My equipment is about 4 feet above my pool and as soon as I open the pump lid, the water gets sucked out of the pump basket on its way back to the pool as mas mentioned. I do have a check valve on the suction side (pb put it there) and I like it since it primes in seconds. I have a 2hp pump right next to it for the slide and it does not have a check valve. It takes over 2 minutes to prime after allowing it to drain.Ouch 2mins! I was told by more than one pool store guy when i was fixing my pump problems that if you don't reach prime in 30 secs you will start hurting your pump.

2 mins is a long time to run dry. I bought 2 jandy check valves and am putting them on my two returns (skimmer and main drain) The instructions call for a min. Of 18' of water above them so gravity can hold the flapper closed and sealed. This required me digging up the area in front of my slab.

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I decided since these are nice valves and $50 ea. I want to be able to look into the clear service window occasionaly so i'm installing them a few feet from the slab where the pipes go vertical and am putting a irrigation box with cover over them. The valves belong on the suction side to hold the water prime. Ive seen the valve on the output side and yes that will keep the filter from dumping as you open the strainer cover but thats why you should move your multi port valve/switch to off first. There should also be 2 valves the way i'm doing it. The other thing that happens with the valve after the pump is that if you don't close all the jandy valves on the suction lines before you pull the lid all the water will flow back to the pool and youve lost water prime. Windows Activation Code 0x80070005.