The classification standards for air filter elements:

According to the quality level of ISO8573.1, the level achieved by the filter to process compressed air is generally divided according to the size of solid pollutant particles, the content of liquid water, and the content of oil droplets, oil mist, and oil vapor after treatment by the filter element.

The general filter can be divided into pre-filtration, primary filtration, fine filtration and activated carbon filtration. The pre-filter generally removes particles with a diameter of 3-5μm, the primary filter generally removes particles with a diameter of 0.5-1μm and a residual oil mist content of 1 ppm, the fine filter generally removes particles with a diameter of 0.01μm and a residual oil mist content of 0.01 ppm, and the activated charcoal filter is mainly used for removing odours and oil vapours (with residual oil mist content as low as 0.003ppm).

The applications for different grades:

Pre-filters are generally used downstream of the compressor (aftercooler) in less demanding applications.
Primary filters are generally used for tools, motors, cylinders and so on.
Fine filters are generally used for painting, injection moulding, instrumentation, control valves, transmission, mixing, electronic component manufacturing, nitrogen separation, etc.
Activated carbon filters are generally used in food and drug manufacturing, breathing air, gas processing, etc.