How To Set An Air Compressor’s Pressure Switch

There are two kinds of compressor pressures, namely cut-in and cut-out. Once you get the hang of setting the pressure switch yourself, you can save time and money not to mention maintenance and lifespan factors for your compressor.

This is how you can use the pressure switch to set the ideal pressure:

  • Whether it is piston compressors (small) or industrial rotary screw compressors (large), you need to set the pressure properly. Not only is it the most important setting on such machines, they are also easy to do; so no excuses.
  • The pressure switches on small compressors have room for you to set the pressure right there. As for larger compressors, you will find the central compressor controller useful in this regard. The steps are the same, so do not worry about confusing yourself.
  • There comes a time when you must decide, which is the best pressure setting for the air compressor model you own.
  • Set it as low as possible first and make your way up from there. Generally, in a majority of cases at least, 125 psi (or 7 bar) is the pressure setting of choice. This is usually pre-set on the machine itself when you make the purchase.
  • Suppose your circumstance or need has you choosing 5 or 6 bar pressure, you can lower it using the pressure setting.

Bear in mind that any pressure increase warrants more energy to compensate. If you happen to own a compressor 30 kW or larger, you can quite truly save thousands of dollars annually if you set the pressure ideally low so as to save energy and the costs that come with it. Attaining this ‘low pressure set point’ depends on your compressor and is not that hard to do.

What if you have a small air compressor? Your energy demands will understandably be less than a bigger model’s. However, is it a bad idea to save anywhere from ten to a hundred dollars per year on energy costs?

More On Air Compressor Pressure Switch

The cut-out and cut-in setpoints are the two you need to focus on; in fact, those are the only two. The compressor essentially starts (when the pressure value reaches the cut-in setpoint) and stops (at the cut-out pressure value) at those pressures. As you can imagine, the cut-in value is invariably lower than the cut-out value. This difference is termed ‘pressure differential’.

If this difference is too small, the start-stop process in the compressor will occur too quickly; not good. An average difference of 14 psi (or 1 bar) is good. You do not want to burn the motor or cause component wear and tear that will end up damaging the pressure switch.

Example: Air installation in your compressor needs 6 bar pressure. You set things at 7 bar; maximum. There is now sufficiently high pressure in your compressor. It will not start-stop too quickly; the pressure differential is 1 bar. The cut-in pressure is 6 and the cut-out pressure is 7.

Some compressors will need bigger differentials; 3 or 4 bar differences are not uncommon. This is in case of compressors designed to run for brief time periods. By increasing its pressure band, the machine goes on for longer. This means more time for it to heat up and remove internal moisture build-up in the process. Since moisture is a compressor’s arch-nemesis, this is a superb state for your compressor to be in, where it can get rid of moisture as it builds.

Air compressor Pressure Switch Setting

This is the main step in our guide. Know the model and make of your pressure switch before getting started. This will determine if you can adjust the setting and then the differential or both at the same time or if they need separate handling.

  • If the switch has a fixed differential value (range: 0.8 - 1 bar) you will find a note of it on the housing or in the user manual.
  • There will be only one setscrew for fixed differential pressure switches. There will be a small secondary setscrew for the adjustable kind.
  • It can be tricky setting the cut-in and cutout pressures. If the settings are turned too much, you will lose the spot.
  • The big set-screw helps with cut-in pressure setting and the smaller one determines the pressure differential as you set the cut-out mark.
air compressor pressure switch

Basically, the cut-out pressure is the pressure differential plus the cut-in pressure. This makes the cut-in pressure crucial and needs to be set first.

  • Target an empty tank. Turn the compressor on and await its reaching the cut-out pressure point.
  • You need to let some air escape; open the valve accordingly. The pressure lowers, of course.
  • Use the large set-screw and adjust the cut-in pressure. Turning it clockwise increases this pressure.
  • When next you turn the drain valve closed, the compressor carries on until the cut-out pressure is attained.
  • This process need to be cycled until the proper cut-in pressure is reached.
  • The compressed air needs to be let out; open the drain valve but do so gradually. Await the compressor's starting up.
  • The pressure at which it starts needs to be noted; this is the cut-in mark. Tweak as you see fit.

A few repeats is all you need to find the perfect cut-in pressure. In short, whenever pressure lowers beneath the cut-in pressure value you need, simply shut the drain valve to keep the pressure constant. Tweak the set screw, namely the big one, clockwise to increase cut-in until you see the compressor start. A quarter turn maybe less will get the pressure to the cut-in mark you need, if it is low.

As for setting up the cutout pressure, which comes after this...

  • You will work only with the setscrew that is for the differential pressure. This screw is the smaller one. If this screw is absent, then your pressure switch is most probably designed with a pressure differential; no more work required.
  • The last time you ran the compressor (above), what pressure did it run in? Note that down.
  • If you wish for a higher maximum pressure, turn the small screw clockwise to help with pressure differential adjustment. Turning it counterclockwise will get you a lower maximum pressure.
  • The pressure needs to go low enough for the compressor to start up. Open the drain valve accordingly and then shut it again.
  • Wait until the compressor has stopped to check the value, namely the cut-out pressure.
  • Repeat the process.
As you can see, this is a pretty straightforward task. Remember: cut-in pressure first and then cut-out pressure, no interchanging. Depending on the type of pressure switch on your compressor, the cyclical process detailed above could change. For instance, only under pressure can some such switches even be adjusted.
One more thing to bear in mind is to not turn any screws when the pressure in the tank reads zero. The same applies for if you get your new pressure switch attached and ready for use. The user manual will tell you how to go about this.

It is good to know that most pressure switches come factory-set. They have a 6 bar cut-in pressure with a 1 bar pressure differential; this means the cut-out pressure is set at 7 bar.

This is all you need to know about air compressor pressure switches, what they are, and how to set them up.

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