5 TERMINOLOGY
ACCUMULATION
The pressure increase over the maximum allowable working pressure of the vessel, expressed in pressure units or as a percentage of
maximum allowable working pressure (MAWP) or design pressure.
BACK PRESSURE
Back pressure is the static pressure existing at the outlet of a safety valve device due to pressure in the discharge system.
BLOWDOWN
The difference between actual popping pressure of a safety valve and actual reseating pressure expressed as a percentage of set
pressure, or in pressure units.
CDTP (COLD DIFFERENTIAL TEST PRESSURE)
The pressure at which a safety valve is adjusted to open on the factory test bench. The cold differential test pressure includes
corrections for the service conditions of backpressure or temperature or both.
CHATTER
Rapid and erratic motion of the disc from closed to open position. This phenomenon can create damage to the valve internals, the
main effect being on the disc and the nozzle components.
CLOSING PRESSURE
The value of decreasing inlet static pressure at which the valve disc re-establishes contact with the seat or nozzle, or at which the lift
becomes zero.
LIFT
The actual travel of the disc away from closed position when a valve is relieving. LEAK TEST PRESSURE Leak test pressure is the
specified inlet static pressure at which a quantitative seat leakage test is performed in accordance with a standard procedure.
MAWP (maximum allowable working pressure)
The maximum gauge pressure permissible at the top of a vessel in its normal operating position at the designated coincident
temperature specified for that pressure.
OPERATING PRESSURE
The pressure at which protected unit is working and at which the safety valve should be tight.
OVERPRESSURE
The pressure increase over the set pressure of a safety valve, usually expressed as a percentage of the set pressure.
POPPING PRESSURE
The value of increasing inlet static pressure at which the disc moves in the opening direction at a faster rate as compared with
corresponding movement at higher or lower pressures. It applies only to valves in compressible fluid service.
SET PRESSURE
Inlet gauge pressure at which the safety valve is set to open under relief conditions
SIMMER
The audible or visible escape of fluid between the seat and disc at an inlet static pressure below the popping pressure and at no
measurable capacity.
For the purpose of this manual, the following abbreviations, definitions and terms apply
6
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STARFLOW V
™
PRESSURE RELIEF VALVE
SARASIN-RSBD
™
