Abstract: A process and a device for the simultaneous tensioning and loosening of eccentric tension rods (19) of gas turbine rotors assembled from several turbine disks (23). An improved hydraulic tensioning device is used to provide an optimal circular and flat impact quality, and the quiet running of the gas turbine rotor is improved overall at high speeds. Further, it is guaranteed that the same forces act on each tension rod (19), the elongation of each tension rod (19) can be measured as accurately as possible, and a minimization of the setting force losses is achieved. A solid cylindrical ring (1) forms a piston chamber (11) in each case, whereby the piston chambers (11) are connected together with cross holes and are acted on by the hydraulic medium. The catch pin (3), through which a measuring rod (5) is guided, which makes contact with the head of the tension rod (19) by a pressure spring (18), is inserted through a boring in the piston (2).