18-06-2012, 02:12 PM
Seminar on Piston Valves
Piston Valves.pdf (Size: 1.27 MB / Downloads: 53)
Piston Valves
The seat seal is between the lateral faces of the
piston and the seat bore.
At the valve opening, flow can't start until the
piston has been completely withdraw from the seat
bore.
At valve closure, the piston wipe away any solids
deposit on the seat.
Piston valves can handle fluids carry solids in
suspension.
When damage occurs to the seating, the
piston and the seat can be replaced , and the
valve is like new without machining.
Permit good flow control, and if sensitive
flow adjustment is required, the piston may
be fitted with a needle-shaped extension.
Best suited for stopping and starting flow.
Piston Valve Construction
When packing leak, retighten the bolts.
( retightening must be carried out while the
valve is closed to prevent an unrestrained
expansion of the seat packing into the valve
bore).
Disc springs under the cover nuts to
minimize variations in packing stress due to
thermal contraction and expansion.
The piston is pressure
balanced to minimize the
operating effort in large
valves operating against
high fluid pressures.
Piston Valve Construction
• 2 packings around the
piston are seat packing and
a separate packing is
provided for the stem.
Seat packing is carried
on the piston.
The loose compression
ring is replaced by a
friction ring acts as a
spring and pre-stresses
the packing.