A safety valve is a valve that acts as a fail-safe.
An example of safety valve is a pressure relief valve (PRV), which automatically releases a substance from a boiler, pressure vessel, or other system, when the pressure or temperature exceeds preset limits.
Pilot-operated relief valves are a specialized type of pressure safety valve. A leak tight, lower cost, single emergency use option would be a rupture disk.
Safety Valve Operation
Fig : A cross-section of a proportional-safety valve