GB745679A - Improvements in mine roof supports - Google Patents

Abstract

745,679. Mine roof supports. DOWTY AUTO UNITS, Ltd., and FRYE, C. M. July 8, 1954 [July 8, 1953], No. 18977/53. Class 20(2). In a mine roof support of the " walking prop " kind in which two roof-supporting structures, each comprising a group of hydraulically operated props, are interconnected by driving mechanism so that the structures can be freed and displaced in turn to advance the roof support, the pressure chamber. of each prop communicates individually with a source of pressure liquid through a non-return valve which prevents flow from the chamber to the source and also communicates individually with the inlet side of a pressure relief valve through a non- return valve which prevents flow back to the chamber, the relief valve being common to all the pressure chambers of the group. The two structures 11, 12 are diagramatically represented in the drawing as having floor bars 13, 14, roof bars 15, 16 and props 17. Projections 19, 20 from the two structures are inter-connected by a hydraulic jack 18, supplied from a source of fluid pressure 21 through a pipe 22 through a selector switch 23. The pressure may be selectively connected to either side of the piston of the jack through one of the pipes 24, 25 the other pipe then being connected to the return pipe 26. Supply and return pipes 27, 27a, from pipes 22, 26, are connected through non-return valves 29 and pipes 28 to the props 17. The pipes 28 are also connected through one-way valves 30 to a pipe 31 which is connected through a pressure-relief valve 33 to the return pipe 27a. The relief valve is by-passed by a stop valve 40 and a similar stop valve 39, ganged to it, is provided in the supply pipe 27. Pressure is applied through valves 29 which prevent flow back into the pipe 27. The pressure prevailing in the prop carrying the greatest load will prevail in the pipe 31 but will be prevented from being transmitted to the other props by valves 30. However, when a predetermined load is reached the relief valve 33 allows the fluid to escape into the return pipe 27a. The single relief valve is thereby capable of giving relief to any one of a number of props which are overloaded. The valves 39, 40 are ganged so-that one opens when the other closes. To advance the support the valves 39, 40 of structure 11 are operated to close the supply line and open the return line so that pressure on the props is released. The selector valve 23 is then operated to expand the jack 18 and the pressure is re-applied to the props of the structure 11. The structure 12 is drawn up in the same way except that the valve 23 is turned in the opposite direction to contract the jack 18. Specifications 658,998, and 671,955 are referred to.