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Faculty of Mechanical and Power Engineering

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•Types of valves

•Types of actuators

•Valve sizing

•Examples

Avalveisadevice that regulatesthe flow of

substances(either gases,fluidized solids,slurries,

or liquids) byopening,closing,or partially

obstructing various passagew

ays.Valves are

technically pipe fittings, butusually are discussed

separately.

Valves are used inavariety of applications

including industrial, military,commercial,

residential, transportation. Plumbingvalves are the

mostobvious in everyday life, butmany more are

used.

Some valves are driven

bypressure only,they are

mainly usedforsafety purposes in steam engines

and domestic heating or cooking appliances.

Others are used in acontrolled way,like in Otto

cycleenginesdriven

by a camshaft,where they

playa major rolein engine cycle control

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Alarge variety of valves are available and have many applications with sizes ranging

from tinytohuge.The cost of valves ranges from very cheap simple disposable

valves,in some item

stovery expensive valvesforspecialized applications.

Often

notrealized

bysome,sm

all valves are even inside some common household

item

s including liquid or gelmini-pumpdispenser spigots, spraydevices,some

rubber bulbsforpumping air, etc.,manual air pumps and some other pumps,and

laundry washers.Valves are almostasubiquitousaselectrical switches.Often

avalve

is part of some object,the valve bodyand the object made inone piece; forexam

ple,

a separatoryfunnel. Faucets, taps,and spigots are all variations of valves.

Manyfluidsystem

s such

aswater and natural gaslines in houses and other buildings

have valves. Fluidsystem

s in chem

icaland power plantsand other facilities have

numerous valvestocontrolfluidflow.

APPLIC

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MajorComponents of Typical Sliding-Stem Control Valve Assemblies

Body

The majority of the valve consists of

the valvebody,includingmostof the

exterior.The valvebodyis the vessel

or casing that holds thefluidgoing

through inside the valve.Valve bodies

aremostcommonly made of various

metals or plastics,although valve

bodies fused with glass laboratory

item

sinone piece

are also made of

glass.

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Ports

Thebodyconsists of two or more openings,called portsfrom which movement occurs fromone

openingtothe next.These ports are controlled

by avalve.

Valves with two or three ports are themostcommon,while valves consisting of four or more ports

arenot asfrequently used.Extra ports that arenotneeded can

beclosed offbythe valve.

Manufacturing of valves often occurs with the intent that they

will beconnected with another

specific object.These objects can vary, butgenerally these include some type of piping, tubing,or

pump head. Insome cases, avalveportis immediately connected to a spraynozzle or container. To

makeaconnection,valves are commonly measuredbythe outer diameter the ports they connectto.

Forexample, a 1-inch valve is sized

toconnectto 1-inch outer diameter tubing.

Combined withavalve,ports have the abilitytoactasfaucets,taps,or spigots,all whileoneor more

of its remaining ports are left unconnected. Mostvalves are built with some means of connection at

the ports.This includes threads, compression fittings,glue orcementapplication(especiallyfor

plastic),flanges,or welding(formetals).

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Discs and rotors

Inside the valvebody,flow through the valve may

bepartly or fully blocked

byan

object calledadisc.Although valve discs of some kinds of valves are traditionally disc-

shaped,discs can come in various shapes.Although the valvebodyremains stationary

within thefluid system

,the disc in the valve is movable so it can control flow. Around

type of disc withfluidpathway(s)inside which can

berotatedtodirect flow between

certain ports canbecalled

a rotor. Ball valvesare valves which use spherical rotors,

exceptfortheinterior fluidpassagew

ays. Plug valvesuse cylindrically-shaped or

conically-tapered rotors called plugs.Other round shapesforrotors are possible too in

rotorvalves, aslongastherotorcanbeturned inside the valvebody.Howevernotall

round or spherical dics are rotors; forexam

ple, aball check valveuses the balltoblock

reverse flow, butisnot a rotorbecause operating the valve doesnotinvolve rotation of

the ball.

