That is interesting Howard. I did not know there was a distinction.
In that light I don't know whether the Mazda pump is stalling or
cavitating. Since it is a closed loop, pressurized system how can
you tell?

Paul Lamar

Howard wrote:

Paul:
    I don't have an answer to that.... It would require differential
pressure testing.....  If your inlet is less restricted than your outlet it
is very unlikely that you are experiencing cavitation.   It should be noted
that a centrifugal pump progressively stalls as outlet flow is
restricted..... This can be observed easily on a gas or electric driven pump
as the load becomes less as volumn decreases..... That's right..... blocking
the outlet reduces power demand on a centrifugal pump.... just the opposite
from a positive displacement pump..... their behavior is rather strange
until you get used to it.   I often fill a 6000 gallon tanker truck with
water using a 4" pump (15 HP )..... closing the outlet valve you can easily
hear the engine load lighten as flow decreases.  The two stage fire fighting
pumps we use around here ( 10 hp Briggs power ) are an excellent place to
learn about the behavior of non-positive displacement pumps..... close the
nozzle to a trickle and the engine loafs..... open it up and pressure
increases as well as flow and you can really hear the engine bark as the
governor opens.

H.W.

 
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