Hey guys,
I recently upgraded to a 2 stage air compressor rated at 17CFM@ 175psi, I was tired of worrying about not having enough air for my tools. Anyways I didn't want to run 150psi + through my lines, and my current regulators have a max PSI rating of 145psi so I bought a 3/4 regulator/filter good for 120CFM and 300PSI and added it right to the tank.

I debated getting a filter as well over just a regulator since the regulator is right on the tank with hot air and it wouldn't be effective.

I received a huge surprise. After just one cycle of empty to full back to empty the first regulator right on the tank captured a huge amount of water. The cup on the filter holds a bunch of water, but I was able to drain out about 3 tablespoons of water.

Can anyone explain to me why a regulator right on the tank filtering hot air is capturing so much much water? Is it because of the large diameter of the filter's cup that the air expands rapidly and cools down enough to condense? The tank was empty and drained before filling so it couldn't be water inside the tank.

Because it's a cyclone style filter most likely and the high speed centripetal force of the air is "flinging" the water to the outside of the cup, allowing it to be collected. Plus on a large compressor like that chances are the temp is dropping enough to allow that to happen efficiently enough.

To be nicer to that separator you could run some pipe out of the tank (say 15 to 20 feet), then put the separator and regulator in. Also make sure the separator/filter is FIRST then the regulator, otherwise your regulator is seeing dirty wet air first and it will become damaged pretty quickly that way.

Oh the regulator /filter is one piece, and it feeds about 40 feet of copper pipe before going into another filter with a desiccant filter. I am still able to maintain 90PSI or higher at the end of all the pipe and filters.