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Seat

The valve seatis theinteriorsurface in thebodywhich

contacts or could contact the discto form

aseal which

shouldbeleak-tight,particularly when the valve is shut

(closed).If the disc moves linearlyasthe valve is

controlled,the disc comes into contact with the seat

when the valve is shut.When the valve hasa rotor,the

seat is always in contact with therotor, butthe surface

area of contactontherotorchangesastherotoris

turned.If the disc sw

ingson ahinge, asina sw

ing

check valve,it contacts the seattoshut the valve and

stopflow. Inall the above cases,the seat remains

stationary while the disc or rotormoves.Thebodyand

the seat could both come in one piece

of solid material,

or the seat couldbe aseparatepiece

attached or fixed

to

the inside of the valvebody,dependingonthe valve

design.

Stem

The stemisa rodor similarpiece

spanning the

inside and the outside of the valve,transm

itting

motiontocontrol the internal disc orrotorfrom

outside the valve.Inside the valve,therodis joined

toor contacts the disc/rotor.Outside the valve the

stem

is attached

to a handleor another controlling

device.Between inside and outside,the stem

typically goes throughavalve bonnet if there isone.

Insome cases,the stem

and the disc canbe

combined inone piece,or the stem

and thehandle

are combined inone piece.

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Stem

The motion transm

ittedbythe stem can

be alinear

push or pull motion, arotating motion,or some

combination of these. A

valve witha rotorwouldbe

controlled

byturning the stem.The valve and stem

canbethreaded such that the stem can

bescrewed

into or out of the valvebyturning it inonedirection

or the other,thus moving the disc back or forth inside

thebody. Packing is often used between the stem and

the bonnettosealfluidinside the valve inspiteof

turning of the stem.Some valves havenoexternal

control anddo notneedastem; forexample, most

check valves. Check valves are valves which allow

flow inonedirection, butblock flow in the opposite

direction.Some refertothemas one-way valves.

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Stem

Valves in which the disc is between the

seat and the stem

and where the stem

moves inadirection into the valvetoshut

it are normally-seated(also called'front

seated').Valves in which the seat is

between the disc and the stem

and where

the stem

moves inadirection out of the

valvetoshut it are reverse-seated(also

called 'back seated').These termsdo not

applytovalves withnostem

nor to

valves using rotors.

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Bonnet

A bonnetbasically actsas acoveronthe

valvebody.It is commonly sem

i-

permanently screw

ed into the valvebody.

During manufacture of the valve,the

internal parts were put into thebodyand

then the bonnetwasattached

tohold

everything together inside. Toaccess

internal parts ofavalve, auser would take

off the bonnet,usuallyformaintenance.

Many valvesdo nothave bonnets; for

exam

ple,plug valves usuallydo nothave

bonnets.

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Spring

Many valves havea springforspring-

loading, tonormally shift the disc into

some positionbydefaultbutallow

controltoreposition the disc. Relief

valvescommonly useaspringtokeep

the valve shut, butallow excessive

pressuretoforce the valve open against

the spring-loading,

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Valveballs

A valve ball is also usedforsevere

duty,high pressure,high tolerance

applications.They are typically made of

stainless steel,titanium,Stellite,

Hastelloy,brass,and nickel.They can

also

bemade of different types of

plastic,such

as ABS, PVC, PPor

PVDF.

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2-way valves

2-portvalves are commonly called2-way valves.

Operating positionsforsuch valves can

beeither

shut(closed)so thatnoflow at all goes through,

fully open

formaximum flow,or sometimes

partially open

toany degree in between.Many

valves arenotdesigned

toprecisely control

intermediate degree of flow;such valves are

considered

to beeither open or shut,with maybe

qualitative descriptions in between.

2-way valves

Some valves are specially designed

to

regulate varying amounts of flow.Such

valves have been calledbyvarious nam

es

like regulating,throttling,metering,or

needle valves. Forexam

ple,needle valves

have elongated conically-tapered discs and

matching seatsforfine flow control. For

some valves,there may

be amechanismto

indicate howmuch

the valve is open, butin

many cases other indications of flow rate are

used,such

asseparate flow meters.

