GB780345A - Improvements in hydraulic supporting or lifting devices - Google Patents

Abstract

780,345. Hydraulic pit props. EISENWERK WANHEIM GES. Jan. 3,1955 [Jan. 16, 1954], No. 128/55. Class 20(2) [Also in Groups XXVIII and XXX] A hydraulic pit prop has a built in piston pump which comprises a low pressure piston 17 sliding in a cylinder 1 formed in the pressure piston 2 which is connected to the upper element 3 of the prop and which operates in a cylinder formed in the lower element 6. The piston 17 is adapted to be carried along by a plate 19 slidable on a hollow piston rod 4 and loaded by a spring 20 supported at the other end by a member 21 secured to the rod 4. A high pressure piston 15 is slidable in a bore 16 formed in the piston 17. The piston rod 4 passes through a packing 9 loaded by a spring 22 which functions as an outlet valve from the cylinder 1. Secured to the opposite end of the rod 4 is a compensating piston 25 operating in a chamber 8 which also contains an overload valve 26 which may also be manually operated by a shaft 27. Initial actuation of the rod 4 by a manually actuated shaft 12 operates the low pressure piston 17 through the spring 20 to extend the device. When the spring 20 can no longer move the piston 17. against the pressure in the chamber 5, the high pressure piston 15 operates to build up the final pressure. The pressure in the chamber 8 due to its connection through the hollow rod 4 to the chamber 5 acts on the piston 25 to assist the pumping stroke of the rod 4. Driving devices operated by compressed air may be used in place of a hand crank.