We recommend a 5-micron pre-filter for a refrigerated dryer. This removes the larger particles and droplets and helps keep the internal heat exchanger on the dryer cleaner. A high efficiency coalescing filter rated at .01 microns can be placed downstream of the refrigerated dryer for additional cleaning.
On a desiccant air dryer we recommend the 5 micron pre-filter followed immediately by the coalescing .01 micron filter. This helps prevent any oil contamination of the desiccant material. A 1 micron particulate filter should be placed downstream of the desiccant dryer to capture any desiccant dust from migrating downstream.
A vapor filter which removes oil vapor, odors and taste can be used as a final filter in either case.
In all filter selections, the rated pressure drop should be as low as possible (1-3 PSI) to ensure longer element life.