Surfer-thanks for the input. We’re finding that the high speed (3600rpm) pumps associated with the higher head requirements of the process change have some reliability issues. From our work it appears to be related to loss of lubrication in the upper intermediate bearing. Others are reporting shaft stability/ excessive vibration problems as well. The cure appears to be the same with a design change to the bearings and clearances. We have a plan forward, but are still in the testing stage so I can’t confirm that the problem is solved.
If your problems appeared and then seemingly went away, I would not be surprised if you find them return. We have managed to run the pumps for a little over 12 months with no issues, and then suddenly have a rash of events, with no apparent changes in the system. I suspect sulfurcrete/solids lodged in the upper bearing clearances tends to starve the bearing, forcing the lubricant out the lower ports.
Do you have cast iron/steel bushings or the carbon filled/graphite bushings?