Regulators and moisture traps

I have installed many regulators, and I have always put the trap before the regulator.  Keeps the water out of the regulator. 

Either way will work, but as said the regulator is better upstream of the trap.

Congratulations on your first post!

One rationale is that the water trap should be as far from the compressor as possible to let the air cool down as much as possible before the trap, to let water condense.  On the other hand, makes the airbrush heavy if you put it on that end of hose :-)    Anyway, that rationale says put trap last.  I have even seen some folks add a length of pipe between rest of stuff on compressor and the trap.

I have a regulator and trap on the compressor, another regulator and trap on my spray booth, and a third inline trap on my air hose to the AB. That last trap is about 3' away from the AB. In all cases the traps are after any pressure regulation. I've never had water issues.