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2-way valves

In some plants withfluidsystem

s,some2-way valves can

bedesignated

as

normally shut or normally open during regular operation.Exam

ples of

normally shut valves are sam

pling valves,which are only opened whilea

sample is taken.Exam

ples of normally open valves are isolation valves,

which are usually only shut when there isa problemwithaunit orasection

ofa fluid system

such

as a leak.Then,isolation valve(s)are shut inorder to

isolate theproblemfrom the rest of thesystem

.

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2-way valves

Although many2-way valves are made in which the flow can

goin

either direction between the two ports,when

avalve is placed intoa

certain application,flow is often expectedto gofromonecertainport on

the upstream

side of the valve, tothe otherport onthe downstream

side.

Pressure regulators are variations of valves in which flow is controlled

to

produce

acertain downstream

pressure,if possible.They are often used

tocontrol flow of gas froma gascylinder. Aback-pressureregulatorisa

variation ofavalve in which flow is controlled

tomaintainacertain

upstream

pressure,if possible.

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3-way valves

3-way valves have three ports. 3-way valves are commonly made such

that flow coming in atone portcanbedirectedtoeither the secondport

inoneposition or the thirdportin another position or in an intermediate

position so all flow is stopped.Often such

3-way valves are ball orrotor

valves.Many faucets are made so that incoming cold and hot water can

beregulated in varying degreestogive outcoming water atadesired

temperature.Other kinds of3-portvalves can

bedesigned

forother

possible flow-directing schem

es and positions; forexam

ple,see Ball

valve.

Invalves having more than 3ports,even more flow-directing schem

es

are possible. Such valves are often

rotorvalves or ball valves.Slider

valves have been used also.

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Many valves are controlled manually witha handle

attached

tothe valve stem

.If thehandleis turned

a

quarter ofafull turn(90°)between operating

positions,the valve is calledaquarter-turn valve.

Butterfly valves, ball valves,and plug valves are

often quarter-turn valves.Valves can alsobe

controlled

bydevices called actuatorsattached

tothe

stem

.They can

beelectromechanical actuators such

asan electricmotor or solenoid,pneumatic actuators

which are controlled

by air pressure,or hydraulic

actuators which are controlled

bythe pressureofa

liquid such

asoil or water.Actuators can beusedfor

the purposes of automatic control such

as in washing

machine cycles,remote control such

asthe use ofa

centralized control room,or because manual control

is too difficult; forexam

ple,the valve is huge.

Pneumatic actuators and hydraulic actuators need pressurized airor liquid

linestosupply the actuator:an

inletline and an outlet line. Pilotvalvesare

valves which are usedtocontrol other valves. Pilotvalves in the actuator

lines control the supply of air or liquid goingtothe actuators.

The fill valve ina commodewatertankisaliquid level-actuated valve.

When

ahigh water level is reached, amechanism shuts the valve which

fills thetank.

Insome valve designs,the pressure of the flowfluiditself or pressure

difference of the flowfluidbetween the ports automatically controls flow

through the valve. Inan open valve, fluidflows inadirection from higher

pressuretolower pressure.

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Valves are typically rated

formaximum tem

peratureand pressurebythe

manufacturer.The wetted materials inavalve are usually identified also.

Some valves rated at very high pressures are available.When

a designer,

engineer,or user decidestouseavalveforan application,he/she should

ensure the rated maximum tem

perature and pressure are never exceeded

and that the wetted materials are compatible with thefluidthe valve

interioris exposedto.

Somefluid system

designs,especially in chem

ical or power plants,are

schem

atically represented in piping and instrumentation diagrams. Insuch

diagrams,different types of valves are representedbycertain symbols.

Valves in good condition shouldbeleak-free.However,valves may

eventually wear out from use and developa leak,either between the inside

and outside of the valve or,when the valve is shut to stopflow,between

the disc and the seat. Aparticle trapped between the seat and disc could

also cause such leakage.

OT

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HOW TO M

AKE A VALVE?

(A film)

CH

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Ball valve

Butterfly valve

Check valve

Cock (tap)

Flow control valve

Gate valve

Globe valve

Pressure reducing valve

Pressure regulator

Thermostatic valve

Aball valve(like the butterfly valve, oneofafamily of valves called

quarter turn valves)isa valvethat opensbyturninga handleattached

to a

ballinside the valve.The ball hasa hole,orport,through the middle so

that when theportis in line with both ends of the valve,flowwilloccur.

