cavitations is when a pump is running and not pumping, its most commonly
caused by an air pocket not an undersized pump.

kc


"Jon C Rupert" wrote in message
.. .

"Mort" wrote in message
. com...

"Luca Brazi" wrote in message
om...
Just switched out a Mag 3 for a Mag 7 in a closed loop SCWD
circulation system and the blasted thing is churning out microbubbles
and rattling unbearably (neither of which the Mag 3 did). It is
slightly better when I restrict flow a bit on the output side, but
that rather defeats the purpose of using the new pump now doesn't it?
There is a simple U tube connected to the pump inlet by about 2.5 feet
of 3/4" hose. There's got to be air getting in somewhere but I can't
find any leak. I didn't experience a similar "break in" with my Mag
3. Microbubbles means the leak, if any, has to be before the
impeller, right? Anyone with more experience want to tell me what's
happening here?


I could really be reaching here and I'll prolly get slapped for saying
this
but....


In a hydronic heating system (closed loop) there are occurances where if
the
pump is oversized or the line is undersized the pump will actually
reduce
the pressure on its suction side to the point where the water will begin
to
turn to vapor. (ie=make bubbles) This could explain the rattling.

I seriously doubt this is the case. I'd be surprised if a Mag pump
could
even do this but a mag 7 is considerably larger than a 3. Why the
change?

What type of hose is it that you are using? Is there anything else
connected by a tee or otherwise near the outlet of the pump?

~Mort


You may have a good point. I think the technical term is cavitation. It
can destroy a pump and it typically happens when the pump is not properly
sized for the system.