Q:
I am setting up a new shop, and I was told that I shouldn’t use PVC piping for compressed-air lines. Is that correct? What should I use?
John Smith, via e-mail, None
A:
Bill Duckworth, former associate editor at Fine Woodworking magazine, replies: Ask this question on one of the woodworking Internet sites, and you’re sure to find valid and contrary opinions about plumbing your new shop for air using black iron pipe, galvanized pipe, copper, rigid PVC, flexible vinyl, polyethylene and nylon tubing.
Supposedly, you can buy PVC pipe rated to handle the stresses of compressed air. But cold air can make PVC brittle, and an accidental blow to an exposed pipe under pressure can send shrapnel flying. I’ve also read that PVC seriously degrades with exposure to UV-light, which could be a problem if you plan to have windows in your shop. In addition, I’ve seen firsthand the aftermath of an exploded PVC pipe that was used as an air line. That was enough to discourage me.
I’ve seen shops with clear-vinyl tubing run for air lines. But depending on the diameter you need (longer runs require larger diameters to avoid pressure-drop problems), you may have trouble finding the right size bushings and fittings that won’t blow out every time you crank up the pressure. The best plastic-tubing system I’ve heard about is Topring (800-263-8677; www.topring.ca). Topring uses nylon tubing with fittings specifically designed for compressed air.
What type of material would I use? I’ve just finished building a new addition for a walk-out basement shop, and I’m going to plumb it with black iron pipe. Here’s why: Black iron pipe is strong, it’s easy to put together, and the joints are leak-free. Also, you can cut and assemble it into just about any configuration.
The biggest drawback is threading the ends of the pipe. Threaders are available for rent, though, or you can have a local plumbing-supply store do the threading for you. I use Teflon tape on all the joints so that they go together—and come apart—easily. Black iron pipe makes it easy to change or add onto your system down the road. All you need is a monkey wrench.
Another advantage to black iron pipe is that it condenses moisture out of compressed air better than PVC or other plastic tubing, which makes condensation easier to remove with trap valves.
I’d avoid using galvanized pipe because it’s more expensive, and I’ve heard that the zinc coating can flake off, creating debris that can clog filters within the lines or ruin tools. I shy away from copper pipe because I’m no good at sweating joints and because I don’t want to pay a plumber. I also try to avoid open flames in a woodshop.
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