Choose the Right Air Compressor
By Matt Weber
How to Match the Air Supply to Your Air Tools
When you need to run anything from a framing nailer to a sand blaster, the right air compressor can handle the job with power to spare. Air compressors are versatile and economical, providing a single power source for a wide variety of tools that tackle everything from woodworking and metalworking to painting and mechanical work.
Pros and DIY’ers alike can choose from a wide variety of compressor sizes and capacities. Small inflators can air up bike tires and provide an emergency fix for leaky car tires. Also available are powerful portable air compressors for construction work, as well as professional-grade stationary models for carpentry shops and automotive garages.
Air Compressor Anatomy
There are many types of compressors, but they all perform the same function. All compressors increase the pressure and reduce the volume of air by filling a chamber (tank) and then reducing the chamber’s volume. Reciprocating—also called “Piston”—air compressors are the most common type and can be found in a wide range of horsepower output.
Piston compressors can be found in two primary configurations; single-stage and two-stage. Single-stage air compressors work by drawing in air and compressing the air to its final pressure in a single piston stroke. Single-stage compressors can usually reach pressures of up to 150 PSI. Typically, a single-stage pump will have a higher CFM (cubic feet per minute) rating than a two-stage pump, because each cylinder is drawing air and compressing it during every rotation.
The larger two-stage compressors work in a similar manner, but they compress the air in two steps or stages. During the first stage, air is drawn and compressed to an intermediate pressure. After being compressed in the first stage, the air is piped to a second stage where the air is allowed to cool, to be compressed in the final step. Two-stage compressors can usually reach pressures up to 200 PSI. Compressors with two-stage pumps are more efficient at higher pressures and continuous use because the air is cooled between the stages.
Air Tool Value
An air compressor is only as useful as the pneumatic tools that do the work. Although they require connection to a compressor hose, air tools offer some significant advantages over electric tools. One of the biggest benefits is that air tools do not require their own motor. This makes the tools more compact, lighter and easier to handle—with less moving parts to malfunction. For this reason, air tools are also known for their long-lasting value. With electric tools, you have lots of small motors that can wear out. With air tools, you have a single powerful motor to run them all, and as a result air tools can perform for years without failure.
Versatility is another advantage. Whether you’re building a shed, painting a fence or fixing your car, you can easily interchange a variety tools at a single compressor, including a ratchet wrench, paint sprayer, angle nailer, finish nailer or impact wrench.
Assessing Compressor Power
The most popular air compressors among DIY’ers and pros on the move are portable units that can serve as an inflator, and much more. These mid-size units can be toted to the jobsite while still providing ample power. A portable air compressor is a great household tool that can inflate tires, operate an airbrush kit and power short-burst tools like nailers and staplers.
When choosing an air compressor, many people assume the higher the horsepower rating, the more powerful the compressor. However, horsepower can be misleading. Like two race cars with the same horsepower rating, one of the cars can still go faster. There are many other factors influencing how well the machine will perform other than horsepower.
Furthermore, manufacturers provide different variations of horsepower. Some compressor manufacturers rate their products by peak horsepower (also known as brake horsepower). Peak horsepower is the maximum output a motor can produce while the motor has the start windings engaged, which can be as much as 7 times the running horsepower. Under normal operating conditions, the start windings are only engaged for a fraction of a second, so using peak horsepower as a comparison rating can be misleading since the motor only achieves this horsepower during startup.
If the start winding is engaged for an extended period of time, the motor can overheat and fail.
Another misleading rating is a compressor’s air pressure or PSI (pounds per square inch) rating. Most air tools require 90 PSI to operate, and most air compressors produce at least 90 PSI, meaning virtually any compressor intended for pneumatic tool use will achieve the necessary air-pressure output. Although higher PSI can impact run time, it does not necessarily improve tool performance.