When the valve is closed,theholeis perpendiculartothe ends of the

valve,and flow is blocked.Thehandleposition lets you"see"the valve's

position.

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Ball v

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Ball valves are durable and usually worktoachieve perfect shutoff even after

years of disuse.They are therefore an excellent choiceforshutoff

applications(and are often preferred

to globe valvesand gate valvesforthis

purpose).They

do notoffer the fine control that may

benecessary in

throttling applicationsbutare sometimes usedforthis purpose.

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Ball v

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Ball v

alv

eThebodyof ball valves may

bemade ofmetal,ceramic,or plastic.The ball

may

be chromeplatedtomake it more durable.

There are four generalbodystyles of ball valves: single body,splitbody, top

entry,and welded.

There are four general types of ball valves:fullport, standard port,reduced

port,andv port.

•Afullportball valve has an oversized ball so that theholein the ball is

thesamesize

asthe pipelineresulting in lower frictionloss.Flow is

unrestricted, butthe valve is larger.

•A standard portball valve is usuallylessexpensive, buthasasm

aller ball

andacorrespondingly smaller port.Flow through this valve isonepipe

size smaller than the valve's pipe size resulting in slightly restricted flow.

•Inreducedportball valves,flow through the valve isonepipe

sizes sm

aller than the valve's pipe size resulting in restricted

flow.

•A v portball valve has eithera 'v'shaped ball ora 'v'shaped

seat.This allows the orifice

to beopened and closed inamore

controlled manner withaclosertolinear flow characteristic.

When the valve is in the closed position and opening is

commenced the sm

all end of the'v'is opened first allowing

stable flow control during this stage.This type of design requires

agenerally more robust construction duetohigher velocities of

the fluids,which would quickly dam

age a standardvalve.

•A trunnionball valve hasamechanical means of anchoring the

ball at thetopand the bottom,this design is usually applied

on

larger and higher pressure valves(say

4inch and above600 psi

and above)

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Ball v

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Manually operated ball valves can

beclosed quickly and thus there isa

danger of water ham

mer.Some ball valves are equipped with an actuatorthat

may

bepneumatically ormotor (electric)operated.These valves can

beused

eitherfor on/off or flow control. A

pneumatic flow control valve is also

equipped witha positionerwhich transforms the control signal into actuator

position and valve opening accordingly.

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Ball v

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schem

atic3way ball valve-L-shaped

ball right, T-shaped left

Straight Through,Two

WayORThree Way Ball

Valves

Three-way ball valves havea L-orT-

shaped

holethrough the middle.The

different combination of flow are

shown in the picture.Multiportball

valves with4or more ways are also

commercially available,theinletway

often being orthogonaltothe plane of

the outlets.

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Ball v

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Forspecial applications,such

as

driving air powered motors from

forwardtoreversebyrotatinga single

lever operated

4way ball valve.This

valve has twoL-shaped ports in the

ball thatdo notinterconnect,

sometimes referredto asan

"x" port.

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Ball v

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Ball Valves in sizes upto 2inch generally come insingle

piece,two or threepiece

designs. One piece

ball valves

are almost always reduced bore,are relatively

inexpensive and generally are throw-away.Twopiece

ball valves are generally slightly reduced(orstandard)

bore,they can

beeither throw-away or repairable.The3

piece

design allowsforthe center part of the valve

containing the ball,stem

&seatsto beeasily rem

oved

from the pipeline.This facilitates efficient cleaning of

deposited sediments,replacement of seats and gland

packings,polishing out of sm

all scratchesonthe ball,all

this without removing the pipes from the valvebody.

The design concept ofathreepiece

valve isforitto be

repairable.

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Ball v

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Butt

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Abutterfly valve isatype of flow control device,

typically usedtoregulatea fluidflowing througha

section of pipe.The valve is similar in operationto a

ball valve. A

flat circular plate is positioned in the

center of the pipe.The plate hasa rodthrough it

connectedto a handle onthe outside of the valve.

