ball valve design

7/25/2019 Ball Valve Design

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BALL VALVE DESIGN

A valve that uses a spherical obstruction (a ball) to stop and start the hydraulic flow. A ball valve is usually

rotated 90° to open and close. This article will highlight only the important points in short.

The points discussed in this article are:

• Applicable codes

• !educed bore " full bore design

• #oft seated " $etal seated design

• #ide %ntry " Top %ntry " &elded body design

• 'alve ends " 'alve operators

•

loating " trunnion mounted design

• #% " *% " +ody cavity relief features

• *++ " *,+ " %-tended bonnet " weld overlay

• Anti static " ire safe design " #ealant ,nection

• #eat insert materials " /rings " 1ip seals

• #pecial !e2uirement for %#* 'alve 3

• 1ifting 3 supporting re2uirements

The article will be divided in few parts and published in due course.

Ball Valves Features:

• 4uarter turn straight thru valve " fast opening 3 closing

• Tight #hut off as well as very easy to use

• Application as isolation valve (on and off condition)

• #uitable for %mergency shutdown conditions

Disadvantages:

• 5ot suitable for throttling

• luid trapped in the body cavity



• 1imited wor6ing temperature range

Applicable Standards for Ball Valve :

• *esign #td. 7 A, 8* " ,#/ ;; " +# %5 <=9=

• Testing #td. 7 A, 8* " A, >9? " +# 8<>> art ,

• ire testing 7 As per A, 8A@ A, 80<@ ,#/ 09< or +# 8<>> art ,,.

• *imensional #td. 7 A#$% +8.0 " A, 8*

Ball Valves Patterns:

• #hort pattern

• 1ong pattern

enerally long pattern dimension is selected for ease of connection to pipe flanges.

Ball Valve Internals

+all 'alve ,nternals

Ball Valve Design !pes



• #oft seated and $etal seated *esign

• !educed bore and ull bore *esign

• +ody types 7 #plit@ Top entry or welded body

• loating and Trunnion mounted *esign 3

• #ingle " double piston effect design

• *++ " *,+

"educed Bore #"educed Port$ Design

• +ore dia. siBe less than pipe dia. for valve siBe up to =C5+ 3 = siBe less for C5+ to =C5+

(and ; siBes less for siBes above =C5+).

• #maller and lighter valves.

!educed +ore

• Dave lower operating tor2ue@ resulting in lower cost actuated valve pac6age.

• #lightly higher pressure drop than full bore valve.

• revents pigging

• These valves are normally of one piece 7 end entry design for smaller siBes (up to C>0E) 3 two

" three piece 7 side entry design for bigger siBes.

• These valves are also called as regular port valves.

Full Bore #Full Port$ Design



• +ore inside diameter same as pipe inside dia.

• 'ery less pressure drop

• /f higher weight than reduced bore valve@ hence more costly.

• #elected for specific process reasons@ typicallyF minimum pressure drop@ minimal erosion@ pigging

re2uirement and gravity flow (to avoid li2uid poc6et)

Soft Seat Design

• Thermoplastic or %lastomeric seats are inserted in a metallic holder (seat ring) to provide soft

seating action

• rovide good sealing ability

• 1ower in cost than metal seated valves

• 1imited temperature rating

• #hould not be used in dirty services@ particularly on floating ball valves

• #oft seat materials used are 7 T%@ 5ylon@ *evlon@ %%G@ etc

• ,t is generally accepted a lea6age of ,#/ >=0? !ate A

#oft #eat

%etal Seat Design

• *irect metal to metal contact between seat ring 3 ball.

• 'alves are used for abrasive service and for services where soft seated valves can not be used

due to temperature limitations.

• The ball 3 seat contact surfaces are hard faced to improve resistance to wear 3 prevent

scratching caused by the solid particles contained in the process media.



• $etal sealing may be obtained by tungsten carbide coating (up to =00 deg. H)@ chromium

carbide coating (above =00 deg. H)@ electroless nic6el plating (%5) or stellite hard facing.

• Acceptable lea6age of ,#/ >=0? !ate *.

Single Piece Bod! Design

• ,n the single piece design valve@ the body will be cast"forged as one piece. The insertion of the

ball will be through the end of the body and is held in position by body insert.

• This design offers the uni2ue advantage of eliminating the possibility of e-ternal lea6age to the

atmosphere through bolted body oints.

• This design restricts the valve to be of reduced port floating design only (for siBes up to C5+).

#ingle iece *esign

&o piece ' (ree Piece Design

• Twopiece design complements the singlepiece design in siBes of 8C 3 above for reduced bore

and for + design valves.

• ,n two piece design@ the body is constructed in two pieces and the ball is held in position by body

stud. There can be full bore or reduced bore design possible in this construction.

• ,n case of three piece design@ the body has two end pieces and one centre piece.

• Three piece design valves are most easily online maintainable. +y removing the body bolts

6eeping only one@ the body can be swung away using the last bolt as fulcrum@ to carry out any

installation or maintenance operation on the valve. This feature reduces maintenance downtimeto a bare minimum.



$ultipiece *esign

• or larger = piece or ; piece valves the dimensions between the body and flange should be

chec6ed so that sufficient clearance is available for bolting.

• *uring vendor drawing review same should be chec6ed.

+all 'alve *esign

op Entr! Design

• $aintenance and repair possible insitu@ by removing the top flange. This minimises the

maintenance downtime.

• 1imited space is re2uired around the valve for maintenance.

• Available in welded as well as flanged ends@ but welded ends are preferred to reduce potential

lea6 paths and minimise valve weight.

• Deaviest and most e-pensive construction.



Top %ntry *esign

)elded Bod! Design

• &elded body construction eliminates body flanges@ reduces potential lea6 paths and increases

resistance to pipeline stresses.

• $inimum number of lea6 paths@ hence beneficial in fugitive emission and vacuum applications.

• Hompact and light weight design

•

The body draining 3 venting feature allows the valve maintenance technician to test each seatrings sealing ability with the ball in either the full open or full closed positions.

• #ealant inection fittings access directly to each seat ring. This enables the technician to topup

the 2uantity of lubricant inside the valves sealant inection system on a periodic basis.

• 'alve cleaner can also be inected into these fittings to flush out the old grease in the valve and to

clean critical seal faces on the ball.

• Deavier sealants are also inected through the sealant inection fittings during an emergency

when a critical seal is re2uired.

• Applications 7 /il 3 as pipelines@ compressor stations@ measuring s6ids@ etc.



&elded *esign

Valve Ends

The type of valve ends are as follows:

• langed ends with raised face or ring oint face

• Threaded ends

• #oc6et weld ends

• +uttweld ends 7 #oft as well as metal seated buttwelding end valves shall be provided with butt

weld pup pieces.

• This avoids damage to the valve seat as well as soft seal materials due to welding heat.

• The pup piece length shall be =00mm for siBes up to =C5+@ 00mm for up to =C5+ siBe 3

?00mm above =C5+ siBes

Valve *perator

• +all 'alves can be operated by a lever@ wrench@ hand wheel or they can be pneumatic@ hydraulic

or motor operated.

• A ball valve is rotated in cloc6wise direction to close 3 anticloc6wise direction to open.

• The ma-imum lever length shall not e-ceed >0mm 3 ma-. hand wheel diameter shall not

e-ceed the valve face to face dimension or ?00mm whichever is smaller.

• ear operator is re2uired to be provided for valves as per below criteria:

• 8C 3 larger for class >0 valves



• C 3 larger for cl. ;00 3 800 and

• ;C 3 larger for cl. 900 onwards

'alve /perator

Floating or Seat Supported Design

• +all valve design in which the ball is not rigidly held on itIs rotational a-is 3 is free to float

between the seat rings.

• ,n the closed position ball is pushed against the seat by the pressure of the fluid from upstream

and hence can pressure seal the down stream of the valve.

• +all seats on the downstream seat only.

• #eat loading increases at higher pressure and for larger siBe and becomes e-cessive@ for soft

seated valve. Also@ the higher the siBe the heavier the ball@ less li6ely to be moved by pressure.

Dence the need of trunnion mounted design comes into picture.

loating *esign



• loating design valves have lower manufacturing cost.

• 'alves of small siBes and lower pressure rating are seat supported (0C for >0E@ 8C for ;00E 3 =C

for 800E 3 above).

• #eat supported design generally needs higher operating tor2ue.

• $etal seated floating ball valves also incorporate spring loaded seats.

runnion %ounted Design

• The ball is fi-ed in position by the stem 3 the trunnion which are supported in bearings in the

body.

• The seat are spring loaded onto the ball@ giving reliable sealing at low pressures.

