The hydraulic nut consists essentially of an internally and externally threaded piston, a cylinder and a locking nut. The hydraulic nut will be pressurized up to the desired pre tensioning force. This creates a gap between the locking nut and cylinder corresponding to the elongation and compression of the components. The locking nut will be screwed against the cylinder. Then the pressure can be released.

This construction finds its application in the machinery sector where pre tensioning forces on bolt connections must remain for few days or if the elongation of the bolt connections, the compression of the components to be tightened or the assembly lots are not exactly known and if necessary must be pre tensioned again. If identical bolt connections, for ex. on presses, must be pre tensioned with the same force than you don’t need to take care of the different setting losses in the connection because by fastening the locking nut different gap magnitudes can be eliminated. Furthermore this type of hydraulic nuts is suitable for retrofitting on machines, which have not been hydraulically or axially pre tensioned yet. This version finds its application as well in bearing and shaft assembly. The advantages of this design are the easy and safe handling of the hydraulic nut, the low overall installation time and the inspection of the remaining pre tensioning force. Leakage of the sealing system does not affect the operational phase. If it is necessary to retighten a bolt connection, you only need to fasten the locking nut after applying the desired pressure again. For connections with high stiffness (spring characteristic curve) it is advisable to secure the locking nut against loosening.