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Chapter 3

VALVES

3.1 CLASSIFICATION

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Valves are classified according to their action performed. Isolation

Regulation.

Checking

Switching

Discharging

ISOLATION VALVES.

Gate valve

Ball valve

Plug valve

Piston valve

Diaphragm valve.

Butterfl valve.

REGULATION VALVES. Glo!e valve.

"eedle valve.

Butterfl valve.

Diaphragm valve.

Piston valves.

CHECKING VALVES.

Check valve.

#oot valve.

SWITCHING VALVES.

$ultiport valve.

Diverting valve.

DISCHARGING VALVES.

Safet valve.

Relief valve.

Safet relief valve.

#lush !ottom valve.

Rupture disc.

3.2 VALVES ASSEMBLY

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#ollowing are the parts of valve%

Disc:- &he moving part that directl effect the flow is called as disc.

Seat:- &he non'moving part on which the disc !ears is called as seat.

Port:- &he ma(imum internal opening of the valve in full open position.

Stem:- &here are two tpes of screwed stem. &he rising ) non rising stem.

&he rising stem can either !e inside screw or outside screw .&he outside screwtpe has a oke on !onnet ) referred to as *outside screw ) oke+ , -S)/. thehand wheel can either rise with the stem or stem can rise through the handwheel.

In "on' rising stem hand wheel ) stem are in the same position whether thevalve is open or closed. &he screw is inside the !onnet.

Bonnet0'&he !onnet is connected to the !od . &he tpe of connection can !eflanged !olted1 !ellow sealed1 screwed 2on1 welded1 union1 pressure sealed etc.

Body0'&he valves are connected to pipe1 fittings or vessel ! their !od ends1which ma !e flanged1 screwed1 !utt or socket welding.

TERMS USED FOR VALVE SPECIFICATION.

P-T ratings :- &he ma(imum allowa!le sustained non'shock pressure at thecorresponding ta!ulated temperature. &hese are listed in 3"SI B 45.67 ) 3"SIB 45.8.

Class:- &he valve is specified ! the pressure rating of the !od of the valves.&he 3merican standard specifies the following class.Class 489 :Class 699 :Class 799 :Class 599 :Class ;99 :Class 4899 :Class

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Trim:- &he trim mainl comprises of stem1 seat surface1 !ushing ) other internalparts1 which are in contact with the fluid.

3PI 599 specifies trim "o0 ) the material that can !e used for parts with itstpical specification ) grade.

&a!le 6.4 3PI 59 Standard for &rim

3.3 VALVE TYPES

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3.3.1 GATE VALVE

It is an isolation valve1 can+t !e used for regulation.

Designed to operate full open or full closed.

#luid hammer is minimum as it operates slowl.

Pressure drop through gate valve is less. In full closed position gate valve provide positive seal under high

pressure.

>nder low pressure there can !e seepage of 8psi.which is not considered

a!normal.

Si?e range @A 2 4

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Ball valve is an isolation valve !ut in some case it can !e used as a

regulation valve.

It is designed to operate full open or full closed.

Ball valve is uarter turn valve hence it can !e uickl opened or closed.

It is suita!le for gas1 compressed air ) slurr services.

uick opening closing causes fluid hammering.

Pressure drop is less.

#igure 6.4 Ball Valve

3.3.3 GLOBE VALVE.

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Glo!e valve is a regulation valve.

It open ) closes slowl so fluid hammer is minimum.

&here is leakage under low pressure in full close position.

Pressure drop is comparativel higher gate1 !all.

$ain disadvantage is the *E+ pattern design which restrict the flow more

then gate1 !all or !utterfl valve.

Si?e range is @A 2 4

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>sed for the precise flow of fluid.

Generall used for instrument1 gauge ) meter line service.

#igure 6.7 "eedle Valve

3.3.! BUTTERFLY VALVE.

It is an isolation valve.

It can !e used for regulation !ut not for e(tended period.

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3dvantage is the low weight1 compact design hence preferred over gate

valve in large !ore.

Fike !all valve it operates with a 47 thturn.

It is designed for handling large flow of gases or fluid including slurries.

Si?e range

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Valve design is ver compact.

It reuires little headroom.

Steam corrosion is minimum as there is no screw thread.

Suita!le for highl viscous fluid.

3vaila!le in much higher si?e then the !all valve

#igure 6.5 Plug Valve

3.3.# DIAPHRAGM VALVE.

$ainl an isolation valve !ut cat can !e used for regulation also.

$ainl used for low pressure corrosive fluid or where high degree of purit

is reuires e.g.. Pharmaceutical ) food processing industries.

Diaphragm moves ups ) down to operate the valve.

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Bod ) !onnet is made of casting. Bod is lined with corrosive resistant

materials. Diaphragm is generall made of ru!!er or PH.

&here is no 3PI or 3"SI standard availa!le for this valve. these are

covered ! British standards ) $SS'SP standards.

Op$n p%&i'i%n C(%&$ p%&i'i%n

#igure 6. Diaphragm Valve

3.3.) CHECK VALVE.

Check valves are directional control valve1 which prevent the !ack flow in

lines. &he common tpes of check valves used are lift tpe1 swing tpe ) wafer

tpe.

FI#& CJHCK V3FVH

&hese are operated ! lifting action of the disk elements. &he different tpe oflift check valve availa!le are

Piston lift check 0' It can !e placed in hori?ontal pipe line onl.

Ball lift check0 ' It comes in !oth hori?ontal ) vertical pattern hence can !e usedin !oth the position.

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#igure 6.= Fift check valve

SWING CHECK VALVE

Swinging action of disk operates these valves. &he pressure of the fluid lifts thehinged disk ) allows the flow. &he disk return to seat ! its own weight. It can !eused in !oth hori?ontal ) vertical position.

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#igure 6.; Swing Check Valve

L3#HR CJHCK V3FVH

&hese are the flangeless swing check valves. &here are two tpe of wafer checkvalve

4. Single plate wafer check valve

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Lafer check valves are availa!le from suall it+s a glo!e valve tpe.

>sed to drain out piping1 vessel1 reactor.

&he disk in close position matches with the !ottom surface of tanks or

piping.

>suall inlet is one si?e higher then the outlet si?e.

&he outlet port is at an angle of 78' 59 to the inlet port. 3vaila!le in the si?e range of 4A ' 4sed for steam gas or vapor service.

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#igure 6.44 Safet Valve

3.3.11 RELIEF VALVE.

3n automatic pressure relieving device actuated ! the static pressure

upstream of the valve. Lhich opens in proportion to the sstem pressure. 3lsothe valve reseat when the pressure is reduced !elow the set pressure.

>sed primaril in liuid service.

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#igure 6.4< Relief Valve.

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