Patent ID: 7469592

Claim:
A hydraulic threaded bolt clamping device for tightening and releasing large screws, the clamping device comprising a pressure medium connector; a pressure medium supply connected to the pressure medium connector; a cylinder resting against a machine part that is to be clamped by a threaded bolt and a nut; at least one piston periodically pressure-loaded by the pressure medium supply and guided seal-tightly in the cylinder, the at least one piston resting against a threaded bushing screwed onto a threaded end of the threaded bolt; a control device for actuating the pressure medium supply for supplying pressure medium to the threaded bolt clamping device and for switching off the pressure medium supply after a nominal value that corresponds to a nominal screw prestressing force has been reached; a first input device for setting the nominal screw prestressing force or a corresponding nominal pressure of the pressure medium supply; a measuring device for measuring a relative displacement of the threaded end of the threaded bolt relative to the cylinder; and an evaluation device for determining a residual actual screw prestress after pressure relief of the threaded bolt clamping device.