Pump low/no flow while running 24/7

[robertmee]

I'm at my wits end. I have a two year old install, and the pump is losing flow or has very low flow (pump basket emptying). It might run for a few days or it might happen in a few hours. The only way I can maintain flow is to up the RPM's (variable speed Hayward) to around 3000 RPM...Even at 2200 RPM, it will lose prime. And again, i've modified the schedule to run 24/7 to isolate the issue and it is still doing the same, so it's not a matter of losing prime during idle period. The particulars:

Hayward multispeed Pump - 2 years old
Sand filter - running 10 PSI during normal operation
Two main drains (valve wide open) and one skimmer (valve wide Open). I usually proportion the main drain down, but to isolate this problem, I have them both opened
Return valve wide open

Flow - Main, Skimmer tee after valves into pump inlet...pump through SWG then through Sand Filter through return

What I've done:

Increased speed of pump
Run 24/7
Make sure baskets, skimmer are clean
Made sure Pump Impeller was clean
Greased basket seal - have new one on order
Water level is not decreasing so not likely a leak
No air leaks at fittings on suction side best I can tell
I don't see air in the returns in the pool

Each time I find this condition, the pump is running, there's little flow through the basket. As soon as I press speed 4 (3200 RPM), the pump reprimes and I have flow again.

So my questions:

1) Would a bad basket seal cause this problem? I have a new one on order, but less than 2 years old, the seal looks fine and rubbery

2) Is it possible the impeller is damaged?

3) Anything else I should be looking at? Maybe something in the sand filter, but I'm not seeing any pressure spikes like a plugged return. Going to order a new pressure indicator just to be sure.

 

[kadavis]

Try closing the main drain valve and run just the skimmer at different speeds. Check the skimmer weir door to make sure it doesn't hang up. If all okay close the skimmer valve and run just the main drain the same way. One tip I don't no what type suction valves you have but try closing them with pump running and see if there's any air intrusion

 

[robertmee]

Try closing the main drain valve and run just the skimmer at different speeds. Check the skimmer weir door to make sure it doesn't hang up. If all okay close the skimmer valve and run just the main drain the same way. One tip I don't no what type suction valves you have but try closing them with pump running and see if there's any air intrusion

I have two ball valves....one from the pair of main drains, and one from the skimmer.

So, right now, with pump running 3000 rpm, basket is full of water. When I close the skimmer ball valve, I hear water "spraying" (best sound term I can come up with), and I see maybe 20 or so small air bubbles (about the size of a pea) appear in the basket. They dissipate within a minute. If I repeat, the bubbles are less each time. If I do the same on the main drain side, I might see 5 or so bubbles, but doesn't seem as many as on the skimmer side. Water is well above skimmer suction and weir door is operating normally. What do the air bubbles on valve closing mean? According to this thread, it's normal: Bubbles from main drain

 

[pooldv]

Sounds like there is a suction side air leak. More here about tracking that down, Pool School - Suction Side Air Leaks