Applicable Systems
QSI/QGV Series
Symptoms
The minimum pressure valve is not opening at the correct setpoint of 4 bar (58 psi), causing oil to backflow into the air filter housing during startup.
Possible Causes
- Minimum pressure valve spring broken or weakened
- Valve seat damaged by oil contamination or debris
- Valve piston O-ring degraded and leaking
Troubleshooting Steps
- Step 1: Remove the minimum pressure valve and inspect the internals for contamination
Clean the valve body and inspect the spring and seat for damage - Step 2: Check the O-ring for cracks, hardening, or swelling
Replace the O-ring kit if any degradation is found - Step 3: Test the valve opening pressure using a regulated air supply and gauge
The valve should open at 4 bar +/-0.2 bar; replace if outside this range
How to Reset
Reset: Reinstall the repaired or replaced valve. The alarm clears once the system builds pressure normally on the next startup.
Common Replacement Parts
- Minimum pressure valve kit: Spring, piston, O-ring, and seat (Match to compressor model)
- O-ring kit: NBR material, 70 Shore A (Use fluorocarbon for high-temperature applications)
Frequently Asked Questions
- Q: What does the minimum pressure valve do?
It maintains a minimum oil circulation pressure inside the compressor casing and acts as a non-return valve.
- Q: Can I bypass the minimum pressure valve?
No. Without it, the compressor will not build oil pressure and the air end will seize from lack of lubrication.
Source: Service Manual
Category: Compressor