Air from Multiport valve?

[TommySalami]

Hi all,
When the pump has been running all day and I turn it off, air rushes into the pump basket and water blows back and knocks off the skimmer lid!
I have a 15k in ground with a spa, using a Speck sand filter, Pentair pump, Hayward heater, and Intellichlor SWG.
My maintenance crew replumbed the system because the original install (previous owner) had the PVC pipes over the heater. The new install has a check valve and zinc anode that weren't there before.
The system runs well but we get air in, I believe it is from the drain holes at the water level in the spa. It's an old gunite pool that looks like the ones I remember from the 70s.
If I turn off the pump and move the Multiport valve from filter to backwash, air goes in the pump basket. I don't see any obvious leaks and I lubed the pump O rings. The pump lid is on tight.
Any ideas? I took a photo of the setup.
Thanks!

 

[Jimrahbe]

Tom,

Air is getting trapped and compressed inside your filter, so when you shut the pump off, the air forces water backwards through the pump and into the skimmer. I don't know why and have no experience with sand filters so let's see if we can get some help. Calling @JamesW

Thanks,

Jim R.

 

[JamesW]

Probably a suction side air leak.

I would put a check valve between the pump and filter and fix the suction side air leak.

Listen carefully near the suction as someone turns off the pump to see if any water squirts out.

What pump do you have?

Check the skimmer weir to see if it is sticking.

 

[JamesW]

Watch and listen at these three spots to see if you get a spurt when the pump is turned off.

 

[TommySalami]

Thank you both! The simmer weir is almost constantly open, and due to the construction it’s tough to know the best solution without filling the pool to a very high level. Maybe that’s what is needed. I am filling the pool higher and I will test for leaks in those spots.

 

[TommySalami]

I hear an air suction leak at the 3-Way. Going to try to seal it with sealant. It has a few patches on it. Will replace it if needed.

 

[Texas Splash]

I hear an air suction leak at the 3-Way.

Should be a tiny O-ring on the stem inside as well. You might remove the screws to lift that top off and take a peek.

 

[TommySalami]

Y'all. Thank you!
I unscrewed the 3 way inlet and didn't find any gaskets... But when I tightened it back up... THERE ARE NO AIR BUBBLES COMING INTO MY POOL.
the spa isn't gurgling.
This has not happened since we opened it last year.
Thank you all for the help!