a ma"netic field in a coil that attracts a core to

effect openin" the valve. %olenoid valves are normally smaller si;e valves.'hey are commonly used in comple6 control systems needin" amultiplicity of small! fastactin" control valves. !igure ), sho&s a typicalsolenoidoperated valve.


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On some lar"er valves! manually operated "ear heads are fitted on thevalve bonnet or yo(e. 'his allo&s the operator to use the mechanicaladvanta"e inherent to "ear drives. 'hese &ould! of course! re$uire morerevolutions to cycle the valve so these units may be fitted &ith a rin" andpinion "ear that allo& for faster cyclin". !igure ) sho&s a hand&heel &ith

this type setup.

ear

portable air motor may be used to shorten the cyclin" time of thevalve. t is hand held to the pinion "ear and turns the pinion and rin""ear! thus operatin" the valve.

lthou"h not normally a desi"n function! manually operated valvesmay be used to control various parameters of a fluid system. 'heymay be used in throttle valves for the control of temperature!pressure! level! or flo&.



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.0.0 %-'O,! 'K#%! ,D ##-'O,%

?ecause of the diverse nature of valves &ith valve types overlappin"in each other! both in desi"n and application! &e need to loo( at the

selection process for pic(in" a particular valve. n this section &e &illdiscuss valve selection! valve types! and valve applications.

.1.0 %-'O,

lthou"h valve selection may appear to be rather simple there aremany factors &hich must be ta(en into consideration. >uessin" orsettlin" for just any valve is ris(y at best. :nfortunately cost is $uiteeoften an overridin" factor! althou"h e6perience has sho&n that sparin"e6pense no&. may result in additional e6pense at a later date. =henselectin" a valve durin" system desi"n overall system performance ista(en into consideration. Luestions &hich must be as(ed include+

=hat temperature &ill the system be operatin" at re there anyinternal parts &hich &ould be adversely affected! by the temperaturealves &hich are desi"ned for hi"h temperature steam systems are notnecessarily suited for e6treme lo& temperatures! &hich may be foundin a li$uid nitro"en system.

=hat pressure )or vacuum* &ill this valve be operated in @o& doesthe temperature affect the valves pressure ratin" %ystem inte"rity is amajor concern on any system. 'he valve must be rated at or above thema6imum system pressure anticipated. Due to valve desi"n! pac(in"construction or end attachments the valve is often considered a &ea(

point in the system. re there any si;in" constraints t seems rather obvious that a t&o

inch valve &ould not be installed in a ten inch pipe but &hat may notbe that obvious is ho& does the yo(e si;e! hand&heel or operator si;efi"ure in. re &e in a ti"ht spot &here a risin" stem "ate valve &ill notbe able to open fully =ill the operator e6tend into a &al( &ay andcreate a safety ha;ard alve manufacturers provide dimensionaltables to aid in valve selections.

=ill this valve be used for onoff or throttle application 'hrottle valvesare "enerally of the. "lobe valve type althou"h in some applications aball valve or butterfly valve may be used.

=hat type of erosion &ill the valve be e6posed to =ill it re$uirehardened seats and discs =ill it be throttled close to its seat andneed a special pressure drop valve

=hat (ind of pressure drop is allo&ed >lobe valves e6hibit the lar"estpressure drop or head loss characteristics &hereas a ball valve &oulde6hibit the least.

=hat (ind of differential pressure &ill this valve be operated a"ainst=ill this differential pressure be used to seat or unseat the valve =illthe hi"h differential pressure deform the body or disc and bind thevalve =ill this also re$uire a bypass valve.

@o& &ill this valve be connected to the system =ill it be &elded!scre&ed or flan"ed %hould it be butt&elded or soc(et &elded :nion

threaded or pipe threaded %hould the flan"es be raised! flat!phono"raphic! male8female or ton"ue and "roove



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=hat type environment must this be installed in s it a dirtyenvironment &here an e6posed stem &ould score the yoke bushingand cause premature failure Or is it a clean environment &heredifferent stem lubricant should be used

=hat (ind of fluid is bein" handled s it ha;ardous such that pac(in"

lea(a"e may be detrimental s it corrosive to the pac(in" or even thevalve itself =hat9s the life e6pectancy re$uired =ill it re$uire fre$uent

maintenance f so! is it easily repairable or does the manhour laborre$uirements justify replacement instead of repair