• The 6ey feature is that the ball does not shift as it does in a floating valve to press the ball into the

downstream seat. ,nstead@ the line pressure forces the upstream seat onto the ball to cause it to

seal.

• As the area on which the pressure acts is much lower@ the amount of force e-erted on the ball is

much less@ leading to lower friction values and smaller actuators or gear bo-es.

Trunnion $ounted

• #eat designs are either single or double piston effect.



• 'alves of larger siBes and higher pressure rating are trunnion mounted.

• All standard trunnion mounted ball valves shall be provided with self relieving seats allowing

automatic body cavity relief e-ceeding .;; times the valve pressure rating at ;?°H (overpressure

due to thermal e-pansion of trapped fluid).

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Hontinued from part + and part ,--..

Bod! /avit! "elief #Pressure E0ualisation$

• +all valves are double seated valves which incorporate a cavity between the seats.

• +ody cavity will get pressurised only when the seats are damaged.

• Havity relief provision re2uired only for trunnion mounted ball valves. 5ot re2uired for floating ball

valves as the seats are fi-ed 3 the ball is floating.

• &here possible@ cavity relief shall be to the upstream side of the valve.

+ody cavity !elief

Single Piston Effect Seat Design

• #eats are pressed on the ball by means of spring load.

• As the body cavity pressure increases than the spring load@ the seats are pushed bac6 and the

pressure is released in the line. This is called as single piston effect (the pressure in the body

cavity is the only acting parameter)

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• Havity relief to the downstream side@ if both valve seats are of single piston effect design.

• %ach seat is self relieving the body cavity overpressure to the line.

#ingle iston effect #eat *esign

Double Piston Effect Seat Design

•

,n this seat design@ medium pressure as well as the body cavity pressure creates a resultantthrust that pushes the seat rings against the ball. This is called as double piston effect (the

pressure in pipe 3 that in the body cavity both are acting parameters)

• 'alves with this design re2uires a cavity pressure relief device to reduce the body cavity

pressure.

• *% is synonymous with KbidirectionalC@ and #% is synonymous with KunidirectionalC as defined

by A, 8*",#/ ;;.

*ouble iston %ffect #eat *esign

DPE 1 E2ternal pressure relief

• &hen the body cavity pressure increases above the net spring load of the pressure relief valve@

the cavity pressure is vented through ressure !elief 'alve.

• The !' outlet line can be vented to atms " connected to vent system or bac6 to the upstream

piping.



*% 7 %-ternal pressure relief

/o3bination Seats

• ,n some cases@ single piston effect seat is used for upstream side and double piston effect seat is

used for downstream side.

• This enables the cavity overpressure to release to the valve upstream side and also donIt re2uire

an e-ternal relief valve.

• These valves are unidirectional and flow direction is clearly mar6ed on the valve body.

Seat Design for E2port Line

• This seat configuration gives a single barrier against normal flow condition and a double barrier

against reverse flow coming from downstream pipeline.

• or %#*"#* valve@ reverse configuration is re2uired than that shown here. %#* valves re2uires

#% for upstream seat and *% for downstream seat.



#eat *esign for %-port 1ine

Double Bloc4 5 Bleed #DBB$ feature

• &hen the valve is in fully closed or fully open position@ each seat seals off the process medium

independently at the same time between the up"down stream and body cavityF it allows bleeding

of the cavity pressure through drain or vent valve.

• This *++ feature permits inline periodic inspection of the valves and the chec6ing of sealing

integrity when the valve is installed in line.

• This feature is available with self relieving seat (#%) configuration.

DBB Vs DIB

• ,f a ball valve has both seats as unidirectional (#%) seats@ it is called as *ouble +loc6 3 +leed

(*++).

• ,f a ball valve has one or both bidirectional (*%) seats@ it is called as *ouble ,solation 3 +leed

(*,+).

• ,n the *++ valve@ the downstream seat pushes away from the valve once the body cavity

pressure is higher than the downstream pressure@ allowing fluid to flow downstream past the



closed valve. ,n the *,+ valve the downstream seat seals and prevents the upstream pressure

from reaching the downstream piping.

*ouble +loc6 3 +leed (*++) feature

Blo& *ut Proof Ste3 Design

• &hen the valve is in the open " closed position@ pressure is always acting upon the bottom of the

stem@ trying to push the stem up.

• The stem is sealed by orings and graphite pac6ing rings.

