Departments | Shop Talk

Our biggest and smallest air compressors give you an idea of the size range of these valuable tools. The larger compressor can operate anything you can reach with a couple of hoses.

Working Under Pressure

Last week my son Tim and I made two trips to friend Don’s house to do some work to get his house ready to sell. The first time we took our biggest compressor—a 33-gallon shop model—to spray texture on several wall areas Don had repaired. On the second trip we needed only our little “hot dog” style compressor, which worked great to nail casing on a door jamb and install base in a couple of rooms.

The bigger compressor takes two guys to load, and it takes up a lot of room in the truck. It was ideal for the first job, but would have been overkill for installing a few pieces of trim.

As carpenters, my brothers and I have been using air compressors for years, but it wasn’t until Tim started wrenching on cars that we bought a compressor big enough to power automotive tools. Tim’s mechanic’s tools have given me a whole new appreciation for this simple but important air pump.

Air compressors have some basic components. Most non-industrial compressors have a motor connected to a crank that pushes a piston up and down in a cylinder. The repetitive action of the piston crowds more and more air molecules into the confines of a tank, increasing the pressure of its contents.

When the air tank reaches a predetermined pressure, a pressure switch interrupts the process by shutting off the engine, disengaging the crank or releasing additional air through a valve. The air is carried to the tool via a pressure regulator and a hose or pipes.

There is a distinct correlation between the types of jobs you do and the size and style of air compressor you need. One guy using finish nailers can get by with a pretty small compressor. Add more guys to the crew or increase the size of the nail guns for framing and you’ll need a bigger tank and quicker recovery time.

Rapid-fire tasks such as underlayment stapling and roofing means you have to ramp it up again. Tools that require a constant flow of air, like texture sprayers and grinders, need yet another level of capacity and recovery.

Size, quality, convenience and cost are all important considerations when choosing an air compressor. Getting the biggest compressor you can find usually is not the right solution. After all, a big shop unit isn’t much good for nailing on a couple of pieces of trim in a second floor bedroom.

Not only does a compressor need to match your air tools, it must also match the power supply you have available. Our smallest compressors run fine on a 15-amp circuit, but add some horsepower and you’ll need 20 amps. Keep supersizing and a home shop unit can require a 220-volt outlet like you use for a range or dryer.

If you need air in a location where you can’t connect to the power grid, there are plenty of compressors available that run on diesel, gasoline or 12-volt automotive circuits. In fact, most of the framers and roofers I know use gas powered air compressors.

If room and cost were not factors, many of us would like to have the biggest, baddest compressors available. Motor size, tank size and psi rating all contribute to the capability of a compressor. There are several good reasons, however, to scale back, including budget, room, noise, energy requirements and portability.

Pulling Double-Duty

One piece of equipment on my wish list is the Warn PowerPlant Dual Force HP, which is a combination winch and air compressor that runs on a vehicle’s 12-volt system. Warn was able to achieve some impressive air flow and recovery times by employing a gear change when switching between winching and air compressor modes. The winch features a 9,500-pound single-line pull rating, which is good for most full-sized 4x4 recoveries. The air compressor component has a flow rating of 5 cfm @ 90 psi and maximum pressure of 100 psi.

When choosing an air compressor, start with the types of tools you want to use. The impact driver we use in our home garage is our most air hungry tool. The specs say it requires about 7.5 SCFM (standard cubic feet of air per minute) @ 90 psi (pounds per square inch). We bought a 26-gallon, 2 hp, 150 psi compressor to power this tool and to power a spray gun that shoots drywall texture. This compressor is not exactly mobile, which brings me to my next point.

If you have plans for air-driven impact drivers and ratchets for auto mechanic work and you do carpentry away from your shop or house, you’re probably going to need two compressors—one for the shop/garage and another lighter version for doing construction projects at other locations.

My brothers, sons and nephews have several compressors ranging from a little 1 hp with a 1-gallon tank to our 26-gallon shop model. In the field, the rule of thumb is to use the smallest compressor that will get the job done. For a two-man crew doing trim work, a 1 1/2 hp, 1 1/2-gallon SCFM 4.0 works well.

Whatever you buy, follow the safety and maintenance guidelines, including draining the water from the tanks frequently to avoid rust. Corrosion can make the tank weak, and loose rust particles can plug lines and cause valve malfunctions. A quality compressor, properly maintained, will keep your tools working under pressure for years to come.

—Larry Walton