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[Daniel_LaFleur]

Originally Posted by chapman1

I share everyone's rightful concern for safety, and I certainly lack credentials on PVC and air pressure vs. water pressure. At the same time, I have to question whether PVC knows what's inside it (water or air). Pressure, it seems, is pressure.

The documented examples I have seen of PVC failure have occurred at low temperatures, where I will agree, PVC gets brittle and dangerous. If inside a warm building at 1/2 rated pressure, I would tend toward not worrying excessively.

You are incorrect that pressure is pressure. Liquid (which PVC is rated for) is incompressible where gasses (That PVC is not rated for) are compressible.

The issue with PVC is the failure mode. When PVC fails with liquid in it the internal pressure relieved immediately (due to liquid being incompressible) thus there is little time to accelerate the shards that are generated during a failure. Gasses, though, relieve pressure only as fast as the gas can escape, thus giving the force plenty of time to accelerate the PVC shards.

Hope this helps to explain the difference.