SpudFiles

This is an idea i've been working on for a few days now, It is otherwise a plane old air gun except for a fixed pressure c02 regulator (150 psi) where the recharge fitting for the tank would otherwise go. the threaded 16 gram c02 bottle which you can get pre-charged. I got mine at walmart. the can will charge the bigger tank where it will accumulate the volume of air needed to launch the projectile. Thus you will have a simi auto small (But with big power) lightweight cannon. This is my idea for how it will look when done:
Not bad for a 16 year old's mind

nothing out of the ordinary, what do you plan on shooting?

It's not going to be particularly semi automatic. I don't know how large your fire extinguisher is, but you'll probably not get more than two shots per cartridge out of it at 11bar. If I were you, I'd bring it up to 11 with a track pump, then if your sprinkler can take it, go up further.
If you don't mind that (and the money that goes with it), it seems like a fairly good idea. Do be aware that you'll lose some of the potential pressure if you're firing rapidly because of the temperature drop.

It's going to be particularly difficult getting a CO2 powered cannon to fire a blast of air....since there will be no air in the cannon...

I think he muzzle loads the air.

Its not going very semi auto this way:
-you dont have a loading mechanism yet.
-you need to pilot the sprinkler with a VERY short tap in order to conserve some pressure.

But it will surely be a nice cannon.

http://www.spudfiles.com/forums/co2-pow ... 17869.html

That looks like the setup I'm having my club do, Keeping it simple is important.

If you build this, take the filter off the equalization hole in the diaphragm. It makes the diaphragm reset like 50 times faster after each shot. If you leave it on, the valve won't shut until your Co2 tank totally empties.

Where is the safety blow off valve?

The launcher can only hold as much pressure as the weakest part.