SpudFiles

This is my Pneumatic cannon, I call it Big Stuff... until I can think of a better name.

It's built completly out of Sch 40 PVC, save for the Sch 20 barrel (wrapped in duct tape) that I use to launch tennis balls and cans of spray paint. Both barrels are a 2.5 inch outside diameter, but the tank is a 3 inch outside diameter.

I didn't expect it to as a powerful as it really is, but it's got some pretty serious kick behind it. My theories are that I used a large steel ball valve, and a long barrel to allow more time for the projectile to accelerate with the expanding air behind it. I also think that it was because the tank was built large enough to supply air for the projectile's entire trip through the barrel (to not experience a vacuum effect towards the end), so it can really send something flying. Shot at 90 degrees relative to the ground it can, with about 80 or so PSI in the tank, launch a tennis ball into the air for around ten seconds, which is ROUGHLY (without figuring in air resistance.. a rather large factor..) 125 meters. The cannon design was loosely based off of the design of "Pnewton's Petard" from the book "Backyard Ballistics" (An AWESOME book if you like this kind of stuff)
Any Questions or comments?
-Vice

get a sprinkler valve and modify it via the how to

That duct tape won't save you. Get a pressure rated 2.5" SCH-40 barrel if you want to shoot tennis balls... especially on a pneumatic.

Just curious... I have a book called Backyard Ballistics that has a plan in it for a cannon very similar to this. Is that where you got the idea?

*EDIT* Sorry didn't see you did mention that in your post. Cool. I like that book a lot.

Cool cannon! Have you thought of puting a stand on it? Might help with the kick

The "T" design suck really hard ....

why didnt you make a simple over and under cannon ?

and a sprinkler valve is definetly better than your lil ball valve.

Mark, barrels don't need to be pressure rated. As long as they are decently strong then it's fine. But if a chamber were to rupture, duct tape wouldn't do anything.

barrels need to be pressure rated.
let's see you put pvc barrel on a gun.

Benstern, not so much. Barrels are exposed to such pressure over a MUCH shorter time. Since when the projectile moves the volume increases, via dropping the air pressure. So you decide if exposing a barrel to several milliseconds of pressure is suitable.

The Sch 20 barrel works wonders for me, it does really well with tennis balls especially because they slide in very smoothly and don't require a high pressure build up behind them for them to glide out of the barrel, as opposed to being stuck to where it would take much more pressure to launch. I think the Sch 20 is ideal for tennis balls and for things that are not very heavy. Even a can full of soda will launch easily out of it with no problems... the ball valve I think also reduces the risk of it exploding due to the slightly longer amount of time it takes for it to release the air, so maybe I'll save the sprinkler valve for a later project when I use some heavier things.

The "T" design suck really hard ....

why didnt you make a simple over and under cannon ?

and a sprinkler valve is definetly better than your lil ball valve.

P.S. Actually, I like the "T" design because it's easier to aim then an "Over-under cannon", and it works really well for me because the less parts you have in a cannon, the fewer chances you have of something breaking. Where would we be without different designs? How would we improve them? By the way, ball valves are cheaper and can withstand a considerable amount of PSI. A longer barrel would be a simple way to make up for a slower release of air, especially with a Sch 20 and it's lack of friction on a tennis ball (for example).
Cheers!
-Vice

Cool cannon! Have you thought of puting a stand on it? Might help with the kick

Thanks! I did think of putting a stand on it of some sort but tossed the idea because I didn't have too many issues with aiming it and nothing really with the kick.. it's pretty cool the feel the power of that thing sometimes
-Vice

are you sure that isn't a SDR-21 barrel. as i have seen 2.5" in that class

Well to be honest I don't know, but I'm pretty sure it's just regular Sch 20 PVC.. that's what I bought it as.. and the duct tape is covering up the markings.. so I can't really go back and check :\

PVC dosn't come in sch 20 it comes in 10, 40, 80, 120, 160 or SDR- 13.5, 21,26,60

Oh man can't you buy a bigger ball valve?Or you paln to launch heavy steel balls?