Pressure at which the safety valve delivers the stroke required for the mass flow to be discharged. The opening pressure is equal to the response pressure (operating conditions) plus the opening pressure difference (DIN 3320). With pressure-limiting valves under direct control, the size of the opening pressure is adjusted by means of the preload associated with the compression springs. In general, the opening pressure for a pressure-limiting valve is the same as the nominal pressure for the system.
Fluidlexikon