SpudFiles

I've built a few combustion cannons, but after reading around here about how easy it is to mod some common solenoid-activated sprinkler valves, I decided to buy one. I'll head to Lowes in about 2 hours, but one thing I couldn't find from searching was large of a barrel I can use with a 1" valve. Obviously performance is going to be hurt using a 2" barrel, when the reservoir is 4", and it's all bottlenecked down to 1". But how much will it hurt performance? Is it not worth it to even try 2"? Secondly, about what ratio with what kind of barrel should I try with a pneumatic? Sorry for the noobish questions, but I've read and read and haven't really seen a definitive answer. I've seen 4" reservoirs with 1" piping going to a 1" sprinkler, going to a 2.5" barrel, but really, how well does that work? Would it be better than a 2" combustion with a 1.8 ratio?

Thanks,
JohnR

its fine your cannon will work and a have decent power and all just look at the LPs joel sells on spudtech http://www.spudtech.com/detail.asp?id=41 and I think they only use 3" chambers, but this is more like a toy than a beast , but if you want a than you will want 2 valves, and maybe another chamber

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The answear to this question is dependent appon the mass of your projectile; heavier projectiles do pretty well in launchers with small valves and large barrels.

That given, it depends on enough variables that you'd be best to just model the situation using the GGDT (check the spudwiki).

You can estimate the preformance of metered-propane combustions wich have a chamber fan with my EVBEC (check the spudwiki).

It depends on the length of your barrel as well. A longer barrel will negate some of the effect of having a small valve size as it gives more time for the pressure to build up behind the object being shot before it leaves the barrel.

Maethor, you're not quite right on that one, but really close. A longer barrel gives it more time for the pressure to be applied to the object. The pressure is dropping as the projectile moves through the barrel because the chamber's total volume is increasing, which is quite contrary to you saying it's building. That's why there is an optimal barrel legnth for pnuematics. This is insanely large though. With a 2" valve a 1'x 4" chamber will have an optimal barrel legnth of 12'. Basically, just get a decent sized chamber, like maybe a few feet of 3" or 4", and a barrel whatever size you feel. I strongly suggest you use the GGDT to model your gun before you start.

Also, since this will be your first pneumatic remember to buy pressure rated everything. No bell reducers, use bushings. Make sure everything either has a pressure rating written on it or it says nsf-pw.

I use a 40" barrel with a 1" valve and a 24" 4"sch40 chamber. Ammo is golfballs....very consistent weight and size. Almost a friction fit in the barrel. At 115PSI, generally launching 300-325 yds tops. I believe a good wadding material and/or Sabot arrangement could afford better accuracy. A fair amount of slices and hooks because of air turbulence in barrel around outside of dimpled golf ball!

My Pneutrol valve 1.5'" cannon launches the same golf ball a verified 575 yds. It's all about rapid volume flow. The 1" is good but like one writer points out, limited to about a true 9/16" flow opening. I knoe I can get more distance and accuracy with better "wadding" in the barrel, Perhaps I should also purchase one of Joel's rifled barrels!?

I use half-inch sch40 pvc pipe for my paintballs. And its 24 inches long and shoots crazy far. Just dont make it too long or you will actually slow the ball down.