- Tank size. Generally speaking, the bigger the tank, the better the performance. Large tanks require less of the motor (which is used to refill the tank when it drops below a certain point). This not only provides uninterrupted use, it also minimizes motor strain.
- Max pressure. Many popular air tools are engineered for a psi between 90 and 100. This means that the air compressor should be a 7 bar. Be sure to check the manufacturer's specifications as some equipment may require higher levels of max pressure, 15 to 30 bar on the mid range, and 200 to 300 bar on the high end.
- Running power. Power is measured in cubic feet per minute (CFM). Determine your total power requirement by adding the CFM requirements for all air tools connected to the compressor.
- Weight. With portable compressors weighing from 40 to 70 pounds on the light side to stationary models from 250 to 500 pounds and up, weight affects installation and mounting. This is an important consideration for environments that require mobility - automotive shops and spray paint booths being two prime examples.
- Stages. Referring to the number of cylinders in an air compressor, your options will be single stage (offering up to 135 psi) or two-stage (offering up to 175 psi). Most single stage compressors are adequate for smaller shops and individual use. Large operations and industrial applications require the extra storage available through a two-stage air compressor.
- Design. Three different designs exist, including reciprocating, rotary screw, and centrifugal. The one you select will depend on your output requirements, specifically occasional use or continuous duty.
- Power type. Air compressors are fueled by diesel, electric, or gas. Your location will determine the type you need, with gas and diesel models offering slightly higher CFMs but limited to outdoor use due to the fumes they produce. Electric models are among the most popular as they can be used indoors.
Model comparisons
In addition to output and portability, size and continuous use are primary concerns within most businesses. It's also important to note that air compressors pressurize air through either positive displacement (within smaller, portable models) or centrifugal force (within industrial, stationary models).
Reciprocating and rotary screw compressors use positive displacement for its ability to compress a small volume of air into high pressure output. In contrast, centrifugal models compress air through a variety of stages, requiring a large framework. The one advantage is that they are well suited to the continuous use demands of industrial machinery.
Reciprocating Compressors
Using positive displacement, reciprocating compressors are the smallest of the three types available, often available in either single stage or two-stage models. Power outputs range from around 1 to 15 hp, making them well suited to a wide range of air tools.