The drum sieve pre‑cleaner (also called a cylinder pre‑cleaner) is a rotary double‑layer screen that removes coarse impurities (stalks, stones, large debris) through the inner drum and fine impurities (sand, broken grains) through the outer drum, based on particle size. However, it cannot effectively separate light contaminants such as husks, chaff, and dust that are similar in size to the grain. This is where the circulating air aspiration system comes in: it applies an airflow stream to the falling grain, lifting and carrying away lightweight materials, while the air is recirculated in a closed loop to reduce dust emissions and energy use.
