there are a couple of ways to make them. Either becket, countercurrent, downdraft, or needlewheel venturi. Basically its just a difference on how to mix air with water being pushed into a water column and having the bubbles rise and remove the protein that gets to attach to these bubbles on the way up. Its a little more complicated than that but its a general description. The main ones u see these days are needlewheel and becket. The difference between the two are that the beckets process alot of water and produce alot of bubles while the needlewheels dont process as much water but go by the theory of dwell time in which the water is given more time for the protein to bond with the bubbles. Hopes that makes sense