Compressed Air


Don't underestimate your compressed air needs. A compressor like this may seem like overkill until you decide to get busy with a die-grinder or HVLP spay gun.

A Tale Of Three Compressors

It has taken me three tries to get it right. I made the mistake that many hobbyists make—completely underestimating how much compressed air they need.

It all began when I started working on my '64 Nova Wagon. I wanted a compressor for air tools, cleaning, sandblasting, and painting. I picked up a reconditioned 3 HP compressor with a 20 gallon tank, and quickly discovered that it was not up to the task. Sure, it was OK for pumping up tires, blowing things off, or running the occasional air socket. But as soon I started using tools that consume serious amounts of air—a DA (Dual Action) sander, die-grinder, sandblaster, etc., the little compressor had to run nonstop. My tools would behave erratically, and I'd have to waste time waiting for the compressor to catch up. I also noticed that water was spitting out of exhaust ports of my tools even though I had a water trap on the compressor. What's the deal?

I had put up with that little compressor for a year or so when I decided I needed something bigger. A 5 HP, single-stage, 60 gallon unit ought to be enough, right? Things improved somewhat, but not as much as I'd hoped. By now I was getting into painting with a cheap HVLP (High Volume Low Pressure) paint gun. As long as I was painting small areas, things were OK. However, when painting a panel, the spray pattern would become unpredictable. I found that I was still having to wait for the compressor to catch up, and water was causing paint defects.

It was about now that I learned that a water trap mounted on the compressor tank is next to useless. You see, as air is compressed, it is heated, and warm air can hold a lot of moisture. The air coming out of the tank is still quite warm, especially when an under-powered single-stage compressor has to run nonstop. Warm air was carrying the moisture right past the tank-mounted water trap. As the air cooled in the hose, the water condensed just in time to come spitting out the exhaust ports of my tools, or worse yet, my spray gun. I read all I could about compressed air supply lines and set out to build an air system for myself in the hope that I could extend the usefulness of my larger, but still underachieving, air compressor.

The supply line definitely helped, but it still didn't solve my air volume problem. As my skills advanced (and my tool collection grew), I needed more air. The accusation of a pro-quality HVLP spray gun finally pushed things over the edge. It was time to look for a two-stage compressor with a larger tank. After months of searching for something suitable, Home Depot made the decision to discontinue their line of Ingersoll-Rand compressors and liquidated their inventory at significant discounts. Long story short, an Ingersoll-Rand Model 2475 compressor now resides in my garage. It features a 7.5 HP motor, two-stage pump, and an 80 gallon tank. The improvement in the way my tools run is startling, and the quality of my paint jobs is much better. I'm asked from time to time if this compressor is overkill. No, it is just about right.

Compressor Detail

The numbers say it all. 24 CFM @ 175 PSI, finally, enough air!

My advice to anyone considering an air compressor for their home shop is this. Bigger is always better. Get the largest compressor you can afford; you will save money in the long run. I've never heard anyone complain that their compressor was too big. I would consider a 5 HP, two-stage compressor with an 60 gallon tank to be about as small as you can realistically go if you plan on doing any body work on your car.

Supply Line

If you plan on doing much more with compressed air than pumping up tires, an air supply system is essential. A supply line has several benefits:

For most garage applications 3/4" pipe should be adequate. However, it wouldn't hurt to use larger pipe if you can. The increased surface area will aid in cooling. Locate the first drop at least 25 feet a way from the compressor. In humid areas it might be worth considering a cooling tower made of 2" pipe. Run the pipe up and down on a wall, placing drains wherever water could collect.

Black gas pipe and galvanized pipe are the most popular materials, but copper pipe can be used too. It just depends on what material you're most comfortable working with. In spite of what you may hear or read, don't use PVC or ABS plastic pipe! It may be cheap and easy to work with, but there are dangers. If the pressure switch fails on your compressor, pressure levels in the supply line could build to dangerously high levels, possibly resulting in an explosion. Also, plastic pipe could rupture in the event of a fire, providing an additional source of fuel. Plastic pipe doesn't cool the air as much either.

For more information on supply lines, check out the following resources,, or

I built my 35 foot-long supply line system out of 3/4" galvanized pipe with the following features:

Supply Line

The drop is 35 feet from compressor, with drip leg, drain, water trap, regulator, and MotorGuard M60 filter.

Flexible Coupling

An Ingersoll-Rand flexible coupling prevents compressor vibration from damaging the supply line.

Air Filter

I use a MotorGuard M60 0.1 Micron filter after the water trap and regulator. This setup was recommended by my local automobile paint store. It works very well in Colorado's dry climate. Talk to the people at your local paint store for advice on filtration and water separation in your area.

M60 Filter

M60 filters use a "toilet paper" cartridge.

Toliet Paper

I prefer single-ply. The filter element is crushed slightly when the top and bottom halves are assembled. This allows air to pass between the layers of paper.

Tank Drain

It's important to drain air compressor tanks daily, but most people don't do it often enough because the drain is so hard to reach. Make it easier by using an elbow, an appropriate length of pipe, and a ball valve.

Tank Drain

A ball valve, a 90-degree elbow, and a length of pipe makes the chore of draining the tank a lot easier.


They may seem innocent enough, but if you're still using 1/4" quick-connect couplers in your air system, throw 'em in the trash! 3/8" quick-connect couplings flow twice as much air. I prefer the "automotive style" because they can be pushed in without having to pull the collar back.


Note the difference in size between 1/4" and 3/8" couplers. The 3/8" coupler is on the right.

top | back