High flow guarded center overflow with air

[karimwassef]

I realize that this may not be desirable by many others but since it took me a while to get right, I thought I'd post it here in case someone else is looking for a solution.

I had a 2" PVC center overflow that I needed to support >3000 gph flow but without a full siphon. I intentionally wanted it to pull air and create a large mass of bubbles. I also needed to have a large opening mesh guard to keep living things from getting sucked into the sump.

To get the overflow to support the gph, I used a 3" to 2" reducer backwards. The large 3" opening created a large vortex and funneled the frothy flow down the 2" overflow pipe. To get more air, I was able to add a tee.

The difficulty came in adding the protective mesh. It ran fine for a few minutes but then the vortex disappeared as the flow rate dropped dramatically. It wasn't debris getting caught in the mesh. I think it was a thin layer of frothy flow over the center of the mesh that changed the surface tension there and stopped a vortex from forming.

The solution was a short piece of 1" PVC and a 1" coupler above the mesh. This ensured that the flow inside the mesh had a channel of air above it so a vortex could form.

It sounds convoluted but it works great (for my intended application).

Oh - and I did have an emergency overflow that saved the day multiple times while I experimented.

Pics:




The tee alternates as an air inlet and a secondary purge. It oscillates in function.

I'm not sure I understand all the fluid dynamics but it works consistently now.

If anything changes, I'll update here.