The "unable to unload" failure of screw air compressors is a high-frequency operational fault in industrial sites, which means that after the unit pressure reaches the set unloading threshold, it cannot switch from the loaded state to the no-load mode and continues to operate at high pressure. This failure not only causes energy waste and accelerates the aging of equipment components but also may trigger high-pressure protection shutdown, seriously affecting the stable air supply of the compressed air system. This article combines front-line operation and maintenance experience to disassemble the causes of the failure and provide practical troubleshooting steps for technical personnel.
Intake Valve Jamming or Drive Failure
From the root cause of the failure, intake valve jamming or drive failure is the most important reason for being unable to unload. The intake valve is the core component that controls the air intake of the air compressor. After the unloading command is issued, the valve core needs to be completely closed to cut off the intake channel. If the piston and spring inside the intake valve are affected by oil dirt and carbon deposits for a long time, they will appear stuck, causing the valve core to fail to return to its position; the aging and air leakage of the cylinder seals driving the intake valve, the burning of the solenoid valve coil or the blockage of the valve core will also cause insufficient driving force, and the valve core cannot be effectively closed. During troubleshooting, you can first cut off the power supply, manually toggle the valve core to feel if there is any jamming; if the action is not smooth, you need to disassemble the intake valve, use a special cleaning agent to remove oil and carbon deposits, check the spring elasticity, and replace aging seals and faulty solenoid valves.
Control System Command Abnormality
Abnormal control system commands will directly lead to the failure of unloading logic. The unloading command of the air compressor is issued by the PLC according to the pressure sensor signal. If there is a problem with parameter setting or signal transmission, the unloading program cannot be executed. First, it is necessary to check the unloading pressure setting value on the control panel. If the setting value is higher than the rated pressure of the equipment, the unit will continue to load until protection is triggered; then start the machine until the pressure reaches the threshold, use a multimeter to detect the voltage at the PLC unloading command output point, and check whether the corresponding relay is pulled in. Relay failures need to be replaced in time; in addition, the communication line between the control panel and the PLC is loose and poorly contacted, which will also cause signal interruption, and the line connector needs to be tightened and the communication stability tested.
Pressure Sensor Failure
Pressure sensor failure is a key cause that is easily overlooked. The pressure sensor is responsible for collecting pressure data from the exhaust pipeline and feeding it back to the PLC. If the sensor probe is covered with oil, the sensitivity decreases, or the sensor itself is damaged, it will feed back wrong low pressure signals. Even if the actual pressure of the unit has reached the unloading threshold, the PLC still judges that the pressure is not up to standard and continues to maintain the loading state. During troubleshooting, you can first clean the sensor probe, then use a standard pressure gauge to compare the detection values. If the deviation exceeds ±0.02MPa, the sensor needs to be calibrated or replaced in time to ensure accurate pressure signals.
Pipeline and Auxiliary Component Blockage
Pipeline and auxiliary component blockage will indirectly cause the failure of being unable to unload. If the exhaust pipeline is bent and blocked, or the air storage tank outlet valve is not fully opened, it will lead to poor exhaust and pressure accumulation; the blockage of the oil-gas separator will cause excessive internal pressure difference of the unit, increase exhaust resistance, and abnormal pressure rise. During troubleshooting, it is necessary to check whether the pipeline is unobstructed, clean internal impurities and condensate, and confirm that the valve is fully open; detect the pressure difference of the oil-gas separator, and if the pressure difference exceeds 0.08MPa, replace the filter element in time to reduce exhaust resistance.
Troubleshooting Steps
Troubleshooting steps should follow the principle of easy first, then difficult:
Check the unloading pressure setting value and adjust it to the rated range;
Clean and detect the pressure sensor, calibrate or replace faulty parts;
Check the PLC control system signal transmission and relay status;
Manually test the intake valve and driving components, clean or replace damaged parts;
Check the pipeline and oil-gas separator to ensure the exhaust channel is smooth;
Start the machine for trial operation and observe whether it unloads normally after the pressure reaches the threshold.
In daily operation and maintenance, regularly cleaning the air intake filter, replacing special lubricating oil, and checking the status of pneumatic components can effectively reduce the incidence of unable to unload failures. Mastering scientific troubleshooting methods can help enterprises quickly solve problems, reduce downtime losses, and ensure production continuity.