Compressor Pressure Switch: What It Is and How to Adjust It, Explained Simply

What This Part Actually Does

A pressure switch is the compressor’s automatic on/off control. It turns the motor on by itself when the air in the tank runs low, and turns it off by itself once there’s enough air. Without this part, you’d have to stand next to the compressor and flip the switch manually every time pressure dropped.

It works like a fridge thermostat, except instead of temperature, the pressure switch tracks air pressure.

Two Numbers Worth Remembering

The pressure switch only has two important settings:

• Cut-in pressure — the pressure at which the motor turns on. For example, “start when the tank drops to 6 bar.”
• Cut-out pressure — the pressure at which the motor turns off. For example, “stop when the tank reaches 8 bar.”

The gap between these two numbers is called the delta. In the example above, that’s 2 bar (8 minus 6). On household compressors, this gap is usually kept around 1.5–3 bar.

Why have a gap instead of one number? If the motor turned on and off at the exact same pressure, it would cycle on and off almost nonstop — this is called “short cycling,” and it wears out the motor and contacts far faster than normal operation.

Why a Bad Setting Costs You Money

If pressure is set too high:

• The motor runs longer and heats up more
• Your electricity bill goes up
• Springs, seals, and valves wear out faster — meaning more frequent replacements
• There’s no upside if your tool doesn’t actually need that much pressure

If pressure is set too low:

• Pneumatic tools run weak or don’t run at all
• A nail gun won’t drive nails properly
• A spray gun applies paint unevenly, in blotches

The right setting is one where pressure matches what your tool actually needs — no more, no less.

What’s Inside a Pressure Switch

There are only four main parts inside:

1. Spring — holds the tension that determines the pressure at which the switch trips.
2. Diaphragm — a flexible plate that senses the air pressure in the tank.
3. Contacts — open and close the electrical circuit, turning the motor on and off.
4. Terminals — where the power wires connect.

How it all works together: air in the tank pushes up on the diaphragm from below, while the spring pushes down from above. As long as air pressure is weaker than the spring, the contacts stay closed and the motor runs. Once air pressure overcomes the spring, the contacts open and the motor stops. The adjustment screw is what you use to change the spring’s tension — and with it, the pressure at which all of this happens.

Most models also have an unloader valve — it bleeds off the residual air trapped in the tube between the pump and the check valve when the motor stops, making it easier for the motor to start up next time.

How to Adjust the Pressure: Step by Step

Step 1: Preparation — required for safety

• Fully disconnect the compressor from power: flip the breaker or unplug it.
• Open the drain valve at the bottom of the tank and release all the air.
• Make sure tank pressure reads zero before unscrewing the pressure switch cover.
• Carefully remove the pressure switch cover (usually held by 2 screws). Don’t lose the screws.

Step 2: Adjusting the cut-in pressure

Inside, you’ll find the main adjustment screw. It controls the pressure at which the motor turns on.

• Turn the screw clockwise — cut-in pressure increases.
• Turn it counterclockwise — cut-in pressure decreases.
• Turn it in small increments — a quarter turn at a time is enough; check the result before continuing.

Step 3: Adjusting the cut-out pressure (if there’s a separate screw)

If your switch has a second, smaller screw, it adjusts the gap between cut-in and cut-out (the delta) without changing the cut-in pressure itself.

• Turn it the same way, in small steps, checking the result after each adjustment.

Step 4: Testing

• Restore power and start the compressor.
• Watch the pressure gauge on the tank.
• The motor should stop exactly at your set cut-out pressure and start again at the cut-in pressure.
• Repeat the cycle a few times to confirm it’s stable, and listen for any unusual noise or overheating.

For most household compressors, the normal range is roughly 5.5–8 bar (80–120 psi), but your specific model may differ — check the datasheet.

Common Problems and What They Mean