Abstract: The invention concerns apparatus for the determination of the length of stroke of a piston in a working cylinder, especially in a hydraulic, walking, mine-roof support. For this purpose a piston shaft is rotatably mounted in one end portion of the working cylinder and extends into a hollow cylindrical piston rod of the piston. Through a pin on the piston or piston rod which engages in a helical guide groove on the piston shaft, the latter is rotated during movements of the piston. The piston shaft is connected to a code plate provided with a pattern of holes and displaceable on rotation of the shaft between light-emitting elements on one side and light-detecting diodes on the other side. The combination of irradiated and darkened light-detecting diodes represents a digitally-detectable binary numeral sequence which corresponds to a specific piston position.

Abstract: An hydraulic rotation damper comprises a bearing housing with inner stator vanes and a rotor with rotor vanes, the rotor being arranged on a carrier arm journal which is mounted in bearings in the bearing housing with the stator vanes and the rotor vanes forming working chambers. At least one damping valve is provided for transferring working medium from pressure-loaded working chambers into unloaded working chambers. Further, the working chambers are closed at both ends by end walls containing valve-controlled passages leading into annular gaps which are separated by the end walls from the working chambers. This permits pressure medium at a pressure corresponding to the working pressure in the respective working chambers to be fed to the annular gaps where the pressure medium applies pressure to the outer surfaces of the end walls of the working chambers to prevent axial displacement of those walls.

Abstract: The control valve for the re-setting of the props at a predetermined minimum setting pressure is connected at respective junctions to a high pressure conduit, to the pressure chambers of the props, to the prop-setting conduit and to the return-flow conduit leading to the annular chambers of the props. The spring-loaded closure body is guided displaceably in the valve housing by journals on each of the two sides of the valve cone. The ends of the journals are formed as actuation faces. The valve cone seals off the high pressure junction and the junctions leading to the pressure chambers of the prop and opens only when a predetermined minimum setting pressure at the junction is exceeded. For closure, the control valve is loaded through the junction on the actuation area of the journal with the pressure fluid conducted to the annular chambers of the props.