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Re: Pump cavitation
Ok, I'm not Steve, but this is a topic I know something about.
Cavitation is what happens when the water pressure at the trailing edge of the
impeller blade is too low to keep dissolved gasses in solution. This is
dependent on water temperature, water pressure, impeller speed and geometry, and
If the pressure drops low enough, the water itself will actually vaporize,
creating a pocket of cold 'steam'. This is technically 'true' cavitation; gas
coming out of solution doesn't really count, although it's essentially the same.
True cavitation requires one HELL of a pump (like an OHIO-class submarine going
full tilt). I'd be a bit surprised if this happens in an aquarium pump, but who
knows what you people are using! :^)
The noise you hear is from these pockets of gas imploding as they move out of
the low pressure zone. The implosion is also what damages your impeller, as it
packs a lot of force in a very tiny space, leaving pock marks or worse on your
There are only two ways that you can be getting bubbles out of your pump by
restricting the intake.
1) A leak in your casing or hose connection (restrict intake => lower pressure
inside pump => suck air through leak)
2) Very high gas concentration which prevents the released gas from
re-dissolving fast enough.
In either of these cases, you will not hear cavitation noise.
> Gee, thanks for setting me straight on this Steve. Maybe you could
> explain to me what's happening when I get a lot of bubbles in the return
> line of my Iwaki pumps when I restrict the flow at the input of the
> pump. They're amazingly quiet while this is going on. You might also
> explain why the manufacturers of pumps warn against restricting the flow
> at the input of a pump because it causes cavitation which can damage the
> I was under the impression that the restricted flow caused the water to
> vaporize due to the low pressure created.
> Best regards,