Compressor Pressure Switch

The compressor pressure switch provides some key functions on the air compressor.

One purpose of the compressor pressure switch is to shut the compressor off when the air compressed into the tank has reached the correct air pressure.

Another function is to turn the air compressor back on on when the air pressure level in the compressor tank has dropped to the point where more air is needed.

One more key function of the compressor pressure switch is that it is the first defense to over pressurization of the tank and air lines on the air compressor.

Pressure switch appearance

On many of the smaller DIY type air compressors, there will be only a few manufacturers of pressure switches. Two common makes are shown in the photo below.

Compressor Pressure Switch for Smaller Compressors

There are a lot of air compressors sold today that we would classify as mini-air compressors. These are air compressors that can be operated by a 12 VDC power supply from a vehicle accessory port. Some of these mini-air compressors also work on 120 VAC. They all use small,  fractional HP, electric motors to power the small compressor pumps. They do not use the air pressure switch shown above, but rather, theirs may be a tube shaped switch as shown in the next image, one from a DeWalt mini-compressor.

Compressor Pressure Switch Operation

A pressure switch is an ON/OFF device that reacts to pressure. They are used in many industries and in many media. We’re concerned here only about the air compressor pressure switch.

The pressure switch will have a device inside that reacts to pressure applied against it. In the Condor and Lefoo switches shown above,  that internal device is often a diaphragm of some sort, one of which is shown in the photo.

When air pressure in the air compressor tank creates enough back pressure, that back-pressure deforms the switch actuator (diaphragm or other sort)  inside the pressure switch and causes it to move. On the high pressure side, that actuator deformation typically opens contact inside the switch. With the contacts now being open, power stops flowing to the compressor motor circuit, and the compressor stops.

When the air pressure inside the compressor tank and lines drops, the compressor pressure switch internal operator begins to deform or move in the opposite direction. This movement is typically caused by an internal spring. When that deformation or diaphragm movement is far enough the contacts inside the pressure switch are made (come together) and power flows across them. The power flows to the motor circuit on the air compressor, the motor starts, and air starts pumping into the tank.

As the back pressure inside the tank increases, once again, the compressor switch internal actuator begins to deform or move the other way, eventually the contacts break, and the power stops.

The cycle repeats as long as compressed air is being used, or until external power to the air compressor is stopped.

Adjusting the compressor pressure switch

There may come a time when you have to adjust the compressor pressure switch. Typically that will only be when you have replaced the original switch that came with the air compressor, and the new switch cut in and cut out settings are different, and have to be adjusted to the levels of the replaced pressure switch.

As far as we know, you cannot field adjust the pressure settings of the tubular pressure switch similar to those shown in the photo of the DeWalt pressure switch. If your compressor uses this type of pressure switch and the switch fails, you are going to have to replace the failed switch with another of the same size and type. That will typically mean quite a search, as many of the brands of compressors on the market are mass marketed through big box stores which have a dismal record of stocking parts for the air compressors they sell.

Please follow this link for more on adjusting the compressor pressure switch.

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