Okay... look at the bubble plate on a BK... the pump output enters the area straight into it. The problem is that with larger plates, and sometimes ones where the holes arent machined with the same precision, you can get areas where small pockets of bubbles can get stuck, build up, etc... and then you get a parger bubble passing through the plate here & there. If you have the pump's output enter this bubble plate area at a tangent, the contents under the plate will spin. This is what ATI does, and even though there is a large area under the plate where bubbles could stagnate and collect, they cant, because the entire contents under the plate is spinning in a vortex.
Now, the relief is something else. Okay... a bubble plate means all the air and water coming into the plate is getting shot up... but you dont really need all the water. In many cases, the bubble plate may be too small in diameter to reduce turbulence, or the pump being used might move ALOT of water for the small amount of air it moves. In these cases, it helps to bleed off some of the water pressure from under the plate, and there are two ways. The goal is to bleed off as much water as possible, but not so much that the air bubbles under the plate stagnate... a 'sweet spot' of sorts. Heck, even if you cant get to this 'sweet spot', it still helps. But you dont want bubbles coming out of this hole (or you might as well just drill more holes and use a larger plate).
The first way is to use a taller bubble plate chamber... like a skimmer within a skimmer, and inject at the top of the plate. The air and water will go into the plate towards the top, and the bubbles all stay close to the top until they exit... so you can add another outlet at the bottom... a 'bleeder' so you can reduce water turbulence above the bubble plate. The best way to do this is to have a valve on this extra outlet so you can tune it, and then have this feed back into the recirculating pump somehow... or close to it. That way, if you end up with some microbubbles in the bleed, they will just get recycled into the skimmer pump.
The otherway is a bit tricky. If you look at the spinning contents of an ATI under the bubble plate... you will observe something interesting: The centrifugal force of the spin causes the heavier substance, water, to go to the outside, and the lighter substance, air bubbles, to move to the center. So, if you position it right, you can place a bleed outlet right before the water spins in front of the pump inlet again (say, if you remove the inner pump on an ATI BM250 and used it as an outlet), and you will get almost 100% water from this. Either that, or you can use multiple smaller ports around the parimeter so any one port doesnt create enough flow for the bubbles in the center of the bubble plate to wander out. You cant bleed as much with this method, because it is using the pressure/centrifugal force of the pump to sort, and the first method is using the air bubble's natural bouyancy, but it still works. I tried it on an ATI clone... and the turbulence was greatly reduced above the plate.
