Here is the valve:


The valve is a basic self sealing valve. Same type found in Nerf air guns. The air enters behind the seal and applies pressure to the seal making it tighter. The higher the presure the tighter the seal. When the shaft is depresed the seal is broken and the air rushes around the seal and to the outlet.
I built the 3 pieces this morning in about 3 hours and assembled it this afternoon.
I did some pressure testing to see how it performed. Initially I jsut put 20psi into to check functionality. The valve works very well and the activation force is much less than I anticipated. It's very on-off which is good. I then ran it up to almost 100 psi to make sure it woud not fail (ie explode). It didn't. Finally I put 60 psi behind it and left it for an hour. After the hour the pressure didn`t drop at all.
It is a bit large and may be difficult to incorporate into a pistol grip nicely. I may trim it down some and build another.
I decided for this homemade to tackle the hard stuff first instead of the other way around.