Pressure relief critical flow, effect

All relief valves are affected by reaching critical flow, which corre-spond.s to a back-pressure of about 50% of the set pressure. Pilot-operated relief valves can handle up to 50% back-pressure without any significant effect on valve capacity. Back-pressure correction factors can be obtained from the relief valve manufacturers for back-pre.ssures above 50%. API RP 520 gives a generic method for sizing a pilot-operated relief valve for sub-critical flow. [Pg.369]

Sizing, safety relief, 436, 437-441 API liquid valve, 444 Balanced valves, 441 Conventional valves, 438 Critical back pressure, 440 Effects of two-phase flow, 437 Hydraulic expansion, 441 Rupture disks, 434 Sub-critical flow, 449 Slurry flow, process pipe, 142-147 Regimes, 143... [Pg.630]