GB893567A - Improvements in or relating to hydraulic jacks - Google Patents

Abstract

893,567. Wire strainers. P.S.C. EQUIPMENT Ltd., and ELAND ENGINEERING CO. Ltd. Aug. 17, 1960 [Aug. 27, 1959], No. 29324/59. Class 45. [Also in Group X] A hydraulic jack for tensioning concrete reinforcements of helically disposed stranded wire comprises a hollow piston 4 located in an anunlar space 3 between an outer body portion 1 and an inner sleeve 2, in which relative rotational movement of the hollow piston 4 and outer body 1 is positively prevented, e.g. by the provisions of dogs 34 on either the hollow piston or outer body. portion co-operating with splines 35 on the other. The jack at its outer end includes hydraulically operated segments 14 for temporarily gripping the ends of the reinforcement wire, and is provided at its inner end with a hydraulically operated ram 41 which drives home wedges &c. which permanently retain the reinforcement wire in its stressed condition in the concrete. In operation of the jack, the hollow piston 4 is extended by introducing fluid into the chamber 19 through a port 17 and the initial movement of the piston moves an abutment block 30 away from a ring 32 and permits a compressed rubber ring 16 to thrust a segment retaining block 13 into a taper 12 so that the temporary gripping segments 14 engage the wire passing therethrough, and continued movement of the piston tensions the wire. The ram 41 is then operated to drive the permanent retaining wedges by fluid introduced into a chamber 43 through a port 42, and the jack is retracted by fluid introduced into a chamber 21 through a port 18. Towards the end of the retracting stroke the abutment block 30 on the piston 4 engages the ring 32 on the inner sleeves 2, but the outer body 1 continues relative movement to the left so that a duct 26 is opened allowing fluid to pass from the port 18 to a chamber 27 to act upon a piston 28 which in turn acts upon a block 13 to release temporary gripping segments 14. Specification 775,743 is referred to.