OH! - Chato - I meant to write to you before to let you know the reason why there is a drop in PSI when you depress the trigger it is because - the PSI before you depress the trigger is the system "holding pressure", but after the trigger is depressed you lose a few PSI "working pressure" because the air moving down the "hose" tubing creates friction on the sides of the walls of the Hose and this causes a drop in pressure - works the same with fluids in tubing - pipe - hoses etc.
Just wanted to give you a "physics" type explanation of why
Like I said Harbor Freight has a nice little "flow control valve" with a small PSI gauge on it for like $10 when I bought mine and I keep that connected right at the base of the air hose "line" and then a quick connect fitting that connects the airbrush to the "hose" line. That way I can change airbrushes quickly and adjust the pressure for each airbrush and viscosity of paint/clear I am spraying.
I usually airbrush paint at 20-25 PSI - 2K Clear at about 25-30 PSI and then 15-20 PSI for really thinned paint for shading like on heat staining an exhaust.
Remember each compressor-line-airbrush system is a little different so you should experiment a little on a box lid etc and see how your system works best before you spray anything on you hard work.
Don't be afraid to ask questions on this forum - most everyone is very receptive and happy to help. This is one of the best forums I've seen for learning new modeling techniques as most everyone is open to sharing their skills with others.
Hope this helps you some
John