I'.i 1. 1. 1. tin 12d4, V. s. DEPARTMENT OF AGRICULTUBE. 
of air blowing down through the tube had a tendency to create a 
vacuum around its lower end, producing a suction effect which 
would pull the dust out of the hopper into the air stream whenever 
the valve was lifted and would thus carry this dust out through the 
discharge tube. Id other words, it provided an air current running 
down through the hopper and an adjustable opening in the bottom 
of the lmpper so that varying quantities of dust could be drawn 
out with the air. When first tested some trouble was caused by the 
dust packing on the sloping 
bottom and in the corners 
and not feeding out regu- 
larly. This difficulty was 
overcome by fastening a 
small funnel pointing for- 
ward on each side of the 
top of the hopper and 
connecting to each funnel 
three small air tubes run- 
ning down the inside of the 
hopper, discharging along 
the sides where the dust 
had the greatest tendency 
to lodge and in a direction 
tending to force it under 
the feeder valve. Figures 
3 to 5 show the construc- 
tion of these auxiliary air 
lines. This device kept the 
dust loose and gave satis- 
factory operation, except 
for the fact that no method 
of closing these auxiliary 
funnels was provided, and 
when flying with the feeder 
closed. 
and 
itli 
only a 
small amount of dust in 
the hopper, the air blow- 
ing down these would agi- 
tate the dust and force 
some of it out through the 
cracks of the cover. 
To overcome these diffi- 
culties and also to improve 
the general efficiency of 
operation, a modified de- 
sign has been prepared as shown in Figure 6. In this case the aux- 
iliary funnels have been discarded and the same effect obtained by 
connecting these side air lines to the main air duct inside the hopper. 
Back pressure in the hopper is prevented by a butterfly valve in the 
main air duct just below the intake funnel which closes whenever dust 
discharge is cut off, and thus air is passing through the hopper only 
when tin' feeder is open. In addition, the starting and stopping of the 
feed lias been separated from the control of the amount of (vvd. A 
I'h,. i. Air-suction bopper removed from plant 
showing details of exterior construction. 
