Applicable Systems
QSI/QGV Series
Symptoms
The system failed to unload at the set pressure, causing the safety valve to vent excess air. The controller logs an overpressure event.
Possible Causes
- Unloader valve stuck closed or solenoid not de-energizing
- Pressure switch set point drifted higher than the rated working pressure
- Safety valve spring weakened or set too high
Troubleshooting Steps
- Step 1: Test the unloader solenoid by manually toggling load/unload from the controller
Listen for the solenoid click; measure coil resistance if silent - Step 2: Verify the working pressure setpoint in the controller matches the nameplate rating
Adjust if the setpoint has drifted above the rated 7-10 bar - Step 3: Inspect the safety valve for signs of leakage, corrosion, or tampering
Replace if the valve does not reseat cleanly after venting
How to Reset
Reset: Correct the root cause and press Alarm Reset. The safety valve resets automatically once pressure drops below its setpoint.
Common Replacement Parts
- Unloader valve repair kit: Includes solenoid, piston, and spring (OEM part number required)
- Safety valve: Set to 10.5 bar for standard compressors (Do not adjust - replace if faulty)
Frequently Asked Questions
- Q: How often should the safety valve be tested?
Manually lift the safety valve collar quarterly to verify free movement. Replace every 5 years or if it fails to reseat.
- Q: What causes unloader valve failure?
Oil contamination, worn piston seals, or solenoid burnout are the most common causes.
Source: Service Manual
Category: Compressor