Relief valve
safety valve used to control or limit the pressure in a system
A relief valve or pressure relief valve (PRV) is a type of safety valve used to control or limit the pressure in a system; excessive pressure might otherwise build up and create a process upset, instrument or equipment failure, explosion, or fire.
Pressure relief
Excess pressure is relieved by allowing the pressurized 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.
In systems containing flammable fluids, the diverted fluid (liquid, gas or liquid-gas mixture) is either recaptured by a low pressure, high-flow vapor recovery system or is routed through a piping system known as a flare header or relief header to a central, elevated gas flare where it is burned, releasing naked combustion gases into the atmosphere. In non-hazardous systems, the fluid is often discharged to the atmosphere by a suitable discharge pipework designed to prevent rainwater ingress which can affect the set lift pressure, and positioned not to cause a hazard to personnel.
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 roughly 2–20%, and some valves have adjustable blowdowns.
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This entry incorporates text from “Relief valve” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.