General Control Valves

8/9/2019 General Control Valves

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Engineering Centre of ExcellenceECoE - Doha, Qatar

Instrument training 16 th July 2011

eneral Control !al!es"

Prepared by: Gavhane D.V.


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2eneral Control #al!es"

$%&-D'%('E)*+( (#*('E



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I' .D/C I.' &-

Control valves also called final control element are a mostimportant element in the control system of a process plant.

It is the last device in control loop.

DE I'I I.' &-

A control valve is a variable orifice used to re ulate the flo!of a process fluid in accordance !ith re"uirement of process.

/'C I.' &-

It absorbs the proper amount of pressure drop to maintainsystem balance under all operatin conditions.



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#eneral Control #al!es"

eatures of Control !al!es"

*E E ( E ./ E( / E) . C.' . #( #E) &

Capacity$an eability

CharacteristicsPressure drop

C( (CI % & %he capacity is normally measured as Cv&'lo! Coefficient( !hich is defined as :

)%he number of *+ allons per minute of !ater at ,- o' that!ill flo! throu h a valves !ith psi pressure drop .

(' E($I I % & $an eability of a Control Valve is theratio of the ma/imum to the minimum controllable flo!.



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Control !al!es an3 lo4 Characteristics"

%he relationship bet!een control valve capacity and valve stem

travel is 1no!n as the 'lo! Characteristic of the control valve.

%he Curve sho!n are based on constant Pressure drop acrossthe valve and called Inherent flo4 characteristics"



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,eneral Control #al!es"

inear Characteristics"

'lo! Capacity increases linearly !ith valve &stem( travel. In!hich the valve differential pressure drop is Constant over thetravel ran e.

inear valve plu shall for li"uid level control and controlapplication re"uirin constant ain.

LINEAR VALVE TRAVEL IS DIRECTLY PROPORTIONAL TO

THE VALVE STROKE

' $ + 4' *ID%$A5+'6$P$ C6++

7 $6 %8A5#-9

' + %67P$6++*$6D$ P

AC$ ++VA V6



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;eneral Control #al!es"

E5ual ercentage Characteristics"

'lo! Capacity increases e/ponentially !ith valve trim travel .6"ualincrement of valve travel produce e"ual percenta e chan e ine/istin Cv.6"ual Percenta e valve plu shall be used !here only smallpercenta e of system drop is available in Control valve.

EQUAL INCREMENT OF VALVE TRAVEL PRODUCE AN EQUAL PERCENT FLOW CHANGE

' $ 'A+% ' I*D%$A5+'6$P$ C6++

8IG8$A5G6A


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9/42eneral Control #al!es"

Ca!itation"

Cavitation is condition that occurs in li"uid flo! !here the internalpressure of li"uid at set point falls belo! vapour pressure and vapourbubbles form and at do!nstream rises above vapour pressure a ain.

As this pressure recovers so that bubbles collapse and cavitation ta1eplace.It is possible to predict !here cavitation !ill occur by loo1in pressurecondition and valve recovery factor.& si ma 7ethod (Cavitation sounds li1e stone passin throu h the valve.


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-eneral Control #al!es"

Effect of Ca!itation"

6rosion in rotary plu valve body induced by cavitation



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lashing"

'lashin is condition that occurs !ith li"uid flo! !here the Pressure failsbelo! it . %here are then t!o phases flo!in & i.e. i"uid and vapour (do!n stream.+everal dama e can occur inside a valve due to erosion caused by theimpact of li"uid droplet travelin at hi h speed.


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#elocity rofile across )ingle seate3 #al!e"

P

P2

V & i"uid(V 2& i"uid(

P$6++*$6 P$ 'I 6 AC$ +++I5G 6 +6A%6D C 5%$VA V6

Pressure $ecovery:? At vena contracta the velocity is reatest substantiallydecrease in pressure .'urther do!n stream as the fluid stream e/pands into

a lar e area Velocity decreases and pressure increases. %his phenomena iscalled Pressure recovery. As a eneral lobe valves have o!er pressure recovery than


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#eneral Control #al!es"

i7ing Influence8 eynol3s 'um9er8Cho e3 lo4"

Pipin Influenence:? Capacity reduction due to the presence of $educer *p Do!n stream of the valve. Correction factor !ill be available frommanufacturer .$eynolds 5umber :? 'or $eynolds number application such as viscous orsmall flo! the basic siBin e"uation can not be used !ithout correctionsince the e"uation is based on turbulence flo! . Correction factor !ill beavailable from manufacturer .&%he ratio of dynamic forces to viscous forces(*sually the correction can be i nored !hen $eynolds number is reater than#--- the correction !ill be -9 or less .Cho1ed 'lo!:? 4hen the pressure at vena contracta drop belo! the vaporpressure of the li"uids bubbles !ill form in the stream .%he formation ofbubbles causes a cro!din condition at vena contracta !hich tends to

restrict flo! and further increase in pressure drop !ill not produce increasein flo!.In case of as cho1ed flo! means outlet velocity reaches sonic velocity.

%he limitin Pressure difference EPt is called 7a/imum allo!able differentialpressure for siBin .



