Cavitation damage is most probably due to over capacity pumping where NPSHr exceeds available NPSH. Pinching the valve wastes energy. Much better solution, as you suggest, is to trim the impeller. To do this properly, you need the existing pump curve, impeller diameter and static/ friction head...
If the liquid handled is clean water with very little sand or silt, bronze generally offers the most cost effective solution. Bronze does not rust, is eay to cast and machine and generally offer superior surface finish of the waterways leading to efficiency gain. Duplex stainless steel such as...
Horizontal pumps are perfectly capable of working on suction lift aslong as NPSH required is less than NPSH available. When two pumps are running in parallel and one pump fails, the operating pump will intersect the system curve at a higher flow called the run-out flow. Generally, you need to...