Do all air compressors shut off automatically? A good question that came in from a visitor recently.
The answer is, typically yes, with some exceptions as noted below.
All air compressors shut off automatically if they have a functioning compressor pressure switch that is installed on the air compressor to shut it down when the pressure reaches a certain level.
CONDOR 11KC2E Pressure Swtch, Dpst, 40 to 175 Psi, Stndrd
In the photo above you can see a typical compressor switch. This is a Condor brand. This particular pressure switch works within the 40 – 175 PSI range and you can get it on Amazon here. Your air compressor pressure switch may look like this one or it might be similar, but be made by LeFoo, or one of the many other manufacturers of air compressor pressure switches.
Your air compressor may not have a visible pressure switch at all, but may have an internal one, much like the one in the image following.
DEWALT N003306SV Pressure Switch
Regardless of the type of switch, they all work in a similar fashion.
The switch will have a low pressure cut in setting and a higher pressure cut out setting.
When the pressure in your compressor tank drops to the cut in pressure setting, the air compressor should start, and pump air into the tank, raising the pressure in the tank.
When the pressure switch senses that the pressure in the tank has reached the cut out pressure level, the pressure switch trips to off, and the compressor stops.
My Compressor Doesn’t Stop?
So what if my air compressor does not stop? If the pressure in the compressor tank does not get to the cut out pressure setting, the compressor will continue to run. This could be because of a mechanical failure of some sort in the pump. While not necessarily dangerous, a compressor that never reaches cut out and runs on will prematurely wear the motor. If this is happening on your air compressor, get the pump serviced.
If, on the other hand compressor run on may occur when the compressor tank pressure reaches the cut out pressure setting of the pressure switch, and the switch does not react by cutting the power to the motor and stopping the compressor.
If this is your compressor scenario, then the pressure in the tank will rise until the pressure relief valve lets go to vent the over pressure. The air compressor will continue to run increasing wear and tear which is not good, yet this is an unsafe compressor scenario too. If the PRV should fail too, it is possible to have a catastrophic over pressurization.
If your air compressor pressure switch is not shutting the air compressor off when it is supposed to, do not use the air compressor until you get it fixed.
Other Continuous Run Air Compressors
Other air compressors (continuous run) use the pressure switch to “unload” the compressor when the set pressure in the tank is reached, but due to the type of air compressor, it is desired that the compressor motor continue to run even though the air compressor tank pressure has reached the cut out level.
These compressors, typically construction type or industrial compressors, are continuous run, loading and unloading the air production, all the while the compressor motor keeps running.
The motor in these types of air compressors will not shut off automatically, but require an operator to shut them down.