Air space under pump lid - problem or worried about nothing?

[jwesleyh]

Hi all,
I'm a few months into pool ownership of about a 4 yr old in-ground pool (details in signature). Prior owner had the variable speed pump running 3200 RPMs, not sure why. After replacing the very worn/dirty filter cartridges and reading about pump setting recommendations on this site, I adjusted the pump to 2000 RPMs, as it seemed like the energy/flow sweetspot. The clean filters dropped my filter pressure from 25 to 12. The RPM change dropped it further to about 8. But, after changing the speed, I noticed the pump lid has an airspace (see photo with pump running). The flow looks fine and water is fully over the pump inlet and up to the edge of the clear lid, but it's not full. Increasing the pump speed shrinks the air space, but doesn't eliminate it.

Reading more here led me to worry it meant a suction side leak, but I have no bubbling in the pool from return jets, no visible leaks when the system is on or off, and filter pressure and water level in the pump basket hold fairly constant on or off. Nonetheless, I replaced o-rings in all the suction side valves, replaced the pump lid o-ring, and even the lid itself. Didn't change a thing. I've also shaving cream tested everything on the suction side and can find no signs of a leak.

Is this normal and I'm worrying about nothing? Does an efficient pump speed on a low pressure, clean system just look like this? I don't want to ignore a problem, but besides the visual appearance of the lid everything seems to be working great. Any advice appreciated!

 

[ajw22]

It is probably normal.

Does increasing the RPM on the pump clear the air bubble? If so then it is normal.

Schedule your EasyTouch to run the pump for 20 minutes a day at a higher RPM that clears the bubble.

 

[PoolStored]

Bubble will grow faster with a dirty filter.
Run high for a short period a day to clear the bubble.
Anyway, air in the pump basket on low speed is usually caused by one of two issues.

1) Pump lid leak. Sometimes pump basket lids will seal better at higher RPM than lower RPM because the pressure in the pump basket is lower at higher RPM.

2) Outgassing. The pressure in the pump basket is lower than atmospheric so dissolved gasses in the water can come out of solution. The lower the pressure, the more outgassing that will occur. However, at higher RPM/flow rates, any dissolved air that comes out of solution will quickly get taken out of the pump basket because of the higher flow rate. If the RPM is low enough so the flow rate is lower than the rate at which air rises in the pump basket, the air will remain in the pump basket.

There is nothing you can do about #2 but for #1, lubing the pump lid seals and drain plug gaskets can sometimes improve the problem.

Allen'd

 

[jwesleyh]

Thank you both. Higher RPMs shrink the bubble by 1/2 but it doesn't disappear. Admittedly, I haven't tried it above 3000RPM. If a leak, seems to me a higher setting would pull more air, not less, so maybe that's a good sign.

I replaced the drain plug gaskets when doing the others and lubed them all when reinstalling. But, your thought about the lid sitting with less force on the lower speed makes sense.

 

[PoolStored]

Run it up to 3000 or 3450 for a couple minutes a day, it should clear it. It is also colder right now and o-rings shrink in the cold.