12 



BULLETIN 509, U. S. DEPARTMENT OF AGEICULTTJRE. 



conduct it back to the pump, the water being recirculated through 

 the sprays. G is a pipe condenser for use toward the end of the 

 drying operation. K is a baffle plate for diverting the heated air and 

 at the same time shielding the under layer of boards from direct 

 radiation of the steam pipes. 



The operation of the kiln is simple. The heated air rises above the 

 pipes H H at the sides of the piles of lumber. As it comes in con- 

 tact with the piles portions of it are cooled and pass downward and 

 inward through the layers of boards into the space between the con- 



FiG. 2. — Diagrammatic section of improved dry kiln with spray cliambers on sides. Double- 

 truck form. 



densers G G. Here the column of cooled air descends into the spray 

 flue B, where its velocity is increased by the force of the water spray. 

 It then passes out from the baffle plates to the heaters and repeats the 

 cycle. 



Various modifications of this arrangement may be made. For 

 instance, a single-track kiln lanj be used. This -form would be repre- 

 sented by simply dividing the diagram vertically into two parts by 

 extending the wall G (on the left side) upward to represent the outer 

 wall, and era.sing the part to the left of this line. Or, again, the 

 spray chambers may be kept on the sides as shown in figure 2. The 

 lumber would then slope in the opposite direction with respect to 



