Abstract: A gantry support for supporting a roof of a passage includes two parallel supporting units each having a lower frame provided with articulated tracks and an upper frame carried by props and two cross-members. The two cross-members carry an intermediate upper frame in the form of a beam which is slidable on guide elements and adapted to be clamped to the roof by small jacks. As the support advances the beam remains clamped against the roof of the passage until the beam reaches an end stop. The small jack is then released and the beam slidably advanced along the guide elements by means of a further jack.

Abstract: A gantry support for supporting a roof of a passage is advanceable along a floor of the passage. The support has two parallel supporting elements mutually spaced apart laterally of the support, each element including at least two pairs of frames provided with articulated tracks. One frame of each pair is an upper frame and the other is a lower frame, the tracks of which are adapted to be applied respectively against the roof and floor of the passage by loading jacks applying a spreading force between the upper and lower frames. An intermediate upper frame is carried by an upper cross-member extending from one supporting element to the other and at least one loading jack applying a spreading force connects each lower frame to the corresponding end of the upper cross-member.

Abstract: The invention relates to a thrust device using a plurality of hydraulic jacks, and to the automatic control of a plurality of thrust jacks.Two differential jacks have resetting chambers which are permanently under hydraulic pressure. Associated with each jack there is a self-locking piloted valve placed in the active position by a push-rod at the end of a work stroke of the piston of the jack and restored into the inactive position by a piloted valve actuated by a push-rod 39 at the end of the return stroke of the piston to its starting position. In the active position the self-locking piloted valve controls the isolation from the supply of all the work chambers and the venting of the associated work chamber 14.

Abstract: A ball joint for transmitting forces between the prop and the head-piece of a support unit has a spherical head received in the spherical internal surface of a dome. The dome is enclosed by a spherical ring which is fastened to the head. The rod of a prop carries a pivot which is mounted with radial clearance in a cylindrical cavity located within the sphericl head.

Abstract: A device for causing translation of a machine carried on a sledge surrounded by an articulated track comprises a pushing member provided on a jack supported by the sledge, the pushing member cooperating with abutments provided on the inside of the track. The track comprises a plurality of articulated shoes each formed of two L-shaped half-shoes fastened together so that the shorter branches thereof are spaced from one another and are substantially parallel to the direction of movement of the track. Each abutment is carried by the shorter branches of each shoe whereby the passage formed by the space between the two shorter branches is at a position corresponding to that of the respective abutment.