Pressure Relief Valve

Pressure Relief ValveA pressure relief valve (PRV) is a type of valve used to allow a system relieve the pressure at a preset value to maintain system safety. A common application is using a pressure relief valve on the top of a boiler to prevent over-pressurising the system.

Pressure relief valves are often part of a HAZOP discussion when designing a new plant or if a process is changing and there is a risk of higher pressures that the system overall may not be able to take or run close to its design pressure limits.

How does a pressure relief valve work?

A pressure relief valve works by having a seated resistance that the pressure upstream needs to overcome before lifting a pallet and allowing gas / liquid to pass and thereby reduce the pressure on the system

What are the types of pressure relief valves?

There are three main PRV types, namely conventional spring loaded, balanced spring loaded, and pilot operated. In conventional spring loaded the bonnet, spring, and guide are exposed to the released fluids or gases.

Conventional spring loaded – when the bonnet is vented to the atmosphere, relief-system back pressure decreases the set pressure. The conventional spring-loaded valve is typically used in basic services and where back pressure is less than 10% of the set point.

Balanced spring-loaded – these valves can be used in corrosive or dirty service and with variable back pressure.

Pilot operated pressure relief valve – is combined with and controlled by an auxiliary pressure pilot. The resistance force on the piston in the main valve is assisted by the process pressure through an orifice.

How do I select a pressure relief valve?

There are a few basic items that need to be considered when selecting an appropriate valve.

  • The set pressure & back- pressure
  • The relieving volume
  • The connections
  • The media / Service

What is the difference between pressure safety valve (PSV) and pressure relief valve (PRV)?

Generally the difference is in the set point and capacity.

What is an emergency pressure relief valve?

Emergency pressure relief valve has high capacity relief at a preset pressure in the event of emergency such as fire / over-pressure or process upset for the relief of pressure on the system

What is the difference between a rupture disc vs pressure relief valve?

A rupture disc has a single preset pressure and once it exceeds this pressure (depending on the manufactured tolerance), it will rupture and has to be replaced. Pressure relief valves open when above the pressure but reset when the pressure has been lowered

How do you know when you should replace your pressure relief valve?

Regular inspection of the valve and testing of same will give you the indicator of how it is performing in relation to the original installation date. Maintenance then make an informed decision on the suitability of the valve to be returned to service or replaced

Why do pressure relief valves fail?

Relief valves could fail by being incorrectly sized, poorly maintained, blockage, chemical corrosion impact etc. Proper sizing up front is critical and regular inspection is essential for these process safety items.

What is a balanced bellows relief valve?

These are used as a type of control valve to balance the pressure. The valve can prevent fluids leaking to the air and guarantee zero leakage of pipelines

What is a line mounted pressure relief valve?

This is a relief valve and sometimes used in the area of hydraulics to prevent the upstream pressure exceeding the preset pressure

Which Pressure Relief Valve does Flexachem supply?

Flexachem supply a wide range from conventional spring loaded, balanced spring loaded, and pilot operated pressure relief valves within Ireland.

If you have a specific requirement in mind, please contact one of our product specialists to discuss your application.


Contact our Venting Team:

Noel Bracken (External Sales)– Tel: 083 0891204

Conor Foley- Tel: 021 461 7206