Cannon won't work properly. Are there any obvious flaws?

[aaurum]

Hey guys.

I just made my first pneumatic air cannon, which was intended to shoot tennis balls, but it doesn't really work. In the past week, when I was planning and designing the cannon, I checked out some designs on the web but didn't copy any designs exactally. I went for a U shaped cannon with a 2 ft long 2 inch PVC air chamber with a sprinkler valve leading to a 3 inch diameter barrel. I couldn't find 2.5 inch pipe in the store, so I went with 3 inch, hoping it would work. The 3 inch pipe turned out to be too large for tennis ball, but even when I use objects which fit snug in the pipe the cannon just makes loud noises and doesn't shoot them far.

There could be an obvious design flaw that I can't figure out, or it could be an issue with my sprinkler valve. I'm using a Hunter brand valve, and it was just what I had laying around. My next step to diagnosing the issue is to switch to a different brand valve (one that is easy to modify to work non-electronically).

Anyway, here's pictures of the cannon with a small explanation for each:


View of the full cannon.


I use an air compressor and nozzle fitting to add air to the pressure chamber.


To activate the cannon, I just connect the sprinkler valve to a 9 volt battery. I have a switch that I want to install in the loose pipe, but I didn't install that as the cannon isn't working at all.

I have taken a video of me shooting a soft small toy soccer ball. It is the best thing I have found in my house which fits in the barrel, and it fits snug. Here's a picture of it in the barrel and below that is a video of it being fired at 40 PSI.



[youtube][/youtube]

Thanks to anyone that replies with ideas on how to fix this. I haven't tried anything above 40 PSI, but I can't imagine it would help that much to go up to higher pressures. I don't know if this is common or not, but it makes extremely loud noises when I fire (like a train horn deal). Is this a sign the valve is not letting enough air through, or what?

[Ragnarok1]

I would say that the reason its not doing much is that the barrel is simply to big for the tank. At 40 psi the air spreads out to much for it to be very effective. I would suggest using higher air pressure and shoving the projectile to the back of the barrel.

[Ragnarok1]

also use 3 9 volt batteries hooked together, i ran into the exact same problem

[farcticox1]

I think chamber/barrel volume ratio should be at least 4:1.

What voltage & wattage is the valve coil? 1 9v battery may not be enough

[Gun Freak]

I would modify that sprinkler valve for pneumatic actuation. You can even use the compressor blowgun that is already on the gun for the mod. Switch it out for a 1/4" ball valve. Look up modifying a sprinkler valve or use tutorials/examples on Spudfiles! Electronic actuation of the sprinkler valve is never as good!