What is the pressure relief valve on my compressor for?

If you don’t know what they are for and how they protect you, then sure, you want to understand ‘ what is the pressure relief valve on my compressor for?’

Every air compressor has a pressure switch. That switch (lots more info on the compressor pressure switch here) controls the starting and stopping of the air compressor motor and pump by reacting to the pressure in the compressor tank. Pressure is low? The compressor starts. Tank pressure is high enough? The compressor stops.

The pressure switch has settings that dictate the pressure level at which the compressor will start and stop.

What if the pressure switch failed? Worse, what if the pressure switch failed closed, meaning that power was still flowing across the switch to the motor and continues to drive the pump, and the pressure level in the compressor tank kept rising… and rising… and rising?

BOOM!

What is the compressor pressure relief valve for - blown compressor tank
Example of blown air compressor tank – as seen on www.about-air-compressors.com

It’s possible the tank might explode, as shown in the image above, if the pressure in it reached a level beyond the capability of the tank welds or the tank wall to hold the pressure in. People and things in the vicinity may be hurt, damaged or in worst case scenarios someone might get killed.

Yet, pressure switches do fail from time to time, and they can fail closed so that power does continue to flow to the compressor motor and drive the pump. The engineers that design the compressors know this, and the people that actually build the compressors know this too.

The solution? The pressure relief valve or as it’s commonly known, the PRV.

What is the pressure relief valve for - pressure-relief-valve
Pressure Relief Valve
Photo: Grainger.com

On your air compressor you will likely only see the part of the PRV above from the wrench flats out to the ring on the end. The rest of the pressure relief valve will be threaded into a port that has access to the air tank. That means that the air pressure in the tank can reach the internal piston of the PRV.

Each PRV is factory set to have a cracking (opening) pressure at a certain pressure level, in accordance with the design of the air compressor. The cracking pressure will be higher – 15-30 PSI or so depending on the make of PRV – than the pressure level at which the pressure switch is set to cut off power to the motor.

In the event that the pressure switch ever fails, a remote but possible occurrence, and the compressor continues to run on, then the pressure in the tank will increase high enough that the PRV piston shifts and a path to the outside atmosphere opens. The over-pressure will vent to the outside air faster than the compressor can pump it into the tank, and the tank pressure will drop.

The air compressor will continue to run, and that will lead to other issues, but at least the air tank will not blow up!

Got a question about PRV’s? Use the comment form below to ask, and we’ll see if we can help.

 

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Michael Haluska

OK, so my pressure switch fails in the closed position and the presure relief valve opens and vents the pressure. Is there a pressure relief valve that cuts power to the compressor motor so the compressor stops running?