Different forms require different removal principles
Aerosols are separated by suitable coalescing filtration. Vapours are treated, for example, by adsorption on activated carbon or dedicated catalytic technology. Catalytic purification converts suitable hydrocarbons under specified conditions; it is not simply another mechanical sieve.
What total oil means
Oil classification assesses liquid, aerosols and vapours together. Sampling, temperature and pressure must match the method. A single method or sensor may not cover every form. Cooling can change the split between vapour and droplets, so conditions in a hot compressor room may differ from those at the consumer.
What to check in practice
- Distinguish residual aerosol from total oil in the specification.
- Check which components the measurement report documents.
- Check the conditions for pretreatment and subsequent measurement.
Example scenario
In an illustrative measurement, aerosol was 0.008 mg/m³ and vapour 0.007 mg/m³; the liquid component was excluded using an appropriate method. Their sum of 0.015 mg/m³ exceeds the 0.01 mg/m³ limit for oil class 1, even though each value is individually lower.
What to watch out for
- Declaring a total oil class based on vapour alone.
- Confusing aerosol measurement with dust measurement.
- Expecting an ordinary particulate filter to capture gaseous molecules.
Why does the problem appear only on a cold product?
Some gaseous substances may condense or deposit on a surface as they cool. This is why the entire path and forms of contamination must be assessed, rather than checking only visible droplets immediately downstream of the compressor.