We just have to make it work with tennis balls, that wont be what we shoot for fun. In fact some 2 kilo shots are curing tonight. I expect that the additional time the 2 kilo cans are going to see in the barrel is going to let that second valve do some work. 3 of 4 cardinal neighbors are FBI (no jok...

Yes that is a cleanout cap, on the back of the barrel. The 4" fittings are PW, no worries. We were shooting tennis balls straight up today on one valve again (one of the gaskets on a piston came off). We were getting about 9 to 12 second hang times (about 200 ft/s muzzle velocity) discounting air re...

Shes a working!! Everything is going great now that the valves are working. Here was a pic of our testing setup for one valve: http://farm4.static.flickr.com/3110/2891693393_acb9621604.jpg We put together the second valve, pumped her up to 30psi and shoved a tennis ball down the barrel: http://farm4...

If I got you right, its the blowgun and not the diaphragm valve that leaks. If that is the case, I would just go guy a new blowgun, as it appears to be your problem. If you don't want to, try injecting it with some silicone grease and see if that helps. (Don't use regular grease, it will melt any ru...

Hey all! Thanks for the suggestions, we're using the red gasket stuff on top of foam rubber. Looks like it will work nicely. Looking for some approval on the new valves: http://farm4.static.flickr.com/3006/2888856256_241ac65109.jpg Everything says PW on it. Action shots this weekend hopefully (waiti...

Ok, one more question: I am looking for a relatively soft material that will act as a good seal (cushy stuff). What have you guys used? We've been having trouble getting the valves to seal consistently, and seeing as we just annihilated one of the pistons, we're going to start from scratch again (wi...

Ok. I'm calling in backup on this one. From OED (Oxford English Dictionary): Definition 1 of "coaxial": Having a common axis. In the valves on our cannons, in the Ts, there is a pipe, smaller than the t that extends though the T and then meets and seals against a piston. The exhaust (this smaller pi...

There is a very easy way to test where the piston should fall (even though it isn't that easy). If we allow the same pressure before and behind the piston, and then start to move it back mechanically, the point where the piston stops resisting us is the critical point. Essentially what you want is t...

Hey,

I recognize that stuff like the back of my hand. 10 bucks says you are using a mousepad!

Mousepads are made of foam rubber, and very cheap stuff at that. Don't use it.

Head over to a hardware store and ask for gasket material. Most places sell it by the foot(inch).

OBVIOUSLY YOU HAVE A LIMITED KNOWLEDGE ON THIS SUBJECT. TAKE OUR ADVICE YOU ARROGANT FOOL. WE ARE TELLING YOU THESE THINGS SO WE DON'T HAVE TO SEE YOU IN THE NEWS REGARDING A CANNON EXPLOSION IN WHICH YOU LOST YOUR EYES AND HAVE PVC EMBEDDED IN YOUR FLESH. Thanks buddy. I know that the DWV valves a...

Ok, how about some good news? We had a little team meeting, and since the 2" valves would have to be replaced anyway (they were put together in a half hour, for $7 a piece, they were trial runs) we are going to loose the DWV. So now here comes the question, if I walk into Lowes/Home Depot what the h...

Haven't taken it above 20psi on one valve, and we were putting holes in a trash can. I can't get the valves to seal under 15psi, so I intend an operation between 20psi and 30psi. The pistons, large slides, and receivers are made of the stuff they use to fix planes with (forming epoxy). It won't fail...

@ MrCrowley: Show me a "safe" cannon... I am aware of that, that is the point of not using the ball valve design. The piston chambers and receivers are made of forming putty (stuff is stronger than steel in volume:strength). The rest of the stuff is pretty much expected to explode, and that is why m...

Although this is very much after the fact... I wouldn't worry so much about warping your PVC so much as coming back to a gun that is no longer glued together. Active chemical cements, like what PVC cement is made from, rapidly decompose in heat. Don't let your guns get above 100deg.F too much unless...

If I get you right: Your piston seals against a 1.5" barrel (or whatever goes out as exhaust), and you are wondering why air gets around the piston to the space around the 1.5" pipe? So the barrel seals fine (no air is coming out the barrel) but around it? If that is right...well, that's how a barre...