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Pressure relief valve

A pressure relief valve is a safety device that relieves in case of overpressure in a vessel or piping. The generic terms are pressure relief valve (PRV) or pressure safety valve (PSV).

Main types of pressure relief valves include:


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 relieve static pressure on a gas. It specifically opens 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.

Pilot operated safety relief valve (POSRV) automatic system that relief by remote command from a pilot on which the static pressure (from equipment 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.

Legal and code requirements in industry

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 compliant with and those codes include design standards for relief valves.

The main standards, laws or directives are:


ASME (American Society of Mechanical Engineers) Boiler & Pressure Vessel Code, Section VIII, Division 1

API (American Petroleum Institute) Recommended Practice 520 - Sizing, Selection, and Installation of Pressure-Relieving Devices in Refineries: Part I - Sizing and Selection

API Standard 521 - Pressure-relieving and Depressuring Systems

API Standard 526

API Standard 527

ISO 4126

ISO 23251 - Petroleum, petrochemical and natural gas industries - Pressure-relieving and depressuring systems

AD Merckblatt


PED 97/23/EC (Pressure Equipment Directive)

2 comments:

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