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Safety Relief Valves
An automatic pressure relieving device actuated by the static pressure upstream of the valve, which opens in proportion to the increase over the opening pressure.
Start-to-Leak Pressure
The pressure at the valve inlet where the relieved fluid is first detected (on the downstream side of the seat) before normal relieving action takes place
Opening Pressure (Set Pressure)
The valve inlet pop point pressure at which there is a measurable lift or discharge becomes continuous as determined by seeing, hearing or feeling. In the pop type of safety valve, it is the inlet pressure at which the valve opens, allowing a larger amount of fluid as compared with corresponding valve movements at higher or lower pressures
Note: A safety relief valve is not considered to open when it is simmering at a pressure just below the popping point even though the simmering may be audible. This set pressure distinguishes our ASME relief valves from our standard relief valves whose cracking pressure indicates initial flow.
Relieving Pressure
(Opening pressure plus overpressure) The pressure measured at the valve inlet at which the relieving capacity is determined.
Closing Pressure
(Reseat pressure) The pressure measured at the valve inlet, at which the valve closes, flow is substantially shut off , and there is no measurable lift.
Seal-off Pressure
The pressure (measured at the valve inlet) after closing at which no further gas is detected at the downstream side of the seat.
Operating Pressure
The actual pressure at which a vessel is maintained in normal operation.
Accumulation
Pressure buildup or overpressure beyond the set pressure of a safety relief valve, at which capacity flow is rated. Capacities are usually based on 10% accumulation.
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