Why does my pump fill with air when on low-speed but not hi?

[prop]

I have a variable speed Hayward pump that is nicely air-free when on higher speeds (mine is set at 65% as high, 35% as low). However, during the day, electricity is more expensive so I run the pump on low speed (35%).

I have looked in the pump while on high and have never seen any air, but for some reason when on low, as much as a third of the pump that I can see on top of the basket is air! As soon as I turn the pump on high, my returns bubble air for about 30 s and then the system is totally air-free...

I would have thought that if I had a leak or was sucking air somewhere, this would be worse on high speed.

I don't notice any change in water levels. I don't suspect a water leak anywhere...

Any good explanation?

Thanks for any help!

 

[Bama Rambler]

Re: Why does my pump fill with air when on low-speed but not

There is a pretty long discussion about this here and the general concensus is that it just happens with some low speed pump installations.

 

[prop]

Re: Why does my pump fill with air when on low-speed but not

I missed the link in your post, and when I searched for it I didn't come up with any hits? Maybe my poor search strategy - I'll try again. Thanks.

 

[Bama Rambler]

Re: Why does my pump fill with air when on low-speed but not

Use the google search at the bottom of the page.

 

[mas985]

Re: Why does my pump fill with air when on low-speed but not

Here are the links:

is-air-in-pump-basket-while-running-normal-t19777.html
ecostar-and-air-bubbles-t31336.html
hayward-ecostar-air-in-filter-basket-t30065.html
poll-for-users-of-variable-speed-pumps-please-read-t30272.html

I have several theories on this.

First, is when a pump switches to low speed, the suction in the pump basket is reduced and this a make the lid seal worse and thus allows some air into the basket on low speed but not high speed where more suction/seal exists.

Second is that the air leak is so small, that air will only accumulate on low speed where the flow rate is not high enough to expel the air. On high speed, the air leak still exists but the flow rate is high enough to quickly expel any air.

Third theory is that outgassing of dissolved air is playing a part. This is shown by very small air bubbles forming on the pump basket itself. Again, the flow rate on low speed is not sufficient to expel the air bubbles but on higher speeds, flow rate is sufficient to expel the air bubbles. This theory is more likely to add air much slower than the first two theories.

 

[mikespoolfl]

Re: Why does my pump fill with air when on low-speed but not

On my old pump ( single speed 1.5 hp) had the intake and the suction side of the strainer basket straight across from each other. The Eco Star basket design has the suction, water coming into the basket near the top of the basket and the and water leaving the the basket near the bottom. If small bubbles form for whatever reason, there is not enough turbulence to pull the bubbles to the bottom on the slower speeds.

 

[cyclebob]

Re: Why does my pump fill with air when on low-speed but not

I have spoken to several Hayward techs. Yes I called back several times on different days. They say regardless of whatever we have been taught regarding air in the basket, this is normal for VSP. That of course assumes you are sure you have no leaks on the suction side. I have a large air bubble after the prime and than running at 1725RPM the level drops over several hours to about .5inches below the top of the basket. The pump works fine and runs from7:30 AM to 9PM at 1725 than 3250 from 9PM to 10PM for my pool cleaner than shuts down for the night. The basket is filled to the top in the am before the pump primes again at 7:30AM. Note the pump is set to prim for 3minutes. If I try to use Auto sense the pump shuts down on pump error failure to prime. The Techs at Hayward says that I should use the 3min prime cycle instead. I have read and seen the same issues with other VSP from Pentair as well. So for now I will keep an eye on it and take the word from the Hayward techs.
My pool was built in 1978 and has 1.5inch plumbing. I have the skimmer and a dedicated suction line for a great white pool cleaner. Both valves are full open running into a 2inch union going into the suction union on the pump.