Pressure at the inlet of a relief device when the fluid is flowing at the required relieving capacity.
The relieving pressure Relieving pressure The relieving pressure is the vacuum or overpressure at which the valve reaches the lift required for the mass flow to be discharged. is the vacuum Vacuum Vacuum is the pressure in an enclosed space that is lower than the ambient pressure. or overpressure Overpressure Overpressure refers to an increase in pressure in a system or vessel above the normal operating pressure. at which the valve reaches the lift Lift Lift is the actual travel of the valve pallet from the main valve out of the closed position. required for the mass flow to be discharged. It is equal to the set pressure Set pressure Set pressure is the gauge pressure at the device inlet at which the relief device is set to start opening under service conditions. plus the relieving pressure differential.
Source: ISO 28300 - 3.15