• The stem is held in position by the stem housing@ which is bolted to the body.

• The graphite pac6ing rings are compressed and held in position by the gland flange@ which is

bolted to the stem housing.

• Therefore@ when the gland flange is removed to replace the graphite pac6ing rings@ the stem is

still held securely@ by the stem housing.

• That means the blowout proof stem feature ensures that the top graphite pac6ing rings can be

replaced while the valve is under pressure@ without the stem being pushed out (blown out).



+low /ut roof #tem *esign

Anti6Static Design

• +uildup of static electricity can occur as a result of constant rubbing of the ball against the T%

seats. This can be a potential fire haBard@ especially while handling flammable fluids.

• ,n the antistatic feature@ spring loaded balls are provided between the ball 3 stem and stem 3

body which provides electrical continuity.



Anti #tatic #tem *esign

Fire Safe Design

) ,nternal 1ea6age revention (from pipeline to body cavity)

• &hen nonmetal resilient seats are destroyed in a fire@ the upstream medium pressure push the

ball into the downstream metal seat lip to cutoff the line fluid and prevent the internal lea6agedue to a secondary metaltometal seals.

• Another fire safe pac6ing is provided at the seat ring for internal lea6age prevention to body

cavity.

• raphite is normally used as a fire safe pac6ing material@ because the melting point of graphite is

000 deg.H.



ire #afe *esign

=) %-ternal lea6age prevention (from body"stem oints to atms)

• All the possible e-ternal lea6age points between stem 3 gland flange@ gland flange 3 body and

body 3 adapter are sealed with primary /ring then secondary graphite gas6et. &hen fire burned

out the primary /ring seal@ the secondary graphite gas6et seal can prevent the process medium

from e-ternal lea6age.

• ire safe seals are generally not designed for fugitive emission performance (fugitive emission 7

emissions of gases or vapors from pressuriBed e2uipment due to lea6s).

• The fire testing of valves is carried out as per A, 8A@ A, 80<@ ,#/ 09< or +# 8<>> art ,,.

%-ternal 1ea6age revention

Fire Safe Vs Fire ested Design

• Fire safe design is a design that by the nature of itIs features and materials is capable of passing

a fire test.

• ,t is capable of passing a fire test with specified limits on lea6age to the atmosphere and

downstream after being closed subse2uent to fire e-posure.



• A fire tested design is a design subected successfully to fire testing as per the applicable

testing standard.

• That means the fire safe valves are not necessarily be fire tested by the manufacturer.

Valve Fire esting /riteria

• /ne test valve may be used to 2ualify valves larger than the test valve@ not e-ceeding twice the

siBe of the test valve.

• A 8C siBe valve will 2ualify all larger siBes.

• /ne test valve may be used to 2ualify valves with higher pressure ratings but no greater than

twice the pressure rating of the test valve.

• The above criteria is acceptable for valves of same basic design as the test valve 3 same non

metallic materials.

Sealant In7ection S!ste3

• 'alves are to be e2uipped with sealant 3 lubricant inection connections located at stem and

seats area@ if specified by purchaser.

• The valve design 3 material selection should negate the need for such connection.

• ,f specified@ this inection connection is integrated with chec6 valve to provide bac6up sealing@

also a chec6 valve is e2uipped at front of seat sealant inection to avoid blowing out in case of

wrong operation.

• &hen the soft sealing materials (seat inserts and orings) are damaged and lea6age happened

by fire or other accident@ the sealant can be inected through the inection fittings.

#ealant ,nection #ystem



• The sealant inection system through the seat up to the ball contact circle may provide temporary

sealing until it is possible to restore the primary seal.

•

5o seat sealant inection shall be provided for %#* valves.

+A11 'A1'% *%#,5 %ATJ!%#: A 1iteratureart of

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Hontinuation from earlier partsL.

E2tended Bonnet

• The integrity of stem seals at very low temperatures (;0 deg.H 3 below) is the maor hurdle that

must be overcome.

• #pecially designed e-tended bonnets installed to valves offers a safe 3 efficient method to

accomplish stem seal integrity.

• The bonnet e-tension provides a gas column that allows the gas to vaporise from contact with the

warm ambient temperature outside the service line. This vapour column insulates the stem seal

and maintain the seal integrity.

• +onnet e-tension also helps for thermal insulation installation.

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%-tended +onnet

)eld *verla!

