Seed Production of Vegetable, Tuber and Spice Crops

1. Specific gravity separation

• This method makes use of a combination of weight and surface characteristics of the seed to be separated.
  
• The principle of floatation is employed here.
  
• A mixture of seeds is fed onto the lower end of a sloping perforated table.
  
• Air is forced up through the porous deck surface and the bed of seeds by a fan, which stratifies the seeds in layers according to density with the lightest seeds and particles of inert matter at the top and the heaviest at the bottom.
  
• An oscillating movement of the table causes the seeds to move at different rates across the deck.
  
• The lightest seeds float down under gravity and are discharged at the lower end, while the heaviest ones are kicked up the slope by contact with the oscillating deck and are discharged at the upper end.
  
• This machine separates seeds of the same density but of different size and seeds of the same size but of different densities (Fig.2 & 3).

Figure 2: Working principle of the specific gravity separator







Figure 3: A specific gravity separator with triangular deck showing the different fractions: one light, two intermediate and one heavy fraction. The fifth side outer is used when soil clods are present