Air bubbles in pump strainer pot, but no air coming out pool returns

[Mattman1]

Pump/filter/circulation system all seems to work well, but for this one issue. No water leaks visible above ground. Pool does not seem to be losing water.

With pump running the strainer pot is 99% full of water, but there clearly is an excessive amount of air bubbles swirling around in the pump strainer pot. No bubbles coming out of returns in pool.

Turning pump off leaves strainer pot all but completely full of water, just a small air bubble at top of lid. But after 8 hours or so the strainer pot is less than 1/2 full of water. This means the water is being pulled out of the strainer pot through the filter and back to the pool through the return lines, right? (Because water level remaining in strainer pot is well below the suction side input to the pot, so it can't all be going out the suction side piping)...

Pump always starts/primes just fine - even when water in pot is low - and filter pressure is normal, but I'd really like to find the leak allowing the water to leave the pot.

I used a garden hose to flow water over all the usual above ground suction-side leak points, but still no obvious air leak.

Have also replaced the pump lid and replaced and lubed all the rubber in the pump (lid o-ring, diffuser o-ring and pump housing ribbon gasket). Diffuser looks normal - no obvious sign of melting or cracking.

Only thing left is underground pipe leak, right? Pool does not seem to be losing water

Any thoughts/suggestions appreciated...

This afternoon I plan to try the shaving cream test on all above ground areas. If that doesn't work I guess its time to start digging

Thanks,
Matt

 

[mas985]

But after 8 hours or so the strainer pot is less than 1/2 full of water. This means the water is being pulled out of the strainer pot through the filter and back to the pool through the return lines, right?

Correct. There is an air leak somewhere and the water will drain out of both lines, suction and return. But because the water drained down to the impeller inlet, I suspect the air leak is on the suction side of the pump.

Have also replaced the pump lid and replaced and lubed all the rubber in the pump (lid o-ring, diffuser o-ring and pump housing ribbon gasket).

Drain plugs too?

Do you have any valves on the suction side of the pump?

 

[Mattman1]

Thanks for the reply!!! Very much appreciated

Correct. There is an air leak somewhere and the water will drain out of both lines, suction and return. But because the water drained down to the impeller inlet, I suspect the air leak is on the suction side of the pump.

I suspect same. Question though - what would you expect to happen if air leak were on the pressure side of the pump? Would pot only drain down to bottom of suction inlet?

Drain plugs too?

No, but drowned/flooded each drain plug with water from garden hose and saw no change to air bubbles in pot. Also slathered both plugs with shave cream, but still no sign of leak. Will definitely remove drain plugs tomorrow and inspect and lube/replace washers.

Do you have any valves on the suction side of the pump?

Yes, 1.5" PVC ball valves. One valve on skimmer suction and another valve on the main drain suction. Valves are original from when pool was built, probably 25 years old. Valve handles are so brittle they broke years ago... have to open/close with channel lock pliers. Thinking I will replace with Jandy valve, but want to isolate/fix this air leak first before re-piping.
Regarding the suction side valves, I noticed that when I close either valve, the air volume in the pot increases dramatically along with pump/water noise. Was thinking the increased vacuum on the one open suction line exacerbated the air leak, but this happens with *either* valve closed. Perhaps this means both valves are leaking air through their handle stem?

New info... tested with shaving cream this afternoon at 4PM. Didn't notice any obvious air leak, but bubble action in pot did seem much diminished with the shave cream on all suction side joints, drain plugs, lid and valves. So I left shave cream in place and pump running while I started digging to expose the first few feet of pipe underground... about 1/2 hour. Then I turned pump off and noted how much air was in the pot - just one small bubble about 1 inch diameter. Been checking every hour since and so far no more air in pot than when first turned pump off... thinking *maybe* air leak is so small that shave cream blocks leak when pump is off??? Will check again first thing in morning and update

 

[Mattman1]

New info... tested with shaving cream this afternoon at 4PM. Didn't notice any obvious air leak, but bubble action in pot did seem much diminished with the shave cream on all suction side joints, drain plugs, lid and valves. So I left shave cream in place and pump running while I started digging to expose the first few feet of pipe underground... about 1/2 hour. Then I turned pump off and noted how much air was in the pot - just one small bubble about 1 inch diameter. Been checking every hour since and so far no more air in pot than when first turned pump off... thinking *maybe* air leak is so small that shave cream blocks leak when pump is off??? Will check again first thing in morning and update

Update: pump strainer pot was still almost full this morning, so after 12 hours of pump off there was very little leak down. There were several more small air bubbles present in the pot, but I'd say pot was still 98-99% full. Very strange

I plan to service the pump's drain plugs this afternoon. Will then just observe for a few days to see if original leak returns.

 

[covrguy]

if the pool isn't losing water the air may be from the impeller cavitating

 

[mas985]

You wouldn't see cavitation in the pump basket. In a residential pump, cavitation only occurs near the impeller and the vapor bubbles would immediately collapse on the way out of the impeller once the pressure rises.

Plus the pump is draining while off not on.

 

[Mattman1]

Again, thanks for all the replies.

Also curious to me is why is there is air in the pump basket but no air coming out of the pool's returns. Hayward S244T filter, so air escapes through return line exiting top of filter...

 

[JamesW]

Is there any water loss at the waste port of the filter?

When the pump is turned off, listen to the waste port to see if you hear air getting sucked in.

Have someone turn the pump on and off a few times while you check the suction side for leaks. When the pump is turned off, there is a brief surge of back pressure from the filter that can sometimes reveal a suction side air leak because the brief surge can squirt or seep out water.

 

[Mattman1]

Good idea. Haven't notice any water loss at waste port, but honestly I hadn't thought to look there. Will check tomorrow for water loss and listen for air getting sucked in, and update.

Have checked several times for the backpressure surge causing water to squirt/spit out anywhere on suction side, but no joy since I replaced all the pump rubber. That's actually what made me replace all the rubber to start with, when I noticed some water squirt out from the lid o-ring when I turned off the pump. After replacing the lid o-ring, no more squirts/spits from backpressure surge, but bubbles in strainer basket remained, so I replaced/lubed all the rest of the pump rubber (except drain plugs, was hoping to get to them this afternoon but life got in the way...

Bubbles are still very much diminished since I did the shaving cream test yesterday.

Thanks,
Matt