Each year during Labor Day weekend the ISOA holds its annual Potato Fest at the home of Jake and Donna Jacquet. It is traditional to bring a potato cannon to the festival. Potato cannons are usually constructed from PVC pipe. The operator squirts hairspray into the breech, closes it off, and triggers the cannon with a lighter or electronic igniter. The burning hairspray expands rapidly and the pressure launches the potato from the barrel.

I attended my first Potato Fest a few years ago. The announcement for the event included a map and reminded everyone to bring their potato cannon. I had never seen one of these potato cannons nor had I heard a description of one. Undeterred, I decided to build my own version out of some junk from my garage.

WARNING: This is dangerous. Do not try this.
Only a madman or an idiot would actually do this.

Any responsible adult who actually tries this must accept liability for any deaths, injuries, and/or property damage it causes. If you are not a responsible adult (in the legal sense), don't even think about it. Bare skin exposed to dry ice can instantly develop frostbite or 'freezer burn'. A small quantity of dry ice stored in a sealed container can cause a large explosion. The noise caused by a dry ice cannon can damage the hearing of anyone nearby. The recoil from the cannon and the impact from the potato projectile can both cause serious injury or death. In some jurisdictions it may be a crime to even posess such a device. This article is presented merely for entertainment.

The first generation Quackenbush Potato Cannon™ was built from a 1½" ball valve, a 3 foot long 1½" pipe, a surplus 100 PSI filter bag housing from work, and a 0-160 PSI pressure gauge.

To fire the cannon you start by pulverizing a chunk of dry ice. You then pour the crushed dry ice into the filter housing and close the lid. With the ball valve open you pour hot water down the barrel. After a few seconds you will see a nice plume of CO2 spewing out of the barrel. Close the ball valve and watch the pressure gauge very closely. To prevent an explosion, open the valve immediately if the pressure exceeds 50 PSI.

Still with me? OK, once you have closed ball valve the pressure will start to rise very rapidly. You must quickly insert a potato into the barrel and force it down with some kind of ram-rod. Aim the cannon sturdy target (like a tree trunk), make sure no one will be injured by the recoil, and wait for the pressure to build up. Open the ball valve as quickly as possible to fire the cannon. Opening the valve slowly wastes power.

The first time I fired the Mark 1 the 'muzzle flash' of CO2. was over 20 feet long. It launched the potato with so much power that it still had a flat trajectory when it passed beyond visual range.

The Mark 1 potato cannon was a successful design but it took several minutes to load it and fire a single potato. During the initial test of the Mark 1 the ISOA peanut gallery made disparaging remarks about its rate of fire. For the following year I decided answer those criticisms by dramatically improving the cannon's rate of fire.

The Mark 2 was a bolt action carbine. Its 3" PVC stock doubled as a pressure reservoir for a single shot. The sliding bolt was made out of 2" automotive exhaust pipe. The ball valve was replaced with a butterfly valve. For testing purposes, shop air was used instead of dry ice. An adjustable air pressure regulator allowed power adjustment.

The Mark 2 was canibalized to build the Mark 3. An improved bolt action carbine, this version was a joint effort with Andrew Mill whose independant research into SCUBA tank powered potato cannons provided valuable insights. It featured an air powered sliding bolt, using a surplus pneumatic cylinder to force the potato into the bore. We used O-rings to seal the breech, eliminating blowby.

We then decided to build a true semi-automatic cannon,the Mark 4. We used pneumatic cylinders and air valves instead of relying on springs and recoil to operate the mechanism. To use the cannon you fill the magazine with small pre-selected potatoes (Yukon Gold potatoes work well) and turn on the air supply. Each time you press the firing button you launch a potato.

Both pneumatic cylinders are double acting and both control valves are 4-way. Control valve A operates pneumatic cylinder A. At rest cylinder A is retracted, opening the breech and allowing a potato to drop in. Cylinder B is extended, closing the butterfly valve and allowing pressure to build up in the reservoir. Pressing the button on the control valve causes cylinder A to extend. This closes the breech, forcing the potato into the barrel and sealing it.

Just before cylinder A is fully extended it hits the button on control valve B. When control valve B is activated it causes cylinder B to retract. This opens the butterfly valve rapidly, launching the potato.

When the operator releases the trigger (the button on control valve A), cylinder A retracts, opening the breech to accept a new potato. As soon as cylinder A retracts a centimeter or so, it releases control valve B and closes the butterfly valve. With the butteryfly valve closed the air reservoir fills up for another shot.

A single shot from the Mark 4 will blast a hole through ¼" particle board. With a second person feeding the magazine it can sustain 20 rounds per minute.

The cannons are constructed from schedule 40 PVC pipe. The barrels are made of 2" pipe. The reservoirs are made of 3" pipe. Shop around for your 2" pipe- the inner diameter of PVC pipe and the outer diameter of mild steel automotive exhaust pipe vary between manufacturers. My exhaust pipe came from J.C. Whitney. You should choose your PVC and exhaust pipe to get the tightest fit.

The pneumatic plumbing was built using translucent polyethylene tubing, compression fittings, and hose barbs. I used Humphrey MicroTAC 4-way valves from J.H. Foster. The pneumatic cylinders, the 1½" butterfly valve, and the pressure gauge all came from Surplus Center. The spherical rod-ends used in the joints came from Pegasus. The clear pipe for the magazine came from American Science & Surplus. To make the slide we drilled a ½" hole through one side of the exhaust pipe. We then welded a nut inside the pipe to accept a threaded stud. A lathe was used to create O-ring grooves (not shown) at each end of slide.