Jim Sower wrote:

I need a little help here.  I may have got lost back a ways.  Tell

me if

this is

true:
1.  Cavitation happens when the pump can't "suck" (read

Your intuition is correct but the magnitudes may be wrong.  Sucking

>from a

stagnant source will cause the pressure to be lower at the inlet due to
accelerating the fluid.  If the inlet line is of reasonable size this
should be less than 1 psi though.  You are likely to get more pressure

drop

from the fittings to close the loop than from the re-acceleration of the
flow from stagnant.

Jeff Spitzer

you're concern about continuity is valid...what goes out must go in.  But
again, we're talking about magnitudes.  The more flow the higher the
pressures to pump it.  At some point you reach equilibrium where the pump
pressure rise matches the system pressure drop.  The flow rate for this
equilibrium is what changes.  If the pump has localized cavitation and can
only pump so much...thats what you get.  If you fix the cavitation then the
pump does better...more pressure rise...,more flow...new equilibrium point.

Jeff Spitzer

Thanks one and all.  I was aware of vapor pressure and aerated coolant and bubbles
and all, but didn't know the magnitudes and left them out of my paradigm.  The talk
about header tanks with pressure caps at the high point of the system, plumbed slow
flow and parallel makes perfect sense to me.  Eliminate (suspended?) air and raise
the pressure and you have bought yourself another several hundred RPM of
pressure/flow increase before the onset of cavitation. ....
I'm slow, but I'll get there eventually ;-)         Jim S.

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