This is my latest idea...
![Image](http://img207.imageshack.us/img207/3092/apd1.png)
The piston body and the check valve would be made out of UHMWPE. The OD of the piston is 20mm, OD of the check valve sealing face is 6mm. The diameter of the guide hole on the back and 4 vent holes in the front is 3mm. A perfect seal between the piston and its housing is assured by 2 O rings at the back. I didnt draw the screw holding the rubber gasket in place so just imagine its there
![Very Happy :D](./images/smilies/icon_e_biggrin.png)
I plan on using it at or beyond 40 bar. Can UHMWPE even take that much?
My idea is... pumping from the pilot area fills the pilot and opens the check valve, bleeding air into the chamber. I'm guessing that because of the check valve there will be a tendency for the air pressure to be slightly higher in the pilot area then in the chamber area.
I know this will make for a perfect sealing piston and if I get a leak in the pilot area, pressure will not equalize and the gun will fire.
What do you think about this design?