Is the value of increase inlet static pressure at which there is a measurable lift of the disc or at which discharge of the fluid becomes continuous.

Is the value of decreasing inlet static pressure at which the valve disc re-established contact with the seat or at which lift becomes zero as determined by seeing, feeling or hearing.

Is the audible or visible escape of compressible fluid between the seat and disc which may occur at an inlet static pressure below the set pressure prior to opening.

Operating ratio is the ratio of maximum system operating pressure to set pressure.

Overpressure is the pressure increases over the set pressure of relieving device allowed to achieve rated flow.

Maximum allowable working pressure is the maximum gauge pressure permissible at the top of a completed vessel in its normal operating position at designated coincided temperature specified for that pressure.

Is the specified inlet static pressure at which a seat leak test is performed.

The term of relieving condition is used to indicate the inlet pressure and temperature on a Pressure relief device during an overpressure condition.

An annular chamber located downstream of the seat of a pressure relief valve for the purpose of assisting the valve to achieve lift.

The actual travel of the disc from the closed position when a valve is relieving.

Accumulation is the pressure increase over the maximum allowable working pressure of the vessel allowed during discharge through the pressure relief device, expressed units or as a percentage of MAWP or design pressure.

Back pressure is the pressure that exists at the outlet of a pressure relief device as a result of the pressure in the discharge system.

Built up back pressure is the increase in pressure at the outlet of a pressure relief device that develops as a result of flow after the pressure relief device opens.

Is the static pressure that exists at the outlet of a pressure relief device at the time the device is required to operate.

Blowdown is the difference between the set pressure and the closing pressure of a pressure relief valve.

The cold differential test pressure is the pressure at which a pressure relief valve is adjusted to open on the test stand.