Australian Pipeline Valve - Installation, Operation and Maintenance Manual
22
SIDE ENTRY 2P TRUNNION BALL VALVES API6D STANDARD - FS9000 SERIES
10.0 OVERVIEW DESIGN FEATURES
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.
First Seal
Pressure
ENERGISE
Ball
Second Seal
Pressure
RESPONSE
Body Pressure
Ball
Self relieving seat design during cavity over pressurisation
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 29 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.
First Seal
Pressure
ENERGISE
Ball
Second Seal
Pressure
RESPONSE
Body Pressure
Ball
DPE seat design during cavity over pressurisation
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.
Piston-action seat are standard and provide
bi-directional sealing
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.
