A pressure relief valve is a type of safety valve used to control or limit the pressure in a system. Without it, pressure could build up and cause a process upset, instrument or equipment failure, or fire. It is simple to operate, requires no external energy and performs reliably at temperatures from -200 °C to +700 °C. Luna Flow Control supplies pressure relief valves from DN 15 to DN 200 and PN 16 to PN 100 in cast iron, ductile iron, steel, stainless steel and special materials, with flanged or threaded connections.
What Is a Pressure Relief Valve?
A pressure relief valve detects a sudden pressure rise in the system and discharges fluid to bring it back under control. When the pressure exceeds the set value, the valve opens and reduces the pressure, so pipes, valves, pumps and machines are protected and the system continues to operate safely over the long term. It works with line pressure alone and is easy to maintain.
Working Principle
While the system pressure is at or below the set pressure, the valve remains closed. When a higher pressure is detected, the valve starts to open and the fluid is released quickly. As soon as the inlet pressure falls back to the desired level, the valve closes again. In hydraulic lines, this rapidly relieves pressure surges caused by sudden changes in fluid velocity, allowing the installation to keep running without damage.
Types of Pressure Relief Valves
- Differential pressure relief valves – discharge fluid when the differential pressure rises and keep it at the required value, protecting the process from sudden pressure changes.
- Relief valves for combi boilers – prevent excessive pressure and hot water leakage in boiler systems used in homes and workplaces, where they are essential for safety.
- Threaded relief valves – installed on threaded pipework, with automatic operation, in cast iron, ductile iron and steel.
- Fire system relief valves – protect fire pumps and other equipment by discharging water quickly when the pressure rises. They are easily set to the required pressure and are available with flanged or threaded connections.
What Does a Pressure Relief Valve Do?
If pressure is not reduced when it exceeds the permitted limit, pumps, motors, actuators and other machines on the line may be damaged beyond repair. A pressure relief valve prevents this damage and delivers significant savings: it costs far less than replacing failed equipment, and because the installation keeps running, it also avoids repair time and unplanned shutdowns.
Application Areas
- Water supply and sanitary installations
- Oil and hydraulic lines
- Heating and hot water systems, including combi boilers
- Fire protection systems
- Installations in cold climates and heat-preservation systems
Advantages
- Automatic operation without external energy
- Fast response to pressure surges
- Wide operating temperature range
- Low maintenance requirements
Selection Tips
Determine the set pressure according to the maximum allowable pressure of the equipment to be protected, and select the valve size, material and connection type to suit the medium and the required discharge capacity. Correctly sized relief valves keep the installation within safe limits and ensure long-lasting, economical operation.
