Bearing assembly

A centrifugal compressor comprising:

• a rotor shaft having two opposing axial ends;
• a motor mounted centrally on the rotor shaft;
• a first impeller mounted on the rotor shaft and spaced from the motor in a first axial direction and a second impeller mounted on the rotor shaft and spaced from the motor in a second, opposing axial direction;
• a first bearing unit mounted on the rotor shaft between the motor and the first impeller, the first bearing unit being configured to support both radial and axial loads when an axial load acts on the rotor shaft in the first axial direction and to support only a the radial load when the axial load acts on the rotor shaft in the second axial direction;
• and
• a second bearing unit mounted on the rotor shaft between the motor and the second impeller, the second bearing unit being configured to support only a radial load when the axial load acts on the rotor shaft in the first axial direction and to support both radial and axial loads when the axial load acts on the rotor shaft in the second axial direction;
• wherein the first bearing unit is a double row bearing including a first, axially outer angular contact bearing and a second, axially inner angular contact bearing, the first and second angular contact bearings being arranged in a back to back configuration and an axial clearance being defined between an outer ring of the first angular contact bearing and an axial abutment located axially outwardly of the first bearing unit such that when the axial load acts on the rotor shaft in the first axial direction, the first angular contact bearing is configured to support the radial load only and the second angular contact bearing supports the axial load and the radial load while the second bearing unit supports the radial load only;
• and
• wherein the second bearing unit is a double row bearing including a first, axially inner angular contact bearing and a second, axially outer angular contact bearing, the first and second angular contact bearings of the second bearing unit being arranged in a back to back configuration and an axial clearance being defined between an outer ring of the second angular contact bearing of the second bearing unit and an axial abutment located axially outwardly of the second bearing unit such that when the axial load acts on the rotor shaft in the second, opposing axial direction, the second angular contact bearing of the second bearing unit is configured to support the radial load only and the first angular contact bearing of the second bearing unit supports the axial load and the radial load while the first bearing unit supports the radial load only.