Relief Valve Inlet Hydraulics

[rdsproeng]

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?

 

[gocougs1]

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.