144 SCIENCE OF SUCCESSFUL THRESHING. 



when the cylinder is kept full, will carry over grain when 

 the machine runs empty. Steady feeding is therefore impor- 

 tant on this account and the separator tender should let the 

 pitchers understand that he cannot produce the best results 

 without their aid, in keeping an even and continuous stream 

 of grain going into the cylinder. 



The Wind-Board is placed in the machine so that the blast 

 from the fan will strike the conveyor sieve about half way 

 back. The strongest part of the blast will then pass through 

 the shoe sieve near the front end which gives it a cleaning 

 capacity its entire length. If the wind board becomes bent 

 or sagged so that it stands but little above the floor of the 

 shoe, the grain will slide over it into the fan, and then be 

 thrown clear out of the machine. To prevent the liability 

 of this, belts or "traps" should not be kept in the fan drum. 



Fan Speed. The speed of the fan for 12-bar separator 

 should be about 470 and for the 2O-bar about 485 revolutions. 



Sieves. The function of all sieves is to assist the fan in 

 separating the grain from the chaff and in preventing heads 

 and other heavy objects larger in size than the grain from 

 mingling with the clean grain. Sieves are distinguished from 

 screens in that the grain being cleaned passes through them 

 while it passes over a screen. 



Adjustable Sieves. To obviate the delay and trouble of 

 changing sieves each time the machine threshes a different 

 grain, adjustable sieves have been constructed in which the 

 size of the openings may be changed to suit the kind of grain 



