ja3250

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Just purchased a house with a inground pool. I turned on pump and had leaks in pipes. I fixed all leaks and while I was at it I replaced the 3 checkvalves between pump and pool These valves are flapper kind and clear so I can see whats going on inside of them. The are all in vertical pipes. I prime pump and it runs all day fine with no leaks. I can turn it off wait a bit and turn it back on and it works fine cause it is still primed. If I leave pump off for a few hours the water eventuall drains from the pipes back into pool causing pump to lose prime. When I turn pump off I can see that the new flappers are floating (not closing) eventually pipes lose water and flapper drops down First question should the flappers close as soon as I turn off pump stopping water from draining back into pool? If yes what causes flappers to drop down? It appears when I turn off pump there is not a rush of back flow so the flappers float alowing water to slowly drain back into pool. All 3 brand new flappers are doing this!!! Any suggestions is greatly appreciated