Several good links that show why you should NOT use PVC pipe to distribute your compressed air system, or to make any sort of pressurized device, such as a home made pneumatic cylinder, air cannon, spud gun, etc. Although PVC has a PSI rating on it, it is not designed for the types of forces that compressed air exerts upon it. This can result in shrapnel explosions that are very dangerous.
As a side note, I personally was standing next too a 3″ PVC elbow that was installed with an improperly specified pneumatic distribution system, when it exploded. Luckily I only had small cuts. It could have been much worse.