The faster you get the light chaff suspended, the more open area for grain to fall through. The chaffer needs to seperate by air, and the bottom needs to seperate size. With the bottom sieve ten to twelve inches in front of the chaffer, it grabs a huge amount of air making it do the same job as the chaffer. When you close the bottom sieve, you cut the air off to the chaffer, making the chaffer seperate like a straw walker. This allows light thrash that air should have removed, make it to the bottom sieve, overloading it and the return. In corn it didn't make a big differance if at all. In milo and wheat, it makes a very noticeable differance. In pearl millet there is no comparison. Millet is a small seed and has a very high fodder to grain ratio, and the fodder is heavy, making it difficult to keep the fodder off of the bottom sieve. It is easier to get the seperation process started when the materail is coming off of the fingers to the chaffer. Once you get the trash lifted with air, it dose not take much air to keep it lifted and moving out of the back of the machine. I now run the long finger chaffer (corn) chaffer in all crops including millet, with excellent results. I did notice that the new Air Jet chaffer uses a wide open setting on the bottom sieve. My thought is to not starve the chaffer for air. I do like the looks of the Air Jet chaffer if it doesn't plug with stalks like that peterson did.
