GB992405A - Improvements in or relating to hydraulic jacks - Google Patents

Abstract

992,405. Hydraulic apparatus. CHRISTIANI & NIELSEN Ltd., and G. PERSICKE. Oct. 15, 1962 [Oct. 13, 1961], No. 36886/61. Heading F1P. [Also in Division F2] An hydraulic jack comprises an annular piston 13 slidable in an annular cylinder 14 and sealed therein by inner and outer U-section sealing rings 23, -24 expanded by the pressure fluid in the cylinder chamber 18. The sealing rings are secured to the piston by a cover plate 26 fixed to a flange 22 on the piston and having holes 28 for the passage of pressure fluid to the rings. The cylinder has a fluid inlet 19 and a central boss 17, Fig. 4a. In the. embodiment shown in Fig. 2, which is particularly suitable for prestressing a reinforcing rod of a concrete structure, the boss 17 is hollow and has a duct 280 leading from a port 29 which is uncovered by the piston at the outer end of its stroke to thereby relieve the pressure and prevent overload and the rod to be stressed passes through a bore 31 in the piston and is held in conical segments 33 engaging a tapered bore 32 in the boss 17. The gripping action of the segments 33 on the prestressed rod may be augmented at the outer end of the piston stroke by the pressure fluid passing through the duct 280 acting on pistons 37 in cylinders 36 in a plate 35 screwed into the boss 17, the pistons being urged axially against the ends of the segments. In a further embodiment, Fig. 8, the segments 33 engage a tapered bore 48 in a plate 43 between the cylinder and an element 1 and minor pistons 50 secured to the flange 22 move in bores 49 in the cylinder head 15 and control ducts 53 communicating with cylinders 54 so that when the ducts 53 are uncovered during outward movement of the piston 13, pistons 56 in cylinders 54 are forced outwards by pressure fluid against the segments 33 to press the latter into tight engagement with the prestressed rod 4.