I don’t see any signs of cavitation, but it is only one picture. Does it look like mechanical/foreign object damage or cavitation till pieces came off?
To me it appears cavitation till the pieces gave way
Two bad impellers. Foreign matter in the system or pump starvation seems to be the only thing shy of 2 being faulty from the start. So the pump does seem to have been starved.
FPE says the valve can be used in any orientation so disregard my comment on proper installation. But it's still a possible obstruction of flow to the pump. A suspect.
I don't suppose an operator is getting their inline manual valve opening/closing sequence wrong.
