control valve present

7/23/2019 Control Valve Present

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AN INTRODUCTION TO

CONTROL VALVE

2nd May 2002


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TOPICS COVERED

Types of Valves

Details of Globe Valves

Valve Body and Material Selection

Required Information from x-y-

Valve Specification

Siin! Steps

Valve "#aracteristics


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TOPICS COVERED

Valve Be#avior $nder Different

%iquid enomena

Terminolo!y in Valves

&ositioners

Valve &ac'in!

Seat %ea'a!e "lassification

Regulators and Actuators NOT Covered.

Nose and Dyna!c Per"or!ance NOT Covered


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#$at s a Control Valve%

A control valve s a devce ca&a'le o" !odulatng

"lo( at varyng degrees 'et(een !n!al "lo( and

"ull ca&acty n res&onse to a sgnal "ro! an e)ternalcontrol devce. T$e control valve* o"ten re"erred to as

+t$e "nal control ele!ent*+ s a crtcal &art o" any

control loo&* as t &er"or!s t$e &$yscal (or, and s

t$e ele!ent t$at drectly a""ects t$e &rocess.


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Valve Class"caton

(V-)* General Service "ontrol Valves

(V-)+, Re!ulators

(V-), De Super#eatin! Valves

(V-)., /ctuated 0n1 0ff Ball Valves

(V-*2, Severe Service "ontrol Valves


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-near Moton Control Valve

TORTOS /-O# PAT -O# RECOVER1

CAN TROTT-E SMA-- /-O#

RATES

SITED TO I3PRESSRE APP-ICATIONS

SA--1 /-ANED OR TREADED

SEPARA4-E 4ONNET

O//ERS VARIET1 O/ SPECIA- TRIM DESINS


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Rotary Moton Control Valve

STREAM-INED /-O# PAT

I RECOVER1

CAN AND-E S-RR1 AND A4RASIVES

/-ANE-ESS

INTERA- 4ONNET

MORE CAPACIT1

-ESS PAC5IN #EAR


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-O4E VA-VE ST1-E


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T$e &art o" t$e glo'e valve t$at controls "lo(s t$e ds,* ($c$

s attac$ed to t$e valve ste!.T$e valves closed 'y turnng t$e

valve ste! n untl t$e ds, s seated nto t$e valve seat. T$e

edge o" t$e ds, and t$e seat are veryaccurately !ac$ned so

t$at t$ey "or! a tg$t seal($en t$e valve s closed. #$en t$e

valve s o&en* t$e "lud "lo(s t$roug$ t$e s&ace 'et(een t$e

edge o" t$e ds, and t$e seat.

-O4E VA-VES


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T#e valve s#o3n #as a sin!le seat

and a sin!le plu!4 In sin!le seated

valves5 t#e process line pressure

acts on t#e bottom area of t#e

plu!5 creatin! an up3ard force on

t#e valve stem4 T#e diap#ra!m

actuator must act a!ainst andovercome t#is force in order to

move or #old t#e stem do3n3ard4

SIN-E SEATED VA-VE

T#e lar!er t#e valve or t#e #i!#er t#e linepressure5 t#e !reater t#e actuator force must be4

T#erefore it is evident t#at for lar!e sie valves5 or

for #i!# line pressures5 sin!le seated valves

!enerally cannot be used44


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DOUBLE SEATED CONTROL VALVE

Double seated valves #ave t3o plu!s and t3o seats4 T#e

line pressure actin! up3ard on one plu! and do3n3ard on

t#e ot#er produces a balance of forces4 Double seated

valves are 'no3n as balanced or semi balanced valves4

Double seated valves are used for applications involvin!

#i!# pressures or 3#ere t#e valve sie is lar!e.

0ne disadvanta!e of double seat

construction is t#at 3it# variations intemperature5 t#e stem portion

bet3een t#e t3o plu!s contracts or

expands linearly a different amount

t#an t#e valve body4 In t#e closed

position5 t#erefore5 bot# plu!s 3ill notseat simultaneously and a small

lea'a!e flo3 3ill occur4 6or ti!#t

s#utoff5 sin!le seated valves must be

used.


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SIN-E V6S DO4-E SEATED VA-VE

* Sngle Seated Valves are an e)cellent c$oce ($en a $g$er

degree o" s$ut3o"" s re7ured. o(ever* t$s desgn s

un'alanced and l!ted n t$e &ressure t$at t (ll s$ut o""

aganst. T$e lea,age rate s a&&ro)!ately 0.89 o" t$e

!a)!u! ca&acty.

* Dou'le Seated Valves are nearly &ressure 'alanced and*

t$ere"ore* are a'le to close t$e valve &lug aganst $g$er o&eratng

&ressures. o(ever* snce te!&erature "luctuatons !ay cause

e)&anson and contracton across t$e seats* tg$t s$ut3o"" s not

al(ays &oss'le. T$e lea,age rate s a&&ro)!ately 0.:9 o" t$e

!a)!u! ca&acty. Dou'le seated valves $ave a "aster "lo(

res&onse and greater ca&acty t$an sngle seated valves and are

reco!!ended ($en tg$t s$ut3o"" s not re7ured. ;


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4alanced Valves (t$ Cage

T$rottlng Tr!

