Glossary · Pneumatics and hydraulics
Pressure-relief valve
Also known as: Relief valve, Pressure-limiting valve
German: Druckbegrenzungsventil
In fluid power, a pressure-relief valve is a valve that limits the maximum pressure in a system or circuit by opening and diverting fluid to tank or atmosphere when the set pressure is reached.
- Fluid power
In one sentence
A pressure-relief valve limits maximum system pressure by opening to tank or atmosphere when the set pressure is reached.
Example
The hydraulic power unit's main pressure-relief valve is set to 160 bar and sealed after commissioning.
How it applies
- Engineering: Every hydraulic system needs pressure limitation, as a pump delivering against a closed circuit would build pressure until something fails. ISO 4413 requires protection against overpressure.
- Commissioning: Relief pressure is set according to the design, verified with a gauge and protected against unauthorized adjustment, for example by sealing.
- Operation: A relief valve that opens frequently heats the fluid and wastes energy, pointing to a design or setting problem.
- Documentation: State relief settings in the circuit diagram and technical data and forbid unauthorized adjustment. Explain that raising the setting can overload components and invalidate the design basis.
Pressure-relief valve vs. safety valve
In hydraulics the pressure-relief valve protects the circuit in operation. Safety valves on pressure vessels, such as compressed air receivers, are pressure equipment accessories with their own requirements; don't use the terms interchangeably.