FOREST SERVICE WATER SPRAY DRY KILN. 35 
supply. The amount of water to be used being known and a pres- 
sure loss between 1 pound and 2\ pounds per 100 linear feet being 
assumed, the size can be obtained from figure 10. 
In determining the size of mains to supply a given number of 
kiln units, first find the size of supply to each kiln by either method 
described. The diameter of the main then up to any given unit of a 
battery will be the diameter of the supply for one kiln multiplied by the 
square root of the number of kiln units between and including the 
given unit and the end farthest from the source of supply. 
Where four kilns or less are installed, the mains should be pro- 
portioned as follows: 
The cold-water main — full volume of water required in the kiln. 
The recirculating main — full volume of water required in the kiln. 
The hot- water main — two-thirds volume of water required in the kiln. 
Where five or more kilns are installed the mains may be propor- 
tioned as follows: 
The cold-water main — tlrree-fourths volume of water required in kiln. 
The recirculating main— full volume of water required in kiln. 
The hot- water main — one-half volume of water required in kiln. 
For the last four kilns in a battery, proportion the mains accord- 
ing to the first rule ; mains supplying the last kiln should be full size. 
The amount of cold water required to cool the recirculating water 
to the desired degree depends upon (1) the temperature of cold 
water in the warmest season of the year, and (2) the highest tem- 
perature and lowest humidity used in the kiln and the exposure of 
roof and side walls. 
Low temperature runs require colder water through the sprays to 
obtain low humidities than do high temperature runs. A spray- 
water temperature of 65 to 70° F. is required to obtain a humidity 
of 33 to 38 per cent at 135° F.; while for a temperature of 180° and 
a humidity of 38 to 45 per cent the spray- water temperature must 
be from 120 to 135° F., only slightly below the temperature of the 
water as it flows into the recirculating well from the spray-chamber 
gutters. Thus the higher the temperature used, the less cold fresh 
water is required. For this reason, if the installation is to be used 
for low-temperature runs only, the sizes estimated above for mains 
should be changed to full size for cold-water main and three-fourths 
size for recirculating water main. If for high-temperature runs 
only, the hot- water main should be increased to three-fourths 
capacity, the recirculating main to full size, and the cold-water 
main to one-half size. Where only two mains are used, the recir- 
culated and cold water, the recirculating main should be full size 
and the cold water three-fourth size for a battery of five or more 
kilns, and both full size for less than Rye kilns. It is always better 
to have the mains too large than too small. 