Rotating thehandleturns the plate either parallel or

perpendiculartothe flow.Unlikea ball valve,the plate

is always present within the flow,thereforeapressure

dropis always induced in the flow regardless of valve

position.

There are three types of butterfly valve:

1.Resilient butterfly valve which hasa

flexible rubber seat.Working pressure up

to 1.6 megapascals(M

Pa)/232 pounds

persquare inch

(PSI)

2.High performance butterfly valve

which is usually double eccentric in

design.Working pressure upto 5.0

MPa/725 PSI

3.Tricentric butterfly valve which is

usually withmetalseated design.

Working pressure upto 10.0MPa/1450

PSI

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Butt

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Butterfly valves are widely used in water distribution and wastewater processing

(notrecommended, asthe debris may block the operation of the disc).Butterfly

valves can come in twobodytypes,affecting installation and maintenance:

lugged or wafer.Waferstylevalves are more common.They are typically

installed between two flanges using bolts or studs and nuts.Lugstylevalves are

also installed between two flangesbutwithaseparatesetof boltsforeach flange.

The lugstylesetup makes it possibletoremoveoneside of the piping while the

other rem

ains intact.

An additional application is found within the exhaustsystem

of automobiles. By

incorporatingabutterfly valve in the exhaustsystem

,it is possibletocontrol the

backpressure and noise output from the mufflerand catalytic converter.When in

aclosed position,the valve increases the am

ount of back pressure produced and

suppresses noise.The angle of valve canbecontrolled inavariety of ways,

including manual control,vacuum control, aswellasbeing tired directlytothe

throttle.

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Check v

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Aclosed ball check valve

An open ball check valve

Acheck valve isa mechanical device, a valve,that

normally allows fluid(liquidor gas) to flowthrough

it in onlyonedirection.Check valves are two-port

valves,meaning they have two openings in the

body, one for fluid toenter and the otherfor fluid to

leave.There are various types of check valves used

inawide variety of applications.Check valves are

often part of common household items.Although

they are available inawide range of sizes and costs,

many check valves are very small,simple,and/or

cheap.Check valves work automatically andmost

arenotcontrolled

by a personor any external

control;accordingly, most do nothave any valve

handleor stem

.The bodies(external shells)ofmost

check valves are made of plastic ormetal.

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An important concept in check valves is the

cracking pressure which is theminimum

upstream

pressureat which the valvewill

operate.Typically the check valve is designed

forand can thereforebespecifiedfor aspecific

cracking pressure.

Heart valvesare essentiallyinletand outlet

check valvesforthe heartventricles,since the

ventricles actas a pump.

An artificial heart valvemay

be

usedtosurgically replace

a

patient's dam

aged valve.

ABall check valve isacheck valve in which

the disc,the movable parttoblock the flow,is

aspherical ball. Inmany ball check valves,the

ball is spring-loaded

tostay shut, butalso many

do nothaveaspring inside.Theinterior

surface of the seats of ball check valves are

more orlessconically-tapered

toguide the ball

into the seat and/orform apositive seal when

stopping reverse flow.

Aclosed ball check valve.

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Check v

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Ball check valves are often very small,simple,and

cheap(although some are expensive).They are

commonly used in liquid or gelmini-pump

dispenser spigots, spraydevices,some rubber bulbs

forpumping air, etc.,manual air pumps and some

other pumps,and refillable dispensing syringes.

Although the balls aremostoften made ofmetal,

they can

bemade of other materials,or in some

specialized cases out of artificial ruby.High pressure

HPLCpumpsand similar applications commonly

use smallinletand outlet ball check valves with

balls made of artificial ruby and seats made of

artificial sapphire,bothforhardness and chem

ical

resistance.

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Check v

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After prolonged use,such check valves can eventually wear out or the seat

can developacrack,requiring replacement.Therefore,such valves are

madeto bereplaceable,sometimes placed inasm

all plasticbodytightly-

fitted insidea metal fittingwhich can withstand high pressure and which is

screwed into thepumphead.

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Check v

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There are similar check valves where the disc is

not aball, butsome other shape.Ball check

valves shouldnot beconfused with ball valves,

which isadifferent type of valve in whichaball

actsas acontrollablerotor to stopor direct

flow.

