Air Cannon

Last updated: November 30, 2001

Here I am with my air cannon (Mark I). This cannon is made from 2" schedule 40 PVC pipe, an electric sprinkler valve, some batteries, switches, and other miscelaneous items. It is pressurized to 100 psi by a bicycle pump or small compressor. It was built primarily to amuse me, but can also be used for paintball games (with caution!). I got the design from the Not How to Build An Aircannon web page. My cannon can shoot a potato 170 yards or more! I estimate muzzle velocity in the neighborhood of 250 feet per second. Obviously, this calls for great caution in the firing of the cannon. The Mark I cannon was one of only a few of my personal items to survive the '97 flood. The electronics were trashed, but the rest of the cannon, being built from items intended for handling water or sewage, survived. I have since rebuilt the electrical firing system, and the cannon is back in operation.

Next (not surprisingly) came the Mark II cannon. This is based on the pneumatic cannon design I found on the Backyard Ballistics page. I scaled up the design to use a 4" diameter schedule 40 PVC pipe for the air chamber, and a 2" pipe for the barrel. The barrel is 6' long, and the air chamber 4'. I also replaced the blowgun/hole idea with a pneumatic quick-connect coupling system, which seems a better idea (taken from the Spudlaunch Idaho page). The only major part of the construction left is to fashion some sort of mount. The folding one on the _High Performance Spud Gun_ page is pretty cool. I thought about building one and mounting it on a small trailer (like a personal watercraft trailer), but that would lead to storage problems, as well as possible unwanted attention from the authorities (towing around something that looks like an artillery piece would probably get their undivided attention ;). The Mark II project got off to a slow start. The PVC pipe construction went without any problems, but trying to find a appropriate material to make the valve diaphram turned out to be a major headache. This component is the heart of the gun: it has to work perfectly. After months of frustraition, I found a webpage by annother fellow who built the same design gun. He found that 3/16" thick hard neoprene rubber sheet made an ideal diaphram. The sheet can be ordered from McMaster-Carr Supply. The guy who wrote the Green Waters Spudgun Page certainly came up with a winner! I cut a valve diaphram out of this material, and have found it to be excellent. The stuff is actually made with pneumatic use in mind, and is in my opinion, perfect for the task. The Mark II design is far more effecient than the Mark I. Testing with only 50 psi of air pressure, the Mark II put a kooshball through three layers of cardboard, while the Mark I could only punch through one layer when fired at 100 psi. At 100 psi, the Mark II fired the kooshball fast enough to put a 1/4" dent in a steel folding chair! Since a kooshball is soft and only weighs about 2 oz, this is an amazing feat. It also underscores the fact that the Mark II design air cannon is no toy, and needs to be used with utmost caution. Unfortunately, during a firing session the cannon fell off its support and cracked a glue seal. I may try to repair it this summer.

My current project is the Mark III. This is another sprinkler valve cannon, but uses two 1" diameter valves arrainged in parallel to increase the airflow (thanks to Andy for the idea!). It uses a 3" x 5' air chamber and has a 2" x 6' barrel. This cannon also incorporates a pressure gauge and a safety valve that will open at just over 100 psi, keeping me (or anyone else) from overpressurizing the gun. Photos are available here. The Mark III made its public debut at an engineering festival this spring ('99). Friends of mine in the UND Physics Dept set up the cannon and entertained all the visiting grade school kids (and a large number of their fellow university students) by firing soft projectiles across the quad area behind Wittmar Hall. The gun was used with reduced pressure in this demo, since I had not yet fitted the 1/4" hardware cloth explosion shield over the air chamber, and some of the professors were concerned about safety (quite understandable). Even so, running at only 60 PSI my friends managed to shoot my kooshball onto the roof of a four story building over 150' away. After that, they made a new projectile out of a crushed plastic bag wrapped with masking tape. They still haven't bought me a new kooshball yet :).

The discussion I had with the physics profs brings up a good point: safety. Being responsible and careful in terms of where you shoot, what you shoot, and when you shoot it go without saying. However, many folks have recently become concerned about the use of plastic (PVC) pipe with compressed gas. In my research on the topic via the web, the only items I could find on this subject were from the Plastic Pipe Institute, who say (not surprisingly) "Don't Do It". The only exceptions for using plastic pipe for pneumatic applications in industry were if the pipe were completely buried or fitted with explosion shielding. The problem is that compressed gasses like air store a tremendous amount of potential energy. This is what makes compressed air good for launching things in the first place. But if the pipe storing the air cracks or shatters, the plastic shrapnel will be accelerated to very high speed. When used for pressurized fluids like water, which is not compressable, a break will cause the system pressure to drop to zero nearly instantly: you still get a mess, but the pieces won't get driven to such high speeds. Some gun designs I've seen use steel or other metal tanks for their air chambers and PVC pipe only for the barrel. If you do use PVC for the air chamber, you really should fit some sort of shield over it to catch fragments in case of a rupture. Some designers like the idea of using the legs of a pair of denim pants (jeans) to cover the chamber. I personally like the use of 1/4" hardware cloth, which is wire woven in a very coarse pattern. The large holes in the cloth lets the compressed air escape while (hopefully) catching the plastic fragments. Using both would actually be an even better idea, the hardware cloth on the chamber to catch the big stuff, the denim to block smaller stuff and keep sunlight off the pipe. That's another point you should be aware of: direct sunlight is very bad for PVC pipe. It weakens the chemical structure of the plastic and makes it brittle. If you get pipe that has a yellow 'sunburn', cut it up and throw it away (or give it to someone else to use for a nonpressure application, like drainpipe). $40 for new pipe and fittings is a heck of a lot cheaper than a trip to an emergency room, and remember: plastic shrapnel doesn't show up on X-rays. I'm not trying to scare people but you need to be aware of the risks invovled if you build an air cannon. Don't say I didn't warn you.

Some more good pneumatic cannon pages are: The Master Blaster Pneumatic Cannon page. This guys takes his air cannon seriously! Green Waters Spudgun Page, and the Pneumatic Cannons Page. A good combustion 'accelerator' page is the Potato Technology Center (His SP9004 aluminum spudgun is a thing of beauty).

NOTE/DISCLAIMER: The purpose of this page is to relate my personal experiences building pneumatic cannon. I do not recomend building any of these devices. They are not toys and could cause serious injury if misused. If you build an air cannon, you do so at your own risk. If you cannot take responsibility for your own actions, please don't build one.
LEGALITY: The BATF does not consider these devices to be firearms (neither the combustion nor the pneumatic type). However, your local ordinances may ban such devices or restrict their use. Check with state or local authorities regarding construction and possesion/use. If you use one of these devices to injure someone or destroy property, the police will still bust you, and you will make the rest of us look bad. Don't be an idiot.

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