Hydraulic Nuts
Function of a Hydraulic Nut (HM) PG 12
in simplified representation

Hydraulic Nuts do not require a thread projection as Bolt Tensioners do and, therefore, can be used in older constructions to replace conventional torque wrenched bolt connections. For large bolt connections in particular, this eases work and increases the safety of the tension force. Compared with Bolt Tensioners, Hydraulic Nuts enable quicker changing times for connections
that need tightening and loosening on a regular basis. This speeds up checking load forces.

Basic setup
Screw the Hydraulic Nut (HM) on the bolt to be pretensioned, and down to the flanges' surface. A hydraulic high-pressure generator pumps the oil through a high-pressure hose into the space between cylinder and piston. The hydraulic pressure rises.

Bolt elongation
Through the rising pressure and the resulting axial force, the bolt is elongated and the flange parts are compressed. The lock nut is lifted off the cylinder. When the preset pre-tensioning force is achieved, the pressure supply is stopped.

Screwing the lock nut
The pre-tensioning force has been achieved and the lock nut is turned by hand down to the stop face of the cylinder. Thus, the pre-tensioning force is maintained within the screw joint and the hydraulic may be released. The Hydraulic Nut remains on the bolt connection.


Special Solutions


In addition to a number of standardized Bolt Tensioners and Hydraulic Nuts, SCHAAF has already delivered thousands of customized axial Bolt Tensioners. The Design on Demand CAD system allows to realize customer solutions very
quickly. Based on axial pre-tensioning technics, a number of patented, specialized solutions have been developed during the last years. Bolt Tensioners, Hydraulic Nuts and ExpaTen, as well as the A-Loc and EcoRolls, both developed
especially for rolling mills, all represent a 100% system solution with SCHAAF’s accessories such as high-pressure hoses and high-pressure generators.

More Hydraulic Nuts

We distinguish our Hydraulic Nuts into 5 different product groups (designs) which,
in principle, have all the same function.