Purpose and function of safety valves

The primary purpose of a safety valve is the protection of life, property and environment. A safety valve is designed to open and relieve excess pressure from vessels or equipment and to reclose and prevent the further release of fluid after normal conditions have been restored.

A safety valve is a safety device and, in many cases, the last line of defence. It is important to ensure that the safety valve is always capable of operating and under all circumstances. A safety valve is not a process valve or pressure regulator and should not be misused as such. It should have to operate for one purpose only: overpressure protection.

Difference between Pressure Safety Valve and Pressure Relief Valve

Pressure Safety Valve’ and ‘Pressure Relief Valve’ are commonly used terms to identify pressure relief devices on a vessel. Frequently these terms are used interchangeably, and it may entirely depend on a particular project or company standards to identify all the pressure relief devices either as ‘safety valves’ or as ‘relief valves’ or sometimes even as ‘safety relief valves.

Although freely used interchangeably, these terms differ in the following aspect,

Pressure Relief Valve – is the term used to describe relief device on a liquid filled vessel. For such a valve the opening is proportional to increase in the vessel pressure. Hence the opening of valve is not sudden, but gradual if the pressure is increased gradually.

Pressure Safety Valve – is the term used to describe relief device on a compressible fluid or gas filled vessel. For such a valve the opening is sudden. When the set pressure of the valve is reached, the valve opens almost fully.