Instead of using a ball valve or other such contrivance to dump air directly from a reservoir into the chamber of this PVC air cannon, [Ben] is using a much more clever design. This is a barrel ...

The build uses PVC pipes for both the barrel and the air ... and firing is achieved via a ball valve. Of course, if you build such an air cannon yourself, just be careful with your aim.

Glue a 1-1/2-inch PVC x 3/4-inch FIP adapter (A ... Remove the handle from the ball valve so you can assemble all the 3/4-inch fittings. Build a new drain valve with a 3/4-inch full-port brass ...