I will definitely do that, Technician. I'll probably grind it out of a metal plate; gives me an excuse to use my Dremel. :lol:

Well after the gasket maker cured, I slathered the whole thing in grease, physically pushed the piston onto the seat, and closed it up. It still leaked! This was getting ...

Yes, several. A 1/2" in the middle, and four 1/4" holes around that.

Well I redid about half the piston. After a couple of attempts and the subsequent readjusting, I finally got the piston to seal. I pumped it up to 60 psi aaand... nothing. Just the hiss of the pilot valve for a second or so, and then BANG!!
It scared the crap out of me, I wasn't expecting any thing ...

I sanded the piston before putting on the seal, and the 1.5" PVC seat was factory cut; already as smooth and true as it could get. Thanks for highlighting the importance of this. :) I may have to do some more sanding.

The reason I think the issues are due to an undersized/deforming seal is that ...

Well I made it yesterday after a surprisingly short trip to Home Depot. It went together pretty smoothly, but today when I began to test it, some problems came up. It appears the the 1-1/4" end caps I got for the ends of the piston are slightly convex on the inside, so the neoprene check valve in ...

Thanks for the alternative, Mark.
Well, it seems everyone is really pushing Hubbs piston design even though its my first. Alright, assuming I find all the required materials, I'll build it.

I'm having trouble finding the o- ring though. If i'm correct, the 3/16" x 1-1/2" o ring required is the #322 ...

So the 1.5" PVC should stick into the 2" tee a measure between the original and the edit? Like This?

The way I understand it, the gap between the piston sealing face and the barrel sealing face when open should be 1/2 the diameter of the interior of the tee. (2.375/2=1.1875")

EDIT: Wait, I think I ...

Correction: they may carry them, but all stores in a pretty large area are out of stock. I'll check to confirm when I'm actually in store, but I think for my current purposes/ability the simple leaking piston design will suffice. Definitely in the future though. :P

Gun Freak, thanks for the pointer ...

Thanks for the suggestions so far.

I'm going to try to reduce the pilot area. If I can find a 1/4" NPT Schrader valve, I'll thread it directly into the sprinkler valve like Gun Freak did. If I cant find one, I'll just attach my current fill valve into a 3/4" tee between the back of the piston ...

Oops, should have labelled that.

Its a barrel sealing piston, so the top blue pipe is the chamber.

Thanks for catching that.

Hey everyone, allow me to introduce myself:

I'm Adam, and about a week ago I created my first pneumatic cannon using 3/4" PVC for both the chamber and the barrel, as well as a 3/4" sprinkler valve. This was to test out my construction techniques, and give me some experience with a small cannon ...