There are check valves where the pressureon

the upstream

side mustbegreater than the

pressureonthe downstream

sideby acertain

amount,the pressure differential, forthe check

valvetoopen allowing flow.

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Check v

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Tap (

cock)

Cock,colloquialterm for asm

all valve

ora stopcock.

Tap isa valveforcontrolling the release ofa

liquidor gas. Inthe British Isles and normally in

the Commonwealth the word is usedforany

everyday type of valve,particularly the fittings

that control water supplyto bathtubsand sinks. In

theU.S.the usage is sometimes more specialised,

with theterm "tap"restricted

touses such

as beer

tapsand the word faucet being usedforwater

outlets;however some Americans use"tap"in the

broader senseaswell.

Indoor Tap

-commonly found in

the bathroom/laundry and/or

kitchen.ThisGerman

faucet isa

single-handle,double-spout tap

(onespoutforhot, onespoutfor

cold); most modernNorth

American faucets havea single

spout shared

byhot and cold

water supplies allowing warm

flows.

Mostwater and gas taps have adjustable flow.

Turning the knob or working the lever sets the flow

ratebyadjusting the size of an opening in the valve

assembly,giving riseto choked flowthrough the

narrow opening in the valve.The choked flow rate is

independentof the viscosityor temperatureof the

fluidor gas in the pipe,and depends only weaklyon

the supply pressure,so that flow rate is stable ata

given setting.At intermediate flow settings the

pressure at the valve restrictiondropsnearlyto zero

from the venturi effect;in water taps,this causes the

waterto boilmomentarily at room tem

perature asit

passes through the restriction.

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Tap (

cock)

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Tap (

cock)

Bubbles of cool water vaporform

and

collapse at the restriction,causing the

familiar hissing sound.At very low flow

settings,the viscosity of the water

becomes important and the pressuredrop

(and hissing noise)vanish;at full flow

settings,parasitic drag in the pipes

becomes important and the water again

becomes quiet.

Onereason thatmostbeer taps arenot

designed

foradjustable flow is that the

beer itself is dam

aged

bythe pressuredrop

inachoked-flow valve: holding abeer tap

partially open causes the beertofoam

vigorously,ruining the pour.

Mostolder taps useasoft rubberor neoprenewasher

which is screwed down ontoavalve seat inorder to stop

the flow.This is called

a "globe valve"in engineering

and,while it givesaleak-proof seal and good fine

adjustment of flow,both the rubber washer and the valve

seat are subjecttowear(andforthe seat, corrosion)over

time,leadingtoleakage(see photo).The washer can

be

replaced and the valve seat resurfaced

(at leastafew

times), butglobe valves are never maintenance-free.

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Tap (

cock)

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Tap (

cock)

Also,the tortuousS-shaped path the water is forced

to

follow offersasignificant obstructiontothe flow. For

high pressure domestic water system

s this doesnot

matter, but forlow pressure system

s where flowrate is

important,such

as ashower fed

by astoragetank, a

"stoptap"or,in engineering terms, a "gate valve"is

preferred.

Gate valves usea metaldisc thesamediameterasthe

pipe which is screwed intoplace

perpendicularlytothe

flow,cutting it off.There isnoresistance

toflow when

the tap is fully open, butthis type of tap rarely givesa

perfect seal when closed. IntheUKthis type of tap

normally hasawheel-shaped

handlerather than

acrutch

or capstan

handle.

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Aflow control valveregulates the flow or pressure ofa fluid.

Control valves normally respondto signalsgenerated

by

independentdevices such

as flow metersor temperature gauges.

Control valves are normally fitted with actuatorsand

positioners. Pneumatically-actuated globe valves are widely

usedforcontrol purposes in many industries,although quarter-

turn types such

as (modified) balland butterfly valvesare also

used.

