Abstract: The invention relates to a pressurized fluid mechanism comprising a cam, a cylinder-block mounted for rotation with respect to the cam, cylinders disposed radially in said cylinder-block, pistons sliding in said cylinders, supporting rollers supporting the pistons on said cam, each roller being placed inside a transverse bore provided in each piston and a device with abutments to hold each roller in axial position in its bore.Each roller being able to comprise two projecting members on each side, the abutments present interruptions in axial directions which coincide with the radial planes containing said projecting members.The invention finds an application in the production of compact engines with "releasable" pistons.

Abstract: A hydraulic mechanism, e.g. a pump or motor, comprises a plurality of cylinders and pistons and a piston-displacement selector which is provided with blind helical grooves for controlling connection of the cylinders to the main fluid supply.