Intro: How to Build a Generic Air Cannon
Air cannons. Fun for the whole family. Shoots anything, really. Bottles of water for the kids, bottles of liquor for dad, kitchen utensils for mom, food for the dog, the dog (Kidding), stuffed animals for the little tykes..... Good fun. You can also shoot nets, grappling hooks, bricks, smaller air cannons, dumpsters (if they'll fit in the barrel), your mother's china, lit fireworks, and politicians. They are mainly used to shoot projectiles like balls (tennis or golf balls), potatoes, and my personal favorite-water balloons (filled with the liquid of your choice!). The whole point is this-you NEED one of these babies. And you need it NOW. Of course, I'm aware that this isn't the first air cannon instructable on here, and it won't be the last. But I hope that it's helpful, inspiring, and if nothing else I hope it's at least humorous.
Before we begin, there is a point I would like to stress- and that is Stupid hurts. You are building an air cannon (this could be used as a weapon). Because this cannon will belong to you, and it is your cannon, if you decide to do anything..................well, stupid with it, it's also your stupid. So it is your cannon, your responsibility, and anything you do with this thing is your consequence! That being said, END DISCLAIMER, BEGIN INSTRUCTABLE!!!!!!!!
In case you don't know how these amazing devices work, well obviously they use air (DUH-air cannon). Air is pumped and compressed into a chamber on one end of the gun, and on the other the ammunition is stuffed into the barrel. The barrel is connected to the pressure chamber via a ball valve or an electric solenoid valve. The valve lets the all the compressed air flow from the pressure chamber to the barrel, pushing the projectile out of the barrel and into the next county.
Step 1: Scavenge, Scrounge, and Look Around.....
What's wrong? The parts for the cannon aren't just going to appear in front of you! You have to find them (Buying them is optional). You're going to need a lot of things for your cannon (trust me, I built one). Here's the stuff I used to build the cannon shown here, and most of these parts are easily found at your hardware store, or in your annoying neighbor's garage while they're in Florida for their spring break (again, kidding).
-3" Pressure-rated PVC pipe (Never use non-pressure rated pipe for projects that use high pressure air. The results could end with exploding pressure chambers, shrapnel, and a trip to your local emergency room or cemetery. You'll need a good length for the barrel and another for the pressure chamber)
-a 3" end cap (Pressure-rated)
-2 reducers (3" to the size of your bushings)
-Ball valve or solenoid valve of the size or your choice (Bigger is better, I used a ball lever valve on this one)
-Bushings for connecting the reducers to the nipples for the valve (female thread, male slip fit)
-Pipe nipples for the ends of the valve
-Drill and drill bits (needed for making the holes in the pressure chamber)
-Channel lock pliers (used for tightening)
-Thread Tap (threads the hole for pressure gauge)
-Circular saw (for squaring off the ends of the pipe, or for cutting lengths of pipe in general)
-Drill press (optional, used it to make nice straight holes)
Other things you'll need:
-PVC cement and primer
-Schroeder valve (aka- "Tire valve") (with a screw cap)
-Teflon tape for sealing threads
Step 2: Fit Pieces Together
First lay out all of your pipe. Saw off a good foot (maybe more) for the pressure chamber, and leave the rest for the barrel. Saw a slim ring off the ends of the barrel to make sure they're nice and square. Once you've got all your pipe ready, and laid out, pick it all up again and clean it. You could run several of the smaller pieces through the dishwasher or simply just spray them with water and dry them with a towel. Now you can lay them all out again.
Step 3: Pressure Chamber
Let's start with the pressure chamber. You'll want to make a hole for the Schroeder valve (tire valve) on the end cap and you'll want another hole for the pressure gauge. The hole for the pressure gauge has to be threaded, so we'll start there. I drilled two pilot holes, one bigger than the last and tapped the threads in the last one. Tapping threads is important-do some research on the size threads you need (the threads on the tap have to match the threads on the gauge). The size hole that you need to drill varies depending on the size of the threads you're tapping. Make sure you start tapping the threads straight and not crooked or angled. Also, for every turn, work the tap back out about a half turn or so to work loose some of the chips in it (really work that sucker!). Test it to see if it fits. The hole for the Schroeder valve was drilled by hand, and actually the end cap was too thick for the nut to fit on the valve, so a counter borer was used to scrape away some of the end cap so I could fit the nut on it. *Be careful not to bore away too much, as this may weaken the pressure chamber!!!!
Once finished, take the end cap, and apply the primer (purple) on the inside of the pipe. Use the little wand, and work the interior of the piece around where it will make contact with the corresponding pipe. Do the same for the outside of the corresponding pipe. When gluing, you don't have time to make sure it looks good. Add the glue in the same manner as the primer, and join the two pieces of pipe together and give one of them a quarter turn. Apply pressure for about three seconds and you're done gluing! (Now glue the rest of the pipes together.) For threads, wrap them with Teflon tape to seal them.
