Abstract: A drive unit for a mining machine such as a mining plow or conveyor drives a sprocket wheel of the chain thereof by an electric motor through a drive train having a turbocoupling and a transmission driven by the motor. A free-shifting clutch is provided in the case of overload to disconnect the load from the motor, the clutch reengaging upon standstill of the two clutch halves. Alternatively the turbine output of the fluid coupling is branched and is applied through one friction clutch directly to the input shaft of the transmission or through a second friction clutch to a parallel shaft connected by gearing to the transmission input shaft.

Abstract: A mining machine for excavating coal along a coal front of a seam in which a chain displaces excavating tools along an excavating stretch at a leading side across the coal face and a conveying stretch is provided rearwardly thereof, the stretch terminating in direction reversal stations with wheels at opposite ends of the stretches. A linear drive for at least one of the wheels can extend in a gallery alongside the mined cut. According to the invention, the excavating conveyer bottom is at an angular of 70.degree. to 130.degree. to the bottom of the conveying trough and the shafts of the wheels are inclined to the vertical forwardly and upwardly to include angles of 10.degree. to 45.degree..

Abstract: A positioning cylinder assembly for subterranean mining applications has a rotary potentiometer connected through a friction wheel transmission with the spindle of the cylinder which is rotated when the piston is axially displaced therein. The friction wheel assembly comprises a pinion wheel connected to the spindle and a hollow wheel connected to the rotary potentiometer, that not only matches the pitch of the spindle to the rotary spring of the potentiometer but also functions as a slip clutch for zero setting of the potentionmeter and the piston.

Abstract: In a hydraulically operated unit, particularly a prop for a support in an underground excavation, a thin-walled tubular jacket is pressed on an inner element which is movable in an outer tubular element so that the tubular jacket has an inner diameter which is determined with a substantial undersizing relative to the outer diameter of the inner element, and the tubular jacket is clamped on the inner element with exceeding of the flow limit of the inner element and only in a plastic expansion condition which exceeds with a reliable distance and elastic deformation region of the tubular jacket and with a sufficient residual springing part.

Abstract: A shut-off valve has a sealing cone which in a closed position of the valve abuts against a conical sealing seat and is formed as a part of a cylindrical throttling piston, a sealing surface of the sealing seat cooperates at its one end with a cylindrical receiving opening for the throttling piston, and the outer diameter of the throttling piston is selected with respect to the inner diameter of the receiving opening so that a throttling gap is formed between the receiving opening and the the throttling piston.

Abstract: An hydraulic prop utilized for barricades in blasting operations that affords simplified mounting and dismantling and will have minimal functional inefficiency if deformed by the impact of rocks; and it can be made out of unworked pipe of minimal standards. Two specific guide regions disposed on the piston are spaced large enough from each other that comparatively wide tolerances can be achieved between the piston and the cylinder.