Mmmm. Modifying a small spray gun... Interesting.

As far as pressure on PVC. I hear you. The original design was
thought to only have to use 5 or 10 PSI. It looks like it typically
needs 20 to 40 PSI. I don't think that is a problem based on the fact
that PVC pipe is used on water pipes in some cases and they are in the
50 psi area (and I THINK the walls on those types of pipe are thinner).
I would like to know what sched. 40, 4 inch pipe is good for. I think
I will try to look it up. If anyone knows, please speak up.

Believe me, the concern has crossed my mind, but I think I am on solid
ground.