Of course there are many other $uestions &hich may be re$uired.Once these are ans&ered a suitable valve may be selected.

f an installed valve is to be replaced then a valve identical to the oneremoved should be reinstalled. f that valve is no lon"er bein"manufactured or the manufacturer is no lon"er in business then valveselection should be made in the same fashion as a ne& application

e6cept that valve9 dimensions9 are "oin" to be the limitin" factor&ithout the &or(9 re$uired for pipin" alteration+ %everal $uestions9that should be as(ed ho&ever are

re the system parameters the same as &hen desi"ned or has thesystem intent chan"ed

@ave any problems been noted since system fabrication that could beremedied by installin" a different desi"n valve at this time

=hat type operator shbuld9the ne& valve be fitted &ith or is the ne&valve compatible &ith the installed operator

.2.0 'K#% ,D ##-'O,%

s &e have noted from valve selection! there are many factors thatdetermine the application and8or type of valve to be used! some of thefactors include+

the temperature at &hich the system &ill be operatin".

the pressure that the system &ill be operatin" at or the si;in"constraints.

(ind of fluid that is in the system.

type of environment in &hich the valve &ill have to operate.

type of operator the valve &ill use.

=e also (no& that the type of valve used is determined by the applicationof the valve. alve types are+ stop valves! chec( valves! and specialpurpose valves such as safety/relief valves. % ,D ,M#' ,


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1A34. 'o preclude errors in crossreferencin"! the merican ,ational%tandards nstitute 0'1/I2 and the merican %ociety for 'estin" Materials0'/TM2 have adopted the M%% mar(in" system.

'he t&o mar(in"s you are most familiar &ith are the flo& direction arro&

and the brid"e&all mar(in"s! sho&n in!igure *.

'he brid"e&all mar(in"is used e6tensively on "lobe valves and the flo& direction arro& can beused on any type of valve. =ith a "lobe valve! flo& normally enters +underthe9 disc ho&ever! in some applications it may be specified for flo& toenter on the top side of the disc. 'his is especially true in linear flo&throttle and needle valves. t is important! to.9 note that brid"e&allmar(in"s do not sho& direction of flo&! but rather ho& the stern andpac(in" are situated in respect to the inlet and outlet ports.


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re$uirements.


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not necessarily correspond to the valve! pipe! or fittin" inside diameter.

#roducts havin" internal elements &hich are the e$uivalent of one pipesi;e or different than the end9 si;e 9may have dual+ mar(in"s unlessspecified other&ise in a product standard+ :nless these e6ceptions e6ist!9

the first number shall indicate the connectin" end pipe si;e and thesecond the minimum bore diameter or the pipe si;e correspondin" to theclosure si;e! e.".! C 6 4! 4 6 2182! 30 6 24.

t the manufacturer9s option! triple mar(in" si;e desi"nation may be usedfor valves. f triple si;e desi"nation is used! the first number shall indicatethe connectin" end si;e at the other end.


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4. ,umber of threads per inch.

.3. alve %chematic %ymbols'he last and most important aspect of valve identification is the ability toidentify different types of valves from9 blueprints and schematics. n"eneral! the symbols that denote various control valves! actuators! andpositioners are standard symbols as sho&n in !igure *&. @o&ever! incertain cases these symbols &ill vary dependin" on site specific prints.

'he le"end of a typical system print or schematic &ill sho& the symbolsthat represent all components on the dra&in".



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follo&in" &or(s are su""ested+

Piping 4and5oo6# %i6th dition! Mc>ra&@ill! nc.! 1AA2.

%


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4. >iven the follo&in" list of letter desi"nators for valve symbols! fill inthe blan(s &ith the correct name of the valve type.

)a* NNNNNNNNNNNNNNNNN )b* > NNNNNNNNNNNNNNNNN )c* NNNNNNNNNNNNNNNNN )d* O NNNNNNNNNNNNNNNNN )e* = NNNNNNNNNNNNNNNNN )f* D= NNNNNNNNNNNNNNNNN

. =hat is a desirable feature of a pneumatic positionera. =hen used in combination &ith either a sin"le or doubleactin"

actuator! it provides accurate throttlin" of control valves.b. #rovides a &ide ran"e of proportional outputs to valve controls.c. /elatively ine6pensive first time cost.d. 6tended maintenancefree operation.

. Motor operators translate a remote electric si"nal into valve motion.a. 'rue.b.


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#/