Telescopic rock drill mounting

An extendable and retractable rock drill mounting comprising an extendable drill feed leg having a cylinder and a piston rod with a piston movable in the cylinder and adapted to carry a rock drill at its free end, a vertical support to which the cylinder is pivoted at its closed end, and a counterbalancing arm forming a triangle with the vertical support and the cylinder, the counterbalancing arm comprising a piston rod, piston and cylinder assembly adjustable in length, pressure fluid supply means, means to control the admission of fluid to the counterbalancing arm cylinder to adjust the length of the arm and to keep it in any adjusted position, and feed-back means so to alter the admission of pressure fluid to the counterbalancing arm cylinder as to maintain the length of the arm substantially constant in any adjusted configuration.

For use on an extendable and retractable rock-drill mounting a valve comprising a member adapted to be fixed, first and second members adapted to move relatively to one another and the fixed member, an inlet port, an outlet port, an exhaust port, and a handle for moving the first movable member, the first movable member being movable to connect the outlet port to the exhaust port and the inlet port in turn, the second movable member being movable to restore the valve to a position in which the outlet port is between the exhaust port and the inlet port while the first movable member is stationary relatively to the fixed member.