GRAIN-DUST EXPLOSIONS. 
In figure 4, which is a diagrammatic view of the double damper 
and principal parts of the mill equipment, it is seen that the conveyor 
was lowered about 10 inches in order to make room for the double 
damper. Otherwise, the arrangement is practically the same as that 
in figure 2. The relief valve at A was installed with the relief pipe 
'Peffef Valve 
y////////////\ y\ ^//////////////y/////77z 
1,A i\ AF"~r\ A A A A a\ A A )S\ A A 
H \j V V V \J V V/ \T \j ' 
hrTOOt 
•Sbou/ to 
/ D/schar-oe Spout 
Fig. 4. — Elevation-attrition mill and conveyor. Double damper. 
► as explained in Series 13 (p. 18). The " spout to elevator," with its 
slide under the screw conveyor, shows how the ground material could 
be li recirculated," as stated in several series of tests, by means of the 
elevator and spouts shown in Plate II, figure 1. 
The two dampers were positively connected with each other by 
means of a chain and sprocket wheels (fig. 3) and were so arranged 
that they served as a double check for the flame propagated by explo- 
sion in the attrition mill. Plate IV gives two views of this double 
damper from opposite sides, figure 2 of the plate showing also the 
screw conveyor, peepholes, and spout leading to the boot of the meal 
or chop elevator. 
Plate III, figure 2, shows the removable hopper, with the sheet- 
iron lining and swinging relief valve as installed for Series 13. This 
hopper was constructed so as to make a snug fit with the lower part 
of the hood of the attrition mill. When the hopper is in position 
under the attrition mill, the relief pipe (R) (PL II, fig. 2) can be at- 
tached to the stub spout containing the relief valve. 
50220°— 18— Bull. 681 2 