• #ealing areas 3 other wetted parts of ball valve can be cladded in case of corrosive service.

• $ore fre2uent used materials for the overlay process are stainless steel@ *## 3 high nic6el

alloys.

• This technology is cost effective for ball valves in highly corrosive or erosive services.

• Honsiderable cost saving without sacrifice to service life or performance.

• Han be done cost effectively for siBe ?C and larger.

• &elding is performed in accordance with A#$% +' section 9.



&eld /verlay

Seat Insert %aterials

• Thermoplastic seat " seal inserts

Thermoplastic seat " seal inserts

*evlon ' : Temp. !ange 00 deg. H to >0 deg. H

• %lastomeric seat " seal inserts



%lastomeric seat " seal inserts

• Mero lea6age is easier obtained by softer seals (elastomeric)@ while the resistance to scratches

and other factors (temp.@ pressure@ erosion) is obtained by harder seals (thermoplastic).

• T% is generally not recommended for high pressure (cl. 900 3 higher) while it is suitable for a

wide range of temperature and resistant to many fluids.

• 5ylon = is more suitable than T% for higher pressure@ but has a limited range in

temperature.

• 5ylon 8 should not be used as it absorbs humidity.

• *evlon ' is similar to 5ylon =@ but with a wider range of temperature application (lower 3

higher)

• %%G is recommended for high temperature (up to =80 deg.H) but it is very hard compared to

other non metallic materials.

• Gel is specially recommended for cryogenic service.

*6"ings #Elasto3eric$/!ings are used for below applications:

• #tem seals

• #eals between seat and body"closure

• #eals between body and bonnet"closure



$aterials are generally as follows:

• 'iton (fluor elastomer)

• 5+! (nitrilic butadine rubber)

• D5+!

/rings are not allowed in the seat ringbody oint as well as for bodybonnet oint. The ball valve seat ring

shall have primary lip seal with a fire safe graphite ring.

At stem side@ if the seal material specified in re2uisition as thermoplastic@ it shall be of lip seal type with

,nconel <? spring. ,f the seal material is specified as elastomeric@ it shall be of A%* type.

/rings

Lip Seal

• or applications where elastomeric /rings are not reliable@ lip seals are used (for body 3 stem

sealing).

• 1ip seals are self energised seal systems@ made of a Teflon cover and a spring (,nconel <?

material).



1ip #eals

• The spring provides the initial load (due to the low elasticity of Teflon)@ while the fluid pressure

provides the load to force the lips on the sealing surfaces.

• 1ip seal housing on H# valves shall be ##;8 weld overlayed (;mm th6)

Special "e0uire3ent for ESD Valve

• %#* valve shall be of trunnion mounted type with metal seat design.

• $inimum siBe shall be =C 5+.

• Jpstream seat shall be with single piston effect and downstream seat with double piston effect.

• The #% 3 *% shall be mar6ed permanently on the respective seat side and flow arrow shall

be embedded on the body. Dowever@ the valve shall be suitable for bidirectional isolation.

• The seat ring shall have = no. primary leap seals with a fire safe graphite ring. The stem shall

have min. = primary lip seals or J or ' shaped pac6ing with fire safe secondary seals.

• rease inection fitting shall be provided between primary 3 secondary seals on the stem side

with = inbuilt chec6 valves.

• 5o seat sealant inection shall be provided for %#* valves.



Valve lifting 5 Supporting Provision

• 'alves of siBes ?C5+ and above or =>0 Gg 3 heavier shall be e2uipped with lifting lugs.

• Tapped holes 3 eye bolts are not acceptable.

• 'alve shall have support lugs for valve weighing more than <>0Gg and supports should be

designed to ta6e care of the vertical 3 lateral loads of valves. The support height shall be as

minimum as possible.

*t(er "e0uire3ents

Drain 5 Vent connections

• #hall be drilled 3 threaded for ball valves up to 900E pressure class 3 for siBes less than 8C 7+

3 ?C!+. The connections shall be fitted with threaded plug.

• The plug shall be suitable loc6ed by loc6ing ring to prevent loosening .

• The drain 3 vent connections for ball valves above 900E pressure class 3 8C 7+ " ?C !+ 3

above siBes shall be fully welded flanged type@ fitted with a blind flange.

• ,f drain " vent " sealant inection is as6ed@ ensure orientation of the connections is accessible at

site. *uring vendor drawing review same should be chec6ed.

ball valve design

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