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November 15, 2021

What is a Safety Valve?

What is a Safety Relief Valve?

A safety relief valve is designed to open and relieve excess pressure from pressure vessels, boilers, or other industrial equipment and to reclose and prevent the further release of media (air, gas, steam or liquids) after normal conditions have been restored. The pressure is relieved by allowing the pressurized air/gas or fluid to flow from an auxiliary passage out of the system. The safety 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 air/gas or fluid is diverted through the auxiliary route. Safety valves are mainly used in industrial applications to protect against over pressurization. Overpressure can lead to dangerous situations such as an explosion or fire.

Many industrial products such as air compressors, air dryers, steam fired autoclave sterilizers, hyperbaric therapy chambers, fire suppression systems, locomotive brake systems, food & beverage equipment, boilers, and other industrial equipment that incorporate a boiler or pressure vessel are required to follow the American Society of Mechanical Engineers or ASME standards that regulate the design and construction of boilers and pressure vessels to insure safe operating conditions.

ASME Coded Valves versus Non-Code Valves

The term “code valve” means that the valve has been designed, tested, and accredited to ASME Boiler and Pressure Vessel Code, Section I or Section VIII, which establishes safety rules and guidelines that apply to the design, fabrication, and inspection of boilers, pressure vessels, and nuclear power plant components during construction. Section I provides requirements for all methods of construction of power, electric, and miniature boilers; high temperature water boilers, heat recovery steam generators, and certain fired pressure vessels to be used in stationary service; and power boilers used in locomotive, portable, and traction service. Section VIII Division 1 provides requirements applicable to the design, fabrication, inspection, testing, and certification of pressure vessels operating at either internal or external pressures exceeding 15 psig. Such vessels may be fired or unfired. This pressure may be obtained from an external source or by the application of heat from a direct or indirect source, or any combination thereof.

Safety relief valves set to pressure under 15 psig and those not designed, tested, and accredited to ASME standards are considered to be “non-code valves”. These safety relief valves are generally used in low pressure or nonhazardous general-purpose applications.