GB856719A - Improvements in roof supports for underground mines - Google Patents

Abstract

856,719. Mine roof supports. DOBSON Ltd, W. E. & F. June 24, 1957 [July 5, 1956], No. 20819/56. Class 20(2) A mine roof support comprises a forward hydraulic prop 4 and rearward hydraulic props 2, 3 connected by a hydraulic jack 6, 7 adapted to advance the props step-by-step in turn, the necessary contraction and extension of the props being controlled by relief valves 16, 17 operated by control means 14, 15 operated by movement of the jack under the control of the control valve 9. The valve 16 is operated to release the jacks 2, 3 by a lever 21 in which is pivoted a lever 22 carrying a stop arm adapted to be engaged, to open the valve 16, by a stop plate 18 on the jack cylinder 6 when lost motion connection 10 between the jack and the rear prop is taken up, on the initial contracting movement of the jack to move the props 2, 3. When the jack is fully contracted a rod 23 on the lever 22 engages a rod 28 on the forward jack which moves the stop arm to inoperative position and the valve 16 closes. The engagement of the rod 28 by the rod 23 moves into operative position a stop arm on the operating lever 26 of the valve 17 which is opened similarly to the valve 16, when the control valve 9 is operated to extend the jack to move the prop 4. The valve 17 recloses when the jack extension ceases and release of pressure on the stop arm allows the rod 28 and the valve 17 to be spring-returned. Liquid bleeds from the control valve 9 and the jack through non-return 'valves SV, SV1 Fig. 7 to reset the props 2, 3 and the prop 4 respectively. The control valve 9 comprises a cam 33 Fig. 6 which when moved in anti-clockwise direction opens valves VI, V4 to supply liquid from the supply line SL by a port O1 to the jack cylinder space 6b and to release fluid from the space 6a by the valve V4, to contract the jack and allows liquid from the release valve 16 to escape by the jack cylinder space 6a, the interior 7a of the ram jack and the valve forks V4 to the return line RL. Clockwise movement of the cam opens valve V2, V3 to supply liquid through the valve V2 and the interior 7a of the ram to the jack cylinder space 6a and release fluid from the space 6'b by the valve V3, to extend the jack, the relief valve 17 exhausting direct to the line RL. The relief valves 16, 17 also relieve fluid from the props when subject to excessive weight. Specification 854,967 is referred to.