Control valves can also work with hydraulic actuators(also knownas

hydraulic pilots).These types of valves are also knownasAutomatic

Control Valves.The hydraulic actuatorswillrespondtochanges of

pressure or flow andwillopen/close the valve.Automatic Control

Valvesdo notrequire an external power source,meaning that thefluid

pressure is enoughtoopen and close the valve.Automatic control

valves include:pressure reducing valves,flow control valves,back-

pressure sustaining valves,altitude valves,and reliefvalves.An

altitude valve controls the level ofa tank.The altitude valve will

remain open while thetankisnotfull and itwillclose when the tanks

reaches its maximum level.The opening and closing of the valve

requiresnoexternal power source(electric,pneumatic,or man power),

it is done automatically,hence its nam

e.

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Gate

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22 mm Gate Valveon

domestic hot water pipe.

Gate Valves are proneto

corrosion.Here the shaft has

broken.

AGate Valve,or Sluice Valve, asit is

sometimes known,isa valvethat opensby

lifting around or rectangular gate/wedge out

of the path of the fluid.The distinct feature of

agate valve is the sealing surfaces between

the gate and seats are planar.The gate faces

canform awedge shape or they can

be

parallel.Gate valves are sometimes usedfor

regulating flow, butmany arenotsuited

for

that purpose,having been designed

to befully

opened or closed.When fully open,the

typical gate valve hasnoobstruction in the

flow path,resulting in very low frictionloss.

AGlobe valve isadeviceforregulating flow ina pipeline,

consisting ofamovable disk-typeelem

entandastationaryring

seat inagenerally sphericalbody.

Globe Valves are nam

edfortheir sphericalbodyshape with the

two halves of thebodybeing separated

byan internal baffle. This

has an opening that formsaseat onto whichamovable plug can

be

screwed intoclose(or shut)the valve. Inglobe valves,the plug is

connectedto astem

which is operated

byscrew action in manual

valves.Typically,automated valves use sliding stems.Globe

valves haveasm

ooth stem rather than threaded

and are opened

and closedbyan actuatorassembly.When aglobe valve is

manually operated,the stem

is turned

by ahandwheel.

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Although globe valves in thepasthad the spherical bodies

which gave them

their nam

e,manymodernglobe valvesdo

nothavemuch

ofaspherical shape.However,theterm

globe valve is still often usedforvalves that have such an

internal mechanism. In plumbing,valves with such

a

mechanism are also often calledstopvalves since they don't

have the global appearance, buttheterm stopvalve may

refertovalves which are usedto stopflow even when they

have other mechanisms or designs.

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Globe valves are usedforapplications requiring throttling

and frequent operation. Forexam

ple,globe valves or

valves withasimilar mechanism may

beusedassampling

valves,which are normally shut except when liquid

samples are being taken.Since the baffle restricts flow,

they'renotrecommended where full,unobstructed flow is

required.

Globe valves are typically two-port valves,although three

portvalves are also produced.Ports are openings in the

body for fluidflowing in or out.The two ports may

be

oriented straight across from each otheronthebody,or

oriented at an angle such

as a 90°angle.Globe valves with

ports at such an angle are called angle globe valves.

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Asafety valve isa valvemechanismforthe

automatic release ofagas froma boiler,

pressure vessel,or other system

when the

pressure or temperature exceeds preset limits.

They are often calledbymore specific nam

es

such

as pressurereliefvalves, T&Pvalves,or

temperature and pressurereliefvalves.

Safety valves were first usedonsteam boilers

during the industrial revolution.Early boilers

without them

were pronetoaccidental

explosionwhen theoperatorallowed the

pressuretobecome too high,either

deliberately or through incompetence

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regulato

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Oxygen Safety Valve

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Pre

ssure

reducin

g valv

e (pressure

regulato

r)

Function and design

The earliest and simplest safety valve used

aweighttohold the pressure of the steam,

butthese were easily tam

pered with or

accidentally released. Onthe Stockton and

Darlington Railway,the safety valve

tended

to gooff when the enginehit a

bump in the track. Abetter valve useda

springtocontain the steam pressure, but

these(based

onSalter spring balances)

could stillbescrewed downtoincrease the

pressure beyond design limits. In 1856

John Ram

sbottom inventedatamper-proof

spring safety valve which becam

e

universalonrailways.

