Customers occasionally ask why our impellers carry our own part numbers instead of a supplier's catalogue reference. The answer is a few hours at the test bench.
An impeller is where efficiency is won or lost. A millimetre of asymmetry shows up as vibration; a rough vane surface shows up as watts; a sloppy balance shows up as bearing wear two years later. When you buy impellers in bulk, you inherit whatever tolerances the foundry had that week. When you machine your own, you own the tolerance.
It costs us more per part. It saves our customers a pump every few years. That trade is not difficult.