Air Ingress in Lubricating Oil Purifiers: Causes, Risks, and Solutions

Air ingress in a lubricating oil purifier is a common operational issue that can reduce purification efficiency and cause oil oxidation, pump cavitation, noise, vibration, and equipment damage. Understanding the causes and applying correct countermeasures is essential for stable system operation.

Common Causes of Air Entering an Oil Purifier

1. Incomplete Venting After Startup or Maintenance

Residual air in pipelines or filter housings can enter the system if venting procedures are not properly performed.

2. Poor Sealing at Pipe Connections

Loose fittings, aging gaskets, or worn O-rings—especially on the oil inlet (negative pressure) side—allow external air to be drawn into the system.

3. Low Oil Level in the Tank

When the oil level drops below the suction port, the purifier draws in a mixture of oil and air, forming bubbles.

4. Oil Pump or Shaft Seal Leakage

Damaged pump seals or casing defects can cause air to be drawn into the system under negative pressure conditions.

5. Improper Operating Practices

Failing to close the inlet and outlet valves after shutdown may allow air to flow back into the purifier.

6. Vacuum Oil Purifier–Specific Issues

Seal failure, vacuum pump malfunction, or incorrect vacuum settings can prevent effective air separation in vacuum oil purifiers.

Hazards of Air Ingress

Reduced filtration efficiency due to air occupying filter media pores

Accelerated oil oxidation caused by oxygen exposure

Pump cavitation, noise, and vibration

Unstable hydraulic system performance, including sluggish or creeping motion

Troubleshooting and Solutions

1. Standard Operating Procedures

Fully vent the system before startup until oil flows without bubbles.

Close the inlet valve first during shutdown to prevent air backflow.

2. Seal and Pipeline Inspection

Check inlet-side joints, flanges, and valves.

Use soapy water to detect air leaks and ｒｅｐｌａｃｅ worn seals promptly.

3. Maintain Proper Oil Level

Keep the suction port fully submerged.

Recommended oil level: at least 15 cm above the suction port.

4. Inspect Pump and Vacuum System

ｒｅｐｌａｃｅ leaking oil pump shaft seals immediately.

For vacuum oil purifiers, ensure stable vacuum pressure and good tank sealing.

5. Check Filter Housing and Exhaust System

Tighten filter housing bolts evenly.

Ensure manual or automatic exhaust valves operate correctly.

6. System Optimization

Install a transparent inlet hose to locate air bubbles.

Add a float valve or level controller to stabilize oil level if needed.

Emergency Handling

If air bubbles, abnormal noise, or vibration occur:

Check and replenish the oil level as soon as possible.

Stop the purifier and close the inlet valve.

Inspect seals and pipelines, then re-bleed the system.

Restart slowly and monitor the operation.

Prevention Recommendations

Perform sealing inspections every 3–6 months.

Train operators on correct startup, shutdown, and venting procedures.

Use OEM or high-quality compatible seals and fittings.

If air ingress persists, internal issues such as oil pump wear or vacuum system failure may be present. Contact the equipment manufacturer or a professional service provider for further diagnosis.