Recirculating pneumatic separator

A pneumatic separator for separating lighter particles from heavier stem particles and the like, as in tobacco threshing, comprising a separating chamber, means for circulating air in a generally upward path through said chamber, inlet rotary impeller means mounted on one side of said separating chamber having vanes for thrusting particles to be separated into and across the chamber toward a generally upwardly extending opposite wall of said chamber, an inclined perforated plate member defining a bottom wall portion of said chamber below the level of said impeller means for directing larger particles discharged toward or falling onto the inclined plate member for collecting and carrying heavier particles from the chamber, an air jet impeller means located immediately above said inclined plate at a lowermost portion of said opposite wall and means for conducing air to said jet impeller means to discharge an air jet therefrom for directing material into a high arc trajectory into said chamber, an air diffusion grating assembly below said inclined perforated plate member receiving air discharged from a fan and having a plurality of adjustable directional vanes and a plurality of fixed direction vanes, a first group of said vanes being positioned and oriented to reduce air flow and velocity in selected portions of the separating chamber lying above said first group and a second group of said vanes being positioned and oriented to increase air flow and velocity in other portions of the separating chamber lying above said second group to selectively direct upward air flow through said chamber for maximum separating efficiency, and said upwardly opening opposite wall having discharge openings located at a vertical position above said level of said impeller means and means for supplying air through said openings to provide air flow therethrough into said chamber in zones located above the height of said openings.