Choosing Air Compressors
The ability to compress air allows a wide array of tools and functions to be used. A few examples include; nailing on a roof, painting a car, and changing tires on a tractor. This diversity has made air compressors popular and important tools.
Performance Rating
The most important rating of a compressor is the volume of air it can deliver at the required PSI (pounds per square inch) pressure rating. Air volume delivery is measured in Cubic Feet per Minute or CFM. Most tools operate at 90 PSI, making this the standard measurement. Every air tool consumes a certain amount of air, this needs to be kept in mind when buying a compressor. A compressor can run an over-powered air tool as long as it has air reserve in its tank, but will not be able to keep up long term.
Duty Cycle
This describes how long an air compressor can run within a ten-minute period without overheating. Every motor will run at 100% duty cycle, however, the reciprocating pump will need breaks to cool down because if they run non-stop, they will fail from overheating. Quality pumps can have a duty cycle of up to 80%, meaning that for every ten-minute time span, it can run for eight minutes, but should rest for two.
Maximum PSI
This should also be considered, especially for heavier tool applications. An average user may only need 90 PSI, but industrial users often require up to 175 PSI, which can be attained with a
two-stage compressor.
required air volume
The chart below includes some common air tools and their average CFM measurements. Reference this chart to determine what continuous CFM rating is required of your air compressor.
*If you plan on using an air tool on a continuous basis, it is a good idea to multiply the “Average CFM” x4 to get a continuous CFM rating for the tool.
| Air Tool | Average CFM @ 90 PSI |
| 7″ Angle Grinder | 5-8 |
| Brad Nailer | 0.3 |
| Chisel / Hammer | 3-11 |
| Cut-off Tool | 4-10 |
| Drill | 3-6 |
| Dual Sander | 11-13 |
| Framing Nailer | 2.2 |
| Grease Gun | 4 |
| Hydraulic Riveter | 4 |
| 3/8″ Impact Wrench | 2.5-4 |
| 1/2″ Impact Wrench | 4-5 |
| 1″ Impact Wrench | 10 |
| Mini Die Grinder | 4-6 |
| Needle Scaler | 8-16 |
| Nibbler | 4 |
| Orbital Sander | 6-9 |
| 1/4″ Ratchet | 2.5-4 |
| 3/8″ Ratchet | 4-5 |
| Rotational Sander | 8-12.5 |
| Shears | 8-16 |
| Speed Saw | 5 |
Key Parts Of Air Compressors
Every air compressor is a collaboration of several parts working together. The more power the machine has, the greater number of tools and operators it can support.
Motor / Engine System
This is the electric motor, or gas engine, that spins the pump. Electric motors have the advantages of running quieter, less maintenance, and zero emissions allowing them to be used indoors.
Gas engines greatest advantage is unlimited portability. They can be driven to any jobsite on the back of a truck.
Storage Tank
Having a reserve of stored air allows the compressor to operate tools that the pump and motor combination normally couldn’t keep up with. It also gives the pump and motor a chance to turn off and cool down. Bigger is not always better because it will limit portability, and the smaller pump and motor combinations should be mated with a small tank so they don’t overheat trying to fill an oversized tank.
Pump
Attached to the engine and compresses the air then sends it to the storage tank. While there are several types of pumps, the reciprocating pump is the most common on everything except the heavy industrial machines. Reciprocating pumps are either single stage, which usually have a maximum capability up to 125 PSI, or two-stage that can get up to 175 PSI.
Plumbing System
This refers to all the connecting pipes, fittings and hoses that allow everything to work together. The most critical part is the system that senses the tank pressure and signals the machine to stop building pressure. For electric air compressors this is the pressure switch, which is the black box that will turn the electric motor on or off to maintain tank pressure.
Gas engine models have a brass pilot unloader system that controls the engine idle, and and directs the pressurized air into the tank, or out to atmosphere once the tank is full.
