When we first consulted with the UT Facilities department to find out what it would cost to replace the air system, the head of their plumbing shop gave us an estimate of two guys for two weeks, at thirty bucks an hour, plus supplies and materials. That quickly comes out to a number around $6000, plus all of that downtime for the 4-5 people who work in the lab in a normal week. In dismay (and disbelief, since I know how difficult this sort of plumbing is), we asked if we could do it ourselves. The answer was yes, but clearly they didn't think it was a good idea.
After a few trips to the hardware store, some consultations, and a few hours online weighing the options, I decided to go with copper pipe to replace the mix of materials already in place and causing problems. Then, with this pile of fittings and tools, and 100 feet of schedule L pipe, Sebastian and I took to the task of installing the system. Instead of two weeks, it took two long days, with much of that time spent by me running around buying parts to make sure Sebastian had everything needed to keep the project moving. The following pictorial is a brief outline of the steps involved in sweating copper pipe.
Step 1: (Currently no photo) After cutting the pipe to length, all surfaces to be joined are scrubbed bright with a wire brush and painted with a thin coat of flux to ensure flow of solder.
Step 2: Pipe sections are mated with fittings, then heated with a propane torch for 10-20 seconds, until the metal is hot enough to melt the solder on contact.
Step 3: The torch is withdrawn, and the solder is applied to the hot joint. It will melt instantly and be drawn into any gap space, solidly connecting the two separate pieces of metal.
Step 4: The joint is wiped with a cloth to remove remaining flux and excess solder from the surface.