Dou'le3Seated


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Control Valves End ConnectonINType of fluid and its p#ysical properties7

6luid p#ase 8!as5 liquid5 slurry5 multip#ase5 etc497

Density 8specific !ravity5 molecular 3ei!#t5 specific

3ei!#t5 etc497Vapor pressure7

Viscosity7

"ritical temperature and pressure7

De!rees of super#eat or existence of flas#in!8vaporiation curve across t#e valve97

"orrosive properties due to contaminants 8:;S5

c#lorides5 etc497


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RE=IRED IN/ORMATIOM /OR

SI>IN


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RE=IRED IN/ORMATIOM /OR

SI>IN S#utoff lea'a!e requirements7

Startup conditions1procedures7

$pset condition inlet pressure and temperature7

Inlet and outlet pipe sie and sc#edule7

Maximum permissible noise level and reference point7

Installation environmental conditions7 and

Type of erosion occurrin! or expected 8abrasive particle5cavitation5 erosive-corrosive5 or #i!# liquid velocity

impin!ement94


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SPECI/ICATION O/ A VA-VE

Valve body construction 8an!le5 double-port5

butterfly5 etc497

Body material 82*= stainless steel5 Inconel5 ceramic5

etc497

>nd connections and ratin!7

Valve plu! or dis' style 8quic' openin!5 linear5 etc497

Valve plu! or dis' action 8air to open or close97

&ort sie 8full or restricted97

Valve trim materials7


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SPECI/ICATION O/ A VA-VE

/ction desired on failure of input si!nal 8open5

closed5 or fail-in-place97

6lo3 action 8flo3 tends to open or close97

Input si!nal type 8pneumatic5 electric5 etc497

/ctuator type and sie7

>nvironmental requirements7

&ac'in! material 8Teflon5 !rap#ite5 etc497 /rea classification7 and

/ccessories required 8controller5 limit s3itc#5

#and3#eel5etc494


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SE-ECTIN A CONTRO- VA-VE

8 "alculate required "v

;4 Select body material

24 Select body ratin!?4 Select s#ut-off "lass required

+4 "#oose body style

=4 "#oose body sie4 Select trim sie

@4 Select trim material


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VA-VE SI>IN E?AMP-ESTEP @8< S&ec"y Process Data

T#e system is pumpin! 3ater from one tan' to anot#er

t#rou!# a pipin! system4

Total System &ressure drop is *+) psi4 Temperature of 3ater ) )64 Maximum flo3rate of *+) !pm5 0peratin! flo3rate of **) !pm5 Minimum flo3rate of ;+ !pm4

T#e pipe diameter is 2 inc#es4 Specific !ravity of *4)4

Key Variables: Total pressure drop, design flow, operating flow,

minimum flow, pipe diameter, specific gravity.


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PMPIN CIRCIT

Pump discharge head = frici!" #!sses$ %ead #!ss$

de#i&er' pressur

DPc&

(rici!" #!ss = #i"e #!ss $ e)uipme" #!ssD!es "! cha"ge ih f#!


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S1STEM CRVE

Pe"dPe"d$%

DP c&

Pump Cur&e

S'sem cur&e

($Pe"d$%

+" + ma,

(#!


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S1STEM PRESSRE DROP

A Maximum flo3

"ompute

6riction loss in equipment 3it#out "V4 8

p

nd pressure and static #ead remain

unc#an!ed4

Read pump #ead at max flo3 from pump curve8 or assume flat curve94

D&cv &s-6-&end-:


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S1STEM PRESSRE DROP

PRESSRE DROP A--O#ANCE-

SIN-E P- VA-VE 88 PSI

DO4-E P- PSI

CAE VA-VE 3 N4A-ANCE B PSI

CAE VA-VE 4A-ANCE B PSI

4TTER/-1 0.2 PSI

V 4A-- 8 PSI

RE=IRED DE-TA P 0.0:Ps 8.8 F=!6=dG238H / 4


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S1STEM PRESSRE DROP

Bec#tel practice to specify pumps for a rated flo3

3#ic# is #i!#er t#an t#e normal flo34

:o3ever for t#e rated flo35 it is t#e normal practice tospecify t#e pump differential at t#e same value as

calculated for t#e normal flo34

T#e delivery pressure is maintained by reducin! t#e

control valve pressure drop to compensate for t#e

increased frictional 8dynamic9 losses for t#e #i!#er

flo34


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S1STEM PRESSRE DROP

In order to obtain effective control under all flo3 conditions5

t#e control valve must represent a relatively #i!# proportion

of t#e pressure drop in t#e system4 T#erefore5 t#e control

valve pressure drop at normal flo3 s#ould be,

)4 bar 8*) psi9 ;)C of dynamic losses +C of t#e total pump differential #ead4

/t t#e rated flo35 t#e control valve pressure drop s#ould

be,

)4 bar 8*) psi9 *+ of d namic losses


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VA-VE SI>IN E?AMP-E

TRADE OFF:

-ARER PRESSRE DROPS INCREASE TE PMPIN

COST FOPERATING AND SMA--ER PRESSRE DROPSINCREASE TE VA-VE COST 4ECASE A -ARER

VA-VE IS RE=IRED FCAPITA- COSTG.

THUMB RULE:

DESIN TE VA-VE TO SE 8038:9 O/ TE TOTA-

PRESSRE DROP OR 80 PSI* #ICEVER IS REATER.

/OR OR S1STEM* 809 O/ TE TOTA- PRESSRE

DROP IS 8: PSI #IC IS #AT #E #I-- SE.


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Reco!!endaton

6or 6ixed Speed B6&5 use valve &ressure

drop of 2)) psi and *)) psi for fixed speed

condensate pump46or variable speed B6&5 use *)) psi as

valve pressure drop4

T#ese are initial values for start but finally

it #as to be c#ec'ed by system en!ineer4


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VA-VE SI>IN E?AMP-ESTEP @< Calculate Valve C$aracterstc


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VA-VE CARACTERISTICS

Equal percentage c#aracteristics produce an equal

percenta!e c#an!e in flo3 for eac# equal increment of

travel4 "#an!e in flo3 rate is proportional to t#e flo3 rate

ust before a c#an!e in valve plu!5 disc5 or ball position4

>qual percenta!e c#aracteristic is common 3#ere t#e

system itself absorbs a lar!e percenta!e of t#e pressure

drop5 suc# as pressure control applications4

$sed in processes 3#ere a small percenta!e of t#e total

pressure drop is permitted by t#e valve4

$sed in temperature and pressure control loops


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Linear characteristics provide a flo3 rate directly

proportional to travel4 T#is proportional relations#ip

produces a constant slope t#at yields a constant

valve !ain 3it# a constant pressure drop4

%inear c#aracteristics are commonly specified for

liquid-level and flo3-control applications4

$sed in liquid level or flo3 loops$sed in systems 3#ere t#e pressure drop across t#e

valve is expected to remain fairly constant 8ie4 steady

state systems9


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INERENT CARACTERISTICS O/ A VA-VE IS TE RE-ATIONSIP

4ET#EEN VA-VE /-O# CAPACIT1 AND TE VA-VE TRAVE-

#EN TE DI//ERENTIA- PRESSRE ACROSS TE VA-VE IS E-D

CONSTANT. SO NDER SPECI/IC CONDITION VA-VE /-O# IS

ON-1 /NCTION O/ VA-VE TRAVE-.

INSTA--EDCARACTERISTICS

IT IS TE RE-ATIONSIP 4ET#EEN /-O# TRO TE

VA-VE AND VA-VE ASSEM4-1 INPT #EN INSTA--ED IN

TE S1STEM. TE O4JECTIVE IS TO AVE -INE-ARISED

INSTA--ED CARACTERISTICS.

INSTA--ED CARACTERISTICS IS TE /-O# VS. PERCENT

OPEN CRVE CANES DE TO TE EAD -OSS IN TE

PIPIN


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The i"sa##ed characerisic differs fr!m he i"here".A valve (t$ an e7ual &ercentage c$aracterstc (ll e)$'t a

!ore lnear "lo( curve ($en nstalled 'ecause o" t$ereducton n &ressure dro& avala'le across t$e valve. T$s

!a,es t$e c$aracterstc curve "latter.

-near nstalled c$aracterstcs are desra'le 'ecause t$ey

&rovde constant gan regardless o" valve o&enng* !a,ng

t$e loo& easer to tune and !&rovng control &er"or!ance.

A valve (t$ a lnear n$erent curve !ay c$ange to 7uc,3

o&enng c$aracterstc ($en nstalled


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In real l"e stuatons* t$e valve s nstalled n a &&e(or,

con"guraton ($ere t$e d""erental &ressure across t$e valve

can vary as t$e "lo( t$roug$ t$e valve c$anges.

T$ere"ore ($ere t$e d""erental &ressure across t$e valve s

"ree to c$ange* t$e nstalled valve c$aracterstc s "ar "ro!

lnear. To counteract t$s* t$e valve !anu"acturers o""er a

c$aracterstc called +e7ual &ercentage+* ($ere t$e &ercentage

ncrease n ste! &oston e7uals t$e &ercentage ncrease n "lo(.


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#$y s lnearty !&ortant% T$e ans(er les n t$e "act t$at

t$e tunng o" t$e controllerKs P ter! s largely de&endent on

t$e &rocess gan. I" t$e &rocess $as not got nstalled lnearty*

t$en t$s (ould !ean t$at t$e tunng (ould only 'e good at

t$e one &lace on t$e !easurng range ($ere t$e &artcular

&rocess gan (as used n t$e tunng calculaton. At ot$er

&laces ($ere t$e &rocess gan (as s!aller* t$e control

res&onse (ould 'e !ore sluggs$* and ($ere t (as 'gger*t$e res&onse (ould 'e "aster and !ore cyclc* and could n

"act even 'eco!e unsta'le.


47/120


Peo&le are very o"ten con"used as to ($y one doesnKt al(ays

Lust use an n$erent lnear c$aracterstc a"ter all t$e gra&$

s$o(s a strag$t lne relatons$& 'et(een "lo( t$roug$ t$e

valve* and valve ste! &oston.

One !ust understand $o( t$e n$erent c$aracterstcs are

generated. T$e test &er"or!ed 'y t$e !anu"acturer to generate

t$e curve s acco!&ls$ed 'y &lacng t$e valve n a "lo( rg

($c$ s so arranged t$at t$e valve $as got a co!&letely

constant d""erental &ressure across t at all t!es.

VA-VE SI>IN E?AMP-E


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VA-VE SI>IN E?AMP-ESTEP @8< S&ec"y Process Data

T#e system is pumpin! 3ater from one tan' to anot#er

t#rou!# a pipin! system4

Total System &ressure drop is *+) psi4

Temperature of 3ater ))

64 Maximum flo3rate of *+) !pm5 0peratin! flo3rate of **) !pm5 Minimum flo3rate of ;+ !pm4 T#e pipe diameter is 2 inc#es4 Specific !ravity of *4)4

Key Variables: Total pressure drop, design flow,

operating flow, minimum flow, pipe diameter, specific

gravity.


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VA-VE SI>IN E?AMP-E

(!r !ur s'semCv 8:0 F 868:G E

AVOID SIN TE -O#ER 809 AND PPER 209 O/ TE VA-VESTRO5E. TE VA-VE IS MC EASIER TO CONTRO- IN TE 80309 STRO5E RANE.

