Relief Valve Inlet Hydraulics Relief Valve Inlet Hydraulics rdsproeng (Chemical) (OP) 22 Jul 15 21:42 At what pressure is the inlet/outlet hydraulic losses calculated for on a pressure relief valve? Is is set pressure + accumulation? Or set pressure only? RE: Relief Valve Inlet Hydraulics gocougs1 (Chemical) 23 Jul 15 00:07 Inlet line losses are calculated with the vessel at MAWP + accumulation. Inlet line losses must then be less than 3% of set pressure per API 520 guidelines, however, some clients allow up to 5% of set pressure for existing relief valves.