Tim Bloom,
You are right..pressure is pressure! I too have a system plumbed with PVC, and I don't live in fear when in the shop.
From a purely technical standpoint, the manufacturer of the PVC doesn't recommend it for compressed air service so that should be the bottom line.
I don't think the plastic is 'inert'..its chemistry can be gradually changed through contact with oil and oil vapor. This will sometimes make it brittle, and although it will still hold 600 psi, a sharp blow will fracture it and cause it to fail.
When a pressure vessel is hydro-tested, it is filled with water and pumped up to the required pressure. If it fails, there is no explosion because the water, being incompressible doesn't have a bunch of stored energy behind it.
If you took the same vessel and pumped it full of air, when it failed it would blow its top, and maybe yours too.
I'm betting the pressure rating of the PVC pipe is for a liquid and not a gas.
I will use my PVC system and won't worry about it, but technically, it should be iron pipe or maybe copper pipe...something that won't fail when blasted with the flying chiesl or hammer.
So the statement that 'pressure is pressure' is only partially true when it comes to exploding things.
Stuart
