GB794547A - Improvements in or relating to extensible pit-props - Google Patents

Abstract

794,547. Fluid pressure pit props. VERSCHURE & CO'S SCHEEPSWERF EN MACHINEFABRIEK, N. V. April 25, 1956 [April 25, 1955], No. 12734/56. Class 20(2) [Also in Group XXVIII] In an extensible pit prop actuated by compressed air, a first admission of compressed air into the space above a floating piston 5 forces the piston 5 downwardly to displace pressure liquid from the tube 4 of the upper prop member through one way valves 12, 13 into the working space beneath the piston 3 of the upper prop member, thereby extending the prop into engagement with the mine roof. The space above the piston 5 is then vented and thereafter successively recharged with compressed air and vented so as to impart reciprocating motion, through the piston 5 and the liquid beneath the piston 5, to an axially bored differential piston having a large diameter part 8 slidable in a tube 6 and a small diameter part 10 slidable in a bore 11 in the piston 3. The piston 10, in co-operation with the one way valves 12, 13 associated with the bores in the pistons 10, 3 respectively, operates to pump liquid 'from the tube 4 to the space beneath the piston 3 to load the prop. The pressure in the working space is limited by a spring loaded relief valve 15 which when open, Fig. 2 (not shown), places the working space in communication with a space surrounding the tube 4 and communicating with the interior of the tube 4 through holes 7. The valve 15 can be manually operated to release the prop. An air filter 20 is provided for the compressed air. The space beneath the piston 8 and within the tube 6 contains resilient compressible cushions, such as tubular air filled bladders 22 to facilitate reciprocating movement of the piston 8, 10.