Abstract: A centrifugal compressor has at least one stage with its own impeller shaft, an inlet and an outlet for gas, and an epicyclic gear train for driving the impeller shaft. The epicyclic gear train comprises three members, a sun gear, a ring gear and a carrier on which a series of planet gears are mounted in mesh with the sun and ring gears. Means is provided for connecting a power input to one of the members of the epicyclic gear train, and means is provided connecting a second of the members to the impeller shaft. Means are provided for controlling the rotational speed of the third of the members to vary the speed of the impeller shaft of the compressor, and actuating means are provided for actuating the control means in response to the pressure of the compressed gas at the outlet.

Abstract: A centrifugal compressor has at least one stage with its own impeller shaft and a gear train for driving the impeller shaft. The gear train includes a plurality of meshing parallel shaft gears comprising two input gears either of which can receive drive from a prime mover. The ratio of the number of teeth of the input gears is such that the relative shaft speeds of the input gears are 5n: 6N where n is 1 or 2 and N is 1 or 2.

Abstract: A rotary piston machine is provided in which the, or each, auxiliary rotary piston has a portion projecting axially beyond at least one end face of the main rotary piston, and in which a transfer port is provided in an end wall of the main rotor bore leading to the part of the auxiliary rotor bore containing said projecting portion of the auxiliary rotary piston and a discharge port is provided leading from said part of the auxiliary rotor bore at a position spaced from the transfer port, said projecting part of the auxiliary rotary piston providing a rotary valve for opening and closing communication between the transfer port and the discharge port at the required times during the rotational cycle of the machine.