46 



BULLETIN 681^ U. S. DEPARTMENT OF AGRICULTURE. 



TESTS OF REVOLVING DAMPERS OR FIRE TRAPS. 



The tests with the revolving dampers gave the following important 

 results : 



Table 18. — Tests of revolving dampers or fire traps. 



Observations. 



Single 

 damper. 



Double 

 damper. 



Observations. 



Single 

 damper. 



Double 

 damper. 



Explosions with dampers in 



29 

 6 

 



69 

 14 

 10 



Flashes at D . . 





8 



Puffs at D 





1 





Flashes at E 





 



1 





Puffs at E 













These results indicate that the double damper showed no superi- 

 ority over the single damper as a preventive of flame 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 convej^or. 



Fig. o. — Attrition mills, sbov.'ing fire traps or dampers. 



An interesting practical apphcation of the revolving damper as a 

 "fire trap" is noted in tlie following report of an investigation by 

 R. L. Sackett: 



A large milling company in Buffalo, N. 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 mil ls 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 fiame to the conveyor mil be retarded or prevented. This damper 



