What do I have in my Main Pool Drain

[ruralreality]

We're installing a new liner and have had some rain and water behind the liner. We're wondering if we have the 20.00 gizmo in the drain that will auto pump the water out once it gets more full. It's dry now so things have improved and we did pump a lot of water out from behind the liner. Looking good. Just curious. We've never had floating liner in our pool for 6 years.

I attempted to take a photo through all the water. Not a great shot. Can anyone tell me what is in my drain?

 

[JoyfulNoise]

Looks like a hydrostatic valve. They pop open when the water pressure under the pool exceeds the pressure of water inside the pool. They are designed to keep your pool from popping out of the ground if you drain them too much. When people do drain pools, they are usually opened to allow the water from underneath the pool to be pumped out to keep the pressure balanced.

Just leave it alone and put the cover back on the main drain.

 

[ruralreality]

I am so happy to hear this - my understanding is that once 4' deep of water (enough pressure) it will remove the ground water behind the liner automatically? Which explains why we never had an issue until we drained the pool and popped in the new liner (this was when the deep end was only 1/2 full) ---

THANK YOU!