Non-Cycling Refrigerated Air Dryers, 5 to 50 SCFM

Only when the air has cooled before it arrives. A piston unit with no aftercooler can deliver 180°F air through a short run, and at that temperature a dryer in this band is down to about half its rating while seeing several times the moisture. The tell is a warm outlet pipe and water at the first drop. Run enough pipe to cool the air, fit an aftercooler and separator, or choose the high inlet temperature models.

For a shop with one booth and nothing else that needs dry air, a small dryer at the booth works and costs less. Everywhere else in the shop, though, water still condenses in the lines, rusts the pipe and reaches the tools. A dryer at the compressor protects the whole system and the booth with it. Where the piping runs through a cold area, dry at the compressor; a point-of-use unit can not help water that has already formed upstream.

On the wall where it can. A bracket keeps the cabinet out of floor dust, oil and wash water, keeps the condenser face clear so it can breathe, and lets the drain line fall naturally to the floor drain or oil-water separator. A dryer pushed against a wall at floor level ends up drawing hot, dirty air and losing capacity. Wall-mount brackets for these cabinets are catalog items, so there is no reason to fabricate one.

Because summer is when it is overloaded. Ratings assume 100°F inlet air and a 100°F room, and a hot shop or a compressor working harder pushes both above that, so a dryer that copes in spring runs past its rating in July. Check the inlet pipe temperature at the end of a busy afternoon and make sure the receiver drain has not stuck shut. If both look normal, the dryer is simply one size too small.

Yes, the 7 to 15 SCFM units sit comfortably behind most dental and lab compressors and run from an ordinary 115 V outlet. Oil-free compressors still make water, so the dryer is just as necessary there. Put a particulate filter ahead of it and an afterfilter behind it suited to the use, and route the drain to a proper outlet rather than a bucket, which overflows the first humid week someone forgets to empty it.

Watch it through a loaded cycle. The 7 to 15 SCFM units use a pneumatic float drain and the 25 to 50 SCFM units an electronic drain, and on either one you should see a short discharge of water when condensate builds up. A drain that never discharges is stuck or plugged, the separator floods, and water carries straight through the dryer. Clean the strainer at the drain inlet when the prefilter element is changed.