A two-stage rotary screw air compressor contains two sets of synchronized rotors and can be housed in a common stator housing (over/under design) or two separate stator housings bolted together in tandem (end-to-end design).

The over/under design utilities “interstate” cooling via an injected “curtain” of lubricant/coolant, which improves overall efficiency. Two-stage rotary screw air compressors are typically direct or gear drive. A single –stage rotary screw air compressor takes in atmospheric air and does “the work” (x rate of flow, at y pressure) in one compression process. A two-stage rotary screw compressor takes in atmospheric air but “shares the work” over two separate compression processes and cools it in between.

The difference between the two is not the end result, rather the energy required to produce the end result.