BULLETIN 1373. IT. S. DEPARTMENT OF AGEICTJLTUKE 
The hood is designed to exhaust from the inclosure only the dust- 
laden air > which is brought to it by the belt. It is not meant to 
induce a flow of air over the grain, so that particles of chaff, etc., 
may be picked up and interfere with the grain weights. A velocity- 
control valve and an inspection trap (tig. 29) can be used with this 
hood if desired. 
The main objection to these installations is that the curtain 
hampers inspection of the gates beneath the hoppers, although 
many of the receiving nits in elevators are so inaccessible that in- 
spection of the gates is difficult under any circumstances. An 
interlocking device, such as is used in railroad switch controls, on 
the receiving pit gates should overcome any objection to the use of 
the curtain inclosures. One elevator has used the system success- 
fully for several years. 
Fig. 3.— Application of suction to elevator boot by vertical hood 
As the receiving pits are usually below the level of the basement 
floor, sweep hoods should be placed in the tunnels or areaways in 
which the belt runs. The conveying belt should be far enough from 
the floor to permit easy cleaning beneath the belt. 
AT ELEVATOR BOOTS 
Feeding grain into an elevator boot, by either a belt or a spout, 
produces heavy dust clouds. As a large volume of air in the elevator 
buckets is being displaced by grain there is within the boot a surplus 
of air, which in coming in contact with the disturbed grain becomes 
heavily laden with dust. As a result, dust clouds issuing from the 
elevator boot fill the basement, which is the most difficult floor in an 
elevator to ventilate and keep clean. The control of this dust 
