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Solution: Trial Repair of Pump Bell

One pump was in the workshop with a severely damaged suction bell, awaiting repairs. We grit-blasted the bell, so that the surface was clean and had a rough texture to ensure the epoxy bonded with the metal. We added chopped fiber-glass to the epoxy mixture and applied it in layers of about 1/8", allowing plenty of curing time between layers. We laid a clear plastic sheet over the final coat and smoothed the surface. Once the epoxy dried, we could peel off the plastic sheet, leaving a smooth, glassy surface. Some minor machining was required to clean up the flange face and bolt holes. The whole job took four days to complete. Meanwhile we repaired the rest of the mechanical parts of the pump. We reinstalled the pump and found it mechanically satisfactory, though the capacity loss problem remained. Over the next three weeks, we did the same type of repair to the remaining two pumps.

Solution: Aeration of Water

The white water posed a much more difficult challenge. Our hypothesis was that if we restricted the flow downstream of the waterfall, the level would build up in the box section, reducing air entrainment during the free fall and, hence, the frothing.

The first idea was to hang a sheet of 1/2" thick rubber at the box outlet. It would have a steel flat along the horizontal edges to give it some stiffness, but would allow it to flex. A simple Strength-Weakness-Opportunities-Threat or SWOT analysis showed there were some threats to be managed. First, the sheet could break into pieces and enter through the trash rack into the pump suctions. Second, the horizontal force of the water might be excessive. This might destabilize the crane that would be used for hanging the sheet. The

 
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