Problems were discovered when the Pelton wheels were being serviced to replace the eroded faces of the turbine. With a head 1748M, the water is travelling at 380mph before its strikes the turbines and any debris carried down with the water, especially low water conditions, erodes the Hydro Turbine bucket faces. Such is the impact of the water that fretting between the wheel and shaft, which, with “conventional bolts” failed to prevent, resulting in damage to the components and full non-destructive testing of the turbine hub. Damage caused by forcible removal of the interference fit bolts also necessitates their renewal, adding to an already slow and expensive overhaul procedure. It was with this that PILGRIM where given the challenged to find a solution.
PILGRIM selected its Radial Fit Bolts to solve the problem. The principle of the bolt is of a taper shank bolt drawn into a matching taper sleeve with parallel outer diameter which expands fractionally to produce a perfect interference condition in to the bolt hole. This condition, which “conventional” fitted bolts do not achieve, eliminates movement between mating components. Also with the expansion of the sleeve], exact flange alignment and concentricity is achieved. Axial clamp load is then created by a hydraulic puller. Once the puller draws the tapered bolt into its sleeve it is then used to tension the bolt once the nuts are fitted>