Pressure relief valves, also called safety valves or relief valves (they are different elements, please review the ASME standard for overpressure elements for containers), are designed to relieve pressure when a fluid exceeds a pre-established limit (working pressure). Its mission is to prevent the explosion of the protected system or the failure of equipment or pipes due to excess pressure. There are also valves that relieve the pressure of a fluid when the temperature (and therefore the pressure) exceeds a limit established by the manufacturer.

Safety valves can be found in industrial, commercial and domestic installations. In general, they are mandatory in installations that circulate or contain fluids subjected, at times, to inadmissible pressures.

Among the most common examples that are visible to everyone are storage water heaters. Safety or relief valves installed on heaters or in the heater line are designed to open and release pressure, letting water out, in case the pressure exceeds a certain limit (typically about 8...10 bar) to prevent bursting in the event of thermostat failure, which could bring the water temperature above boiling and produce steam.

In the industry there are also examples such as air compressors or pressure reduction systems for the supply of natural gas or LPG.

Other common uses of these valves are to relieve pressure in a blockage in the delivery system of a pump, or to relieve pressure increase due to thermal expansion of a fluid confined in a closed system.[1]​.

It is very important in these valves that the release of the fluid be made to the outside, in a visible place, since usually the leak indicates a failure of the normal regulation system, and in this way the operator can know that there is a problem and that he must take measures to correct it. However, in industry not all valves must release the fluid to the outside: in the case of dangerous gases or liquids, the release must be made into special containers.

Pressure relief valves are also used to control processes, in these cases the valves act by sending fluids to certain places depending on system pressure.