Step 4: Attaching the Valve and Barrel
The valve has a lot of threaded pieces that need to be sealed air-tight, and this requires Teflon thread-sealing tape. Wrap each end of the two pipe nipples, and tightly screw them into the valve and bushings. Glue the bushings to the reducers. To finish the cannon, glue the barrel to the remaining reducer, and celebrate. I chose not to glue the barrel of my cannon for transport reasons-it's really hard to fit it in a car without taking it apart, so I drilled three holes through my reducer and barrel and inserted sheet metal screws to keep the barrel in place. Of course, this was entirely optional and can be glued later if desired.
Step 5: Operation
Ok, so here's where the real fun begins. Grab whatever you intend to shoot (that I'm not responsible for-remember, stupid hurts!), and grab some plastic grocery bags (yes, you heard me correctly). You'll also want a ramming rod to shove everything down to the very back of the barrel with-I just used a wooden broom stick/handle. First, before you do ANYTHING, close the ball valve. If it's already closed, well then you should feel special because you're a step ahead of me. You don't want air leaking out of it during pressurization. Now, load the cannon already. Stuff the plastic bags in there first (use one or two). These are used for wadding. Wadding makes a solid "foot" or "pad" for the air to push against the projectile(s) with, and it keeps the air from going around the projectile and escaping out the barrel. Then throw in your ammo, and ram it down there if necessary.
Unscrew the cap off or your Schroeder valve/tire valve (you should have one included with the valve, if not you should feel ashamed of yourself because dirt will get in it and clog it), and then use the correct chuck to pressurize the pressure chamber to a pressure that is well under the specified psi pressure rating of the pipe. I think the pipe I used was 260 psi max, and I took it up to 90 psi (partially because I couldn't get it any higher due to an air leak). Once the desired pressure has been reached, aim the cannon, and quickly open the ball valve.
You should hear a loud "PFFFFFFFFFFT" noise and hopefully nothing else. If you hear any other noises following your loud "PFFFFFFFFFFT" noise, such as breaking glass, car alarms, police sirens, yelling or shouting of profanity, or returning gunfire, you should (A) run very quickly to your nearest panic room, (B) panic, and (C) sulk and feel bad for not listening to my disclaimer at the beginning of this instructable! If you notice any leaks or any constant drop in air pressure, or some other obscene problem, continue to the next step. If nothing seems to have gone wrong, continue to the next step, because something will go wrong, and when it does, you'll need to know what to do.
Step 6: Troubleshooting
Okay, so you're losing air pressure in the pressure chamber. This is because you've got a leak somewhere. No matter how much PVC cement you used, leaks are usually inevitable. But there is only one part of the air cannon that they're found at-the pressure chamber. To seal them, you have to find where you're losing pressure. There are methods to finding air leaks that range from simply listening for a fizzing noise and trying to find it that way, by coating the pipe with a film of soapy water and looking for the formation of bubbles due to escaping air, or even submerging the unit under water and looking for streams of bubbles traveling upwards. All of these methods work with different results. It's how you seal the leak that matters. Any other weird problems, please leave a comment southward on this instructable, and I'll see what I can do.
Step 7: Conclusion
Now that you're all done, what are you waiting for!?!? Get out there, and fire your cannon soldier! Fire some confetti to celebrate! Don't miss out on another super-soaker fight! Fill it with water, aim into a crowd of them and FIRE! (Just don't aim for the eyes). Getting out-staged by that nerd with the water balloon slingshot or trebuchet? Show him the might of your cannon! Burglars again? They'll tremble in fear when they see your cannon loaded with a ferocious pit bull! Aspiring artist? Fill it with paint balloons, and splatter them on a canvas! Collection day at church? Fill it with money, and make it RAIN riches for the needy! Zombie invasion? Save the human race, and fend them off with a barrel-load of bombs! Tired of pitching in a game of baseball? Load a baseball and strike 'em out! THE POSSIBILITIES ARE ENDLESS!!!!!!!!!!!!!!!!! (Please use responsibly, my disclaimer still applies; stupid hurts.)
I tested mine and it worked, but could use some improvement. It had a few leaks, and lost pressure a little too fast, but it was operational. I fired a few tennis balls in a parking lot, and the ranges varied. I shot one straight up, another one about 100 yards, and another probably 130. These are very rough estimates, and I do not own a tachometer to measure the distances with. I intend to seal the leaks, and possibly use a smaller diameter barrel for other projectiles. But first, I want to shoot a few water balloons during 4H camp this year........ :D