THIS ISSUE IS RANGEBILITY OF VALVE ( DISCUSS ED LATER )

NOW SELECT THE VALVE CHARACTRSTICS


50/120

VA-VE SI>IN E?AMP-E

-et us assu!e (e $ave e7ual &ercentage valve so ($en

(e co!&are our Cv Ta'le* t see!s t$at 2 valve (ll

(or, "ne. Notce t$at (eKre not tryng to s7ueeQe our

Cv nto t$e 8 862 valve ($c$ (ould need to 'e at

8009 stro,e to $andle our !a)!u! "lo(. I" t$svalve (ere used* t(o conse7uences (ould 'e

e)&erencedIN E?AMP-E

Valve SQe Ma) Travel

!!

Valve O&enng F 9 o" Total TravelG

DN Cv

/0 10 20 /00 /-

DN2: 8 0.AI 2.20 A.I 8A.2 0.

DN B0 8 8.:2 I.A 8A.B I:. 0.B

DN :0 2 8.RR B.RR 2:.B :.A 0.:DN R: I I.BI 80. B.2 .B 0.B

DN 0 I B.I2 80. RR.0 8IR 0.2


52/120

VA-VE SI>IN E?AMP-ESTEP @:< C$ec, t$e Cv and stro,e &ercentage at

t$e !n!u! "lo(I" t$e stro,e &ercentage "alls 'elo( 809 at our !n!u!

"lo(* a s!aller valve !ay $ave to 'e used n so!e cases.

Judge!ents &lays role n !any cases./or e)a!&le* n our syste! !ore l,ely to o&erate closer

to t$e !a)!u! "lo(rates !ore o"ten t$an t$e !n!u!

"lo(rates% Or s t !ore l,ely to o&erate near t$e

!n!u! "lo(rate "or e)tended &erods o" t!e. ItKsd""cult to "nd t$e &er"ect valve* 'ut you s$ould "nd one

t$at o&erates (ell !ost o" t$e t!e. -etKs c$ec, t$e valve

(eKve selected "or our syste!IN E?AMP-E

At a !n!u! "lo( o" 2: g&!* valve Cv s .:#e see t$at a Cv o" .: (ould corres&ond to a stro,e

&ercentage o" around :3B09 ($c$ s certanly acce&ta'le.

Notce t$at (e used t$e !a)!u! &ressure dro& o" 8: &s

once agan n our calculaton. Alt$oug$ t$e &ressure dro&

across t$e valve (ll 'e lo(er at s!aller "lo(rates* usng t$e

!a)!u! value gves us a +(orst case+ scenaro.

I" our Cv at t$e !n!u! "lo( (ould $ave 'een around 8.:*

t$ere (ould not really 'e a &ro'le! 'ecause t$e valve $as a

Cv o" 8. at 809 stro,e and snce (e use t$e !a)!u!

&ressure dro&* our est!ate s conservatve.

VA-VE SI>IN E?AMP-E


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VA-VE SI>IN E?AMP-E

STEP @ < C$ec, t$e gan across a&&lca'le/lo(rates

AIN /-O#6 STRO5E

No(* at our t$ree "lo(rates

IN TE /O--O#IN S-IDES #E #I-- SEE O#

TESE A//ECT OR VA-VE SI>IN.


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VENA CONTRACTA DIARAM

/-O# AREA O/ -I=ISD IS AT MINIMM AND VE-OCIT1 AT

MA?IMM. TE -OCATION O/ VENA CONTRACTA VAR1 #IT

PROCESS CONDITION.


58/120

CO5ED /-O#

/t t#is point5 liquid becomes unstable and may vaporie4

So t#ere is t3o p#ase flo3 at t#is point and fluid is no

lon!er J IncompressibleK4

:ere pressure at Vena "ontracta decreases4 So 3it# t#e

increase of differential pressure5 vena contracta

pressure 'eeps on decreasin! and may attain a value3#ic# is lo3er t#an vapor pressure4


59/120

CO5ED /-O#

-et us see t$e 'e$avor o" gas a&&lcaton. In gas "lo(*

($en t$e "lud velocty s e7ual to t$e s&eed o" sound n

t$e "lud* t 'eco!es crtcal and CO5ED condtone)sts. Inco!&ress'le "lud $ave very $g$ sound

s&eed so &ractcally t$ey donKt c$o,e ($ereas t$e

!)ture $ave very lo( sound s&eed so t$e CO5IN

!ay occur.


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Prediced (#!Acua# (#!

+

P

Ch!5ed f#!

+

acua# dpma, dp

P

Cv


61/120

T$e c$o,ed "lo( s related to t$e ter! /- value

"ound on t$e valve c$art.

T$s !ust 'e c$ec,ed "or vastly d""erent !a)!u!and !n!u! "lo(rates. /or e)a!&le " t$e

d""erence 'et(een t$e !a)!u! and !n!u!

"lo(s s a'ove 09 o" t$e !a)!u! "lo(*

MUST CHECK THE CHOKED FLOW CONDITION.

CONTRO- VA-VE 4EAVIOR


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T$e Constants Plays a Vtal Role

Ar Tr! A&&lcaton Rato

5c Cavtaton Inde)

5! Pressure Recovery Coe""cent /-2

/& P&ng Correcton /actor

rc Crtcal Pressure Rato //

5! P83P26 P83Pvc

Pvc rc ;Pv


63/120

CO5ED /-O#

T:> M/LIM$M DR0& / V/%V> "/H T0%>R/T> /T

S:$T-066 0R /T &/RTI/% 0&>H1 "%0S> &0SITI0H4

T:> ":0>D 6%0 "0HDITI0H IS R>%/T>D T0J Maximum allo3able Siin! &ressure DropK

T#e 60RM$%/ T0 D>T>RMIH> IS /S 60%%0,

& max 6%;

8 &*- 66 &V9#ere 66 %iquid "ritical &ressure Ratio 6actor

66 )4.=-)4;@ 8 &V1&"9)4+


64/120

CO5ED /-O#...

