DUST CONTROL IN GRAIN ELEVATORS 
13 
The results in Tables 1 and 2 show that the air flow up the vent 
was greatest when the elevator was not running, that this flow was 
decidedly smaller when the elevator was running empty, and that 
the flow of air was down, not up, when grain was being elevated. 
These readings do not bear out the common belief that a pressure 
exists in the head at all times, and that a vent over the front leg is 
necessary to relieve this pressure. 
To ascertain why the updraft is greatest when the elevator is not 
running and is reduced when the elevator is running empty, all 
factors which might tend to produce or change the air movements 
in the leg when operating were considered. It is logical to conclude 
that when the elevator is not running, both legs, aided by the venti- 
lating hood on the vent, act as flues for conducting the warmer base- 
ment air to the exterior. When the elevator is running empty, 
however, there is a reduced draft up the vent, because the natural 
Vent 
Roof 
zzzzzzzzu 
_ Pipe flared to a/most 
fu/f width of leg 
Fig. 10.— Vent on elevator head serving both leg and garner 
flow of air up the back leg is disturbed and directed downward and 
because a large quantity of air from the front leg is recirculated by 
the fan action of the buckets. Observations have shown also that 
the fan action of the buckets at the head discharge forces some air 
down into the garner to escape through the garner vent, thereby 
reducing the head-vent readings. 
A consideration of the air requirements and air supply in the 
elevator head and legs led to the formulation of a theory which 
probably accounts for the reversed air currents that are directed 
down into the head through the vent when grain is being elevated. 
When the buckets discharge their contents, a certain quantity of 
air is carried with the grain to the garner through the discharge 
spout. The space occupied by this air, and also the space occupied 
by the grain in the buckets, must be filled by the same volume of 
air. If the garner is vented, the air within the garner which is 
being replaced by the grain does not satisfy the air requirements of 
the buckets. Air for these empty buckets must therefore come from 
some other source. 
