After being in my shop for 5 years (but only using a decent compressor for 3) I have finally plumbed the shop for air a organized all those loose hoses I kept tripping over. After much reading I decided to go with Type L copper pipe. From what I could tell it is the second best pipe for running air in the shop. If you have the time and extra tools, consider using galvanized iron pipe. I chose copper over iron pipe because of the ease of assembly. I didn’t want to have to thread all the ends I cut to make it fit in my shop. But the advantages of iron pipe are quietness and cools the air (better heat sink) to condense the most moisture out. One other option I read about is PVC pipe. Some sites reported the ability of PVC to explode if damaged, sending sharp fragments flying through the air. I also heard of it’s ability to build up a static charge (especially if you dry your air).
The only difficulty with the copper is learning to sweat it properly, although this is much easier than it sounds. I looked around the internet and youtube and found many good demonstrations on sweating (or soldering) copper pipe.
For the bulk of the project (120 feet in my application) I used 3/4″ pipe with 10 of 1/2″ pipe used in the drain valves and quick disconnects. I decided it would be easiest on my project if I pre-assembled as many of the parts as I could. I started where the air takes off from the main line. I made some large U shaped pieces that go up from a T then turn around down for the drop to the quick connects. I continued with the quick connects for the hoses. Each one is at the end of a drop from the over head line and has a drain valve at the bottom of a receiver for the moisture. For the quick connects, I used a 45 deg elbow turned up from the pipe (last attempt to remove moisture). I finished by tieing all the pieces together with the main line and the drops. I put a 3/4″ ball valve where it connects to the compressor as a service disconnect.
A few more of the parts: