Abstract: A mechanism for rotating the grab bucket of an excavator is formed with a stator having a shaft extending into the bore of a rotor with hydraulic ducts being provided in the stator and the rotor in flow communication with each other for activating the grab bucket by means of a hydraulic drive mechanism externally connected therewith. The ducts in the stator and the rotor are hydraulically connected by circular passages formed on the outer circumference of the stator shaft and shoulders formed in the rotor and the stator operate to have arranged therebetween bearing means on opposite sides of the circular passages which interconnect the ducts between the stator and the rotor.

Abstract: The clam-shell bucket of an excavating machine is rotatably connected with the arm or boom of the machine by a hydraulic motor which also provides passages for transmitting pressure fluid from the body of the machine to jacks opening and closing the bucket. Radial cylinder bores in the stator of the motor contain respective pistons and spherical cam followers which engage a radially undulating cam face of the rotor when sequentially supplied with hydraulic fluid by a distributor rotating with the rotor in an axial bore of the stator. The passages for the fluid supply of the bucket jacks extend partly in the rotor and partly in the stator and communicate through a bearing interface remote from the distributor and the axial bore containing the same.