Oil Carryover in Compressors: Causes, Problems & How to Reduce It
Oil carryover occurs when excessive compressor oil passes into the compressed air system.
While small traces of oil are normal in oil-injected compressors, excessive carryover can damage equipment, contaminate air, and significantly increase operating costs.
What Is Oil Carryover?
Oil carryover refers to oil leaving the compressor with the compressed air rather than being separated and returned to the lubrication system.
This oil can travel through pipework, receivers, filters, dryers, and point-of-use equipment.
Why Oil Carryover Is a Problem
- Contaminates compressed air
- Damages downstream filters and dryers
- Increases oil consumption
- Creates mess in pipework and receivers
- Causes product contamination in sensitive applications
Unchecked oil carryover often leads to higher maintenance costs and reduced air quality.
Common Causes of Oil Carryover
Worn or blocked air oil separator
A separator that has reached the end of its service life cannot effectively remove oil from compressed air.
Incorrect compressor oil
Oil not designed for compressor use may foam or vaporise more easily.
High operating temperatures
Excessive heat reduces oil viscosity and increases vapour carryover.
Overfilled oil system
Too much oil increases the amount of oil entering the separation process.
How Oil Carryover Affects System Efficiency
Oil contamination forces air treatment equipment to work harder.
- Higher pressure drop across filters
- Shortened filter and dryer life
- Increased energy consumption
- More frequent maintenance intervals
Reducing carryover improves efficiency and lowers running costs.
Signs You May Have Oil Carryover
- Oil residue in pipework or air receivers
- Rapid filter saturation
- Increased oil top-up frequency
- Visible oil mist at point of use
- Decline in air quality
These signs indicate separation efficiency may be compromised.
Reducing Oil Carryover in Compressed Air Systems
Oil carryover can often be reduced by addressing key components.
- Use the correct compressor oil specification
- Replace air oil separators at recommended intervals
- Maintain clean cooling surfaces
- Avoid overfilling oil systems
- Ensure downstream filtration is correctly rated
Attention to these areas helps maintain clean, reliable compressed air.
Final Thoughts
Oil carryover is a clear indicator that a compressed air system is not operating as efficiently as it should.
Understanding the causes and addressing them early helps protect downstream equipment, improve air quality, and reduce long-term operating costs.