[JohnFogarty]

Lets consider PVCs pressure rating for a moment. PVC is only pressure rated for liquids (and for a very good reason):
Water is incompressable, much like a steel block ... if you push down on a steel block with 50 PSI it will not compress and if you release that force instantly the steel block will not move.
Air, on the other, hand is compressable, like a 50 pound spring. Apply 50 psi to it and the sprin compresses. release that force instantly and the spring not only goes back to it's original shape but rockets off of the surface it was on.????

Umm Yeah the principle of compressing water has to happen other wise when you put your finger over the end of a hose nothing would happen. Water is compressable. 1000psi water jets are used to cut steel.....so again logic isn't following here. It's compressable to a very very small degree.