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,eneral Control #al!es"

Contents of Control #al!e& Data )heet" 1>

I'E

I E I'E )IAE B )C*ED/ E

I5 # +C82- =6

(C/(.

'E/:(

IC

% E +I5G 6?AC%I5G 'AI +A'6 +P$I5G $6%*$5 KDIAP8$AG7 % P6

1? *% # +C82- => : B :.DE V%+

1@ I E I'E I')/ ( I.'86A% C 5+6$VA%I 5

&6 6C%$ICA %$ACI5G( =? )IAE 8 E "( E( V%+20

) EC"BC.DE)

#( #E )IAI' I+A +;0.- =@ .'8. 7 D* A%I5G 6+

21 #( #E )E( E( ( E C ()) IV A+ P6$ 'CI ;-?2 60 ) I' (C I.' .' (I C +6

22 61 :(F ( .+($ E E))" V%+

2; 62 :I' EQ/I ED E))" V%+2< 6; (#(I ($ E (I )/ %

E))/ E ag7I5 5 $ 7A D6+IG5

2=

#(#E$.D%

% E


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;eneral Control #al!es"

Contents of Control #al!e& Data )heet "


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=eneral Control #al!es"

lo9e Control #al!e Construction" "



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eneral Control #al!es"

eneral Control #al!e Classification"

C 5%$ VA V6

I56A$

7 %I 5

$ %A$

7 %I 5

Diaphra m valveGate valve

G


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Eccentric lug 8 Camflex #al!e Construction"

+ide vie! of an eccentric plu valve+ho!n in partially openO..



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Eccentric Dis 8$all8 nife #al!e Construction

22

V?5otch


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$utterfly8(ngle8 hree +ay #al!e Construction

23eneral Control #al!es" Prepared by: Gavhane D.V.


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eneral y7es of (ctuators " Actuator is the part of the valve that responds to the applied si nal andcauses modification of the fluid flo! throu h stem plu .

% E) . (C /( . )&1 Dia7hragm (ctuator Direct Actin $everse Actin +iBe depends on output thrust re"uired and supply air pressure

available.2 iston (ctuator *se of hi h pressure air to 0- psi . eliminatin the need ofpressure re ulator. *sed !here 8i h 'ast +tro1in +peed is re"uired.; Electro hy3raulic (ctuator&

6lectro?hydraulic Actuator is sin le unit contains 8ydraulic Pump and $eservoir 6lectric 7otor. Ideal for isolated locations< :anual (ctuator

*sed !here no auto control is re"uired Prepared by: Gavhane D.V.


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2,eneral Control #al!es"

Direct (cting (ctuators "



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2;eneral Control #al!es"

(ctuators ail-)afe e5uirements"

'ail +afe is the action of the actuator by !hich the valve C +6+ &'C(or P65+ &' ( fully in case of air supply failure.



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2=eneral Control #al!es"

eneral y7es of $onnet B (ccessories "$onnet -


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eneral Construction of $onnet "

'or ed KValve


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3-eneral Control #al!es"

Control !al!es Characteristics"

P$ C6++ APP ICA%I 5 I586$A5%C8A$AC%6$I+%IC+

P$6++*$6 I>*ID+GA+ & 4 ' 4+ (GA+ & A$G6 ' 4+(

EPma/HEpmin J 0 EPma/HEpmin 0

6>*A 96>*A 9

I56A$6>*A 9

%emperature i"uids Gases 6>*A 9

'lo! oad Chan es+et point chan e

6>*A 9I56A$

evel EPma/HEpmin J 0 EPma/HEpmin 0

I56A$6>*A 9



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Control !al!es &- Interface

.CE)) I' E (CE

Process to provide process data to Instrument for specifyin thevalveInstrument to provide slected valve siBe to Process forincorporatin in P IDsInstrument to provide instrument air consumption fi ures for thevalves to Process to decide air line header siBes.

I I' I' E (CEInstrument to provide 'ace to 'ace Dimensions 6nd Connection+iBe $atin Actuator 8ei ht rientation 6nvelopeDimensions &for 3?D 7odel( 4ei ht etc.

Pipin to provide location of control valves to Instrument fordecidin instrument air manifolds.Pipin to provide Pipe 7aterial +pecification to Instrument forspecifyin the valves.



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Control !al!es $o3y :aterial"

re5uently /se3 #al!e $o3y Cast :aterials (re&

CA$< 5 +%66 &A+%7 A2 , G$ 4CC( up to #2; - CC8$ 76 7 +%66 &A+%7 A2 ; G$ 4C ( up to 0 3 - CCA$< 5 7 +%66 &A+%7 A2 ; G$ C0( up to 0 3 - C3-# +%AI5 6++ +%66 &A+%7 A30 G$ C'3( up to = , - C3 , +%AI5 6++ +%66 &A+%7 A30 G$ C'=7( up to = , - C

CA+% I$ 5 &A+%7 A 2,( up to 232-

C

)7ecial :aterials /se3 De7en3ing .n he rocess e5uirements

8A+%6A

Documents

General Control Valves