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KATUB KATUB

4.1.3 Specific Types 

4.1.3.1 Gate Valves 

Purpose: gate valves are used when a tight shut-off is required. The !ust not "e used for throttling #i.e. !ust

 "e full off or full on$ as a restri%ted flow through a gate valve will erode the seat of the wedge dis%.

&'('& T)*+ A,+ 

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The wedge-shaped dis% is !oved up to open the valve " turning the wheel anti-%lo%/wise. To shut off the flow0

the wheel is turned full %lo%/wise until the dis% is properl seated and %overs the opening.

ne %o!!on tpe is the rising ste! tpe. *n other designs0 the wheel is fied to the ste! and rises with it.

The position of the ste!2ste! and hand wheel indi%ates whether the valve is open or shut. *f the ste! is raised0

the valve is open.

4.1.3. Ball/Plug Valves

Purpose: Ball and plug valves are used to provide a qui%/0 si!ple shut-off. The are operated " turning the "all

or plug through 56. Ball and plug valves should not "e used for throttling0 as a restri%tion in the flow will lead

to erosion of the valve.

peration: &efer to (igure 

The "all or plug has an opening through the %entre. 7hen this opening is in line with the inlet and outlet ports0

flow will "e allowed. 7hen the "all or plug is turned through 58 no flow %an ta/e pla%e. 9ood sealing %an "e

o"tained0 parti%ularl when spe%ial sealing rings !ade of PT('2Teflon are used.

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+o!e "all and plug valves are lu"ri%ated to provide a seal and prevent wear0 and should "e regularl lu"ri%ated

with the proper lu"ri%ant.

4.1.3.3 Globe Valves

Purpose 9lo"e valves are used to %ontrol flow as the %an operate quite safel at part openings. A good shutoff

%an also "e a%hieved if required

peration: &efer to (igure 

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7hen the hand wheel is turned %lo%/wise0 the dis% is against a seat0 stopping the flow. Turning the hand wheel

anti-%lo%/wise lifts the dis% fro! its seat and allows flow to %ontinue.

The high pressure is usuall on the "otto! of the plug0 so that the ste!0 seal0 et%. are not under %ontinuous

 pressure. Appli%ations are widespread0 in%luding do!esti% water taps.

.

.

4.1.3.4 Butterfly Valves

Purpose: Butterfl valves are used for %ontrolling flow and %an a%t as a shutuoff va1ve0 if the sealingarrange!ent is designed a%%ordingl.

peration: &efer to (igure 

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The dis% or wafer rotates a"out a verti%al ais and %an "e turned through 56. The dis% seals against the opening

to %ut off flow and %an "e positioned at a point "etween full %losed and full open as required.

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+o!e "utterfl valves have a dire%t a%ting lever0 others are operated through gear"oes when finer %ontrol is

required. *n !ost %ases0 a %lo%/wise !ove!ent will %lose the valve.

4.1.3.; Relief Valves

Purpose: &elief valves are used to prote%t sste!s fro! over-pressure or to %ontrol pro%esses " allowing flow

to %o!!en%e when a %ertain pressure has "een rea%hed.

peration: &efer to (igure 

A spring holds the valve dis% in pla%e against the seat. The valve0 therefore0 will not open until the for%e eerted

on the valve dis% " the fluid pressure e%eeds the for%e eerted " the spring. 7hen this o%%urs0 flow %an ta/e

 pla%e through the outlet port until the fluid pressure is redu%ed to "elow the valve operating

 pressure. The spring for%e will then release the valve.

&elief valves operate auto!ati%all and are usuall pre-set to a spe%ified relief setting " the !anufa%turers or

ad<usted when in use0 if required. &e-%ali"ration is then required.

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4.1.3.= Check Valves

Purpose: >he%/ valves allow flow in one dire%tion onl. ne %o!!on appli%ation is in the dis%harge line of a

%entrifugal pu!p to prevent reverse su%tion.

&efer to (igure  

peration:

The two designs operate on the sa!e prin%iple: flow through the valve holds the plug or dis% in an open

 position. *f flow %eases or falls to "elow the "a%/pressure ahead of the valve0 then gravit or the "a%/ pressure

will tend to return the plug to its seat.

>he%/ valves are auto!ati% in a%tion.

4.1.3.? Twin-Seal Valves 

Purpose: Twin-seal valves !a "e used when an etra tight shut-off is required. The are "asi%all plug valves0

 "ut have an additional a%tion whi%h for%es sealing seg!ents against the inlet and outlet ports providing a

 positive seal.

