How a Two-Stage Air Compressor Works

by Vance Holloman

An air compressor, much like its name indicates, compresses air, which can then be used for a variety of purposes. Air compressors work much like car engines, using combustion to a drive a piston. The most common kind of air compressor, and the most portable, in use today is the single-stage air compressor, which can achieve a psi rating of around 125 by using a single piston to compress air. The two-stage air compressor can achieve substantially higher psi ratings due to adding a second piston to the mix.

All air compressors consist of a motor, a piston and a storage tank. Smaller compressors typically can store between one gallon and five gallons of compressed air. This is accomplished when the piston drives air into the tank repeatedly, forcing a large cubic volume of air into the smaller, confined space of the tank. It works on the same principle as hand pumps used to inflate sports balls or bicycle tires. The upstroke draws air into the tube and the down stroke forces the air through the hose and into the ball. Each subsequent stroke adds more air into the confined space of the ball, increasing the air pressure. If enough air is added, the pressure will cause the ball to burst.

The two-stage air compressor adds a second piston to the process that fires after the first to further compress the air in the tank. By using a second piston, the compressor can produce air compressed to 175 psi or greater, which is roughly 50 psi more than the more common single-stage air compressor. All two-stage compressors have cast iron storage tanks due to the higher air pressure they are capable of delivering. Many of they single-stage compressors use aluminum tanks, which aren't as strong as cast iron and could burst if subjected to the higher psi generated by two-stage air compressors.

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