Abstract: A hydraulically actuable piston and cylinder unit comprising a hollow piston rod, slidably housing, at least partially, an elongate extension piece having a circular outer periphery, means to connect mechanically, the extension piece to the piston rod at the outer end of the latter remote from the piston head, at least one fluid passageway communicating between the annulus side of the piston head and the hollow interior of the piston rod, and a fluid seal carried by the extension piece and sealing against the internal periphery of the hollow piston rod, the arrangement being such that the seal always lies between the passageway and the outer end of the hollow piston rod.

Abstract: A mine roof support comprises a plurality of hydraulically extensible chock legs articulated at upper ends thereof to one or more roof beams and at lower ends thereof to one or more base members, a shield pivotally connected to a rearward part of the base member(s) and also pivotally connected to a rearward part of the roof beam(s) with a permanently loaded force applying means reacting via the shield on the roof beam(s), in such a manner that the force applying means resists displacement of the roof beam(s) and, upon a sufficient fall in pressure in the chock legs, restores any displaced chock legs to a predetermined position.

Abstract: A mining installation comprises an armoured conveyor made up of a plurality of pans articulated together end-to-end, a plurality of hydraulically powered, self-advancing mine roof supports located side by side along the goaf side of the conveyor, each roof support being connected to a pan by one or more double-acting advancing rams, and each having a base means incorporating a pair of spaced, elongate base members seating on a mine fooor, each support further having a forward end intended to be located, in use, adjacent the goaf side of the conveyor and a rearward end intended to be remote from the conveyor, a rail located between the base members and attached at a forward end thereof to a pan of the conveyor, and a lifting jack carried by the base members at or near the front end thereof and operable on the rail to lift the front ends of the base members from the mine floor and in this condition be advanced towards the conveyor by operation of the one or more double-acting advancing rams.

Abstract: A self-advancing, hydraulically powered, mine roof support comprises at least one advancing piston and cylinder unit located in or adjacent a base means of the support and attached at or towards the front of the roof support to a lifting ram operable along an axis normal to the general plane of the base means.

Abstract: A mine roof support comprises at least one pair of hydraulically extensible chock legs connected at upper ends in articulated manner between one or more roof beams of the support and connected at lower end in articulated manner to one or more base members of the support, a rigid yoke located at a position spaced from the base member(s) between and connecting either the pair of chock legs, the yoke containing between the chock legs a projecting pin secured in a bearing attached to the yoke, or one of the pairs of chock legs, the yoke containing two projecting pins each pin being secured in a bearing attached to the yoke, and the or each pin having a lateral base contained at one side between abutment surfaces secured to the base member(s) and at the other to one end of a load applying means, the other end of the load applying means being supported from the base member(s).