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Compressed Air Filters Testing and Ratings

What is a DOP test?
The DOP Test is the older testing method for compressed air filters. When possible use the new ISO8573 ratings to compare filters.

Here is how a DOP test is conducted. DOP is condensed into a mist with a high concentration of particles of 0.3 micron diameter. Filtration efficiency is determined by measuring and comparing the concentration of DOP in the inlet and outlet air streams.

This test of filtration media often cited in ratings of compressed air filters. The benefit of using this test is its consistency in particle size generated (0.3 micron), and its common use by media manufacturers. The drawbacks of this test are that it is conducted at atmospheric pressure, it does not take the media to saturation, and it does not simulate the mixed contamination of oil and water that compressed air filters commonly see in service.

ISO8573

ISO8573 sets standards for compressed air cleanliness. Particulate, oil vapor, and moisture removal are addressed by ISO8573. ISO has set six standard levels of cleanliness. There are three factors at each level...

Solid Particles - Maximum remaining dirt particle size in microns.
Dewpoint - Maximum allowable dewpoint.
Oil/Oil Vapor - Maximum remaining oil content.

ISO Quality Class	Solid Particles maximum number of particles per m³			Dewpoint °C (ppm. vol.) at 7 bar g	Oil/Oil Vapor mg/m³
	0.1-0.5 micron	0.5&-1.0 micron	1.0-5.0 micron
1	100	1	0	-70 (0.3)	0.01
2	100,000	1,000	10	-40 (16)	0.1
3		10,000	500	-20 (128)	1
4			1,000	+3 (940)	5
5			20,000	+7 (1240)
6				+10 (1500)

Comparing Performance Claims

These standards do not simulate the true conditions seen by a compressed air filter; but, both the DOP and the ISO8573 standards offer useful information.

The older DOP efficiency claims and the new ISO8573 standards allow us to compare filters between manufacturers.

A word of caution when using the DOP claims. The DOP test uses a 0.3 micron test contaminant to challenge the filter. This contaminant does not represent actual operating conditions in a compressed air system. ISO8573 does a better job of reflecting real World conditions. So when possible use the new standards to compare compressed air filters.

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