GB954660A - Hydraulic pit prop - Google Patents

Abstract

954,660. Hydraulic pit props. GEWERKSCHAFT EISENHUTTE WESTFALIA. June 28, 1960 [July 3, 1959], No. 22674/60. Heading E1E. In an hydraulic pit prop, Fig. 1, having an inlet valve 14 and a release valve 19, the foot plate 12 is provided with an extension 16 adapted to co-operate with a recess 17 in the piston 11 and with an adjustable pressure relief valve 20, the arrangement being such that during initial retraction of the prop the chamber 15 is vented direct through the valve 20 and later when the members 16, 17 interengage it is vented through the said valve 20 under control of the valve 19. In a modification, Fig. 2 (not shown), the inlet duct communicates with the bottom portion 15a of the chamber 15 whilst the duct in the extension 16 communicates by way of non-return valves with said inlet and outlet ducts, said two valves being operable at different pressures to one another and jointly controlled by mechanically coupled push rods. In a second modification, Fig. 3, the prop is provided with valve controlled inlet and outlet conduits 31, 33 together with interconnecting ducts 36, 39 arranged as shown, a check valve 40 being disposed in the duct 39 and a plunger operable release valve 37 being disposed in the duct 36.