What Is an Air Compressor Switch?

Lori Kilchermann

An air compressor switch is also known as a pressure switch and is used to turn off an air compressor when the storage tank air pressure reaches a certain point. Comprised of a system of springs and diaphragms, the air compressor switch is threaded into a bung, welded onto the air compressor tank and reacts to the air pressure pushing against the switch. Working as an on/off type of switch, the air compressor switch is wired into the power supply line and interrupts the flow of power between the switch and the compressor motor.

Some garages may feature a pneumatic controller in each service bay.
Some garages may feature a pneumatic controller in each service bay.

The air compressor is an air pump mounted onto a large storage tank that is used to compress air and keep it stored under pressure until needed for a task, such as powering air tools, inflating tires or using a paint gun. As the compressor pumps air into the storage tank, the pressure begins to rise inside of the tank. Left unchecked, the compressor could theoretically pump air into the tank until the stored pressure causes the tank to fail and a dangerous explosion results. By installing an air compressor switch into the air tank, this problem is eliminated as the compressor pump and motor is turned off at a safe pressure setting.

The amount of pressure that an air compressor switch is programmed to turn on and off is typically metered in pounds per square inch (PSI) of air pressure. The air compressor switch is rated by using two numbers, such as an 85/130 switch. This means that the switch is designed to switch on at 85 PSI inside the air tank and switch the power off at 130 PSI inside the air tank. Some switches have a small amount of adjustment built into the design and can be adjusted to a slightly higher pressure setting before switching off.

The type of switch used to regulate the air pressure inside of the air compressor tank is very similar to the type of pressure switch used to regulate a water pump on a home water well. As the water pressure reaches a predetermined point, the water pump is turned off. Some of the compressor switches include a special bypass that will prevent the compressor pump from being started while the compressor cylinders are under pressure. This will prevent the compressor from being damaged as the pressurized air pushes against the compressor pump piston while the compressor motor attempts to move the pump piston at the same time.

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