API-RP-576

4.5 Safety-relief Valve.
A safety-relief valve is a direct spring-loaded pressure-relief valve that may be used as
either a safety or relief valve depending on the application. A safety-relief valve is
normally fully open at 10 % overpressure when in gas or vapor service. When installed
in liquid service, full lift will be achieved at approximately 10 % or 25 % overpressure,
depending on trim type.
Safety Valve: Compressible fluid (steam, air, gas, or other vapor
services)
Relieve valve: Incompressible fluids
Safety relieve valve: Both compressible and incompressible fluids.
Fion Zhnag/ Charlie Chong