A safety valve is a valve which has the function of increasing the safety of a thermal-hydraulics plant. An example of safety valve could be a pressure safety valve (PSV), i.e. 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. Also pilot-operated relief valves could have the function of safety valves.

Vacuum safety valves (or combined pressure/vacuum safety valves) are used to prevent a tank from collapsing while it is being emptied.