Any difference between a Pressure Safety Valve and a Safety Relief Valve? A Safety Relief Valve (SRV) will (automatically) open in case of too high upstream pressure. And relief the excess pressure. An Emergency Shutdown Valve (ESD) will close in case of an emergency like a high pressure. And block the high upstream pressure. A Pressure Safety Valve (PSV) can be both. However be carefull! PSV is also often used for Pressure Shutdown Valve. Which will be the closing type again. I have always understood a Safety valve to be a Section 1 valve; i.e. Boiler (Fired Pressure Vessel) . 3% overpressure, spring-loaded, adjustable pop and blowdown ring. Manual lifting gear mandated, but really scary to think about using. Usually has an open spring. A Safety-relief valve is a Section VIII valve: Unfired pressure vessel. 10% OP (16% for combination valves, 21% for fire). Can be Spring, Pilot, Rupture disc, Breaking pin. Steam, Gas, Liquid. Manual lifting gear mandated for steam, air, water at over 140F. Bonnet is usually closed/vented.

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