[JP_79Formula]

about 20 psi seems to work for me, at 30 it's like a hurricane out of the cap.

I think the 30 psi inlet is the Maximum.

But like bammbam says, pressure too low at the inlet,
or improper fluid/air mix can ruin the finish.

[Birdguy]

The 30 psi to the gun with the trigger pulled ought to put you in the ballpark with most guns, but you still have to account for the individual characteristics of the material you are using, the ambient temperature, etc. Doing a few test-sprays on masking paper will allow you to fine-tune the gun for the best atomization (determined by air pressure and material viscosity) as well as spray pattern. When you get it looking good you can move on to the metal.