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FOREST SERVICE WATER SPRAY DRY KILN. 31 
to increase the humidity in the kiln when the water in the well is 
not sufficiently hot to hold the desired humidit} T , but otherwise 
should not be used in conjunction with the water sprays or with 
the condenser. 
By placing the steam jet in the spray chamber as shown, a strong, 
positive circulation of air is produced during the steaming period, 
while the proper temperature and humidity conditions are main- 
tained throughout the lumber pile. 
The supply to the steam J3t line is taken from the high-pressure 
main direct, as high-pressure steam is necessary, and, if desired, may 
be by-passed through the thermostat to facilitate control of tem- 
perature when steaming with the coils turned off. 
WATER SUPPLY. 
WATER SPRAY. 
Hf The water sprays, which are the essential feature of this kiln, 
perform two distinct functions. (1) They create circulation by the 
condensing effect produced and by the force of the spray down the 
chamber, and (2) they control humidity. The principle of their 
operation has been fully described on page 9. 
With a pressure of from 45 to 50 pounds at the spray heads the 
velocity of the air down the spray chamber averages between 120 
and 140 feet per minute. The pressure of the water available at 
the spray heads should not be less than 45 pounds, and from 50 to 
60 pounds is desirable. 
As a medium for controlling the humidity in the kiln, hot and 
cold water are required for circulation through the spray. The 
water is mixed to the proper temperature in a thermostatic water 
| f mixer. 
There are two methods of controlling the temperature of the 
spray water itself — (1) by a thermostatic water-mixing valve on the 
water supply line to each kiln, which automatically mixes warm 
and cold water to maintain the desired temperature condition; 
(2) by mixing cold water with the spent water returning from the 
sprays to the well. The second method is adapted only to kilns in 
which the battery is designed to dry one thickness of stock and using 
only one temperature schedule, such as heavy oak bolsters, at low 
temperatures and high humidities. 
The water from the sprays collecting in the drain flows by gravity 
P to a well, from which it is recirculated back to the sprays by means 
of a pump. As the spray water picks up heat in cooling to the dew 
point the air which has passed through the lumber pile and then 
into the spray chamber, the water returning to the well establishes 
the hot water supply needed for low-temperature runs. This drain- 
age water is not hot enough for high-temperature runs when high 
