check valve above spa water level

[BrianPool]

According to the previous posts about the spa water level going down when the pump is off, I need to install a check valve on the spa side. In my case, blocking the pool/spa bypass will cause the spa water level to remain as is (NOT go down). I could not find any reading that explains why this happens exactly. I understand that check valves are installed so the water at the elevated spa will not drain down to the swimming pool. My valves are above the spa level, so I don't understand how the spa water will make it to the pool just due to gravity. Is there another pipe connection other than the visible manual valves? Could someone help explaining it?

Before I install a check valve, I'd like to understand why it will solve my problem. BTW, can someone confirm if installing a check valve on the spa return line will correct this problem?

Thanks!

 

[jblizzle]

Welcome to TFP!!!

It does not matter that the pipes go above the spa level and back down to the pool, when the pipes are full, then they can siphon out of the spa into the pool until the water levels are equal.

Add some pictures of your plumbing setup and we will be better able to suggest a solution.

 

[BrianPool]

Ah of course, siphoning due to atmospheric pressure. Here is a picture of the system.



The top 3-way is the return pipe. Install a check valve on the spa return pipe below the bypass?

And if I may ask another question ... someone just installed a new salt system but it says "No flow" when running pump at 1000 rpm. I increased to 2400 rpm and now it says "Check salt" and "Inspect cell". It might be hard to see in the picture, but the salt system sensor was installed before the cell in the diagonal pipe. Is this setup ok?

Thanks again!