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What Is Quality of Compressed Air, and

Who Cares?ISO 8573.1s quality classes of compressed air

Quality of compressed air is a broad term. One person may deem hiscompressed air quality as poor if he finds water at the end-use point. Anothermay tell you that her compressed air is high quality because she is able to

maintain a dew point temperature at40F or lower. As with any measurement,

in order to be consistent, we must have a reference for comparison. In theworld of compressed air, the most common reference is ISO 8573.1. ad:22097]

The quality of compressed air is determined primarily by measuring three

contaminants: solid particles as measured by their size or concentration, water

vapor content as measured by pressure dew point temperature, and oil content

as measured by concentration. The contamination level is influenced by the

type of compressor, dryer, filtration, and other related components used. Ahigher quality of air in any of these categories usually equates to more

expensive equipment.

A more subjective qualification of compressed air divides air quality into one

of four categories: power air, instrument air, process air or breathing air.

Power air is typically used for applications such as power-tool operation, sand

blasting, or pneumatic pumps.

Water in the air is more of an annoyance than a major concern, as are oil and

particles. Power air might equate to compressed air at ISO 8573.1 class 4 or 5,

as seen in figure 1.Instrument air is a cleaner quality of compressed air used in more sensitiveareas where particulates or water could cause significant quality issues in the

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process. Powder coating and paint spraying are good examples of where

contaminants affect product quality. This type of air may be dried to a higherstandard and filtered for oil or particles. Instrument air might equate to

compressed air at ISO 8573.1 class 3 or 4.

Process air is used during actual production of a product likely to be ingested

by a human or animal. For example food or drug production would require a

higher quality of air because the product would come into contact with the

compressed air at one or more points in the production line. Air may have to be

completely oil free and with very few parts of water vapor. Process air might

equate to compressed air at ISO 8573.1 class 1 or 2.

Breathing air must be suitable for a human to safely breathe. This type of airmust contain a certain amount of water vapor and be completely free of

contaminants. Compressed air for diving or hospital use is common

applications. Breathing air would fall into ISO 8573.1 class 1 for particles and

oil, but would be class 4, 5, or 6 for humidity.