Do not use PVC for compressed air purposes.

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.