Air Compressors For 4x4 Trucks - Willie's WorkbenchPosted in How To: Tech Qa on August 1, 2008
Just about everyone I know who works even partly on their own vehicle owns an air compressor of some sort. Admittedly, they're one of the handiest tools you can own. Filling tires is the first thing that comes to mind, then probably airtool use.
I've got a whole flock of airtools-three impacts, two ratchets, a nibbler, a flanger, a riveter, an air chisel, and three or four spray guns come to mind. Plus a plasma cutter, an air jack, a bead blast cabinet, an air drill, two air-powered end-lift jacks, and a bunch of sanders. Oh yes, not to forget the air-blowing nozzles. I even made one up with a brake line on the end that's about 4 feet long. Now I don't have to bend down to blow out the junk from under the benches or in corners.
Over the years I've collected a few tips on air compressors that I'd like to pass on. The first one, and most likely the most important, is "Buy a compressor bigger than what you figure you'll need." For instance, 27 years ago I bought a 5hp model one that in reality satisfied all my needs at the time. It has served me well as I change the oil about every year using a synthetic lubricant, and drain the air storage tank about once a month. However, with more air-demanding tools, I found the compressor was running nearly continuously. I read somewhere that with every 20-degree increase in temperature above 180 degrees, lubricant life is cut in half, and that a 20-degree decrease in air temperature produced a 50-percent reduction in water vapor content.
OK, so some 10 years ago I started thinking I needed a bigger (cfm flow) compressor. But big compressors are expensive, and I already had a good (but not enough-capacity) compressor. Besides, big compressors take more electricity. Then I stumbled on a garage sale that had a like-new compressor very similar to mine for about one third the original cost. It was a no-brainer: use two compressors with a couple of shut-off valves. I could use one for the majority of my air needs and run both when high demands were needed. No more waiting for air pressure to play catch-up. Yes, the two running together most likely use more electricity than one large model, but in most cases, just one of them suffices.
Something else I would like to touch on is air lines. Do not use PVC piping for air lines! First off, think about what would happen if you were to accidently bang something into the PVC line and it broke. Being under 125 or more psi, it's going to shatter into multiple fragments, a good portion of them aimed at you. Secondly, PVC does not drop heat anywhere near as fast as metal pipe does to allow moisture to condense, and we all know moisture is the enemy of any airtool. PVC also gets brittle over time when exposed to heat, compounding the breakage problem.
Running hard lines along the walls of your shop/garage is a much better deal than running long lengths of rubber hose across the floor. The trick is to run the pipe (with a flexible hose between the compressor and pipe) up the wall to the ceiling, then across the wall at a slight downward slope, and then back down the wall to a drain valve. All this pipe acts as a heat sink, and as the moisture condenses, it runs to the lowest point-your drain valve. Then come off the ceiling pipe with an upward-facing T and a couple of elbows to turn the pipe back down to a point wherever you need an air outlet. It's still not a bad idea to put a moisture trap at each outlet. I even have a filter on one outlet that has a hose reel attached. There is an automatic oiler on one of my outlets with a dedicated hose just for airtools.
Right now I use 3/4-inch galvanized pipe for my air lines, but when I do it again, I'll go with copper. Why? Over time, even the galvanization will break down and rust. The rust will break off and-yep, you got it-go into your airtool. Plus the buildup can, and actually will, restrict airflow. Copper pipe is more expensive but so much easier to use once you've mastered the proper soldering technique.
And one more thing: my opinion is that you don't really need a 150- to 175psi compressor, as you regulate most airtools down to 125 psi or less. Sure, more pressure relates to more usable volume before the compressor kicks on. But also check out the additional run time it takes to build back up to that higher pressure. More pressure also means more heat buildup. Again, I read some place that for every 2 pounds in pressure buildup, energy consumption is 11 percent more. The only thing I believe you gain is a more expensive compressor with a longer run time.