Pump Loses Prime At 20 Psi

[PoolUser999]

Hi,

I've looked all over and can't find any answer touching on this specific problem. When the pool pump turns on in the morning there are bubbles in the pool outlets, but then it primes right away, the pressure builds to about 20-25 psi but then immediately sinks down to 5 psi (within a few seconds). While the pressure falls I get tons of bubbles in the pump strainer and bubbles come out of the outlets in the pool. Then the pump primes again within a minute or two, the pressure gets to 20-25 psi and the process repeats.

The o ring on the pump strainer seems fine. I was going to replace it, but while taking it off the other day, water and air squirted everywhere, so that tells me it's holding a good seal. I guess it could still be a problem, what do I know? Also, the area around the pump and tank is bone dry, so no obvious above-ground leaks.

A pool company recently replaced the filters. I'm wondering if that has something to do with it. Maybe the tank lid isn't seated correctly or the drain in the filter tank isn't closed all the way? What could cause a pump to lose prime while running? This is an old system on an old pool. My worst fear is that a leaking pipe or connection underground is responsible.

I'd really appreciate any advice!