GB882246A - Improvements in and relating to props - Google Patents

Abstract

882,246. Hydraulic pit props. ACROW (ENGINEERS) Ltd. March 21, 1958 [March 22, 1957], No. 9475/57. Class 20(2) In an hydraulic telescopic pit prop comprising a pump adapted to transfer liquid from a reservoir 63 in the ram 12 past a valve 46 to the prop pressure chamber 44, the valve 46 is adapted to be opened manually, to release liquid from the chamber 44 to the reservoir 63 to release the prop, by a rod 26 extending through the ram and having a valve 42 which prevents liquid leaking past the valve 46 when closed and escaping to the reservoir. The prop is adapted to be extended rapidly by a low pressure pump piston 32 operated by a lever 19 and when under load by a high pressure pump piston 22, and also comprises a pressure relief valve 48. The rod 26 is operated by a lever 56 at the upper end of the ram and the released fluid flows to the reservoir 63 past the release rod 26 and lubricates it. The low pressure piston 32 fits inside the ram 12 and draws fluid from the reservoir 63 through a passage 51 between itself and the high pressure piston by means of which it is moved and forces the fluid past a valve 50 through the pressure chamber of the high pressure piston and past the valve 46 to the chamber 44. A valve 34 in the piston 32 yields and renders it inoperative at a predetermined pressure. The lever 56 operates, by a cam 54, a plunger 52 having a cam 58 engaging the top of the rod 26.