E?AMP-E

P8 B.:* P2 8.* = 2880 ,g6$r* Pv 0.02 'ar

T$e Value o" /-F Valve Recovery /actorG s 0. "or sngle6dou'le

seated valves* 0.B "or 'utter"ly valves and 0. "or &lug6'all

valves

T$e a'ove e7uaton results as P !a) B8. 'ar. T$e actual P s

B.:3 8. 2. 'ar


65/120

CO5ED /-O#...

ERE P !a) IS MORE TAN ACTA- P

4T I/ I/ P !a)IS -ESS TAN P* IT IS AN INDICATION

TAT CO5ED /-O# CONDITION #I-- E?IST NDER

TIS SERVICE CONDITION.TA5E AN E?AMP-E /OR PROCESS CONDITION< F Cond. ReLect to Tan,G

P8 8.0* P2 2.8* =8 B0 ,g6$r* T :0 deg C

Pv0.82B 'ar* Pc 228 'ar* P83P2 8B. 'ar

SIN TE /ORM-A

rosion resultin! from #i!# velocity

microets impin!in! on material surface

"#emical /ttac' , Material deformation and failure resultin!

from s#oc' 3aves impin!in! on t#e

material surface

u H0IS>


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CAVITATION INDE?

Cavtaton SQng Coe""cent< F 5cG

TIS IS TE VA-E SED TO DETERMINE TE

PRESSRE DROP AT #IC CAVITATION #I-- 4EIN

TO OCCR . TIS IS IN/-ENCED 41 MAN1 /ACTORSAND PRIMAR1 INDICATOR O/ VA-VE PER/ORMANCE

IN CAVITATIN SERVICE.

T$s can 'e e)&ressed n ter!s o" 5! value. 5c 0. 5!

Sg!a F

G FP23PvG6 FP83P2G

Rato o" Potental "or resstng Cavty "or!aton to t$e &otental

"or causng Cavty "or!aton.


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CAVITATION INDE?

CO5ED CAVITATION INDE?

OPERATIN CAVITATION INDE?

DAMAE CAVITATION INDE?

One E)a!&le TRIM SIQ> c

Butterfly /ll /ll )4+ m

V Ball Trim *1 ;Trim 2

/ll;- @ K

m*4)

GlobeGlobe

:ard Mat4Microform

/ll/ll

*4))4@+ m

T$e 5! value s used to &redct t$e "lo( rate at c$o,ed "lo(

condton ($ereas 5c &redcts t$e &ont ($ere Cavtaton (ll

occur.


80/120

CAVITATION INDE?

Cavtaton SQng Coe""cent< F 5cG

TIS IS TE VA-E SED TO DETERMINE TEPRESSRE DROP AT #IC CAVITATION #I-- 4EIN

TO OCCR . TIS IS IN/-ENCED 41 MAN1 /ACTORS

AND PRIMAR1 INDICATOR O/ VA-VE PER/ORMANCE

IN CAVITATIN SERVICE.T$s can 'e e)&ressed n ter!s o" 5! value. 5c 0. 5!


81/120

CAV@TAT@ON @NDE

TP&> TRIM SIQ> c

Butterfly /ll /ll )4+ m

V Ball Trim *1 ;Trim 2

/ll;- @ K

m*4)

Globe

Globe

:ard Mat4

Microform

/ll

/ll

*4)

)4@+ m


82/120

RECOVER1 /ACTOR

ven t(o valves (t$ e7ual "lo( area and &assng sa!e

"lo(* g$ recovery valve (ll &roduce less &ressure dro&

t$an lo( recovery valve. T$e crtcal &ressure dro& rato

F

P6 P8G "or g$ Recovery (ll 'e !uc$ less t$an -o(

Recovery Valve

lo'e valve ty&cally e)$'ts a crtcal "lo( at a &ressure

dro& rato o" 0.: ($le g$ Recovery valve as value as

lo( as 0.8:

T$e recovery "actor o" a $g$ recovery valve (ll vary

(t$ ts &lug travel.


83/120

-O# RECOVER1 VA-VE

-O# RECOVER1 VA-VE< A valve desgn t$at dss&ates

a consdera'le a!ount o" "lo( strea! energy due to

tur'ulence created 'y t$e contours o" t$e "lo( &at$.

Conse7uently* &ressure do(nstrea! o" t$e valve VENA

CONTRACTA recovers to a lesser &ercentage o" ts nlet

value t$an a valve (t$ a !ore strea!lned "lo( &at$. T$e

conventonal -O4E ST1-E control valve s n t$s

category.

T$e recovery "actor does not vary (t$ travel to any

sgn"cant degree.


84/120

I RECOVER1 VA-VE

g$ and -o( recovery re"ers to valve a'lty to convert velocty

at t$e Vena Contracta 'ac, nto &ressure do(nstrea! o" valve.

I RECOVER1 VA-VE< A valve desgn t$at dss&ates

relatvely lttle "lo( strea! energy due to strea!lned nternal

contours and !n!al "lo( tur'ulence. T$ere"ore* &ressure

do(n strea! o" t$e valve VENA CONTRACTA recovers to a$g$ &ercentage o" ts nlet value. T$ese ty&es o" valves are

dent"a'le 'y t$er strag$t3t$roug$ "lo( &at$s. E)a!&les are

!ost rotary control valves* suc$ as t$e eccentrc &lug* 'utter"ly*

and 'all valve.

A -O# RECOVER1 VA-VE RE=IRES MORE PRESSRE DROP

TO PASS TE SAME /-O# TAN I RECOVER1 VA-VE.


