When a safety valve blows on a rotary screw compressor, pressure has exceeded the valve's relief setting—typically 10-15% above normal operating pressure. This means the compressor isn't unloading when it should, or there's a restriction preventing air from leaving the separator tank.
A safety valve blow is a serious symptom that indicates something has failed in the pressure control system. Don't just reset and continue—find the root cause before restarting.
Rotary Screw Troubleshooting
Safety Valve Blows / Too High Pressure – Rotary Screw Air Compressor Troubleshooting
Safety valve opens or pressure exceeds setpoint—the compressor isn't unloading properly or there's a restriction in the discharge path.
Industrial systems
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Safety Notice
Never plug, cap, or tamper with a safety valve. It's your last line of defense against catastrophic overpressure. If the safety valve keeps blowing, shut down the compressor and diagnose the root cause.
What this problem usually means
Check these first
5–10 minute checks before diving deeper
- Check if the compressor is unloading when it should—watch the controller and listen for unload cycle
- Verify pressure switch/transducer settings—are cut-out pressures set correctly?
- Check solenoid valve operation—does it click when unloading?
- Inspect inlet valve—is it closing properly during unload?
- If safety valve is before separator: check separator differential pressure
- Check minimum pressure valve operation—stuck closed can cause overpressure
- Verify no downstream valve is closed that could trap pressure
- Check for fault codes on the controller display
Common root causes
Why this happens in rotary screw compressors
Compressor not unloading
The inlet valve isn't closing when pressure reaches setpoint. Check solenoid valve, control air supply, and inlet valve operation.
Pressure switch/transducer fault
Pressure switch not triggering unload, or transducer giving wrong reading to controller. Verify settings and calibration.
Clogged oil separator
If safety valve is on the separator tank, high differential pressure from a clogged separator can trigger it before the compressor reaches normal unload pressure.
Minimum pressure valve stuck
Minimum pressure valve stuck closed prevents discharge flow, causing pressure to build until the safety valve opens.
Downstream restriction
Closed isolation valve, blocked check valve, or other restriction in the discharge piping trapping pressure in the compressor.
What NOT to do
Don't simply replace the safety valve with one set to a higher pressure. If the valve is blowing, something is wrong with the control system or discharge path. Raising the relief pressure doesn't fix the problem—it just raises the risk of a catastrophic failure.
Full Rotary Screw Troubleshooting Manual
Step-by-step diagnostics, root cause logic, and practical fixes for oil-injected rotary screw compressors. Save time and reduce downtime with proven methods.
- Step-by-step diagnostics for common failures
- Root cause analysis techniques
- Practical fixes with parts notes
- Works across all major brands