Discussion and Theory:

I like air powered potato cannons because there is no combustion, no flames, no explosions, no heat, and no ignition problems. You get 100% reliability and an extremely controllable power source. I believe air powered 'tater cannons are both safer and more powerful - how many times do you see that anymore?

The main components of a potato cannon are a barrel, a control valve, an air chamber, and a fill valve. You also need connections between these components.

The air chamber needs to have more volume than the barrel - so the projectile gets pushed out, right? The general rule of thumb is that the air chamber should have a minimum of 1.5 times the volume of the barrel. You gain more power with more volume - up to about 5x. After 5 times the volume, the Return on Investment (ROI) drops off.

The weakest component of the cannon is the control valve. It is a the control valve for a garden sprinkler system and it is rated to 110lbs of pressure. The barrel and air chamber (and some of the connectors) is Sched 40 PVC, which is rated at 240lbs pressure. The other connectors are Sched 80 PVC and are rated for over 300lbs pressure (as far as I can tell.)

I strongly recommend you limit your air chamber pressure to 60lbs. It is PLENTY of power. When you decide to ignore my advice and see just how much pressure the system can take, don't tell me about the results - I don't care and I don't want to hear about it.