DUST CONTROL IN GRAIN" ELEVATORS 
43 
the hood. No grain was lifted from the screen when it was placed 
directly in the hood intake. 
At a velocity of 4,975 feet per minute, fine wheat scourings on a 
tray 12 inches from the hood intake were but slightly disturbed, 
chaff was picked up from a screen 4 inches from the intake, and the 
very lightest chaff was picked up from mixed grains and dockage on 
a screen placed in the mouth of the hood. 
At a velocity of 4,000 feet per minute, the air currents were barely 
able, even with eddies, to move the fine wheat scourings on a tray 12 
inches from the face of the hood. Light chaff was picked from a 
screen 3^ inches from the intake. Only the very lightest chaff and 
wheat scourings were picked from a screen covered with grains and 
dockage placed in the mouth of the hood, Grains of oats were not 
even disturbed on a screen placed in the mouth of the hood. 
-D- 
W 
Fig. 32.— United 
Department of Agriculture hood. Dimensions are given in Table 6 
The intake of the United States Department of Agriculture hood 
should be from 12 to 18 inches from the grain stream, never closer 
than 12 inches. When the hood is placed in a horizontal position, 
the distance between the bottom of the hood and the grain should 
never be less than the width of the hood. The hood should never be 
installed at a point where grain can be thrown into it. In all cases 
it should be placed as close as possible to the point of dust dissemi- 
nation, within 12 to 18 inches from the grain stream. 
Sometimes the space available may not be large enough for a hood 
of the required proportions. In placing a hood over an extremely 
wide belt or piece of equipment which requires a long hood opening, 
the hood must be extremely high in order to function satisfactorily 
over the entire length of the opening. To apply suction over a 
wide space, it is well to use two or more hoods fed by branches and 
