Oil carryover means oil is escaping with the compressed air into the downstream system, contaminating tools and product. In a screw compressor, a small amount of oil always circulates, but visible oil in the line points to a specific fault.
Common causes
- Worn or damaged oil separator element
- Excessive oil level in the separator tank
- High discharge temperature thinning the oil
- Blocked scavenge line returning separated oil
- Wrong oil grade or degraded oil
- Operating below minimum pressure for long periods
Diagnosis
Check the separator differential pressure and inspect the scavenge line for blockage. High temperature causes more vapour and more carryover, so investigate cooling first if the machine runs hot. The oil level must be within range, because overfilling forces oil into the air stream.
Fixing it
Replace the separator element and any blocked scavenge components, correct the oil level and grade, and resolve the temperature issue. Then confirm the air quality with a test before returning the system to sensitive service.