85/120


86/120

Pressure Recovery /actor

T$e gra&$ 'elo( re&resents actual test data o" a 'utter"ly valve

s$o(ng c$ange n recovery "actor (t$ &lug rotaton. T$e data

de!onstrate ($y a rotary control valve can suddenly go nto

Cavtaton as t$e valve o&ens u&.


87/120

/-ASIN IN CONTRO- VA-VES

6las#in! is dependent solely on t#e relations#ip of t#e

do3nstream pressure 8 &; 9 and t#e fluid vapor pressure8 &v 94 T#e relations#ip is &; &v 4 It is independent

of valve type5 style5 or recovery c#aracteristic4 T#ere are

no trim !eometries available to eliminate flas#in!4

/ fluid is said to flas# 3#en t#e do3nstream pressure

of t#e fluid is less t#an itEs vapor pressure4

T#e vapor bubbles t#at are formed 3#en t#e pressure

falls belo3 t#e vapor pressure continue to !ro3 andeventually t#e liquid liquid flas#es to a vapor4


88/120


:ard3are c#oices for flas#in! application Valve Desi!n ,

It does not prevent flas#in! but reduces t#e impact of

flas#in!.

/n!le Valve 3it# standard trim6las#in! dama!e occurs by #i!# velocity vapor bubbles

impin!in! t#e surface of a valve 3#ic# erodes t#e

surface4

/n!le valve reduces t#e amount of vapor bubbles t#at

impin!e on t#e 3all by directin! t#e flo3 stream to t#e

centre of t#e pipe and not in t#e valve body4


89/120


System Desi!n ,

6i! * ,

6las#in! 3ill occur in t#e do3nstream pipe bet3een t#e control

valve and t#e condenser4 /ny dama!e t#at occurs 3ill do so in

t#at area4

6i! ; ,

6las#in! 3ill occur do3nstream of t#e valve and in t#e

condenser 4 Since condenser #as a muc# lar!er volume compared

to t#e pipe5 #i!# velocity impin!ement on a material surface 3ill

not occur since t#ere is no essentially material surface4

C!"de"ser78 (ee

C!"de"ser/ (!!

(ig /(ig 7


90/120


>xamples are boiler feed 3ater pump recirculation5

condensate pump recirculation5 and #eater drain

lines5 many of 3#ic# disc#ar!e into t#e main

condenser4 &roblems encountered include severe

vibration due to flo3 and pressure pulsation in t#e

valve disc#ar!e pipin! 3it# consequent dama!e to

t#e control valve and1or pipin! system5 and

condenser internals4T#e pressure pulsation or s#oc' 3aves are t#e

result of liquid flas#in!5 liquid separation or a

combination of t#ese t3o events4


91/120


92/120


6i!ures * and ; indicate a typical pump recirculation or

#eater drain flo3 control system and t#e pressure

!radient resultin! from flas#in! due to a sudden

pressure drop of t#e liquid belo3 its vapor pressure

due to a ne!li!ible do3nstream bac'pressure4

If a bac'pressure device is placed at t#e condenser

inlet to maintain &;above t#e vapor pressure5 t#eresultant pressure !radient 3ill appear as 6i!ure 24


93/120

Hote t#at &vis t#e same as in 6IG4 ; but &; is #i!#er t#an in

6IG4 ;4

6i!ures ; and 2 typify systems 3#ere t#e liquid vaporpressure is raised above &+5 3#ic# in t#is case is t#e

condenser pressure4

T#e case of a condensate pump recirculation system5 t#e

vapor pressure of t#e liquid is essentially t#e same as t#econdenser pressure4 T#e ener!y remainin! in t#e liquid after

passin! t#rou!# t#e control valve is t#en dissipated 3it#in

t#e do3nstream pipin! system 3#ere little or no bac'

pressure exists5 or 3it#in t#e condenser if bac'pressure is

rovided4


94/120

6i!ure ? also depicts t#e pressure !radient in t#is type

system 3#ere bac'pressure is or is not provided4


95/120

&R0">SS "0HDITI0HS

&rimary process variables in valve selection are pressure and

temperature4 e normally loo' at operatin! pressure 80&9 and

operatin! temperature 80T9 3#ic# is t#e #i!#est pressure and

temperature under any expected operatin! conditions and desi!n

pressure 8D&9 and desi!n temperature 8DT9 3#ic# #as somemar!in above t#e operatin! conditions4

/ common error re!ardin! desi!n pressure is to use t#e pump

desi!n point #ead instead of t#e s#ut-off #ead4

#en calculatin! t#e mar!in5 consideration s#ould be !iven to t#e

li'eli#ood of up3ard excursions or any uncertainty in t#e values

used for desi!n4

&R0">SS "0HDITI0HS


96/120

&R0">SS "0HDITI0HS

Revised

'!1#r

'!1#r per

data

s#eet

Difference

in t3o

flo3s

&* &; T Sp Gr

2.5@?) 36,320 3,520 21.0 0.34 28.5 0.996

*..5;)) 181,600 17,600 21.0 0.34 28.5 0.996

2.-5;)) 363,200 34,000 20.9 0.364 37.4 0.993+.25?)) 544,800 48,600 20.8 0.402 46.77 0.989

SP. r (as ta,en as 0.0


97/120

RANE4I-IT1 ISSE

CASE38

CASE32

v rave

+5..? @4+ )42?) ;4 2@**5.;@ @4+ )42=) +4+ +

;.5)) @4? )4?); *24= @*

v rave

;?5.-+ @4+ )42?) ** 2)

*2.52)) -4) )42=) -) -2

*=@52)) =4+ )4?); @- @*

Mn

Travel

:9 to

Ma)

