On the other hand, I also just found this site, which makes me change my mind. In the event the PVC does fail, it would be 1) catestrophic 2) throwing high speed pieces of plastic everywhere that could be dangerous or even fatal if struck by, 3) fail without any indication and 4) would have an incredible amount of reserve energy in the stored gas (air) in the system. This is totally different than a low pressure metal pipe failure which will crack but not explode, and even more dangerous because the fluid is a gas, not a liquid, which PVC was designed and rated for.
http://www.woodweb.com/knowledge_base/C ... ystem.html
I was an Engineer in the Navy, and I have seen photos of high pressure air system ruptures and they were not pretty. These were 4500 psi stainless steel air systems, which is not much different in comparison to 150 psi of pressure in a PVC systems. The strengths we are talking here are proportional, but the results would be the same.
This is also why PVC is not allowed by OSHA for any gas system.
Many articles also indicate the metal fittings threaded into PVC connections fail as well due to inadvertant overtightening of the connection, as it is very hard to "feel" the tightening of metal in PVC, and most often, the connection is over tightened and results in either cracks or cracks waiting to break later. Should this threaded air fitting fail without a hose on it, it would become a very high speed missle, just like a bullet, capable of severely damaging something or hurting someone or even killing someone.
Since I am looking at a cost of about $200 for a metal system compared to $75 for a PVC system, it just doesn't seem woth the possible problems.