GB904866A - Improvements in hydraulic props - Google Patents

Abstract

904,866. Hydraulic pit props. DOWTY MINING EQUIPMENT Ltd. June 29, 1959 [June 30, 1958; July 11, 1958; Oct. 8, 1958], Nos. 20820/58, 22356/58 and 32144/58. Class 20 (2). [Also in Group XXVIII] An hydraulic telescopic pit prop comprises a piston 25 adapted to be forced out of a cylinder 13 to extend the prop, and an outermost cylinder 10 in which the cylinder 13 slides and to which the piston 25 is secured. The cylinder 13 comprises two concentric cylinders 17, 18 joined at their upper and lower ends respectively by a roof-engaging cap 19 and a gland ring 21. The outermost cylinder 10 has welded to its upper end a bearing-ring 12 having two bearing surfaces 14, 15 engaging the cylinder 13. There is clearance between the piston 25 and the cylinder 18 except at the gland 21 and the base 27 of the cylinder 25 has lateral play and curved engaging surfaces within a recess 31 of the base 11 of the outermost cylinder 10. The pit prop reservoir is the space 35 between the cylinders 17, 18. The pump for extending the prop comprises a plunger 37, Fig. 3, in a bore 36 in the cap 19 which is adapted to draw liquid from the reservoir 35 by a port 44 and force it into the pit prop pressure space 34 by a valve 53 and a passage 54. To release the prop the plunger 37 is moved beyond its normal range, causing a pin 55 in the plunger to open the valve 53 to discharge liquid from the space 34 by the passage 54, a transverse bore 56 in the plunger 37 and a bore 57 which is in register with the bore 56 in this position of the plunger, and a passage 59 to the reservoir 35. The reservoir 35 breathes through a passage 65 and bores 63, 64 in the plunger 37 when it is moved away from a packing-ring 39. The plunger 37 is operated by a lever 46 having a head 47 held in a clevis 49 pivoted at 51 on the cap 19, the lever engaging the plunger by a roller 48. A modified pump, Figs. 4 and 5, comprises a piston 80 in the upper portion of the cylinder 18 reciprocated by a manually-operated crank-shaft 72. On the downstroke of the piston, liquid is drawn from the reservoir by a tube 78, a passage 79 and an inlet valve 81 to the space 83 above the piston 80 and on the upstroke, liquid is forced into the prop pressure space 34 through a valve-plate 76. The valve-plate 76 is opened by a pin 77 when the piston 80 is left in its highest position when the prop is set, so that excess pressure in the pit prop can be relieved through a relief valve 85, which discharges back to the reservoir, and the prop can be released by raising a valve 87 in the valve 81 by a spring-returned pin 92 and a lever 88, the valve 81 eventually also opening.