Based on my research and discussions with a few automatic control system vendors, type L or K copper with brazed joints is the preferred piping system, followed next by galvanized pipe, then black steel pipe (never PVC). The prevailing issue is the water in the air which will eventually condense within the piping. Copper won't corrode and form sludge. Neither will galvanized pipe. Black steel pipe will corrode and sludge will form within the pipe. The sludge will eventaully find its way out the point-of-use device. Since a galvanized pipe system is not that much more expensive, I'll go that route...unless I can talk my old man into dusting off his torch rig and brazing copper for me! Another good (I think) tip I found is a recommendation to use a short length (2 or 3 feet) of new high-pressure hydraulic hose to connect the compressor to the galvanized pipe. This is to allow the compressor to vibrate without affecting the rigid metal pipe system, to avoid a fatigue/stress failure. I think I now have a plan. Thanks again guys.