14
SEMPELL MODEL PSRV - PRESSURIZER SAFETY RELIEF VALVES
TYPE VS99 PILOT OPERATED
System pressure under closing pressure
Disc 1 Open
Chamber A System pressure
Chamber B Rising pressure
System pressure through opening pressure
Disc 1 Open
Chamber A System pressure
Chamber B Further reduced pressure
The pressure continues to drop in pilot
chamber B and pressure differences arise
at the actuation piston. These differences
generate actuating forces in the opening
direction, which cause the valve to open.
The opening movement of the valve disc is
dampened because the steam volume is
encased above the piston and compressed
by additional stroke movements. In the open
position of the valve disc, a refill bore is
enabled. The size of this refill bore and the
size of the other refill cross-sections are
dimensioned so that the entire volume of
medium flowing into the relief chambers can
be safely released through the control line.
Therefore a sufficient pressure difference
remains at the actuating piston and the valve
disc is held safety open.
If the pressure in the system or the pressure
relief line to the pilot valve drops to the
previously set closing pressure, the pilot valve
closes again the pilot line is blocked again.
The pressure equalizes in the relieved pilot
chambers. Closing forces result from the
pressure difference above and below the valve
disc because of the flow and from the weight of
the valve disc.
THE FUNCTION OF THE MAIN VALVE
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