Travel09

?F valve in = J line >mer!ency #ot3ell ma'e-up4

;F valve in 2 J Hormal #ot3ell ma'e-up4

Valve Ter!nology


98/120

gy

T$RHD0H, / term used to describe t#e ratio bet3een t#e

minimum and maximum flo3 conditions seen in a particular system4>xample, If t#e minimum flo3 3ere *) G4&4M4 and t#e maximum flo3

3ere *)) G4&4M4 t#e turndo3n 3ould be *),*4 T#is term is sometimes

incorrectly applied to valves4 See R/HG>/BI%ITP4

TRIMT5 and body flan!es and!as'ets4 T#e plu!5 seats5 stem5 !uides5 bus#in!s5 and ca!e are some

of t#e parts included in t#e term trim4

E?TENSION 4ONNET


99/120

Valve Ter!nology

RANEA4I-IT1HTS4 T#is is also called T$RHD0H alt#ou!#

tec#nically it is not t#e same t#in!4 T#ere are t3o types of

ran!eability - in#erent and installed4 In#erent ran!eability is a

property of t#e valve alone and may be defined as t#e ran!e of flo3

coefficients bet3een 3#ic# t#e !ain of t#e valve does not deviate

from a specified !ain by some stated tolerance limit4 Installed

ran!eability is t#e ran!e 3it#in 3#ic# t#e deviation from a desired

IHST/%%>D 6%0 ":/R/"T>RISTI" does not exceed some stated

tolerance limit4

4ENC SET


100/120

INERENT DIAPRAM PRESSRE RANE* ($c$ s t$e

$g$ and lo( values o" &ressure a&&led to t$e da&$rag! to

&roduce rated valve &lug travel (t$ at!os&$erc &ressure nt$e valve 'ody. T$s test s o"ten &er"or!ed on a (or, 'enc$ n

t$e nstru!ent s$o& &ror to &lacng t$e valve nto servce and

s t$us ,no(n as 4enc$ Set.

4ONNET


101/120

CAE


102/120

Valve Ter!nology

REDCED TRIM


103/120

Valve Ter!nology

>66>"TIV> /R>/,6or a DI/&:R/GM /"T$/T0R5 t#e effective area

is t#at part of t#e diap#ra!m area t#at is effective in producin! a

stem force4 $sually t#e effective area 3ill c#an!e as t#e valve is

stro'ed - bein! at a maximum at t#e start and at a minimum at t#e

end of t#e travel ran!e4 6lat s#eet diap#ra!ms are most affected by

t#is7 3#ile moulded diap#ra!ms 3ill improve t#e actuator

performance5 and a rollin! diap#ra!m 3ill provide a constant stem

force t#rou!#out t#e entire stro'e of t#evalve4

-ANTERN RIN


104/120

Valve Ter!nology

PS3DO#N3TO3C-OSE


105/120

V V C ON

T$e acton o" a valve s generally de"ned as et$er ar to close or

ar to o&en. T$ese ter!s sgn"y t$at an ncrease n ar &ressure

actng over t$e e""ectve area o" t$e da&$rag! (ll et$er close

or o&en t$e valve* de&endng u&on t$e ty&e o" actuator used and

t$e &lug to seat rng relatons$&.

&0SITI0H>RS


106/120

&0SITI0H>RS

/ positioner is a device5 pneumatic5 electro-pneumatic or di!ital53#ic#5 by usin! a control si!nal precisely positions t#e movin! parts

of a control valve in accordance 3it# t#e si!nal value4

&ositioners may be used for t#e follo3in! reasons,

&ermit !reater accuracy U process control

Maintain position re!ardless of c#an!in! forces

:andle #i!# air pressures 5

Increase speed of operation

&ermit faster speed of response

"#an!e c#aracteristics

&rovide simple adustments includin! split ran!in!


107/120

DIRECT ACTIN POSITIONER

INPT INCREASES

OTPT INCREASES

E=A-S

Increasng Sgnal

/ro! Controller

Increasng

Out&ut /ro! Postoner

INPT DECREASES

OTPT DECREASES

E=A-S

Decreasng Sgnal

/ro! Controller

Decreasng



108/120

REVERSE ACTIN POSITIONER

INPT INCREASES

OTPT DECREASES

E=A-S

Increasng Sgnal

/ro! Controller

Decreasng


INPT DECREASES

OTPT INCREASES

E=A-S

Decreasng Sgnal

/ro! Controller

Increasng


" t l V l & 'i


109/120

"ontrol Valve &ac'in!

&ac'in! is a sealin! system 3#ic# normally consists of a deformable

material suc# as T6>5 !rap#ite5 asbestos5 etc4 $sually t#e material is

in t#e form of solid or split rin!s contained in a pac'in! box4

&ac'in! material is compressed to provide an effective pressure seal

bet3een t#e fluid in t#e valve body and t#e outside atmosp#ere4 /t one

time it 3as believed t#at t#e more pac'in! you #ad in a control valve

t#e better it 3ould seal4

Snce /ITIVE EMISSIONS $as 'eco!e a concern* e)tensve

studes $ave 'een !ade ($c$ $ave s$o(n t$at 'etter sealng can

'e o'taned 'y !n!sng t$e nu!'er o" &ac,ng rngs


110/120


In maority of t#e valves45 t#e valve pressure boundary is penetrated

in order to provide t#e required movement to its main sealin!

