Safety relief valves

  • 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).

SMU / SMG / SML-7000

Flanged, spring loaded, direct acting, full nozzle safety relief valves.

Media: gas, steam and liquid.

SMFN / SMF / SU / SHL / SUL-7000

Screwed and flanged, spring loaded, direct acting, full nozzle safety relief valves.

Media: gas, steam and liquid.


Flanged, spring loaded, direct acting, full nozzle safety relief valves for steam service (ASME Sect.I).

Media: steam (suitable also for gas).


Flanged, spring loaded, direct acting, full nozzle safety relief valves. The valve series 7000, are available with heating jacket in special execution where the body is made by machining a block of forged material.

Media: gas, steam and liquid.

SMU-7000/ASV & /SLSV

These valves represent the capability of AST to develop special valves for customer needs.

Assisted Safety Relief Valves (ASV)

This is a standard safety valve equipped with a pneumatic actuator that allows to open the valve with a pneumatic or electronic remote signal. It may be used to depressurize the vessel in case of fire or to check the functionality of the valve when the process medium tends to solidify. Overpressure can also be controlled and reduced to 2%.

The connection between the actuator and the valve stem is done in such a way that a failure of the assisting mechanism does not impair the functionality of the valve.


Flanged, pop and modulating action, full nozzle pilot operating safety valves (ASME Sect.VIII).

Media: gas, steam and liquid.

Orifices: from “D” to “T”; intermediate orifices (K2, P2, Q2, R2) and full bore orifices available.

Set pressure range: from 1 bar to 690 bar. Back pressure: up to 80%.

Temperature range: from –252 °C to 288 °C (high temperature special design available)


Two safety valves can be installed together and one can be kept as spare.

Change-over valves have been designed to minimize pressure drop; flow areas are always bigger than inlet or outlet connections.