46 
BULLETIN 6S1. L T . S. DEPARTMENT OF AGRICULTURE. 
TESTS OF REVOLVING DAMPERS OR FIRE TRAPS. 
The tests with the revolving dampers gave the following important 
results : 
Table IS. — Tests of re vol ring dampers or fire traps. 
Observations. 
Single 
damper. 
Double 
damper. 
Observations. \ d ^ 
Double 
damper. 
Explosions with dampers in 
29 
6 
69 
14 
Flashes at D 
8 
Puffs at D . . . 
1 
Flashes at E 
Pulls at E 
1 


These results indicate that the double damper showed no superi- 
ority over the single damper as a preventive of name propagation. 
With both single and double dampers there were cases in which 
flames got past with enough force to shoot out of the peephole (B) 
for several feet toward the observer. The devices, however, were 
effective to the extent that no puffs of smoke and only one flame 
were observed at the end (E) of the convevor. 
k 
J Ij, 
"" SS.V3 
Fig. o. — Attrition mills, showing fire traps or dampers. 
An interesting practical application of the revolving damper as a 
"fire trap" is noted in the following report of an investigation by 
R. L. Sackett: 
A large milling company in Buffalo. X. Y., has placed its battery of attrition mills 
in a separate building of corrugated iron (fig. 5). 
Before the oats pass to the mill they have been screened and have passed a mag- 
netic separator, which removes splinters of wood, metallic substances, and other 
foreign matter. 
The material passes through the attrition mills and drops down toward the con- 
veyor below. 
The vertical leg below the mill has a 6-inch galvanized spout running horizontally 
through the side of the mill. On the end of this pipe is a flap valve with a circuit so 
arranged that if an explosion takes place in the mill the pressure will open the flap 
valve, break the electric circuit, which will in turn stop the motor which drives the 
mills. The pipe serves as a safety valve for the escape of gases in case of explosion. 
Below the safety valve is a "fire trap" or "damper." consisting of four blades 
revolving on a shaft, within a casing, so designed that in case of an explosion the 
propagation of flame to the conveyor will be retarded or prevented. This damper 