components4 T#is requirement necessitates a need for an external

secondary sealin! system to prevent t#e loss of t#e pressuried

fluid at t#e point of penetration of t#e valve pressure boundary4 T#issecondary sealin! is ac#ieved by a set of pac'in! rin!s pac'ed

around t#e valve stem in t#e valves stuffin! box5 also called t#e

pac'in! c#amber4

Valve pac'in! provides a positive and reliable sealin! barrier

bet3een t#e system fluid in t#e valves pressure boundary and t#e

outside atmosp#ere and yet ma'es t#e actuation of t#e valve

internals possible from a point external to t#e valve pressure

boundary4



111/120


Stuffin! Box, /lso called a pac'in! c#amber5 is a mac#ined cavity in

t#e valve bonnet or ot#er pressure retainin! part t#rou!# 3#ic# t#e

valves actuatin! s#aft 8stem9 penetrates in to t#e valve pressure

boundary4 T#is cavity #ouses t#e pac'in! rin!s4

%antern Rin!, / lantern rin! is a spacer bet3een t#e t3o sets of !land

pac'in!4 It is !enerally relieved in t#e middle to provide a void to

collect t#e fluid lea's t#rou!# t#e lo3er set of pac'in! rin!s4 %antern

rin!s are used on valve stuffin! boxes 3#ere stem lea'a!e detection is

desirable4 In case of smaller sie valves and lar!e valves not requirin!

stem lea'a!e detection5 lantern rin!s are omitted from t#eir stuffin!

boxes4 T#ese valves employ a sin!le set of !land pac'in!4

Stem, / s#aft li'e component directly attac#ed to t#e main sealin! part

8e4!45 3ed!e or disc9 of t#e valve4 T#e stem of t#e valve passes

t#rou!# t#e stuffin! box and externally actuates t#e sealin! parts of

t#e valve4


112/120


%ea'-0ff "onnections / pipe or tube #oo' up to detect lea's t#rou!#

t#e lo3er set of pac'in! rin!s4 0ne end of t#is pipe or tubin! is

connected to t#e lantern rin! installed in t#e valve stuffin! box and t#e

ot#er and drains off in a remote #oldin! tan'4 In most smaller valves

and ot#ers 3#ere no lantern rin!s are installed5 t#e lea'-off connectionis provided in t#e middle of t#e stuffin! box1pac'in! c#amber if a

specific valve application requires monitorin! of lea's t#rou!# t#e

valve stem4


113/120

Sprin!-%oaded &ac'in!

Dual &ac'in!

Dual &ac'in! it# %ea'-0ff

"onnection


114/120

Seat %ea'a!e "lassifications

R!"e o# T$!%& ' T$ere s no suc$ t$ng as +4u''le Tg$t.+

"ontrol valves are desi!ned to t#rottle4 :o3ever5 t#is is

not a perfect 3orld5 and control valves are also usuallyexpected to provide some type of s#ut-off capability4 /

control valves ability to s#ut off #as to do 3it# many

factors4 T#e type of valves for instance4 / double-seated

control valve 3ill usually #ave very poor s#ut-offcapability4 T#e !uidin!5 seat material5 actuator t#rust5

pressure drop5 and t#e type of fluid can all play a part in

#o3 3ell a particular control valve s#uts off4


115/120


T#ere are actually six different seat lea'a!e classifications as

defined by /HSI16"I )-;-*.=4 But for t#e most part you 3ill be

concerned 3it# ust t3o of t#em,

"%/SS IV and "%/SS VI4"%/SS IV is also 'no3n as M>T/% T0 M>T/%4 It is t#e 'ind of

lea'a!e rate you can expect from a valve 3it# a metal plu! and

metal seat4

"%/SS VI is 'no3n as a S06T S>/T classification4 S06T S>/T

V/%V>S are t#ose 3#ere eit#er t#e plu! or seat or bot# are madefrom some 'ind of composition material suc# as Teflon4


116/120


Class I. Identcal to Class II* III* and IV n constructon and

desgn ntent* 'ut no actual s$o& test s !ade.

Class II. Intended "or dou'le3&ort or 'alanced snge3&ort

valves (t$ a !etal &ston rng seal and !etal3to3!etal seats.

Ar or (ater at B: to 0 &sg s t$e test "lud. Allo(a'le lea,age

s 0.:9 o" t$e rated "ull o&en ca&acty.

Class III.Intended "or t$e sa!e ty&es o" valves as n Class II.

Allo(a'le lea,age s l!ted to 0.89 o" rated valve ca&acty.


117/120


Class IV. Intended "or sngle3&ort and 'alanced sngle3&ort

valves (t$ e)tra3tg$t &ston seals and !etal3to3!etal seats.

-ea,age rate s l!ted to 0.089 o" rated valve ca&acty.

Class V. Intended "or t$e sa!e ty&es o" valves as Class IV.T$e test "lud s (ater at 800 &sg or o&eratng &ressure.

-ea,age allo(ed s l!ted to : ? 80 !l &er !nute &er nc$

o" or"ce da!eter &er &s d""erental.

Class VI.Intended "or reslent3seatng valves. T$e test "lud sar or ntrogen. Pressure s t$e lesser o" :0 &sg or o&eratng

&ressure. T$e lea,age l!t de&ends on valve sQe and ranges

"ro! 0.8: to .: !l &er !nute "or valve sQes 8 t$roug$

nc$es.

S t % ' "l ifi ti


118/120


"lass VI %ea'a!e /llo3ance

Hominal &ort Diameter 8inc#9 %ea' Rate 8ml1minute9

*4+ )42) 8; Bubble1Minute9; )4?+ 82 Bubble1Minute9

;4+ )4=) 8? Bubble1Minute92 )4.) 8= Bubble1Minute9

? *4) 8** Bubble1Minute9

= ?4)) 8; Bubble1Minute9@ =4+ 8?+ Bubble1 Minute9

Bubbles per minute are based on W inc# L )4)2; inc# 3all tube

Submer!ed in 3ater to a dept# of *1@ inc# to W inc#4


119/120

TAN51O


120/120

AN1 =ESTIONS

control valve present

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