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I cobbed up a compressed air dryer for painting using spare parts. It's cheap and it works great: Began with an evaporator coil out of an old dehumidifier (a pancake-shaped affair consisting of about 20' of coiled 3/8 ID copper tubing). Laid the coil flat in a 5 gallon plastic pail with one tube end extending above the top of the bucket, and the other end penetrating the bottom of the bucket via a bulkhead fitting. Supply air from the compressor goes into the upper coil connection and exits at the bottom via the bulkhead fitting. From there the air goes to an aux reservoir tank, a coalescing filter, a primary regulator and finally to the secondary filter/regulator and paint gun. The coalescing filter is optional - I used it simply because I had it lying around. It traps traces of water mist (also oil) that might otherwise escape the aux tank. To use the dryer, I simply dump a bag of cubed ice into the pail. Then add enough cold water to the pail to submerge the coil and hook the compressor supply to the coil inlet. The incoming air gets chilled as it passes thru the coil - most of the moisture condenses out. The condensation drains out of the coil and accumulates in the aux tank. The key is to get the air as cold as possible at the highest pressure possible. That's why the reducing regulators are located AFTER the cold coil. Also the aux tank it gives the dried but now cold air a chance to warm back up before it gets to the paint gun. Mine is a 20 gallon receiver tank salvaged from a burned out oil-free compressor. However an old 20# propane tank, length of large diameter pipe or even another coil of tubing with a suitable tee fitting and drain valve will do the job. With outside temperature in the 80's the ice will be good for a couple hours of spraying before it needs to be replenished. (In really hot weather I'll toss a couple "Silver Bullets" - or other brew - into the icewater in bucket for a treat when I'm finished!) It's amazing the amount of condensation that collects in the aux tank - on a humid day it'll accumulate a gallon or more of water in a couple hours of spraying.
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