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The best way to remove moisture from compressed air is to cool it after it is compressed. This condenses the water out of the hot compressed air as it is cooled. If you cool it while it's in a reasonably large reservoir, the moisture will fall to the bottom, where it can be drained off. You want the outlet from this reservoir to be located somewhere at mid height, so you don't get warm humid air out. A refrigerated dryer located in the output line between the compressor and the tank will work best, so the moisture in the air condenses out of the air at that point, and will fall directly to the bottom of the reservoir/storage tank, where it can be drained off frequently. The second best way is to refrigerate the air as it leaves the storage tank. This refrigeration point will need a reservoir to collect the condensed water and with a drain to remove this water frequently. Cooling the air to about 35-40 deg F works best, as it is above freezing, so no ice will build up and plug the system. After the air has been cooled and the condensed moisture removed, you can let it warm back up to room temperature and it will be very dry and work well in your tooling, blow-off nozzles, and paint spraying equipment. On the output of my air system I have what they call a toilet paper filter. It is designed to hold a roll of toilet paper as the filter medium. It catches the finest of oil droplets and moisture so my tools and paint sprayers never have air supply problems. This filter sells for about $40 at auto paint stores or online.

Charley
 

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Just getting the air that's entering your tank from the compressor down to ambient temperature makes a huge difference. I modified a 2 hp 20 gallon compressor by plumbing the outlet of the compressor into a re-purposed large transmission oil cooler that was positioned where the fan blades in the compressor pulley could pull air through it before passing this cooling air past the compressor fins. The outlet of the transmission cooler was then connected to the inlet of the tank where the outlet of the compressor had been connected. It cooled the compressor air enough that the compressed air temperature had dropped to ambient and most of the moisture had turned into water drops and fell into the bottom of the compressor tank. I had to drain the tank more often, but never had water in my tools or blow guns. When spray painting, I have always used one of the toilet paper filters in the line to the spray gun to guarantee that I never got moisture or oil drops in my spray guns. After considerable use there was always a little bit of oil and moisture in it, but I could use the same filter medium for several entire paint and stain jobs without any problems.

I now have an 80 gallon 18 cfm 5 hp compressor and have modified it in a similar manor. My results have been the same. For this compressor I piped the condensate drain into a 2' length of 4" pipe using pipe reducers from 3/4 - 4" and then the same to reduce the other end back down to 3/4" and added a ball valve before piping this out of my compressor shed. Any condensate collected builds up in this large pipe section and not inside the air tank. I just make it a point to open the ball valve after significant use, so the condensate is blown out of it. I have a regulator and filter in the line feeding my shop, but it never collects anything, and I still use the toilet paper filter to be absolutely certain of clean dry air when spray painting and staining. I also came into a refrigerated dryer 2 years ago, and now add that in the line too whenever spray painting, staining, or sand blasting.

Charley
 
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