If these bolts are tensioned one at a time, the likelihood is that the first one will be loose by the time the 24 th one has been tensioned, this loss of pre-load is due to friction. Recognizing that uneven tension is the primary cause of plant failure, many companies now insist on multiple tensioning. Hydraulic tensioning systems designed by H.B.I allow any number of hydraulic nuts to be tensioned simultaneously, by simply coupling the hydraulic nuts together with flexible hoses, and quick hose couplers. Hydraulic tensioning using hydraulic nuts, does not rely upon trying to rotate the nut, it simply applies an axial force, similar to what you have seen, at college when you applied loads to steel specimens, using a tensile test machine. The hydraulic nut is simply screwed onto the bolt and run down until it firmly seats on the surface to be tensioned.
Hydraulic pressure does all the work.
Hydraulic pressure is applied to the nut, which stretches the bolt, very much like stretching a spring. Once the bolt is stretched, a threaded collar on the hydraulic nut is rotated to maintain the bolt in this condition, then the hydraulic pressure is released, to loosen the nut re-apply the hydraulic pressure, and rotate the threaded collar remove the hydraulic nut. Another feature that is extremely useful using hydraulic nuts, is that you can use them to pull two surfaces together, such as drive couplings, crusher shells, and continuous caster sections, in fact any heavy piece of equipment prior to tensioning. H.B.I offer orbital washers, which are de-signed to insure proper alignment, when dealing with uneven surfaces. With a regular nut the nut corners can dig into the surface, creating greater friction, and lead to failure later of the fastener.