&efer to (igure 

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peration:

The opening a%tion %onsists of two stages:

1. Unsealing the sealing seg!ents.

. &otating the plug.

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The first stage "rea/s the seal and retra%ts the seg!ents fro! the ports8 the se%ond stage allows proper flow to

 "egin. Usuall 1 to 12 turns are required to withdraw the seg!ents and a further 124 turn to rotate the plug.

#Up to @ turns to open the valve.$

4.1.3. Sei-!ee"le Valves

Purpose: +e!i-needle valves are used to %ontrol instru!ents and %an stand high pressures of up to 0555 psi.

peration: &efer to (igure

7hen used with an instru!ent0 the valve should onl "e opened enough to per!it flow and allow the

instru!ent to register %orre%tl. ne or two turns should "e suffi%ient The valve wor/s " pushing a needleC or 

s!all rod into a slightl tapered seat 7hen the needle is full ho!e0 then flow is shut off. The

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rate of flow %an "e ad<usted as required " raising the needle.

4.1.3. Ball-Check Gauge Glass Valves 

Purpose: These valves are used to prevent loss of liquid and %onsequent da!age or in<ur0 in %ase of "rea/age

of gauge glasses.

peration: &efer to (igure 

7hen a reading is required0 "oth valves should "e opened slowl 1 to 1 12 turns to allow the fluid to find its

level. The tip of the valve ste! prevents the "all fro! seating at this point As soon as flow stops and the level

sta"ilises0 the valves !ust "e opened full so that the "all %an "e pushed into the outer seat " the es%aping fluid

if the glass should "rea/. To %lose or reset the valve0 the handle should "e turned %lo%/wise until the valve top is

fir!l against the inner seat0 and then re-opened slowl after the gauge glass has "een repla%ed0 if ne%essar.

4.1.4 #perating Points

7hen using valves0 the following points should "e o"served:

Dire%tion of (low: Dire%tion of flow is usuall !ar/ed with an arrow in the %ase of %he%/ valves and glo"e

valves.

Dire%tion of pening2>losing: )and wheels and levers - %lo%/wise to %lose0 anti-%lo%/wise to open.

,evers - usuall lever in line with pipe - open0 lever at 56 to pipe - %losed.

pen and %lose valves slowl.

Ealves should alwas "e opened and %losed slowl0 e%ept in e!ergen%ies. Too rapid %losing %an %ause pressure

waves to "uild up and travel "a%/ through the sste!0 possi"l %ausing severe da!age0 "urst or in<uries. This

 pheno!enon is /nown as water ha!!erC in do!esti% water sste!s and a loud /no%/ing noise %an "e heard in

the pipe.

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Gate an" Ball/Plug Valves: 9ate and "all valves !ust onl "e used in the full open or %losed positions.

*nter!ediate setting %an %ause tur"ulen%e0 whi%h %an wear awa the valve ver qui%/l and %ause internal

lea/age. Gauge Glass Valves: 9auge or sight glass valves !ust "e full opened as soon as the fluid has rea%hed

its level or there will "e no prote%tion if the glass "rea/s.

$nterlock/%eys: +o!e valves are not fitted with hand wheels or levers and %an onl "e operated " spe%ial /es

or spanners. This is "e%ause the setting of the valve is %riti%al and !ust not "e altered e%ept " an authorised person.

+i!ilarl0 so!e valves are sealed with wire8 lo%/s or other !eans and !ust not "e ta!pered with or altered as

serious da!age %ould result.

Do not pen2>lose too far or use unne%essar for%e.

*f gate and glo"e valves are <a!!ed too far open0 the !a seiFe or "e da!aged. This is %alled "a%/seatingC

and puts unne%essar strain on the dis%0 whi%h !a "rea/ off. *t is "est to re-%lose gate and glo"e valves " 12

to 1 full turn after the are full opened.

+i!ilarl0 over-tightening the valve when %losing it !a da!age the dis% and seat leading to seiFure or lea/age.

*f valves prove stu""orn to open0 !e%hani%al assistan%e su%h as a valve wren%h or spanner %an "e used. The

!ini!u! a!ount of for%e should "e used and "efore appling the persuaderC0 %he%/ that the valve is not

alread open. Do not use persuaders on twin seal valves or on ver s!all valves0 whi%h !a "rea/ off.