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The Ultimate Air Cannon

This design came from the wild thinking of TJ Christiansen. (Note: I briefly looked at the plans (actual shape, & reducing from chamber) and then went to the hardware store to find the parts ot make a similar shape. I "assembled" the gun there and put it together at home. I was aimed in the other direction of filling means.) His model uses a Solenoid Sprinkler Valve to dump all the air into the gun. This valve needs batteries, switches, and wiring. Although I am an Electrician and wiring is really easy, it takes the look away with wires running everywhere. I put a 3/4" ball valve in it's place.

He uses a tire valve stem to fill the gun. I put a 1/2" gate valve with a 1/4" male quick connect in the end. You can modify the length of the air chamber-I think the longer it is, the more air behind the potato at the end of the barrel, but longer to fill. The size of the ball valve can go bigger (bigger might mean faster air flow through the valve setup, but I wouldn't recommend any smaller. The list of parts is quite extensive, and here it is:

Note: All parts are Schedule 40 PVC.

Buy 10 foot lengths of pipe to save for future guns or sell to friends.

Check out McMaster-Carr Page 27 of their catalog, they sell all of the fittings needed, and instead of buying many reducers, you can buy one to do the job (real cheap!). They even sell transparent PVC if you want to see the potato fly in the barrel!
And parts with a * indicate a coupling that's threaded (either male or female) on one end, and slip-joint on the other.

• 3 feet of 3"
• 5 feet of 1-1/2"
• 1 foot of 3/4" (rest can be used for ramrod)
• 2 3/4" Male Threaded Couplers*
• 2 1" x 3/4" Bushing Reducers
• 2 1-1/2" x 1" Bushing Reducers
• 1 2" x 1-1/2" Bushing Reducer
• 2 3" x 1-1/2" Bushing Reducers
• 1 3" Female Coupler*
• 1 3" Male Coupler*
• 2 2" 90 degree Elbow (1 male end and 1 female end)
• 1 3" x 2" Bell Reducer
• 1 3" End Cap
• 1 3/4" Threaded Ball Valve (you can go bigger, not smaller)
• PVC Glue
• PVC Cleaner (or Purple Primer)
  

I'm sorry if you can't understand these instructions. When I explain things, people don't usualy understand them. Click here if you want a diagram to help you along.

Now is the time to think how to fill it. If you have an air chuck or bike pump, get a rubber tire valve stem, drill a hole in the end of the 3" end cap a little smaller than the size of the big end, and stick it in the hole. Or what I did was buy a bunch of reducers from 3" to 3/4", and put a 1/2" female threaded coupler in the reducers. Then thread a 1/2" nipple in it, stuck a 1/2" threaded gate valve on the nipple, then some metal reducers in the other end of the valve where I have my 1/4" male quick connector. It might be possible to save some money in reducers and put a PVC tee (3/4" x 3/4" x 1/2") (click to view) inbetween the reducers and the pressure end of the ball valve, and put the assembly off the tee. Or you might be able to find a 2" 90 degree elbow with a side input, and place all of the things in that. I never tried it, so I don't know if it works.

Now cut all the pipe to size (cut the 3/4" pipe into two pieces of 5-1/2" and 3"). Sand all the fittings and pipe where it will be glued (help make it strong). All the metal fittings should have teflon tape wrapped on the threads.

1. Take the 3" Male threaded coupler, and glue a 3" x 1-1/2" reducer into the end.
2. Glue an end of the 5-1/2" 3/4" pipe into the 1" x 3/4" reducer. On that reducer, put the 1-1/2" x 1" reducer on the fitting attached to the pipe. Then glue the whole assembly into the reducer in the male coupling.
3. On the other end of the 3/4" piece in the fittings, glue the 3/4" male threaded coupling (for the valve, install that later).
4. Take the other piece of 3/4", Glue an end into the other 1" x 3/4" reducer (or tee, then cut another small piece from the tee to valve). On that reducer, put the 1-1/2" x 1" reducer on the fitting attached to the pipe. Then glue the 2" x 1-1/2" reducer. Then glue the whole thing into the female end of one of the elbows. And then glue on the other 3/4" male threaded coupling.
5. Glue the end cap onto the 3" piece of pipe. Then glue the 3" x 2" bell reducer onto the other end. Then glue the other elbow's male end into the reducer.
6. Lube up the ball valve with some oil on the ball when closed and work until somewhat free moving. Then with the valve open, screw the part with the 3" male connector into the side of the valve with the handle pointing to it. There should be enough clearance between the handle and reducers.
7. Screw the other end of the piece with the elbow into the other end of the valve.
8. Now glue the two elbows together, making sure the 3" male coupler and valve are aligned with the chamber.
9. Taper the end of the 1-1/2" pipe with a file or belt sander to a point (to cut the projectile when loading). Take the end you didn't file and glue into the other 3" x 1-1/2" reducer. Then glue the reducer into the 3" female coupler.

Now you're gun is done! Wait about 5 hours for the glue to cure (bring it inside). The purpose of the 3" male and female connectors is so you can take the barrel off for transportation and to fit alot of other guns.

When you put the barrel on the chamber, it will be very rocky. I notched a 2 by 4 to fit between the chamber and the barrel, then wrapped it with a bungee cord.

To load: ram a potato into the muzzel of the barrel. Ram it down with a piece of 3/4" pipe that you didn't need (mark 4'-8" from the end, puts the potato in the right position) to the mark. Now put the air chuck on the valve stem and fill until a sound in the chamber quiets down. If using a compressor with a regulator and quick connect, set the designated pressure with the regulator, and open the gate valve until you don't hear it filling up with air. Close the valve and disconnect the air line.

To fire: put the elbows into the elbow of your right arm, hold the chamber with your left, and use your right to push the valve open quickly. And your spud is flying!

If you want to, put a tee between the nipple and gate valve if using the quick connect setup, and put a psi gauge in the tee. This would give accurate psi ratings for comparing shots.

Pictures

Click on thumbnail for full-size picture

A shot of me with the gun (sorry, they're all dark, but you can see the gun)

Another picture of the device

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Created 1997-98, Mike Gagnon "Spud Man"

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