I made a pvc pipe cannon about a month ago. The pvc only cost about $18 at Home Depot. The tire valves cost about $4 for a set of two. All you need is two pieces of pvc of the same diameter, an end-cap for one of them, a ball valve that will connect the two pipes, and a car tire valve. You need pvc primer cement to put it together. Constructing is really straight forward. The two pipes fit into either side of the ball valve. You need to drill a hole in the end-cap, and secure the tire valve there. Then secure the end-cap to one of the ends, and you're done. Mine pumps up to 70 psi with the help of an air compressor. Make sure to close the ball valve before pressurizing.
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