Air classifier - Whizzer type is a compact and dust tight machine for fine classification of various powdered materials. It is used to separate dry materials into different particle size fractions by their size, mass or shape. It is also used to modify a particle size distribution, remove the fines fraction of a material or the over size or coarse particles of a material or create two grades of material.

Modern air classifiers are used to separate the protein fraction from the starch granules of ground cereals and legumes, based on difference of size, shape, and density. The basic elements in an air classifier consist of a rotating plate and air circulation fan, installed in a special chamber. The basic forces acting on the particles in the air classifier are the centrifugal, the gravity and the drag force. The air sucked by the fan, removes the fine particles from the plates and separates them from the coarse particles. The selection of an air classifier for a particular application is dependent primarily on the separation efficiency required and the money and facility space that can be committed. The least expensive equipment is a vertical column that requires a minimum of space. The zigzag air classifier is taller than the vertical column unit and has internal veins that add to the cost. The horizontal air classifier can process materials having larger particle size than a zigzag unit; however it requires more amount of floor space.

Air cleaning systems are designed to reduce contaminant levels after contaminants become airborne. It can be designed to control PM (dust), gas-phase contaminants or both. A minimal level of air cleaning is used in most building to protect mechanical equipment from soiling. Separate air cleaning systems are commonly used with radiant heating systems. The general type of technologies used in air cleaners include mechanical filters, electronic air cleaners, and hybrid filters for the capture of particles, plus gas phase filters to control odors.