Abstract: A wheel hub (10), primarily for a wheelchair wheel, can be manually operated by rotating a cover (168) to give three different operating states for the wheel which includes the hub. In the first position, the wheel is free to rotate relative to the chair. In the second position, the wheel is locked to the chair, i.e. the chair is braked. In the third position, the wheel can turn in the direction corresponding to forward motion of the chair, but cannot rotate in the opposite direction. This prevents the wheelchair from undesired backward rolling movement.

Abstract: A rotary machine has two rotors (16,18) mounted for rotation on parallel axes, each in one of two intersecting cylindrical chambers (12,14). The rotor (16) has a hub (24) and a flap (26) extending radially from the hub into close proximity with, but not into contact with, the cylindrical wall of chamber (14). The rotor (18) has a hub and a radial recess (30) which accommodates the flap (26) as the rotors rotate. The rotors are linked to one another so that they rotate at the same angular speed but in opposite angular directions. The flap (26) divides the chamber (14) into two volumes, one either side of the flap. Working fluid is introduced through the first rotor and passes along a radial passage through the rotor to direct incoming working fluid from one side of the flap. into a volume on one side of the rotor. The working fluid can be provided from an external combustion chamber.