Lots of air in filter pump on low speed - full on high speed

[poolside]

I have a new IG pool, ~20,000 gal and went with a 1.5HP Hayward Northstar pump.
When the pump is running at high speed, the pump is full of water, however, at low speed it does not fill up.

The pump is about 70 feet from the further skimmer - 35 from the closer, and I have a bottom drain as well. 1.5 inch lines. Two returns.

Any idea what is going on? Am I losing energy efficiency if the pump has air in it? (Strangely, there are no bubbles noticable in the return.)

Thanks.

 

[DaveNJ]

Mine is 5 years old and does the same thing. Try putting some lube on the o-ring, not vaseline. I've replaced the o-ring a couple of times with no improvement. When it switches to high you can see the lid pull down.

 

[JasonLion]

Welcome to TFP!

It depends on how much air you are talking about. If the pump runs smoothly and the air remains constant and doesn't fill the strainer basket then things are probably just fine. If the pump speeds up and slows down or the amount of air varies significantly over time then you are getting too much air into the system and need to find and fix the air leak.

 

[poolside]

Thanks for the welcome. I've lurked on and off since last fall.

To quantify the amount of air, I would say that there are about 2 to 3 inches of void space at low speed.
I did put a fresh coat of plumber's grease on the O-ring, but that did not seem to help.

 

[mas985]

When switching from high to low, does the air enter quickly or does it take time for the air to show up?

 

[poolside]

It takes a while. The strainer basket looks full for a couple of minutes, but actually the water level in the strainer basket is dropping until it reaches the "normal" low level (in about 15 to 20 minutes).

 

[mas985]

That definitely sounds like an air leak somewhere. Can you hear air entering from somewhere? Does the pump basket also drain when the pump is shut off?

 

[poolside]

Yes, the pump basket will drain when the pump is not on.
No, I cannot hear any air leak.

 

[mas985]

If air is entering the pump on low speed but not high speed, it is most likely the pump lid that is leaking. You might try another inspection of the seal and/or even replacing the seal. Also, check the basket lip to see if it has been damaged in any way to prevent a seal. Another trick is to tighten the pump lid while the pump is running for a better seal.

 

[poolside]

Thanks. I will try that over the weekend.

 

[DaveNJ]

The Northstar lid rotates and engages four tapered tabs with stops. Mine hits the stops, I can see the air enter from the edge of the lid. I tried to get the pressure test o-ring they came with, no luck. When I get the chance I'm going make measurements and try to find something.