After building my first combustion cannon I wanted to try a cannon that was slightly different. The pneumatic cannon works on the principal of using compressed air in a sealed pressure chamber to be suddenly released via a valve to propel a potato projectile rather than using the pressure generated from the combustion of a propellant. This cannon was built using heavy duty plumbing materials and operated up to a pressure of about 100psi. Be sure to always used suitably pressure rated fittings and materials!
All piping/plumbing components are made from pressure rated ABS (Class C – 9bar/130.5psi).
- Two 50mm Ø 90° bend
- 50mm Ø x 1200mm long pipe
- 40mm Ø x 1200mm long pipe
- Two 50mm Ø double socket
- 50mm Ø access plug
- 50mm Ø x 60mm long pipe
- Two 50mm Ø to 22mm Ø tundish
- Two 22mm Ø x 80mm long pipe
- 50mm Ø to 40mm Ø reducer
- 50mm Ø x 190mm long pipe
- 50mm Ø x 220mm long pipe
- 22mm Ø levered ball valve
- A car tire valve (Schrader valve)
- 50mm Ø x 10mm long pipe (or ring)
- 50mm x 50mm sheet of 5mm square steel wire mesh
- Solvent weld cement
Construction of the cannon
I solvent welded the two 50mm Ø 90° bends together to form the U-bend. I then solvent welded one of the tundish adapters into one end of the U-bend. The pressure chamber pipe, 50mm Ø x 1200mm, was then solvent welded into the other end of the U-bend.
In the end of the pressure chamber pipe I solvent welded a double socket and access plug to terminate the pipe. The cap of the access plug simply required a tight fitting hole drilled in the centre to accommodate the car tyre valve.
I then assembled the ball valve fittings. Using a 22mm Ø 80mm long pipe I assembled the tundish seal and threaded cap, and the ball valve threaded nut and compression olive as shown in the photo below. To ensure the tundish fitting would not blow out I permanently solvent welded the 22mm Ø pipe into the tundish fitting. I screwed the ball valve parts together making sure that the ball valve was oriented in the correct position for firing and made sure the threaded fittings were all tight and secure. I repeated this for the other tundish to complete the valve section.
The barrel section consisted of a 40mm Ø x 1200mm long pipe and a 50mm Ø to 40mm Ø reducer that were solvent welded together. To stop potato projectiles from getting stuck in the tundish/reducer section if inserted too far into the barrel, I used some wire mesh and a ring cut from an ABS pipe to make a screen stop. I solvent welded the mesh to the inner face of the reducer and then solvent welded the ring inside to hold the mesh securely in place. The barrel was then solvent welded to the tundish adapter using a 50mm Ø double socket.
To make the cannon structurally strong, I made two separator supports to fit between the barrel and the pressure chamber pipe. The supports were made from short lengths of 50mm Ø generic thin walled ABS pipe. The support nearest the ball valve required an intersecting pattern cut out at both ends of to make for a flush mounting between the tundish adapter and pressure chamber.
The other support towards the breach end of the cannon required the same intersection pattern cut at one end to mate with the pressure chamber pipe and an orthogonal 40mm Ø hole cut through the other end which would thread over the barrel (unfortunately I forgot to photograph this support piece before solvent welding it to the cannon). Both supports were solvent welded into position using strap clamps to hold it securely together while curing.
Here is the completed cannon, I really like the look of the U-shaped duel pipe design!