A FLUID MOTOR AND A FLUID PUMP

A fluid machine for a pneumatic or hydraulic drive system, said fluid machine being able to work as a fluid motor or as a fluid pump, comprising: at least two piston assemblies each comprising a piston means (-), the at least two piston assemblies being operable to cause sequential reciprocating movement of the pistons means (-); a drive member () rotatable about an axis and providing an annular, wave-like surface () extending at least partially radially to the axis, towards which the piston means (-) project, wherein, in case of working as a fluid motor, the pistons means (-) are arranged to drive rotation of the drive member () about the axis at least by a pushing action on said wave-like surface () or, in the case of working as a fluid pump, the piston means (-) are arranged to cooperate with said wave-like surface () so that rotation of the drive member () drives sequential reciprocating motion of the piston means (-).