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 "accelerate") the

coolant

into the impeller with the flow rate (velocity) that is required by
output flow  rate.

 Cavitation is when the pressure of the fluid being pumped is locally
reduced below the boiling
point. The liquid flashes into vapor and the vapor bubble is carried thru
the pump.  As the bubble
moves to a higher pressure location (sometimes only a few millimeters from
the initiation
location) it reaches a pressure above the boiling point and collapses.
Usually this is
a very violent collapse and can literally pick chunks of metal out of the
impeller.

2.  The event under discussion took place with the coolant being drawn

from and

returned to an open tank with coolant level at some distance below the

impeller.

If these things are so, it occurs to me that in a closed system, the coolant
supply to the pump would not be stagnant as in the experiment, but moving

at the

same flow rate as the output side of the pump, and under steady state

conditions

(no acceleration of the coolant supply) no cavitation would or could occur.

I intuit that the coolant supply to the pump being a stagnant pool rather

than a

flowing, closed stream rendered the experiment bogus at the rpm where the
onset of  cavitation occurred.

I think this is probably correct.  Most pumps are designed for a particular
inlet condition
called a NPSH, which means net positive suction head.  This translates into
the intended
POSITIVE pressure at the suction (head means pressure, measured in feet of
the liquid being pumped) port.

Bill Freeman

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