Australian Pipeline Valve - Installation, Operation and Maintenance Manual
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SIDE ENTRY 3P TRUNNION BALL VALVES API6D STANDARD - BVF100 SERIES
Piston-action seats
As line pressure increases the seat reacts to the force of the
pressure to form an effective seal. In the absence of line
pressure, coil springs behind the seat provide a tight seal by
keeping the seat in contact with the ball surface. Independent
floating spring loaded seats are always in contact with the ball
to provide an effective tight seal even at low differential
pressure. Independent upstream and downstream seats permit
draining of fluid from the body cavity, so allowing double block
and bleed operation (closed position only). With the optional
single sealing feature, there is automatic body cavity release
of over pressure to the line through the downstream seat.
Self relieving seats (standard)
In self relieving condition, excessive internal cavity
pressure is automatically relieved both upstream and
downstream into the line by excessive pressure forcing the
seats away from the ball. Refer Appendix 4 page 28 for
more information.
Double piston effect (DPE) seats
With the ‘DPE’ seat option, if a leakage occurs in the
upstream seat, the pressure entering the body cavity
pushes the downstream seat against the ball and the
valve seals. Line pressure forces a seal against the floating
seat.
An external body relief valve is installed to protect the
body cavity from excess pressure which can be vented to
atmosphere or recycled back to the downstream side of
the valve or to flare.
Triple barrier stem seal design
Leakage from the stem area is prevented by double
barrier sealing with O-rings as well as graphite fire seals.
Leakage through the valve body joint is also protected by
double sealing with an O-ring and a flexible graphite
gasket. After a fire has deteriorated the -rings, graphite
packing and secondary seal ensure prevention of external
fluid leakage.
Double block and bleed
Whether in the open or closed position, pressure on each side
of the ball is blocked from the body cavity by the seat ring.
The cavity can be blown down or drained (only in the closed
position) through the body port to indicate line isolation is
effective.
Emergency sealing function
In case of fluid leaks from the seat or
stem sealing area, a sealant can be
supplied through the injection fitting to
temporarily prevent leakage.
Piston-action seat are standard and provide
bi-directional sealing
First Seal
Pressure
ENERGISE
Ball
Second Seal
Pressure
RESPONSE
Body Pressure
Ball
DPE seat design during cavity over pressurisation
First Seal
Pressure
ENERGISE
Ball
Second Seal
Pressure
RESPONSE
Body Pressure
Ball
Self relieving seat design during cavity over pressurisation
10.0 OVERVIEW DESIGN FEATURES
