GB1045302A - Hydraulically operated roof supports - Google Patents

Abstract

1,045,302. Hydraulic pit props. ELECTROHYDRAULICS Ltd. March 13, 1964 [March 14, 1963], No. 10144/63. Heading E1E. An hydraulic pit prop having two or more telescopic stages controlled by a single relief valve (not shown) comprises an inner piston 22 moving in the hollow piston rod 6 of an outer piston 7, there being two cylindrical chambers A, C and two annular chambers B, D. A pair of valves 43, 44 inter-connecting the opposite side of the piston 22 are closed by a common spring 45, the valve 44 being opened by a plunger 46. Before use the chambers B, C, D and the space E are filled via connection 30 with fluid under sufficient pressure to hold piston 22 slightly raised and hence valve 44 closed, air being exhausted through subsquently-closed passages 33, 17. Connection 30 is then connected to tank and to raise the prop fluid pressure is applied through a relief valve (not shown) and inlet 4 to chamber A. As piston 7 rises it displaces fluid from the annular chamber B through a hole 13 into the cylindrical chamber C, thus raising piston 22 and expelling fluid from chamber D through bores 48, 50 into chamber E, and from chamber E through connection 30 to tank. Yielding of the prop under load is thus determined by a relief valve controlling the constantdiameter chamber A. The prop is retracted by releasing fluid pressure from chamber A and applying fluid pressure to the chambers B, D through connection 30. As piston 22 completes its retraction stroke the valve 44 is opened and allows any fluid losses to be made good through valve 43. In a modification the space E is replaced by conduits between the passages 30, 50, 33. In a further modification an inlet to chamber D is provided in the gland 28. If desired the connections 4, 30, may be both at the same end of the prop, telescopic pipes being passed through the pistons.