Compressors are separated into two major groups, positive displacement and dynamic. Positive displacement compressors bring in air, trap it, and then reduce its volume mechanically.
Reciprocating compressors use a piston driven by a crankshaft to deliver high pressure air. The small size, simple maintenance, and ability to set-up near the point of use are some of the benefits of a reciprocating compressor. They run start/stop, only producing air when needed, which is very efficient.
Scroll compressors use intermeshing spiral scrolls, with one being stationary and the other orbiting in relation to it. Although these compressors are limited in size, they are relatively efficient, oil-free and have low noise levels.
Screw compressors use two mated screws to mechanically reduce the volume of the air. These compressors are typically better for industrial uses and are much more durable and have a higher performance than reciprocating or scroll compressors. They are available in oil-free and oil lubricated depending on the application.
Dynamic type compressors, for example centrifugal, use a high speed rotating impeller to transfer energy to the air. Disadvantages include limited capacity control modulation, specialized maintenance considerations, and high initial costs. These compressors are perfect for larger applications and are designed to be oil-free.