Patent GB-720106-A (GB)
Title: Improvements in or relating to props especially pit props
IPC: E21D15/44
Filed: 1952-01-02
Abstract: 720,106. Pit props. EGGEMANN, W., and CAMPENHAUSEN, E. VON, [trading as SCHWARZ KOMMANDIT-GES., H.]. Jan. 2, 1952 [Jan. 5, 1951], No. 112/52. Class 20 (2). A two-part telescopic pit prop has a frictional brake device determining the resistance to telescoping under load, the brake device being housed in a dust-proof enclosure and being drivingly connected with the upper prop part so that movement of this part is accompanied by movement of frictional elements of the brake device and vice versa. In one form the upper prop part 4, Fig. 2, is formed with a toothed rack 7 drivingly connected by gearwheels 6, 10, 12 to a rotatable shaft 11. on which are mounted clutch plates 14 adapted to engage frictionally with plates 15 mounted in a dust-proof housing 13 forming part of a larger housing 5 containing the gear mechanism and mounted on the lower prop part 2. A small downward movement of the part 4 results in considerable rotation of the. plates 14 which may run in an oil bath. Pressure between the clutch plates 14, 15 is adjusted by a lever 16. By connecting a crank handle or a power driven device to the stub 17 of the shaft 11, the transmission mechanism may be used to raise the upper prop part 4. The plate clutch may be replaced by a cone clutch or wedge gearing may serve as the brake device; the connection between the upper prop part and the transmission mechanism may be effected by a Galls chain. In another form a fluid drive is used as the transmission means connecting the upper prop parts 21, Fig. 4, of two props, with a common brake device. The props are connected by upper and lower members 22, 20 to form a frame structure, the upper prop parts 21 forming pistons which slide in the lower parts 24 which contain liquid and are connected by a pipe 31. A pipe 32, Fig. 5, connected directly to one lower part 24 opens at its end to a cup leather 33 in a longitudinally movable cylinder 34, which on one side of the cup leather is filled with air and is connected by a pipe 35, Fig. 4, via valve 37 either to a source of compressed air or to atmospheric pressure. The cylinder 34 has a pivoted crosshead 38 having on each end elongated friction plates 40 arranged to be gripped by brake blocks 41. The cylinder 34 and plates 40 are disposed in an oil filled housing 45. The pipe 31 is connected by a pipe 46 via a valve 47 with another vessel 48 which contains liquid but has an air space which may be opened to atmospheric pressure or to compressed air by a valve 49. The spaces 28 in the lower prop parts 24 may also be placed under atmospheric pressure by pipes 50 and valve 37. With the spaces 28 vented to atmosphere and the props set, the cylinder 34 as shown in Figs. 4, 5 has one end bearing against the wall 51 of the housing 45. When one or both of the upper prop parts is, by roof pressure, moved downwards, liquid is displaced from the lower prop part 24 and pushes the cylinder 34 to the right, taking with it the plates 40, this movement being restrained by the brake blocks 41. To release the props, the brake device is first released and the spaces 28 placed under pressure by operating the valve 37 to admit compressed air via the pipes 50. The upper prop parts 21 are thus lowered and the cylinder 34 moves to the right. If during operation, the ports 21 have descended so far that the cylinder 34 has already moved to the right to an end position, putting the spaces 28 under pressure will not cause the parts 21 to descend further. In such case the valve 47 is opened to permit liquid from the lower parts 24 to flow into the vessel 48. The valve 47 also acts as a relief valve to release liquid from the pipe 31 on sudden overloading. To set the props, the valve 47 is closed, the spaces 28 are vented to atmospheric pressure and compressed air is admitted via valve 37 and pipe 35 into the cylinder 34. With the brake blocks in the freed position, the cylinder 34 and plates 40 are returned to the position shown in Figs. 4, 5 and the upper prop parts 21 are raised. Valve 49 may be actuated to admit compressed air to the air space of the vessel 48 to ensure adequate raising of the prop parts 21.