The first air compressor I owned was a small, pancake-style unit, similar to the one above. It worked great for powering a brad nailer. But some time later, I tried to use it with more demanding tools. That’s when I discovered the compressor’s limitations.
Whether you’re buying your first compressor or thinking of upgrading, knowing what to look for will go a long way in helping you make a decision.
CRITERIA. There are three key aspects to consider when it comes to choosing an air compressor: air pressure, air flow (measured in cubic feet per minute, or CFM), and the amount of air that can be stored in the tank. Since air pressure, air flow, and storage all influence performance, it’s important to know how they work together. Later, I’ll talk about other features to look for when buying a compressor.
AIR PRESSURE. Air pressure is a simple concept. It’s the number of pounds per square inch (PSI) of compressed air that the compressor can produce. Most tools run at 90 PSI (maximum). But it’s a good idea to have a compressor that will produce a higher PSI than you need because the air pressure will drop as it’s used. A good rule of thumb is to have at least 35% more than the required 90 PSI for the tool, or about 120 PSI. This way, you’ll be assured of consistent pressure.
AIR FLOW. Air pressure isn’t the only way to measure the output of a compressor. Another factor is the volume of air produced by the compressor per minute (CFM). In order to operate tools at peak effciency, you need an adequate volume of air. Without it, you’ll be disappointed in the tool’s performance. In addition, operating high-demand tools with a compressor that has a low CFM rating may cause the compressor to run more frequently, resulting in faster wear and shorter pump life.
Most tools have a rating tag that states the CFM needed for optimum performance of the tool. The box at left gives you a range for a common woodworking tools. Compare these requirements to the air compressor so you make the right choice.
STORAGE. In addition to the PSI and CFM, another factor in determining the right compressor is the amount of air that can be stored in the compressor tank. Storage is measured by the size of the tank. So naturally, the larger the tank, the more compressed air it will store. And that means more compressed air is ready for the tool. If the tank is small, the compressor motor will have to work harder to keep up with the air demand. If it’s larger, the motor won’t run as often.
CONNECTION. As you can see, these three aspects of an air compressor are interrelated. You need to have enough CFM and a large enough tank to maintain the necessary air pressure to power tools without over-taxing the motor. There are just a couple of other factors to consider before you decide on a compressor. Those are noise levels and electrical needs.
NOISE. Compressors tend to be noisy by nature. But some designs are louder than others. I’ve found that oil-less compressors make more noise than ones that use oil because the piston is usually small and runs faster than an oil-lubricated piston.
Another way to reduce the noise of a compressor is to buy one with a low RPM rating on the motor. A motor with a low RPM rating will make less noise and will cause less wear on the pump. And a belt-driven motor is also superior to direct drive. It’s quieter and if the pump or the motor give out on the compressor, you don’t have the expense of replacing both at the same time.
ELECTRIC SUPPLY. Most home-shop compressors can be plugged into a common, 110-volt outlet. But you’ll need to make sure the circuit breaker is rated high enough to carry the load. For larger compressors, it’s a good idea have to a dedicated 20-amp circuit.
CONSIDER YOUR TOOLS. Along with a basic understanding of air com- pressor performance, you should also consider the type of tools you’ll want to use in your shop. Assuming you’re going to use air in your shop for the occasional tacking job or to blow dust off your saw, a pancake compressor will do just fine (main photo).
If you have more tools to run in your home shop, then you’ll need something a little larger, like the one in the photo above. A compressor this size will power a nailer, blow gun, drill, and an impact wrench without a problem. You’ll find it fine for a spray finisher for short periods of time, and possibly a sander (if it’s not used continuously).
For longer periods of sanding or spraying, you’ll need a larger compressor like the one shown above. This compressor delivers a higher CFM to power tools that demand a lot of air.
Armed with this information, the compressor aisle in the tool store won’t seem nearly as intimidating as it did before. And you’ll be able to make the right choice about an air compressor for your home shop.