Difference between PSV and PRV

While terms Pressure Safety valves and Pressure Relief valve are used interchangeably, these two are different pressure relieving devices. These devices are used in chemical industries and refineries to prevent pressure vessels and other equipment from overpressurization by releasing excess pressure. Properly functioning pressure valves are important for safety of plant personnel and to prevent equipment damage.

Figure 1: SV and RV diagrams


  1. PRV opens gradually with pressure whereas PSV is fully opened immediately when the pressure hits the set point pressure. Relief valve is used to limit pressure in the system while safety valve is designed to release excess pressure from the system.
  2. Safety valves can be used manually but the same cannot be done with relief valves.
  3. Safety valves are used in most of the vapor and steam systems whereas relief valves are used in liquid systems.
  4. The relief valve releases pressure before the set point and then returns it to the system whereas the safety valve releases pressure from the system to the surrounding atmosphere.


  1. https://inspectioneering.com/tag/pressure+relieving+devices#:~:text=While%20the%20term%20PRV%20is,a%20potential%20process%20safety%20incident.
  2. https://automationforum.in/t/what-are-the-difference-between-psv-and-prv/4539
  3. http://www.differencebetween.net/technology/industrial/difference-between-relief-valve-and-safety-valve/

Image source

  1. http://www.pipingguide.net/2013/11/what-are-safety-valves-and-pressure.html?m=1