What is a safety valve?

A safety valve, or relief valve, is one of the safety devices used in the oil, gas, refining, and petrochemical industries, and generally for various types of industrial facilities. It prevents the occurrence of overpressure in pipelines, vessels, pressure-storage tanks, and more, by automatically relieving excess pressure beyond a designed limit. Pressure safety valves (PSV) are examples of safety valves that open automatically when the pressure or temperature of the pressure vessels or other systems exceeds the permissible limit, releasing a certain amount of the substance inside the equipment or pipeline. Safety valves were first used in steam boilers during the Industrial Revolution. Without safety valves, steam boilers would have been at risk of explosive failure.

Two general types of protection encountered in the industry are:

1. Thermal protection
2. Flow protection

For piping systems, thermal safety valves are generally sized relative to the small size of the valve to provide protection against additional pressure caused by specified thermal connections. In this case, a small valve is sufficient due to the fact that most fluids are nearly incompressible, and therefore a relatively small amount of fluid discharged through the safety valve results in a noticeable reduction in pressure.

Safety valves used for flow protection are much larger than similar safety valves for thermal protection. The size of these valves is significant because a considerable amount of gas or liquid must be discharged quickly to ensure the safety of the pipeline or storage system.

In many countries, industries are required to use safety valves for protecting pressure vessels and other equipment. Additionally, in most countries, the standards developed by ASME and API, as well as other organizations, must be complied with.