- The safety valves are the last barrier for overpressure. The valves should open to a safe area for a proper pressure relief. They should open at a given pressure even after standing without movement over a longer period.
- Safety valves do not necessarily hold tight, and downstream Pressure build -up must therefore be prevented.
- There are two types of safety valves, spring operated as the most common and pilot -operated valves for higher pressure and volume.
A safety valve can be designed in different ways by the different ones valve manufacturers, but they all have the same regulations to comply with. A valve that should used on pressure tanks must be in accordance with ASME VIII rules, while pressure relief valves used to protect hydrocarbon systems under pressure shall be in accordance with API 526.
ASME has defined different groups of safety valves.
- Pressure relief valve: Safety valve that closes after normal conditions in the system has been recovered (spring or pilot operated).
- Safety valve: Safety valve that is controlled directly by the static pressure, opens quickly (pop action). Used on compressible media.
- Relief valve: Actuated safety valve controlled by static pressure, opens according to increase in pressure. Used on non-compressible media.
- Safety relief valve: Safety valve that opens quickly after use (pop action), or according to increase in pressure. In other words, a common term. Pilot operated pressure relief valve: Safety valve where main relief device is combined and controlled with a self-actuated auxiliary PSV (pilot controlled).
- Non-re closing pressure relief device: Explosive membrane that bursts and cannot shut down after normal state of the system is restored (rupture disk).