do you understand the way weatherson has his air injection system setup with the open ended cylinder? i actually found it kinda confusing the first few times i looked at it. it took me a bit to understand exactly what was going on there?
basically the cylinder is submerged in water. he has his in the overflow box er something? you could put it in the sump and im sure that'd be just fine? the cylinder is basically just a drinking glass turned upside down. on the top end of the cylinder, he has a hole for the airline tube to pass through. there are also 2 more holes where 2 more pieces of tubing are attached. thoes 2 tubes go to each of his return pumps, and attach to a venturi. when the air pump turns on, it fills the cylinder with air, and the cylinder fills up. when the cylinder fills with air, the venturis attached to the return pumps draw air in through the 2 tubes attached to the air filled cylinder. thats when the injection system blows air into the tank. when the air pump turns off, the venturis draw out all of the air left in the cylinders. when all the air is out of the cylinder, the venturis draw water through the pumps, instead of air.
that cylinder is what makes that system function so well. if he was to simply attach the venturi lines directly from air pump to return pump, then when the air pumps were off, the venturis would still draw a small amount of air through the return pumps. this would mean constant micro bubbles.
if you wanted to use an air stone attached to the end of an airline which is attached to an air pump, and put the air stone under a power head, that would have the same result on a smaller scale. different method, same result. and by doing it that way, you wouldnt have to worry about the powerhead drawing air into the tank without the air pump being turned on.
i like that little sun diagram you have there. where did you get it?