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Encyclopedia > Relief valve

The relief valve is a type of valve used to control or limit the pressure in a system or vessel which can build up by 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 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 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 drop. Once it reaches the valve's re-seating pressure, the valve will re-close. This pressure, also called blowdown, is usually within several percent of the set-pressure. // These water valves are operated by handles. ... This article is about pressure in the physical sciences. ... Steel Pressure Vessel A pressure vessel is a closed, rigid container designed to hold gases or liquids at a pressure different from the ambient pressure. ... Hikers choose the easy way to cross hills. ... Piping is used to convey fluids (usually liquids and gases but sometimes loose solids) from one location to another. ... A gas flare at an oil refinery. ... This article is about the chemical reaction combustion. ...

In high-pressure gas systems, it is recommended that the outlet of the relief valve is in the open air. In systems where the outlet is connected to piping, the opening of a relief valve will give a pressure build up in the piping system downstream of the relief valve. This often means that the relief valve will not re-seat once the set pressure is reached. For these systems often so called "differential" relief valves are used. This means that the pressure is only working on an area, that is much smaller than the openings area of the valve. If the valve is opened the pressure has to decrease enormously before the valve closes and also the outlet pressure of the valve can easily keep the valve open. Another consideration is that if other relief valves are connected to the outlet pipe system, they may open as the pressure in exhaust pipe system increases. This may cause undesired operation. [1]

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). This article is about a mechanical device. ... A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume. ...

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. Look up Vacuum in Wiktionary, the free dictionary. ... An inert gas is any gas that is not reactive under normal circumstances. ...


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 assoiated with the terms pressure relief valve (PRV), pressure safety valve (PSV) and safety valve. View of Shell Oil Refinery in Martinez, California. ... Petrochemicals are chemical products made from raw materials of petroleum (hydrocarbon) origin. ... A Chemical plant is an industrial process plant that manufactures chemicals, usually on a large scale. ... A natural gas processing plant Natural gas processing plants are used to purify the raw natural gas extracted from underground gas fields and brought up to the surface by gas wells. ... For other uses, see Power station (disambiguation). ...

The generic term is or Pressure Relief Valve (PRV) or Pressure Safety Valve (PSV) Relief Valve A relief valve opens to release excess pressure when the pressure is too high to protect the vessel or other equipment from overpressurization. ...

Relief Valve (RV): automatic system that relief by static pressure on a liquid. It specifically open proportionally with pressure increasing.

Safety Valve (SV): automatic system that relief by static pressure on a gas. It specifically open almost straight to full lift after a pop sound.

Safety Relief Valve (SRV): automatic system that relief by static pressure on both gas and liquid.

Pilote Operated Safety Relief Valve (POSRV): automatic system that relief by remote command from a pilote on which the static pressure (from equipent to protect) is connected.

Low Pressure Safety Valve (LPSV): automatic system that relief by static pressure on a gas. The pressure is small and near the atmospheric pressure.

Vacuum Pressure Safety Valve (VPSV): automatic system that relief by static pressure on a gas. The pressure is small, negative and near the atmospheric pressure.

Low and Vacuum Pressure Safety Valve (LVPSV): automatic system that relief by static pressure on a gas. The pressure is small, negative or positive and near the atmospheric pressure.

RV, SV and SRV are spring operated (even said spring loaded). LPSV and VPSV are spring operated or weight loaded.

In most countries, 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 like ISO (ISO 4126) must be complied with and those codes include design standards for relief valves.[2][3] ASME redirects here. ... The American Petroleum Institute, commonly referred to as API, is the main U.S. trade association for the oil and natural gas industry, representing about 400 corporate members involved in all aspects of the industry. ...

The main standards, laws or directives are:

The main manufacturers of pressure safety valves are: The American Society of Mechanical Engineers (ASME) is a professional body, specifically an engineering society, focused on mechanical engineering. ... ASME redirects here. ... API may refer to: In computing, application programming interface In petroleum industry, American Petroleum Institute In education, Academic Performance Index This page concerning a three-letter acronym or abbreviation is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... The American Petroleum Institute, commonly referred to as API, is the main U.S. trade association for the oil and natural gas industry, representing about 400 corporate members involved in all aspects of the industry. ...

  • Sarasin-RSBD (France)
  • Sapag (France)
  • Crosby (USA)
  • Consolidated (USA)
  • Anderson-Greenwood (USA)
  • Farris (Canada)
  • Fukui (Japan)
  • Besa (Italy)
  • Leser (Germany)
  • Bopp & Reuter (Germany)

Pressure relief valves in oil hydraulics

Whereas gay pressure relief valves in gas pressure systems are always used to protect the system, in oil hydraulic systems a pressure relief valve can act as part of the control system. The easiest use of the relief valve is as a sort of check valve, a seat with a ball and an adjustable spring. More sophisticated relief valves are pilot operated, so that the pressure can be set at zero (by-pass) and sometimes at 2 or 3 other pressures. In these cases, the highest pressure acts as the maximum working pressure and the others as a set pressure during a certain operation of the installation. Hydraulic fluids are a large group of mineral oils, water-based or water used as the medium in hydraulic systems. ... this siamese clappered inlet allows one or two inputs into a deluge gun A check valve is a mechanical device, a valve, that normally allows fluid or gas to flow through it in only one direction. ...

See also

Oxygen Safety Valve A safety valve is a valve mechanism for the automatic release of a gas from a boiler, pressure vessel, or other system when the pressure or temperature exceeds preset limits. ... A blowoff valve is a pressure release system present in turbocharged engines, its purpose is to prevent compressor surge and reduce wear on the engine. ... A rupture disk is a pressure relief device that protects a vessel or system from overpressurization. ...


  1. ^ 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.
  2. ^ List of countries accepting the ASME Boiler & Pressure Vessel Code
  3. ^ API 5210-1, Sizing and Selection of Pressure-Relieving Devices

  Results from FactBites:
Reseat relief valve - Patent 4432389 (1951 words)
A relief valve with a low hysteresis closing curve with a fixed seat and a spring-biased poppet which is guided for longitudinal movement by an axial guide sleeve and aligns with its seat by pivoting about a fixed point through a small angle of rotation.
Relief valves, from their beginning with a simple ball and spring, have had widely varying characteristics as well as problems, many of which were ignored in the past.
To machine the parts of a relief valve with close enough tolerance to control the maximum misalignment is impractical and would cause the parts to bind, which destroys the ability of the valve to open and close at a specific pressure level.
Sewer relief valve - Patent 5645099 (2308 words)
The sewer relief valve of claim 6 wherein said flange is conformed to seal and mate with said rising walls of said raised head.
The sewer relief valve of claim 1 wherein said float means comprises a polyethylene foam material comprising a rectangular parrallelpiped shape, wherein said float means is attached to a bottom portion of said cap means to maintain and seal said cap across said central passageway.
Sewer relief valve 40 is necessarily manufactured of a lightweight substance, one possibility being plastic, and has the outward general appearance of standard plastic raised head plug 28.
  More results at FactBites »



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