Pressure Relief Valves

Pressure Relief Valves (PRV) serve to provide the last line of defence safeguarding life and property, against the dangerous build up of excess pressure in vessels and systems. Essentially, a PRV is a self contained and self operating device which respond to fluctuations in system pressure and prevent catastrophic failure.

Pressure Relief Valves (PRV) are precision instruments, even though PRVs consist of a fairly simple design (we say this with caution) PRVs must be selected, handled, installed and maintained with care to ensure they are ready to respond when other instrument and control systems fail to adequately control process limits. rv-xp-260x185

Pressure Relief Valve (PRV) Types

There are several different types of PRV and numerous makes. The following section provides a little bit of gen regarding the different types of PRV.

Relief Valves

Relief valves are self-operating, spring-loaded, pressure relieving devices actuated by static pressure upstream of the valve, which lifts in proportion to the increase in pressure over the opening pressure.


Relief valves are used primarily on liquid services.

Relief valves should not be used generally:

  • In air, gas, steam or vapour service.
  • In variable back pressure service.
  • As bypass or pressure control valves.

Safety Valves

Safety valves are self operating, spring loaded, pressure relieving valves actuated by the static pressure upstream of the valve and characterised by rapid opening or pop action. Typically seen on steam systems, these valves are usually supplied with the spring exposed to atmosphere, with an open bonnet so that it will be protected from contact with escaping steam. They are usually supplied with a lifting lever to manually open the valve ensuring the working parts are free.


Safety valves are used on superheaters and steam boiler drums. In a refinery, they may also be used for general air and steam services.

Safety valves  should not be used:

  • In any backpressure service.
  • Where any discharge is required to be piped to a remote location.
  • Where the escape of the process fluid around the blowing valve is not desirable.
  • As bypass or pressure control valves.
  • In liquid service.

Continue to part 2.