ball valve design features_ a literature-part-3 of 4 _ what is piping
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8/11/2019 Ball Valve Design Features_ a Literature-part-3 of 4 _ What is Piping
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Continued from part 1 and part 2……..
Body Cavity Relief (Pressure Equalisation)
Ball valves are do uble seated valv es which
incorporate a cav ity betwe en the seats.
Body cav ity will get pressurised only when the seats
are damaged.
Cavity relief prov ision required only for trunnion
mounted ball valv es. Not required for floating ball
valv es as the se ats are fixed & the ball is floating.
Where possib le, cav ity relief shall be to the upstream
side of the valv e.
What is Piping An attempt to ex plain pr oc ess piping engineering basic s in detail to help all the pro ce ss piping engineering
professionals around the world.
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20th July 2014 wa nt 2lea rn interview 1 Comment
BALL VALVE DESIGN FEATURES: A Literature-
Part-3 of 4
21 1
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Body cav ity Relief
Single Piston Effect Seat Design
Seats are pressed on the ball by means of spring load.
As the body cav ity pressure inc rease s than the spring load, the seats are pushed back and the p ressure is
released in the line. This is called as single piston effect (the pressure in the body cav ity is the o nly ac ting
parameter)
Cavity relief to the downstream side, if both valv e seats are of single piston effect design.
Each seat is self relieving the body cav ity o verpressure to the line.
Singl e Piston effect Seat Design
Double Piston Effect Seat Design
In this seat design, medium pressure as well as the body cav ity pressure c reates a resultant thrust that
pushes the seat rings against the ball. This is called as double piston effect (the pressure in pipe & that in
the body c avity both are acting parameters)
Valv es with this de sign requires a c av ity pressure relief dev ice to reduc e the b ody cavity pressure.
DPE is synonymous with “bi-directional”, and SPE is synonymous with “uni-directional” as defined by
API 6D/ISO 14313.
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Double Piston Effect Sea t Design
DPE – External pressure relief
When the b ody cavity pressure inc rease s abov e the net spr ing load of the pre ssure relief valv e, the
cav ity pressure is vented through Pressure Relief Valve.
The RV o utlet line can be v ented to atms / connected to vent sy stem or back to the upstream piping.
DPE – External pressure relief
Com bination Seats
In 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 ov erpressure to release to the v alve upstream side and also don’t require an
external relief valv e.
These valves are unidirectional and flow direction is clearly marked on the valv e body .
Seat Design for Export Line
This seat configuration give s a single barrier against normal flow condition and a double barrier against
reverse flow coming from downstream pipeline.
For ESD/PSD v alv e, rev erse c onfiguration is required than that sho wn here. ESD valve s require s SPE for
upstream se at and DPE for downstre am seat.
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Seat Design for Export Line
Double Blo ck & Bleed (DBB) feature
When the v alv e is in fully closed o r fully open positio n, eac h seat seals o ff the pro ce ss medium
independently at the same time between the up/down stream and body cav ity; it allows bleeding of the
cavity pressure through drain or vent valve.
This DBB feature permits in-line periodic inspect ion of the valv es and the chec king of sealing integrity when the v alv e is installed in line .
This feature is av ailable with self reliev ing seat (SPE) co nfiguration.
DBB Vs DIB
If a ball v alv e has bo th seats as unidirectio nal (SPE) seats, it is called as Double Block & Bleed (DBB).
If a ball va lve has one o r both bidirect ional (DPE) seats, it is called as Double I solation & Bleed (DIB).
In the DBB valve, the downstream seat pushes away from the valv e once the b ody cav ity pressure is
higher than the downstream pressure, allowing fluid to flow downstream past the closed v alve. I n the
DIB valv e the do wnstream seat seals and prevents the upstream pressure from reaching the downstream
piping.
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Double Block & Bleed (DBB) featu re
Blow Out Proof Stem Design
When the v alv e is in the open / c losed po sition, pr essure is alway s ac ting upo n the botto m of the ste m,
trying to push the stem up.
The stem is sealed by o-rings and graphite packing rings.
The stem is held in position by the stem housing, which is bolted to the body .
The graphite packing rings are compressed and held in position by the gland flange, which is bolted to
the stem ho using.
Therefore, when the gland flange is removed to replace the graphite packing rings, the stem is still held
securely , by the stem housing.
That means the blow-out proof stem feature ensures that the top graphite packing rings can be re placed
while the v alv e is under pr essure, without the stem being pushe d out (blo wn o ut).
3-Way Pig Valveshillsflow.com
HFC 3-way pig valves are design for oil and gas industries.
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Blow Out Proof Stem Design
Ant i-Stat ic Design
Build-up of static electricity can oc cur as a result of constant rubbing of the ball against the PTFE seats.
This can be a potential fire hazard, especially while handling flammable fluids.
In the anti-static feature, spring loaded balls are prov ided between the ball & stem and stem & body
whic h pr ov ides elec trical c ontinuity .
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An ti Stat ic Stem Design
Fire Safe Design
1) Internal Leakage Prevention (from pipeline to body cav ity)
When no n-me tal resilie nt seats are destr oy ed in a fire, the upstream medium pressur e push the b all into
the downstream metal seat lip to c ut-off the line fluid and prevent the internal leakage due to a
secondary metal-to-metal seals.
Anothe r fire safe packing is prov ided at the se at r ing fo r internal leakage prev ent ion to bo dy cav ity .
Graphite is normally used as a fire safe packing material, because the melting point of graphite is 1000
deg.C.
Fire Safe Design
2) External leakage prev ention (from bo dy/ stem joints to atms)
All the p ossible e xternal leakage points b etwee n stem & gland flange, g land flange & bo dy and bo dy &
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if specified by purchaser.
The valve design & material selection should negate the need for such c onnection.
If specified, this injection connection is integrated with check v alve to prov ide backup sealing, also a
check v alve is equipped at front of seat sealant injection to avo id blowing out in case of wrong operation.
When the soft sealing materials (seat inse rts and o-rings) ar e damaged and leakage happened by fire o r
other acc ident, the sealant can be injected through the injection fittings.
Sealant Injection Sy stem
The sealant injection system thro ugh the seat up to the ball contact circle may provide temporary
sealing until it is possible to restore the primary seal.
No seat sealant injection shall be provided for ESD valves.
Final part will be published soon…
Click h ere to read part 1
Click h ere to read part 2
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sciric
Wednesday 23 July 2014, 12:35 pm
Is it possible to give us example of modeling Air Cooler Haeders and Nozles in CaesarII?
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