Views: 8937 Author: Site Editor Publish Time: 2025-04-15 Origin: Site
1. Introduction: Oil Carryover – The Hidden Cost
Oil carryover (also called "oil bleeding") is one of the most common yet often overlooked faults in screw air compressors. Many users only pay attention when oil consumption rises sharply or downstream equipment becomes contaminated. In reality, oil in the discharge not only increases operating costs but may also signal other serious issues. To solve this problem completely, we must address the root causes instead of blindly disassembling the machine.
2. Six Direct Causes of Oil Carryover
Cause | Mechanism | Typical Symptoms |
|---|---|---|
1. Damaged Oil Separator Element | Oil-air mixture bypasses separation and goes directly to discharge | High oil carryover; obvious increase in return line sight glass flow |
2. Return Line Failure | Separated oil cannot be sucked back to the compressor | Oil accumulates at separator bottom; no or very little return flow |
3. System Pressure Too Low | Reduced centrifugal force in separator lowers separation efficiency | Oil carryover under low load; pressure below rated value |
4. Minimum Pressure Valve Failure | Unable to maintain minimum system pressure; return flow cannot be established | Pressure drops when discharge valve fully opens; continuous oil carryover |
5. Overfilled Cooling Oil | Oil level too high; gas directly entrains oil mist | Oil level above middle of sight glass; heavy oil carryover |
6. Poor Oil Quality | Aged or substandard oil affects separation and cooling | Oil darkens, smells bad, poor separation performance |
3. Three-Step Fault Diagnosis
Tissue Paper Test – After reaching rated pressure, open the discharge valve slightly and hold a dry tissue in the airflow. If the tissue quickly changes color and shows oil droplets, carryover exceeds normal limits.
Observe Return Line Sight Glass –
Obvious increase in return flow → usually damaged separator element or overfilled oil
No return flow → usually blocked or broken return line
Pressure Correlation – If pressure drops below the minimum pressure valve setting when the discharge valve is fully opened, and oil carryover continues, the minimum pressure valve has failed.
4. Corrective Actions & Installation Precautions
1. Damaged Oil Separator Element
Action: Replace immediately with a qualified element
Precautions: Check the new element for deformation before installation; clean the mating surfaces of the housing and cover; inspect the top sealing gasket for conductive particles (to prevent static discharge)
2. Return Line Failure
Action: Clean and unblock, or reweld if broken
Precautions: Do not reduce inner diameter during welding; maintain a 3–4 mm gap between the return line tip and the bottom center recess of the separator element
3. System Pressure Too Low
Action: Reduce system load to ensure operating pressure reaches the rated value
Precaution: Operators must know the minimum pressure requirement of the equipment
4. Minimum Pressure Valve Failure
Action: Replace the valve (cannot be repaired)
Precaution: Confirm model and pressure setting match before replacement
5. Overfilled Cooling Oil
Action: Drain excess oil to normal level
Precautions: Keep oil level below the middle of the sight glass; the unit must be level when checking oil level; check before startup or 30 minutes after shutdown
6. Poor Oil Quality
Action: Replace with qualified, recommended oil; record the change date
Precautions: Different compressors require different oil specifications; never exceed oil service life
5. Conclusion: From Reactive Repair to Proactive Maintenance
Although screw compressors are known for high reliability, they are not maintenance-free. Most oil carryover faults can be prevented through regular inspections, correct operation, and timely maintenance. Users must adopt the mindset of "three parts operation, seven parts maintenance." By regularly checking the separator element, return line, minimum pressure valve, and oil level, and by using qualified oil, faults can be eliminated in their early stages, ensuring efficient, low-cost, and long-term stable compressor operation.
