Hydraulic jack for stressing elongate elements

摘要

A hydraulic jack with an unlocking plate which moves with the clamping plate and which has its own separate actuating structure. Therefore the unlocking plate can be actuated to release the clamping wedges in any position of the clamping plate. Preferably the actuating structure is a piston-and-cylinder arrangement which can be removed rearwardly from the jack without breaking any seals. The clamping plate may be spaced from the lock-off plate even in its forwardmost position. The front end of the jack may be provided by legs, allowing access between the lock-off plate and the clamping plate. Alternatively a cage of element-guiding sleeves may be provided between the lock-off plate and the clamping plate to guide the elements during threading. The clamping plate may be arranged to be removable from the jack rearwardly.