Improvements in or relating to hydropneumatic pit props

911,588. Hydro-pneumatic pit props. NIKEX NEHEZIPARI KULKERESKEDELMI VALLALAT. Nov. 29, 1960, No. 41005/60. Class 20 (2). A hydro-pneumatic pit prop comprises a base 1 for liquid, a working cylinder 4 connected thereto by an intermediate member 3 and an inner tubular member, see Fig. 1 (not shown) which is slidable in said cylinder and carries a head plate and a bell-shaped rubber piston, said intermediate member having ports 12, 15 for establishing communication between the bell-shaped piston and a conduit 13 carried by the intermediate member and extending into the base. A normally operable control valve 16-21 incorporating automatic safety relief means is mounted in the intermediate member 3 and is adapted to be connected to a source of compressed air to feed liquid from the bore 1 through the ports 12, 15 to the underside of the piston until the prop head engages the main roof at the desired pressure whereupon the pressure hose is disconnected and a closure cap fitted.