GB1459070A - Hydraulic jacks - Google Patents

Abstract

1459070 Step-by-step jacks SHIMIZU CONSTRUCTION CO Ltd 8 April 1975 [24 July 1974] 14456/75 Heading B8J [Also in Divisions E1-E2] A step-by-step jack comprises an hydraulic cylinder 11 to the upper end of which is attached a chuck unit 30A while a similar chuck unit 30B is attached to the lower end of a piston rod 13 extending through the cylinder 11 from a double acting piston 12 in the cylinder 11. The chuck units 30A, 30B each comprise a casing 31 with collet pieces 32 urged out of engagement with a jack rod 1 passing through the jack by a release spring 35. An iron core 33 forces the collet pieces 32 into gripping engagement with the rod 1 when an excitation coil 34 is energized to attract action flange 36. The length of stroke of the jack can be adjusted by selecting one of three limit switches (22a, 22b, 22c), Fig. 4 (not shown), on switch section 22, arranged to cooperate with a switching member 24 on the upper end 13a of the piston rod 13. A level controlling mechanism 21 is provided to inter-relate the action of a plurality of the above jacks utilized to lift a structure. This includes a float chamber 21 with a float 212 having slits (213a, 213b), Fig. 4 (not shown), arranged to co-operate with a photo-electric device 23. At the end of, for example, a lifting stroke the corresponding lower chucks 30B may not be level one with the other owing to differential slipping (which difference may be increased by relative slipping between the corresponding upper chucks 30A), Fig. 7 (not shown). The float chambers 21 are placed in communication and the return stroke of the piston 12 is controlled by the photo-electric devices 23 ensuring that the next working cycle starts with both the lower chucks 30B at the same level (regardless of the positions of the upper chucks 30A). Fig. 3 shows a modification of the chucks 30A, 30B wherein the upper surfaces of the collet pieces 32 are dished to improve release of the collet pieces 32 from the rod 1 under the action of the spring 35. Jacks of the above kind are used, for example, in the slip form method for building chimneys, silos and storage towers or in the lift-up method for lifting roofs, beams and slabs formed on the ground. As shown in Fig. 9 the inclination of a tower structure can be converted by disposing the jacks on the circumference of the structure, the pipes to the water reservoirs being closed. The limit switches (22a, 22b, 22c) in the section 22 and the slits (213a, 213b) can be selectively operated so that the jacks on the X 1 , X 2 side have different strokes, enabling the structure to be inclined as required.