Quick View Table
| Adjustment Type | Screw/Spring | Clockwise (CW) | Counterclockwise (CCW) | Effect on Cut-In | Effect on Cut-Out |
|---|---|---|---|---|---|
| Overall Pressure | Main (large) screw | ⬆ Increases pressure | ⬇ Decreases pressure | Changes | Changes |
| Differential Pressure | Secondary (small) screw | ⬆ Increases cut-out | ⬇ Decreases cut-out | Unchanged | Changes |
| Cut-In Only | Center metallic screw (69W type) | ⬆ Increases cut-in | ⬇ Decreases cut-in | Changes | Unchanged |
| Cut-Out Only | Black plastic screw (69W type) | ⬆ Increases cut-out | ⬇ Decreases cut-out | Unchanged | Changes |
| ⚠️ Warning: Always maintain a minimum differential of 13 psi (0.9 bar) between cut-in and cut-out pressure to prevent contact chattering and motor damage. | |||||
Air compressor pressure switch is used in the air compressor is mainly to adjust the start and stop state of the air compressor, by adjusting the pressure in the air tank to let the air compressor stop and rest, the machine has a maintenance effect.so how should the air compressor pressure switch be adjusted?
Key Components of a Pressure Switch
Understanding the internal parts of a pressure switch makes adjustment much easier:
- Contacts: Made from a conductive metal (typically 90% silver, 10% nickel), the contacts complete the electrical circuit. When separated, the circuit is interrupted and the motor shuts off.
- Diaphragm: Also called a membrane, this flexible piece moves when pressure inside the tank changes. When the desired pressure is reached, it pulls the contact points apart, breaking the circuit.
- Adjustment Springs: A typical pressure switch contains one or two large adjustable springs whose tension can be varied to set the pressure set-points. Some switches include an additional smaller spring to vary differential pressure.
- Pressure Switch Relief Valve: This safety valve relieves pressure trapped between the pump and the check valve, allowing for easier starts.
Understanding Cut-In and Cut-Out Pressure
The two most important pressure values to know are:
- Cut-in pressure (low pressure): The pressure level at which the compressor restarts after the tank pressure drops.
- Cut-out pressure (high pressure): The pressure level at which the compressor stops or unloads.
- Differential pressure: The difference between these two values. Generally, 0.8 bar–1 bar (12–14 psi) is set as the differential pressure, unless specific applications require a higher setting.
Example: A compressor may be set to cut out (stop) at 10 bar and cut in (restart) at 7 bar, giving a differential of 3 bar. This rest period between cycles is what protects the motor from overheating.
Types of Pressure Switches
Depending on the make and model, a pressure switch may allow adjustment of only the pressure setting with a fixed differential, or it may allow adjustment of both the pressure setting and the differential. Fixed differential pressure switches have only one set screw, while switches with an adjustable differential have a smaller second set screw.
- Type 1 – Fixed Differential: Only the overall pressure range can be adjusted. Both cut-in and cut-out values shift together. These have a single main adjustment knob or screw.
- Type 2 – Adjustable Differential: Both the cut-in (starting) pressure and the cut-out (stopping) pressure can be set independently using two separate screws.
⚠️ Important: On fixed-differential switches with two knobs, both must be adjusted simultaneously. Adjusting only one can cause the compressor to short-cycle, overheating and burning out electrical components.
Safety Precautions Before Adjustment
Always follow these steps before touching the pressure switch:
Step-by-Step Adjustment Guide
Step 1 – Set the Cut-In Pressure (Main Spring)
Start the compressor and let it run until it reaches cut-out pressure. Then open a drain valve to slowly let air escape. Watch the pressure drop and note the pressure at which the compressor restarts — this is your cut-in pressure. Adjust the main (large) set screw clockwise to increase cut-in pressure, or counterclockwise to decrease it.
Step 2 – Set the Cut-Out Pressure (Differential Spring)
The cut-out pressure is adjusted by pre-tensioning the small spring. Note that on some switches, the small spring adjusts the cut-in pressure instead — always verify with your manual.
Step 3 – Verify the Settings
Run the compressor and verify that the motor stops when pressure reaches the cut-out point. Then use the drain valve to check that the compressor restarts at the correct cut-in point. Adjust if necessary and repeat the cycle until both values are correct.
Pressure Adjustment Quick Reference
Adjusting Overall Pressure (Main Screw)
- Clockwise → Increases both cut-in and cut-out pressures simultaneously
- Counterclockwise → Decreases both cut-in and cut-out pressures simultaneously
Adjusting Differential Pressure (Secondary Screw)
- Clockwise → Keeps cut-in pressure unchanged; increases cut-out pressure (wider gap)
- Counterclockwise → Keeps cut-in pressure unchanged; decreases cut-out pressure (narrower gap)
Setting the Right Pressure for Your Application
The pressure set-point of the air compressor should be dictated by the pressure requirements of the pneumatic devices connected to it — even if that is lower than the compressor’s maximum rated pressure. Setting pressure higher than needed results in greater running costs. Each extra bar or psi of pressure comes at a high energy cost, so the goal is to keep pressure as low as possible without negatively affecting end users.
Common Issues and Warnings
- Contact Chattering: If the differential between cut-in and cut-out pressure is too small (below 13 psi), the pressure switch contacts may chatter — causing the compressor to turn on and off rapidly with no time for the motor or contacts to cool. This can destroy the motor very quickly. Always maintain a safe differential.
- Diaphragm Leaks: Over time, the diaphragm inside the pressure switch can crack or develop a hole, causing air to leak from the tank through the switch housing. If you notice air leaking from the switch, inspect and replace the diaphragm promptly.
- Switch Replacement: If the switch operates at incorrect pressures even after adjustment, or fails to respond, replacement is usually the most reliable fix.
Summary
Correctly adjusting your air compressor pressure switch ensures efficient operation, extends motor life, and protects your pneumatic tools by delivering consistent, appropriate pressure. Always consult your specific compressor’s manual before making adjustments, as screw locations and spring arrangements vary by model. When in doubt, contact a qualified technician.
