Relief valve

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The relief valve is a type of valve used to control or limit the pressure in a system by allowing the pressure source fluid to flow from an auxiliary passage, away from the main flow path. The relief valve is designed or set to open at a predetermined pressure to protect pressure vessels and other equipment from being subjected to pressures that exceed their design limits. When the pressure setting 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 (liquid, gas or liquid-gas mixture) is usually routed through a piping system known as a flare header to a central, elevated gas flare where it is burned and the resulting combustion gases are released to the atmosphere.<ref>Beychok, Milton R. (2005). Fundamentals Of Stack Gas Dispersion, 4th Edition, author-published. ISBN 0-9644588-0-2. See Chapter 11, Flare Stack Plume Rise.</ref>

In some cases, a so-called bypass valve acts as a relief valve by being used to return all or part of the fluid discharged by a pump or gas compressor back to either a storage reservoir or the inlet of the pump or gas compressor. This is done to protect the pump or gas compressor and any associated equipment from too high a pressure. The bypass valve and bypass path can be internal (an integral part of the pump or compressor) or external (installed as a component in the fluid path).

In other cases, equipment must be protected against being subjected to an internal vacuum (i.e., low pressure) that is lower than the equipment can withstand. In such cases, vacuum relief valves are used to open at a predetermined low pressure limit and to admit air or an inert gas into the equipment so as control the amount of vacuum.

1 Legal and code requirements in industry
2 See also
3 External links
4 References

[edit] Legal and code requirements in industry

In the petroleum refining, petrochemical and chemical manufacturing, natural gas processing and power generation industries, the term relief valve is synonymous with the terms pressure relief valve (PRV), pressure safety valve (PSV) and safety valve. In most countries, such industries are legally required to protect pressure vessels and other equipment by using relief valves. Also in most countries, equipment design codes such as those provided by the ASME, API and other organizations must be complied with and those codes include design standards for relief valves.<ref>List of countries accepting the ASME Boiler & Pressure Vessel Code</ref><ref>API 5210-1, Sizing and Selection of Pressure-Relieving Devices</ref>