GB947397A - Improvements in or relating to hydraulic pit props comprising three or more telescopic parts - Google Patents

Abstract

947,397. Hydraulic pit props. GUTEHOFFNUNGSHUTTE STERKRADE A.G. June 9, 1960 [June 12, 1959], No. 20254/60. Heading E1E. [Also in Division F2] In an hydraulic pit prop comprising telescopic members 1, 2, 3 incorporating a relief valve adapted to maintain the resistance to lowering of the prop constant as disclosed in Specification 860,164, the telescopic members define a common pressure chamber having a single pressure duct. The pressure within the prop acts by way of a conduit 6, Fig. 1, on a spring- loaded valve 9, the force exerted by the spring being additionally opposed by pressure fluid fed through a check valve 13 and a branch duct 11 to an offset annular surface 12 of the valve 9 when the prop head 5 engages the member 3 to depress a plunger 14 and open the valve 13. In a modification, see Figs. 3, 3a and 4 (not shown), applicable to pit props incorporating four telescopic members, two valvecontrolled branch ducts are provided leading respectively to two offset annular surfaces in the valve 9. In a second modification, Fig. 5, the plunger 14 carries a ported abutment 20 acted on by opposed springs 21, 18, a ported conical member 17 blocking the connection 19 to the pressure chamber during the first lowering stage of the prop. The prop head may be provided with a series of relief valves connected in parallel and having different response pressures, see Fig. 6 (not shown).