MAC Air Classifier

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Prater MAC Air Classifiers process dry materials to exceptional fineness and uniformity over a wide range of feed variations. Offering separations from 3 to 150 micron, they are ideal for use in closed-circuit with a conventional milling system or as independent “stand-alone” systems incorporating feeder, fan, and product collection equipment.

The MAC Air Classifier’s superior performance is due to a design that ensures feed material entering the classifying vortex is unimpeded by re-circulating coarse fractions and an adjustable secondary air stream that improves collection of near-size particles. The MAC can easily be installed in existing air systems with minimal modification.


  • HD construction in carbon or stainless steel
  • Constant diameter, precision fit rotor for excellent sharpness of cut
  • Precise on-stream control of cut point simply by varying rotor speed
  • Adjustable secondary air system for greater capture of near-size particles
  • Low system resistance for less power consumption
  • Optional ceramic, tungsten, polyurethane, or rubber lining for abrasive service

Theory of Operation

Prater MAC Air Classifiers utilize adjustable centrifugal force to separate particles in a pneumatic circuit. As product is conveyed thru the primary air inlet, individual particles are subjected to aerodynamic drag by the pneumatic air. This drag force varies with the size and density of the individual particles. As particles spiral toward the classifier rotor, one of two things occur: 

  1. drag force of smaller, more aerodynamic particles exceeds the centrifugal force exerted by the rotor, and particles pass through the machine as fines; or
  2. centrifugal force overcomes the drag force, causing larger, less aerodynamic particles to accelerate away from the rotor, where a cyclonic chamber collects the coarse particles and discharges them through a rotary airlock fitted to the bottom of the machine. 

Cut-point is determined when the forces are equal, in which case particles have a 50/50 chance of passing as fines. Cut-point is variable and can be controlled by adjusting the rotor speed. A secondary air inlet introduces a controllable amount of air that moves upward into the classification zone, increasing agglomerated and near-size particles' residence time. This air helps to increase collection efficiency of the desirable product.

Here is a sample of materials that have been used in our air classifier equipment (keep in mind that there are more dry free-flowing materials that can be easily processed in our air classifier that are not be listed below):

  • Almond Hulls
  • Aluminum Oxide
  • Ammonium Salt
  • Calcite
  • Calcium Carbonate, Calcium Hydroxide, Calcium Oxide, Calcium Silicate, Calcium Stearate, and Calcium Tungstate
  • Carbon
  • Carbon Black
  • Chemicals
  • Coal Dust
  • Cocoa Powder
  • Corn Fiber, Corn Flour, Corn Starch and Corn Syrup Solids
  • Detergent
  • Dextrose
  • Diatomaceous Earth
  • Dry Nonfat Milk
  • Expanded Perlite
  • Faba Bean
  • Flour
  • Fritted Glass
  • Fumed Silica
  • Garnet
  • Gelatin
  • Graphite
  • Ground Glass
  • Ground Pea Hulls
  • Gypsum
  • Hydrated Alumina
  • Hydrated Lime
  • Iron Oxide
  • Kaolin Clay
  • Lentil Flour
  • Magnesium Hydroxide and Magnesium Oxide
  • Maltodextrin
  • Manganese Dioxide
  • Metal Alloys
  • Mica
  • Milo Grits
  • Mung Bean
  • Navy Beans
  • Nylon Powder
  • Oat Flour and Oat Groats
  • Pea Flour
  • Pea Protein
  • Phenolic Resin
  • Pinto Beans
  • Polyamide – Imide
  • Potassium Chloride
  • Potato Starch
  • Powder Coatings
  • PVC Powder
  • Quartz
  • Silica Gel and Silica Sand
  • Silicon Dioxide
  • Sodium Bicarbonate
  • Sodium Phosphate
  • Soy Meal and Soy Protein
  • Starch
  • Sugar 8x, 10x, 12x (MAC-4)
  • Toner
  • Vanilla Bean
  • Zeolite
  • Zinc, Zinc Diacrylate, Zinc Oxide, and Zinc Stearate
  • Zirconia