Abstract: Hydraulic control apparatus serves to operate roof support props of a mineral mining installation. An automatic setting arrangement with a valve device ensures the props become set against the roof with a high uniform force by connecting a prop pressure chamber to a pressure fluid source once a threshold pressure is exceeded signifying the prop has been extended. To disable the automatic setting arrangement during prop retraction the valve device thereof is provided with a control piston which is subjected to pressure during retraction to oppose the action of another control piston which responds to the threshold pressure.

Abstract: A pressure-relief valve device has a housing with bores for admitting and discharging pressure fluid. The fluid admitted to the housing passes via a hollow member or sleeve to a valve inlet. The sleeve has at its upper end a chamfered seating surface for engaging with a sealing surface of a valve member and these surfaces form the valve. The valve member has a head with the sealing surface at its periphery and a stem which is guided within the sleeve. The stem is axially and circumferentially grooved to allow pressure fluid to pass through the housing to flush dirt away from the valve inlet even while the valve is closed. Opposed spring forces bias the surfaces of the valve together and a stop member limits the movement of the sleeve. The spring or springs acting on the valve member engage on a support member and this support member engages via a punctiform contact with a thrust piece.

Abstract: Chain-tension control apparatus for use with mine installations utilizes a hydraulic multi-piston engine motor driving a reduction gearing which can be selectively coupled to a drive system for a chain or chains used in the installation. The motive fluid for the motor is derived from the main pressure fluid source supplying fluid to other components of the installation and is preferably a 2-5% oil in water emulsion supplied via a pressure-reducing device. Pipe means in the form of a siphon conveys waste fluid as an overflow back to a storage tank independently of the main flow and return lines to the motor and the pipe means provides a fluid trap to maintain a certain quantity of fluid in the motor at all times.