a crank case comprising a two stage air compressor;

a first functional physical unit comprising an electric motor and an air dryer disposed in a first housing with the air dryer directly adjacent to the electric motor, wherein the electric motor is configured to drive the two stage air compresso and the electric motor has a first central longitudinal axis and the air dryer has a second central longitudinal axis which is parallel to the first longitudinal axis of the electric motor;

a second functional physical unit comprising a valve assembly and an electronic control device disposed in a second housing;

a compressed air container;

wherein the first functional physical unit is removably attached to the second functional physical unit and the crank case,

wherein the valve assembly comprises a first control valve and a second control valve, the first control valve configured to control air flow in a line from an outlet of a second stage of the two stage air compressor to the compressed air container, and the second control valve configured to control air flow from the compressed air container to an inlet of the second stage of the two stage compressor, the inlet disposed in an air passage between a first stage and the second stage of the two stage air compressor.