Reciprocating - high pressure, low to high flow. Versatile workhorse for many applications. Vendors include Ariel, GE, Dresser-Rand, Gardner-Denver, Mycom

Flooded screw - versatile, good turndown, vacuum capability, low to medium discharge pressures,low to medium flows. Vendors include Howden, Kobelco, Ariel, Frick, Sullair

Centrifugal - versatile, high pressure and high flow. Vendors include GE, Cameron

Vane - low pressure and low differential. Vendors include RoFlo, Gardner-Denver

Scroll - for gas and refrigerants, low hp, canned design. Vendors include Copeland (Emerson)