cavitation; please explain
As a know-nothing, I hesitate to venture once again into this astonishingly complex discussion. I can follow the arguments in general terms but do not pretend any more than that. But I previously posted on my own experience of cavitation effects in a centrifugal pump (in a mining context) and would appreciate a layman's-level explanation.
I have seen cavitation cause a 6" Ajax water pump to repeatedly fail to deliver. The cause was restricted flow at the foot-valve which resulted in air coming out of solution and gradually accumulating in the pump casing until sufficient volume was attained to cause cavitation and loss of delivery pressure.
I have seen many references to cavitation in this thread; it seems to be a generally accepted factor in the events leading up to the accident. In my ignorance I keep thinking that if there was cavitation, where did the air/gas come from if not out of solution? And if there was cavitation in a pump, it's hardly surprising that fuel ceased to be delivered (if indeed it did cease...)
When I experienced this phenomenon, there was not a gradual drop in pressure, it was more like a sudden failure (at the head of about 200 ft where the pump delivered).
Could someone please suggest why the cavitation isn't a sufficient explanation in itself? I ask this not as a contentious "stir", merely out of puzzlement. In all the posts I recall cavitation is mentioned in passing as if it is just symptomatic rather than possibly critical - which may well be the case; I simply don't understand why.
Apologies once more for the layman's question.