Pressure Relief Valve (PRV) Types – part 2

This is the second part of our description of the types of pressure relief valve (PRV) types. If you’ve missed part one, see here.

Safety Relief Valves

Safety relief valves are self -operating, spring loaded, pressure relieving devices actuated by the static pressure upstream of the valve. The valve is characterised by rapid opening or pop action, or by the opening in proportion to the increase in pressure over the opening pressure. They may be used on either for liquid or a compressible medium. There are several different types of safety relief valve.


Safety relief valves were designed for use in process industries where the material discharged by the valve may be toxic, flammable or the discharge may have to be at a remote safe point through a closed discharge system.

Safety relief valves are normally used:

  • When the escape of the process fluid around the open valve is not desirable.
  • When the discharge of the valve must be piped to a remote point.
  • In corrosive refinery services.
  • In general refinery service for gas, vapour, steam, air or liquids.


Safety relief valves should not be used:

  • On superheaters or steam boiler drums.
  • As bypass or pressure control valves.

Conventional Pressure Relief Valves

Conventional pressure relief valves are constructed in such a manner that any back pressures on the downstream side of the valve adversely affects the action of the valve causing erratic action of the valve.


Conventional pressure relief valves are normally used in all of the services mentioned for pressure relief valves where any superimposed back pressure is constant or any built up back pressure does not exceed 10% of the set pressure.


Conventional pressure relief valves should not be used on:
  • On steam boiler drums or superheaters.
  • In cases of variable back pressure.
  • As pressure control or bypass valves.

Continue to part 3