Can someone explain to me how a needle wheel works in a skimmer?

[FloridaFishMan]

Hi,
I am looking at diy skimmers and I don't really understand how the needle wheel works? I understand that it makes the bubble extra fine but how is it set up in a skimmer? Also, how is the air delivered, via an air pump?
Chris

 

[cward]

Air is pulled into a venturi and then it sucked into the needle wheel impeller that chops the bubbles up into smaller bubbles. It's kinda like chewing food. More smaller bubbles have more surface area for the organics to stick to.