Relief Valves

A relief valve or pressure relief valve (PRV) is a type of safety valve used to control or limit the pressure in a system; pressure might otherwise build up and create a process upset, instrument or equipment failure, or fire. The pressure is relieved by allowing the pressurised fluid to flow from an auxiliary passage out of the system.

The relief valve is designed or set to open at a predetermined set pressure to protect pressure vessels and other equipment from being subjected to pressures that exceed their design limits. When the set pressure is exceeded, the relief valve becomes the "path of least resistance" as the valve is forced open and a portion of the fluid is diverted through the auxiliary route.

The diverted fluid is usually routed through a piping system known as a flare header or relief header to a central, elevated gas flare where it is usually burned and the resulting combustion gases are released to the atmosphere. As the fluid is diverted, the pressure inside the vessel will stop rising. Once it reaches the valve's reseating pressure, the valve will close. The blowdown is usually stated as a percentage of set pressure and refers to how much the pressure needs to drop before the valve reseats. The blowdown can vary from roughly 2–20%, and some valves have adjustable blowdowns.

While some basic components and activations in relieving pressure may differ between the specific types of relief valves, each aims to be 100% effective in keeping your equipment running safely. Our current range includes all forms of valve, from flanged to spring loaded, threaded to wireless, pilot operated, and much more.

Pressure excess can be generated in a number of different ways including:

  • Failure of a cooling system allowing vapour or fluid to expand
  • Compressed air or electrical power failure to control instrumentation
  • Plant fires
  • During the start-up conditions of a plant
Call Mhpumps for high quality relief valves to assist in all pressure excess situations.