Abstract: A hydraulic ram for use as an advance ram in mining operations has a plurality of permanent magnets embedded in its piston rod. At least one sensor is associated with a guide bush fixed to the piston rod end of the cylinder of the ram. The or each sensor is accommodated within a respective pocket formed in the guide bush. The pocket(s) can be closed off by a detachable closure member.

Abstract: A telescopic prop for use in mine workings extends and retracts over three stages. The prop has an outer main base member 1 with respective first, second and third concentric inner members 2, 3, 4 disposed one within another. The first inner member has a piston 6 in which is arranged a non-return valve 23 which normally shuts off communication between a working chamber 20 associated with the first and base members and the working chambers 22, 27, 29 pertaining to the other members. A plunger 24 is provided to open the non-return valve when the first inner member is nearly fully retracted inside the base member so that after retraction of this stage the other stages can be retracted. The second or intermediate member also employs a piston 9 which is connected via a rod 13 with an auxiliary piston 15 disposed in a working chamber associated with the uppermost third member.

Abstract: A hydraulic ram for use in thrust-jacking of tunnel linings comprises a cylindrical outer member, a cylindrical inner member reciprocable within the outer member, and an extension member reciprocable within the inner member. A two-part clamping ring is provided for releasably locking the extension member to the inner member. An auxiliary drive is provided for retracting the extension member rapidly within the inner member. The auxiliary drive may be a mechanical spindle drive, or a hydraulic drive having an auxiliary piston reciprocable within an axial bore formed in the extension member. The clamping ring comprises spring means for urging the parts of the clamping ring in to the closed position, and piston-and-cylinder means for urging the parts of the clamping ring apart, against the biasing force of the spring means, to open the clamping ring.

Abstract: A mineral mining installation includes a longwall conveyor and a plurality of roof support units positioned side-by-side on the goaf side of the conveyor. The conveyor is braced longitudinally by a block bracing system having a plurality of hydraulic bracing rams each of which is disposed at an acute angle to the conveyor. The bracing rams act between the conveyor and floor girders of the roof support units. Each bracing ram is attached to a respective floor girder by means of a bracket. Each bracket has first and second bracket parts welded together, the first bracket part comprising means for connecting the bracket to its floor girder, and the second bracket part forming an extension of the first bracket part and carrying a pivot joint member for pivotally supporting the cylinder of the associated bracing ram. The first bracket part is a standard cast member, to which second bracket parts of differing lengths can be welded.

Abstract: A device for limiting the stroke of a hydraulic ram of mining apparatus employs a segmental stop which partly surrounds the piston rod of the ram. The stop locates between the cylinder of the ram and a head piece at the end of the piston rod. The cylinder of the ram makes contact with the stop during retraction of the ram thereby limiting the stroke of the ram. The stop is connected to the head piece via replaceable or adjustable pins. These pins permit the distance between the head piece and the stop element to be altered at will. The connection pins also enable the stop to be arranged to partly surround the piston rod periphery over different regions thereof.

Abstract: A mineral mining installation comprises a longwall structure, such as a conveyor or a winning installation, and a roof support assembly constituted by a plurality of roof support units positioned side-by-side. At least some of the roof support units are provided with hydraulic bracing rams for bracing the longwall structure longitudinally. Each bracing ram is pivotally connected between the longwall structure and the floor sill of a respective roof support unit. Each ram is connected to its floor sill by connection means constituted by a bracket slidably mounted on that floor sill for movement towards, and away from, the longwall structure. Means are provided for securing each of the brackets to its floor sill in any one of a plurality of positions.

Abstract: A three-stage hydraulically-operated telescopic prop is disclosed having working chambers which can be charged with hydraulic pressure fluid to extend a central prop member relative to an outer prop member and an inner prop member relative to the central member. A pressure-operated spring biased non-return valve is operated by pressure to open communication between the working chambers to extend the inner member once the central member has been fully extended. The valve is also operated mechanically to open communication between the working chambers to allow retraction of the inner member when the central member has been retracted to a certain extent. Further chambers are provided between the central and outer member, and between the central and inner member, and these chambers can be charged with hydraulic pressure fluid to retract the central member relative to the outer member and the inner member relative to the central member.