SAFETY has to come first. A few people have forgotten this simple concept and have done some serious harm to them selves and others. Lets not make the art of potato launching illegal in your area. Some of us still like the freedoms that we have left.
First of all, you must never fire this device at anybody or anything. Even simple items, like a shop rag, that are propelled at high speeds, become extremely dangerous. This device has the capability of putting a potato through 1/2" plywood at 50 feet with no problem. Just like a gun, you need to know what is down range for at least 3/4 of a mile.
PVC pipe was never meant for air. Is is rated to carry liquids. Even though it may have a pressure rating written on the side, it is still not meant for air. (Recent developments have given us an air rated plastic. It is green in color, and very, very expensive. It is a modified ABS plastic.) PVC tends to shatter when struck, and therefore would produce many, many, small flying, sharp projectiles if it were to rupture. I am advising you to shield yourself when you charge this devise with air.
Just by there nature, these devices are inherently dangerous.
These devices are not meant as a weapon, lets keep it that way or big brother may someday
take it away from us. Lets have a little common sense when using these devices.