Abstract: An improved compressor shaft and impeller for an overhung centrifugal compressor are disclosed that enable the hydraulic attachment and release of the impeller and shaft. The shaft and impeller are also keyed together to enhance their torsional load carrying ability. The impeller and shaft have mating tapered turns that provide precision alignment and mating keyed turns axially adjacent to the mating tapered turns that are mechanically coupled, typically by a removable key. The shaft has a hydraulic passageway that connects to the tapered interface between the shaft and the impeller. By providing hydraulic pressure to this passageway, the tapered surfaces can be forced apart to more easily remove the impeller. An annular piston is disposed between the shaft and the impeller that also communicates with the hydraulic passageway. Hydraulic fluid acting on the piston forces the impeller and the shaft apart in an axial direction.