Air in pump basket

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kd9917

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Mar 24, 2010
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Topic split from this thread air-in-pump-basket-t19261 by moderator for better response

I have what I believe is a simular issue but want clarification. With pump running I can shine a flashlight (night time is easier to see) into the pump basket lid and I see "Champaign" bubbles. Is that caused by the pump action and churning of the water or is that an official air leak? I never have any air at the filter air bleed valve nor do I have air bubbles coming from the returns.
 
If what you're seeing is truly air bubbles you may have a small suction side leak. The first thing I'd try is lubing the pump basket lid with silicon o-ring lube and see if that helps. Also check to make sure the skimmer(s) aren't creating a vortex and sucking a small amount of air in.
 
watch those bubbles as you turn the pump off. If they instantly disappear, its cavitation,
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According to that explanation link, I'm not sure cavitation occurs inside the pump basket. They seem to think it occurs right at the impellor, hence the potential for damage to the impellor if it (cavitation) is allowed to remain for an extended period.
 
No, that's not normal. After several minutes of running there should be no (or a very small bubble) of air in the basket housing. Sounds like the lid seal is leaking. Lube it up and see if that helps the problem.
 
Bama Rambler said:
No, that's not normal. After several minutes of running there should be no (or a very small bubble) of air in the basket housing. Sounds like the lid seal is leaking. Lube it up and see if that helps the problem.
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Not sure I understand that. How could you have a small bubble, I mean with the force that water is sloshing around in that basket area how could one small bubble stay intact? I could see having one small bubble that sits in the center of the basket area just under the lid with the pump off. However once that pump starts I cannot see how that one bubble survives. Maybe that one normal bubble gets all churned up and breaks up into thousands of tiny bubble which is what I am seeing????
 
My lid has a small circular boss molded in the center and will sometimes hold a small bubble of air for a good long time. Eventually it will go away but sometimes not for a long time.

Since you're seeing bubbles constantly I still suspect an air leak.
 
duraleigh said:
According to that explanation link, I'm not sure cavitation occurs inside the pump basket. They seem to think it occurs right at the impellor, hence the potential for damage to the impellor if it (cavitation) is allowed to remain for an extended period.
Click to expand...

Dave, you are correct, true cavitation cannot normally be seen in the pump basket. The bubbles only exist where the pressure is low enough to support water vapor which is usually above 29" hg and that can only occur at the impeller. The bubbles will typically form near the impeller inlet and then collapse at the impeller exit, only existing inside the impeller. This is where most of the damage occurs. Youtube has a few videos showing how the bubbles only exist around the impeller.

However, because the suction is so high when cavitation occurs, it is normally accompanied by an air leak which is why it is often confused with cavitation.

Also, a couple of really good articles on cavitation:

http://www.pumped101.com/cavitation.pdf
http://www.pumped101.com/bubbles.pdf
 
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