Compressed Air Systems Equipment Reliability & Maintenance Center

Select the Correct Filter

Jane Alexander | September 19, 2017

Compressed air systems can’t help it: They will contain contaminants that can lead to issues and increased costs through contamination of product, damage to air-operated devices, and air-line clogging and restriction.

According to a recent blog post by Brian Bergmann of Exair Corp. (, Cincinnati), that’s why proper filtration is crucial. But all filters aren’t created equal.

The different types of contaminants associated with compressed air systems, including solid particles, liquid water, and vapors of water and oil, call for different types of filters. Understanding how each type works and the advantages it offers is essential for achieving maximum contaminant removal.

Bergmann provided a breakdown to help compressed air users select the correct types of filters for their applications:

randmParticulate filters

In these designs, compressed air flows from the outside to the inside of the filter element. The compressed air first passes through a baffle arrangement that causes centrifugal separation of the largest particles and liquid drops, but not liquid vapors. The air then passes through the filter element. The filter element is usually a sintered material such as bronze. Particulate filters are inexpensive and easy to replace. Filter elements generally range from 40-micron down to 5-micron.

Coalescing filters

This type of filter operates differently than the particulate type. The compressed air flows from the inside to the outside through a coalescing media. Very fine water and oil aerosols come into contact with fibers in the filter media and, as they collect, coalesce (combine) to form larger droplets toward the outside of the filter element. When the droplets reach a certain size, they fall off and collect at the bottom of the filter housing. The filter element is typically made up of some type of glass fiber. As is the case with particulate-filter elements, coalescing-filter elements are relatively inexpensive and easy to replace. Filtration down to 0.01 micron at 99.999% efficiency is possible.

Adsorption filters

This type of filtration typically uses activated carbon to remove the finest oil vapors, hydrocarbon residues, and odors from compressed air systems. The mechanism of filtration involves molecules of the gas or liquid adhering to the surface of the activated carbon. This is usually the final stage of filtration, and only required for certain applications where the product would be affected, such as in blow molding or food processing. MT

Brian Bergmann is an application engineer with Cincinnati-based Exair Corp. For more information on various compressed air topics and solutions, visit



Jane Alexander

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