Air Compressor Won’t Stop When Fully Pressurized: Troubleshooting and Solution Guide

Many users have encountered this situation: even though the air receiver pressure has clearly reached the set value (e.g., 0.8MPa), the air compressor keeps humming away without shutting down or unloading. This not only wastes electricity but also forces the compressor to operate at full load for a long time, shortening its service life. In fact, “failure to stop when fully pressurized” is mostly caused by “control failure” or “hidden air leakage,” and most issues can be resolved through simple troubleshooting.

I. First, Understand the Normal Logic of “Stopping When Fully Pressurized”

II. 4 Common Causes: Troubleshoot from Simple to Complex

1. Most Easily Overlooked: Incorrect or Inaccurate Pressure Settings

• Upper pressure limit set too high: For example, if the actual demand is 0.6MPa but the upper limit is mistakenly set to 1.2MPa, the air receiver pressure of 0.8MPa is still far from the set value, so the compressor will not stop.

  Judgment: Check the “upper pressure limit” display on the control panel and compare it with the actual demand. If it is significantly higher, adjust it back (generally set to “actual air consumption + 0.1MPa,” e.g., set to 0.7MPa for a 0.6MPa demand).

• Pressure sensor/switch malfunction: A faulty sensor or switch cannot accurately detect pressure (e.g., displaying 0.6MPa when the actual pressure is 0.8MPa), so the controller does not receive the “full pressure signal.”

  Judgment: Measure the actual air receiver pressure with an external pressure gauge. If the actual pressure is much higher than the display value on the control panel, the sensor/switch is faulty and should be replaced (low cost, operable by users themselves).

2. Most Common: Stuck or Failed Control Components

• Stuck unloading valve (intake valve): The unloading valve acts as the “gate” controlling air intake. It should close to stop air intake when the compressor is fully pressurized, allowing the compressor to “idle and unload.” If the valve plate is stuck by oil dirt or the spring is aging, the valve cannot close tightly, leading to continuous air intake. Pressure fails to drop, and the compressor keeps running.

  Symptom: The compressor’s noise does not decrease after being fully pressurized (it should soften during normal unloading), and there is a continuous airflow sound at the air intake.

  Solution: Disassemble and clean the unloading valve, remove oil dirt, and replace the aging spring. Replace the entire unloading valve assembly if the issue is severe.

• Solenoid valve malfunction: The solenoid valve is responsible for sending “on/off signals” to the unloading valve. If the solenoid valve coil burns out or the wiring is loose, the unloading valve will not receive the “close signal,” resulting in continuous air intake.

  Judgment: Use a multimeter to check if the solenoid valve is energized when the compressor is fully pressurized. If there is no power supply, inspect the wiring or replace the solenoid valve.

3. Most Hidden: Air Leakage or Excessive Air Consumption at the User End

• Air leakage in pipelines/equipment: Loose pipe joints or damaged seals in pneumatic tools cause continuous air leakage. The air receiver pressure drops immediately after reaching the upper limit, forcing the compressor to keep replenishing air.

  Inspection: Turn off all air-consuming equipment and observe the air receiver pressure drop rate. A normal drop is ≤0.05MPa per hour. If the drop is rapid (e.g., 0.2MPa per hour), there is an air leakage point. Apply soapy water to joints and valves—bubbles indicate the leakage point.

• Air consumption exceeds displacement: For example, operating multiple pneumatic devices simultaneously may result in total air consumption exceeding the compressor’s displacement. The air receiver pressure never reaches the upper limit, so the compressor runs continuously.

  Symptom: The compressor fails to stop when fully pressurized only when “multiple devices are used simultaneously” but operates normally with a single device.

  Solution: Either reduce the number of devices used simultaneously or replace the compressor with a higher displacement model.

4. More Complex: Compressor Hardware Failures

• Insufficient displacement of the screw main unit: Long-term use causes rotor wear and bearing aging, reducing the main unit’s displacement. The pressure replenishment rate cannot keep up with air leakage or consumption, so pressure fails to rise.

  Symptom: The compressor does not stop when fully pressurized, accompanied by increased exhaust temperature, louder operating noise, and gradual reduction in displacement over time.

  Solution: Arrange for professional personnel to inspect the main unit clearance. Replace the rotor or bearing if wear is severe.

• Air leakage from the safety valve: The safety valve is an overpressure protection component. If the valve core is worn, it will leak air before reaching the overpressure threshold, preventing the air receiver pressure from stabilizing at the set value. The compressor runs continuously.

  Judgment: Listen for a “hissing” sound from the safety valve when the compressor is fully pressurized. Replace the safety valve if such a sound is heard.

III. Three-Step Troubleshooting: From Simple to Complex

1. Step 1: Check Settings and Air LeakageFirst, verify if the upper pressure limit on the control panel is reasonable. Then turn off all air-consuming equipment to measure the pressure drop, eliminating setting and air leakage issues (accounting for 80% of cases).
2. Step 2: Inspect Control ComponentsCheck the pressure sensor (compare with an external pressure gauge), unloading valve (listen for airflow sound), and solenoid valve (measure energization status). These components have low replacement costs and should be prioritized.
3. Step 3: Identify Hardware FailuresIf the first two steps do not resolve the issue, contact after-sales personnel to inspect hardware such as the main unit and safety valve. Avoid blind disassembly and repair.

IV. Prevention: Keys to Reducing “Failure to Stop When Fully Pressurized”

• Check pressure settings monthly to avoid incorrect adjustments.
• Inspect pipe joints and valves every three months, and repair air leakage points promptly.
• Replace the air filter and oil filter according to the maintenance cycle (to prevent oil dirt from sticking to the unloading valve) and extend the service life of control components.