Proportional-Safety Valve

Function and design

Safety valves also evolved

toprotect equipment such

as pressure vesselsand

heat exchangers.The two general types of protection encountered in

industry are thermal protection and flow protection.

Thermalreliefvalves are generally characterizedbythe relatively small size

of the safety valve necessarytoprovide protection from thermal expansion

pressure increases in liquid-packed vessels. As mostliquids are considered

fairly incompressible,it takesarelatively small am

ount offluiddischarged

through thereliefvalvetoprovide an adequate level of protection.

Flow protection is characterized bysafety valves that are considerably larger

than those mounted in thermal protection.They are generally sized foruse in

situations where significant quantities of gas or high volumes of liquid must

bequickly discharged inorder toprotect the integrity of the vessel or

pipeline.

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regulato

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Water heaters

They are required

on water heaters,

where they prevent disaster in certain

configurations in the eventa thermostat

should fail.There are still occasional,

spectacular failures of older water

heaters that lack this equipment.Houses

canbelevelledbythe force of the blast.

Pressure and temperature

safety valveon a

water heater

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Pre

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regula

tor

Apressureregulatorisavalve that automatically cuts off the flow ofaliquid or

gas atacertain pressure,usuallyforthe purpose of preventing dam

ageto

plumbing.

Pressure regulators are often used at the main entrance of waterto abuilding.

They are also used at the waterinletof recreational vehicles.They allow sources

of waterto beused which come atahigher pressure than can

betolerated.

Pressure regulators don't simplystopflow when the source pressure is too high.

Rather,they reacttothe pressureontheir output side,and close when the

pressure in the plumbing reaches the designated level.Should the pressure come

down (forexam

ple,if someone weretoopen

afaucet),the valve then opens and

allows flow until the plumbing pressure goes back up(such

aswhen the faucet is

closed).

AThermostatic M

ixing Valve(TMV)isa valvethat blends hot water(stored at

temperatures high enoughtokill bacteria)with cold watertoensure constant,safe

outlet tem

peratures preventing scalding.

The storage of water at high tem

perature rem

ovesonepossible breeding ground

for Legionella;the use ofa thermostatrather than

astatic mixing valve provides

increased safety against scalding,and increased user comfort because the hot-

water tem

perature rem

ains constant.

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Many TMVs useawax thermostatforregulation.They also shut-off rapidly

in the event ofahot or cold supply failuretoprevent scalding or thermal

shock.

It is increasingly common practice around the worldtoregulate the storage

water tem

peraturetoabove60°C,andtocirculate or distribute water ata

temperaturelessthan

50°C.Water above these temperatures can cause life

threatening scald injuries.Many countries,states,or municipalities now

require that the temperature of all bath water in new

build and extensively

refurbished domestic propertiesbecontrolled

to amaximum of48°C.

Installing Thermostatic M

ixing Valves (TMVs)can ensure that water is

delivered at the required tem

perature thereby reducing the risk of scalding

accidents;it also makes the hot water supply last longer than

onethat is

maintained atalower tem

perature.

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Typical Rotary-Shaft Control Valve Constructions

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Typical Rotary-Shaft Control

Valve Constructions

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Typical Reverse-Acting

Diaphragm Actuator

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Valve selection

Ho

w t

o s

ize a

valv

e?

VA

LV

E S

IZIN

G

VA

LV

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GC

rite

rions

VA

LV

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VA

LV

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G

Flo

w c

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kv,

cv

Pressure drop

Resistance coefficient

Density of fluid

velocity

VA

LV

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IZIN

G

Flo

w c

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kv,

cv

Volume flow

Pressuredrop

Vk

p

pv

vo vo

.

=∆

∆ρ

ρ

VA

LV

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IZIN

G

Flo

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Seat area

Orifice equation

metric valve flow coefficient

VA

LV

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IZIN

G

Flo

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kv,

cv

metric valve flow coefficientfor water

VA

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Uw

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liquid

gas

steam

saturated

steam

VA

LV

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Valv

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Linear-and

equal percentage valve

characteristics

VA

LV

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VA

LV

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VA

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Relative flow

VA

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VA

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VA

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VA

LV

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Valv

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EXAMPLES

Thank you for

your attention