Abstract: A cutting machine for mining minerals from a seam thereof, the machine executing reciprocal movements parallel to the face of the seam and being provided with switches for generating signals indicative of the direction of movement of the machine for controlling the removal of protective bumpers on support structures located forwardly of the machine and for moving support structures against the face of the seam and relocating bumpers rearwardly of the machine.

Abstract: A pressure-relief valve device employs a connector welded to the base of mining equipment equipment such as an hydraulic prop, so as to communicate with the pressure fluid in a working chamber thereof. A housing is screwed into the connector and the connector has an outflow passage leading to the surroundings. A valve composed of a fixed valve seating and a movable closure member opens and closes communication between the working chamber and the outflow passage. A spring holds the valve closure member on the seating. The valve closure member is slidably guided on part of a tappet subjected to spring force. The tappet has a piston exposed to the pressure fluid which opposes the spring force. If excess pressure occurs the tappet moves against the spring force and lifts the closure member off the seating. Once the pressure drops the tappet moves back under the action of the spring but the closure member can move more slowly to gently re-establish the valve action.

Abstract: A hydraulic control device is incorporated in a hydraulic control system for a mine roof support assembly. The hydraulic control system includes a plurality of hydraulic control valves which are controlled by the hydraulic control device. The hydraulic control device is constituted by a longitudinal slide valve having a slide member longitudinally reciprocable in a slide valve housing. A rotary drive is provided for moving the slide member within the slide valve housing. The slide member is provided with two axial bores each of which opens into a respective pair of axially-spaced radial bores which terminate at the peripheral surface of the slide member. A first radial bore of each axial bore opens into a respective annular groove formed in the slide valve housing. The second radial bore of each axial bore is connected to a respective group of control ports provided on the slide valve housing.