first *reliable* pneumatic

[cfb_rolley]

All of my attempts at building a piston valve cannon to date have been useless, or failed after a couple of shots. So I thought, "what can I build that's still fun, but not even I can screw up?". A ball valve cannon!
PN12 PVC40 chamber, PN12 PVC25 barrel, a simple ball valve as the main valve, and a schrader valve as the fill valve.




This thing is actually pretty fun, I've only taken it to 70psi so far (lack of a decent pump) and it definitely puts a spud well over the treeline near my house.[/img]

[jackssmirkingrevenge]

Simple and fun as previously suggested though, a burst disk will give you similar simplicity but much better perfomance.

[Labtecpower]

You should really spring-load it, more than doubles the performance

[cfb_rolley]

I think I'll go burst disc for the next one, I already had the ball valve though and union couplings at my local bunnings are damn expensive at the moment.

[mattyzip77]

Put some effort into a sprinkler valve cannon, or try the piston valve again. It took me a few tries, and even someone making me one till I figured it out!! They are alot more fun, and powerful. And or just get a qev, you would be surprised at the balls just a 1 inch qev has!! Kudos!!

[sagthegreat]

for the piston valve, I buit one as my first gun, try using threaded pipes, so you can unscrew the gun to fix piston problems.

for you ball valve gun, do what jsr said, or use a detent

-have fun

[cfb_rolley]

hmmm a detent might not be too bad of an idea to just mod this one with. or I guess I could add the burst disc after the ball valve for more instant firing rather than waiting for the chamber to fill via blowgun, right? as long as the disc holds for long enough for the ball valve to be almost fully open by the time it bursts, that should give me plenty of power, and when I couldn't be bothered fiddling with burst discs I could still use it with just the ball valve...

[sagthegreat]

I would suggest cutting the barrel near the valve, getting 2 threaded fittings and squeezing a oring in the middle for an adjustable detent

[cfb_rolley]

Upgrades! Yay! I've added two 90 degree bends to shorten it a bit, and it makes it at least a little easier to aim. and also a union coupling, for a burst disc. I was going to go with the detent idea but none of the threaded fittings for PVC 25 are the same I.D as the piping itself. I haven't tested it with anything in the barrel since doing the change of setup, but dry firing it now makes a much sharper "crack" which I assume means less opening time and therefore a bit more power.

[jackssmirkingrevenge]

Good on you for the best power, leave the ball valve open and fill, and make sure whatever disk you're using bursts close to your maximum pressure.

[cfb_rolley]

That's what I was thinking, instant shots with the ball valve, powerful shots by filling until the burst disc breaks. so far 4 layers of al. foil works well at 80psi. I might see if I can find a portable 12v compressor that will go to 175psi on the weekend. at the moment I only have a hand pump that gets extremely difficult at about 70psi. I can't wait to see this thing at full power!