The hydraulic nut consists essentially of an internally threaded cylinder, a piston and a splitted spacer plate. The hydraulic nut will be pressurized up to the desired pre-tensioning force. This creates a gap between the piston and cylinder corresponding to the elongation and compression of the components. In this calculated gap the corresponding spacer plate will be inserted. Then the pressure can be released.
This design is particularly used for bolt connections that doesn’t need to be pre tensioned again for a long period, or if the elongation of the bolts and the compression of the components to be tightened are known and do not need to be pre-tensioned again. The advantages of this type of hydraulic nuts are in the simple and inexpensive design as well as an operational phase independent from leakages.