The Four Elements that Affect Quality Instrument Air

The following is an excerpt from the article The ANSI/ISA Instrument Air Standard and Adsorption Type Dryers by Deepak Vetal, product marketing manager for oil-free screw and centrifugal compressors at Atlas Copco. The full version can be read online or in the November issue of Compressed Air Best Practices.

ANSI /ISA–7.0.0–1996 is the globally-recognized quality standard for instrument air as defined by the Instrument Society of America. Below, we’ll go through the Standard’s four elements of instrument air quality for use in pneumatic instruments. 

Pressure Dew Point

According to the Standard, the pressure dew point measured at the dryer outlet should be at least 18°F below the minimum temperature at which any part of the instrument air system is exposed, and the pressure dew point should not exceed 39°F at line pressure. 

Particle Size

A maximum 40-micrometer particle size in the instrument air system is acceptable for most pneumatic devices. Additional filtration should be added for pneumatic devices requiring instrument air with less than 40-micrometer particle sizes. After any maintenance or modification to the air system, the maximum particle size in the instrument air system should be verified to be less than 40 micrometers.

Lubricant Content

Oil content should be as close to zero as possible, and under no circumstances should lubricant content exceed 1 ppm w/w or v/v. Any lubricant in the compressed air system should be evaluated for compatibility with end-use pneumatic devices.

Contaminants

Instrument air should be free of contaminants and hazardous gases. If contamination exists in the compressor intake areas, the intake should be moved to a different elevation or location where it is free from contaminants. Sources of contamination may include painting, chemical cleaning and/or engine exhaust. 

Compressed air quality is an important factor when it comes to meeting instrument air requirements since any amount of particulates, vapors or aerosols can cause damage to the equipment. Operators often install filters to remove particulates and aerosols, and dryers to remove any excess moisture, but sometimes operators can take these measures too far, which would greatly surpass necessary limits and increase energy consumption. That’s why different adsorption drying technologies are available for instrument air applications. Choosing the right drying technology can save energy and reduce carbon emissions. Learn more about adsorption drying technologies when you read the full article here.

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