Ok so back to the cannon. This cannon is a bit of a beast (as well as our first cannon), it is powered by two bridged 3' ft long 3" sch 40 pvc pipe tanks. The tanks and fittings combined is a total of about 780 cubic inches.
The Gun features a detatchable barrel and detatchble tanks, making it a little more transportable considering that the whole thing assembled is a little more than 7.5' long and 3.5' wide.
The fill up system that I use is either a bicicle tire type valve or a direct air compressor hook up w/ a ball valve to keep the air in. the pressure gauge is an old one off of an junked air compressor. The gauge is a -10 to 200 psi gauge. Using the bicicle valve takes about 5 min just to get to 50 psi, but when using the direct hook up it only takes about 30 seconds. Huge improvemnt.
The barrel is just over 6' long and has a flange built onto it from the end of the 20' stick of pvc that we purchased. We got a bit ripped off but it was the only store that had that size pvc pipe within 20 miles. It was a small irrigation store, that provided us with a rusted hack saw to cut the pipe with, they would not cut it for us since we were going to be cutting it into less than 10' lengths, we neeeded to cut it smaller in order to fit it into my 99 Z28 Camaro (belive me when i say that fitting 3 people and 20' of pipe in a Camaro is quite difficult and silly).
I figured that when stuffing very tight fitting objects down the barrel, pressure would build up behind it and force the projectile back out of the barrel. So I got this nifty little bleed valve that we drilled into the back of the gun to relive pressure.
To avoid buying a very large amount of pressure fittings I simplified the trigger system by going from a single modded valve to a modded valve with a treaded T joint sticing out of it. As you can see in this next picture. I'v seen that most people modd all thier valves the same and have them all go to a series of T fittings. Using this method i was able to use less tubing, fittings, clamps, time, ect. Also simplifies the look of the cannon, makes it look cleaner. You can also see in the picture our 4, 1 inch rainbird in-line valves.
Our first shot with this cannon was in a wooded area near a frainds house at 50 psi, we used a very loose fitting spindle reel for steel twine (even had a large hole in the middle). We aimed it at a tree and when the spindle hit the tree the bark on that side of the tree disintigrated and so did the front half of the spindle. The second shot was a gatorade bottle with some gravel inside. It was a little loose fitting so we first stuffed a pringles can into the barrel, witch fit very very snug. On about a 6 deg. inclination angle and 100 psi, the gatorade bottle was launched clearly out of sight, however it did hit the ground and bounce once.
We will be painting the cannon soon and I wil post updated pictures of the cannon and pics of destrution, If you have any questions or picture requests, dont by shy. Ask Away. Also any suggestions and comments will be highly appretiated. 8)
Good idea on hooking up the sprinkler vavle. How about some damage pics 
Looks like you would have trouble attaching a air compressor hose since the hook up is in that little area and next to that schrader vavle. A good paint job should get rid of those glue stains. I dont know if you know this but I would recommend using Krylon Fusion Spray Paint to paint it (should be able walmart). On your next cannon you should use clear primer and glue. Sounds and looks like a powerful cannon.
