Oil Measurement in Compressed Air

What is Oil Contamination?

Oil contamination in compressed air can originate from the compressor, the air inlet or ring main leaks. This oil can be in the form of liquid, aerosol, vapour or a combination of them. The oil removal process takes place in the main filtration system after the compressor but depending on the serviceability of the filters and the level of filtration, some oil may remain in the airstream.

Once in the air stream, tiny droplets of oil (aerosols) can accumulate into liquid form at pipe walls and junctions and become an additional source for oil vapour throughout the distribution system. Point of use filters or filter regulators can help to prevent liquid & aerosols getting into areas where they can cause problems but excluding aerosols and vapour requires much more effective filtration to protect sensitive equipment or processes. Determining the effectiveness of the filtration employed or identifying the level of contamination can only be done through measurement.

Why do I need Oil Vapour Measurement?

Oil vapour is the most difficult form of oil to eradicate from the compressed air system and measuring it can give an excellent indication of system health and overall oil contamination levels. As a guide, wherever there is liquid oil or aerosols, there will also be oil vapour present but vapour can still be present when the liquid and aerosol states have been completely filtered out.

ISO 8573-1 defines a range of purity classes for compressed air including oil. ISO 8573-2 is the section that defines measurement methods for oil liquid and aerosols and ISO 8573-5 for oil vapour. For ISO 8573 compliance, all 3 forms (liquid, aerosol and vapour) must be measured to determine the total oil concentration.

Measuring the oil vapour concentration can be achieved through laboratory analysis of samples that have been taken at suitable test points. The process of using gas chromatography to analyse the sample while accurate is also expensive, time consuming and doesn’t allow instant results for the test engineer.

Currently, ISO 8573-5 does not include other more modern methods for oil vapour measurement use such as PID sensors which can measure according to the limits required by the standard, and provide a quick result for the user on-site.

Monitoring the oil vapour concentration is a key indicator of system health that can be used to guide maintenance tasks as well as contribute to plant compliance with the purity classes set in ISO 8573-1.

Oil Vapour Sensors