Reclosing pressure-relieving devices

Reclosing Pressure-Relieving Devices. A pressure-rehef m valve is a spring-loaded pressure-rehef device, which is de-... 

Reclosing pressure relief devices have a variety of names, although there used to be a clear definition based on the US market and API. However, when the Pressure Equipment Directive (PED) came into effect in 1997, this somewhat added to the confusion, as PED uses the overall term safety valve for every pressure-relieving device subject to the PED code. Originally the following were the definitions for the different terms per API and are still in use today. 

Theoretical relieving capacity The computed capacity expressed in gravimetric or volumetric units of a theoretically perfect nozzle having a minimum cross-sectional flow area equal to the actual discharge area of an SRV or the net flow area of a non-reclosing pressure relief device. 

A diaphragm designed to burst at a predetermined pressure differential. A simple rupture disc device that is composed of a non-reclosing pressure relief device that relieves excessive static inlet pressure via a rupture disc. 

Among the relief devices mentioned above, spring-ioaded and pilot-operated pressure relief valve (PRV) are the ones used most fiequently, PRV is a reclosing pressure relief device, since after it is opened and relieved, it will be reclosed, when equipment or piping pressure is dropped below PRV set pressure. Once it is dosed, h will continue to protect the equipment or piping from overpressure- Rupture disk or pin-actuated relief device is the non-reclosing pressure relief device, since it cannot be reused after it is ruptured or actuated - its rupture disk or pin needs to be replaced. 

Pressure relief valve (PRV) A pressure relief device designed to open and relieve excess pressure and to reclose after normal conditions have been restored. PRV is a generic term applied to relief valve (set up for liquid flow), safety valve (set up for gas or vapor flow), and safety relief valve (set up for either liquid or compressible flow). 

Type CG-7 (pressure relief valves), A pressure relief valve is a spring-loaded, pressure operated device designed to relieve excessive cylinder pressure, reclose, and reseal to prevent further release of product from the cylinder after the cause of excessive pressure is removed and valve reseating pressure has been achieved. 

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