Seed Production of Vegetable, Tuber and Spice Crops (2+1)

6. Spiral Separator

• The separator, which classifies seed according to its shape and rolling ability, consists of sheet metal strips fitted around a central axis in the form of a spiral.
  
• The unit resembles an open screw conveyor standing in a vertical position.
  
• The seed is introduced at the top of the inner spiral.
  
• Round seeds roll faster down the incline than flat or irregularly shaped seeds, which tend to slide or tumble.
  
• The orbit of round seed increases with speed on its flight around the axis, until it rolls over the edge of the inner flight into the outer flight where it is collected separately.
  
• The slower moving seed does not build up enough speed to escape from the inner flight. Most spirals have multiple inner flights arranged one above the other to increase the capacity (Fig.7).




Figure 7: Working principle of spiral separator