The safety valve is the part that stops the pressure exceeding the limit of the receiver and the compressor. When it opens it makes a lot of noise, and that is intended: it is telling you the pressure has risen too high, or that the valve itself is tired.
The absolute rule
Never block a safety valve, never change its setting and never replace it with a plug. It is what prevents a pressure vessel from bursting. A safety valve is only replaced with a model of the same set pressure, suited to the equipment.
Why it blows
The pressure rises above the setting
The control does not cut out in time: pressure setting changed too close to the limit, faulty pressure switch or pressure sensor, solenoid valve stuck. The safety valve is then doing its job. Stop the machine and have the control checked.
Working pressure too close to the set pressure
If the working pressure is set just below the valve's opening pressure, the slightest overshoot opens it. The working pressure must stay well below it, within the limits given in the manual.
The valve is worn or dirty
Over time, with dust, oil or water, a valve can leak slightly below its opening pressure: you hear it hiss. It must then be replaced with an identical part.
On a screw compressor: the minimum pressure valve
In a screw compressor, a valve on the separator tank can open if the air no longer flows out properly: clogged air/oil separator, minimum pressure valve stuck. This diagnosis is for service. See how a screw compressor works.
The checks you can make
- Read the pressure gauge when the valve opens, and compare it with the set pressure.
- Note any message on the controller.
- Check whether the service is overdue, especially the air/oil separator.
- If the valve blows continuously, or the pressure exceeds the setting, stop the machine and make a request from the warranty and service page.
Inspection of valves and receivers
The safety valve is part of the pressure equipment. Depending on the volume and pressure of the receiver, periodic inspections are compulsory: see air receiver regulations and our maintenance and inspections page.
Other symptoms are covered in our compressor troubleshooting guide.