Pump not holding a prime

[PaulE10]

Hi,

I have a 22,000 gunite inground pool with 2.5 hp pump. Last week it made some noise and when I checked on it, it had run dry. Not good, I know. I discovered a wad of leaves where the spa return and the pool return meet just prior to the pump. I cleaned it all out and put the jandy valve back on and presto, it worked great.

Since then, I have caught it a few times in the evening losing it's prime. It seems at night , when the freeze guard kicks in, it will lose the prime when it swithches from pool to spa or vise versa. Just a guess I haven't actually been standing there when it happens. If I turn it off for a few minutes, maybe prime the pump with a bucket of water, it starts right back up and runs fine for hours or even days. Sometimes I just turn it off and then back on and it pulls water and runs fine.

Tonight it lost it's prime again. I played with it,primed it, swithched from pool to spa and from spa to pool. It fired up again and was fine. I watched it for a few minutes and the psi gauge on the filter was jumping around a bit, then it just lost it prime. No freeze guard swithching things, just lost the prime.

I turned it off and left it off. I figure what ever the problem is it has gotten worse and I better get some advice before proceeding on.


Thanks

Paul

[Poconos]

Hi Paul,
Gee...a real question this time of year is odd. Forum is pretty dead. I'm not familiar with the setup and have a question. When it switches between pool and spa is the switch on the return (pressure) or suction side of the pump? You imply it is on the suction side because of what you said about the Jandy valve. If that is the case it sounds like there is air leaking into the suction side somewhere. The jumping pressure gauge indicates this too, or cavitation at the pump impeller but I doubt that. Only takes a tiny air leak to lose prime and then prevent the pump from priming again. I would suspect something in that valve area. Again, not familiar with those valves but from what I've read on this forum that can be disassembled and therefore I guess some seal or O-ring inside could be causing the problem.
Best I can do for now. Hopefully someone more familiar will chime in.
Al

[ChuckD]

(just back in from repairing some snow fencing that got blown down. Needed some Pool talk to boost my spirits.)
I was going to answer this too with the observation that that's a mighty powerful pump for that pool. I have a 22K inground and a 3/4 Superpump does fine. I was wondering if, as Al mentioned, there might be leaks, but also if the draw from that pump isn't exacerbating it.

I think that even if you had a perfectly sealed system, you'd still be running on the verge of cavitation (assuming the lines were 1-3/4" and not able to supply the pump's demand).

Is it a two speed pump? Maybe running it at a lower speed would help.

Chuck

[waste]

Saw this earlier and started to respond, but Mrs. waste wants a "clean house for a clean year", so I had to do some housekeeping

As we nor you know how long the pump ran without a prime, I suspect that, as Al said, some cavitation could have occured while the pump ran w/o a prime (what caused it in the first place, I'm not sure- sounds like it's the return valve you're talking about, and that wouldn't cause a suction side air leak). If the pump did indeed cavitate for a prolonged period, some of the seals (pump housing lid gasket, seal assembly or housing body gasket) may be leaking, though only the lid gasket will allow air into the pump to kill the prime, however, the pump inlet fitting may have warped and is now drawing air

You can tell if you have a suction side leak by looking to see if you have air bubbles in the pump housing. If you do, you can try to isolate the problem by slowly pouring water over any suspect area and watching to see if the bubbles go away.