Air Line Filters are usually two-stage designs that can remove liquid aerosols, rust, scale, dirt and other solid particles one micron and larger. The first stage is coarse media that collects larger particles, and the second stage separates dirt, water, and oil aerosols.
A typical 100 psig air system has 50% of the entrained oil smaller than one micron in size. This will pass through a mechanical separator and cannot be completely removed by an air line filter. Good coalescing oil removal filters can remove 99.999% of these oil droplets by passing them through a maze of submicroscopic glass fibers that coalesce and continuously remove the oil.
