Gas Portable Air Compressors

(Last Updated On: September 29, 2020)

In response to this very interesting question from a visitor to my compressed air information website:, I offer this response.

Compressors in general use a pressure switch to control the ON & the OFF of the motor on an air compressor. It will have a cut in pressure setting, which is the point where the air pressure in the tank has fallen to a specified level, and the switch trips to turn on power to the compressor motor.

gas air compressor

The pressure switch will also have a cut out pressure level, normally around 30-60 PSI higher than the cut in level, and at which point the pressure switch trips again to turn off the power to the motor, stopping the air compressor.

When you say you want an air compressor that “KICKS ON OR CYCLES AT 120 PSI MIN”, this is impossible to find.

The figure of 120 PSI / min is pretty meaningless. Let me tell you why?

PSI is a measure of air pressure. So many pounds per square inch. At 120 PSI, there is a force of 120 lbs. pushing down on every square inch of surface area that the compressed air can get to.

The reference to “Min” suggests a period of time; one minute to be exact. But, pressure does not relate to time. In compressed air lingo, Flow relates to time.  Pressure relates to force on a specific area.

The two don’t mix, so, I can’t do PSI/MIN.

What I think you want is a compressor that has a cut in pressure at xxx pressure (say 100 PSI?) and a cut out pressure level of, say, 150 PSI? That means that as long as the compressor can keep up with the flow demand of the air-using tool, the pressure flowing to that tool will range from 100 PSI to 150 PSI all the time.

Then, you have to find out at what flow (in CFM) that your air tool needs that pressure at.

Then, and only then, can you make a wise choice about what air compressor you need to purchase for your application?

And sorry, I don’t sell air compressors or air components from my website. Only information. My advertisers will be happy to hear from you though, I’m sure.

Hello, I am Bill, the Compressed-Air-Man. I have years of experience in industrial and residential compressed air applications, air compressors and general pneumatics. I created this site to help professionals, students, and DIYers understand and properly implement and maintain compress3ed air systems.


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