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Originally Posted by Daniel Lafleur
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.
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I still don't see how that contributes to making the material fail. I can see how it would make the failure explosive, but it seems to me that if the gauge reads 100 psig, there is a net force on the tank walls of 100 lb/in^2, no? If not, how does the compression add a force that the gauge doesn't see? Don't pressure gauges just measure the deflection of a spring?