as much seems to get ignored in the quest for better solutions,
I would offer (again) some observations about pumps with shaft supported impellers:
the impeller spins on a fixed shaft with a film of the pumped liquid providing a film
(how effective the implementation is can be observed by looking at the sleeve (impeller bore if not sleeved) and the shaft)
- pumps are shipped with some 'assembly' grease, this contaminates the system - but keeps the impeller from rattling on the shaft; cheap pumps rattle quickly, better ones more slowly
a 'quality' pump of this type will have a directional motor (if AC) and curved impeller vanes for better efficiency, and a larger diameter shaft (a good example is the MCP600/50Z)
- but, if bearings are involved then their noise must be addressed, and the pump noise can only increase as the various parts wear
if higher pressure is desired then a closed impeller may provide superior performance depending on the system configuration, and involve high NPSH levels
- not all 'good' pumps do well under these conditions, shitty pumps fail quickly
but superior marketing trumps product performance - most of the time
and superior marketing will trump reliability every time
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