FOREST SERVICE WATER SPRAY DRY KILN. 23 
In assembling coils all pipes should be laid to drain toward the 
return pipe, and have no air or water pockets which can interfere 
with the operation of the coils. 
CEILING COILS. 
Where the roof is exposed to cool or cold outside atmospheric con- 
ditions condensation forms on the ceiling of the kiln, drips on the 
lumber, and makes the control of humidity difficult, as well as staining 
the lumber. To offset this condition, ceiling coils consisting of 1J- 
inch pipes 2 feet to 2 feet 6 inches apart should be installed about 3 
inches below the ceiling, running across the width of the kiln and the 
full length of the kiln. The pipes can be connected with tees and 
nipples in the form of a header coil. 
The steam supply to the ceiling coil does not require thermostatic 
control, but should always be taken through a globe valve from 
the boiler side of the thermostat controlling the heating coils. 
In kilns over 40 feet long the ceiling coils should be fed in the middle. 
The condensation return should not in any case drain into the trap 
for the heating coils ; it must drain through a globe valve into a sepa- 
rate trap. 
The size of the supply and return may be determined from Table 5 ; 
in no case, however, should the supply be less than 1J inch or the 
return less than 1 inch. 
STEAM MAINS. 
One steam main only is required when high-pressure steam (where 
pressure is 30 pounds or more) is. used in the coils, but where low- 
pressure or exhaust steam is used a high-pressure and a low-pressure 
main are required. This is necessary because the high-pressure 
steam is necessary in the steam jets. 
Where an exhaust system is used the exhaust steam from the 
engine and pumps is passed through a check valve, back-pressure 
valve, gate valve, and water and oil separator. Live steam is also 
connected into the main through a gate valve and pressure-reducing 
valve to supplement the exhaust steam when the engines are not in 
use, or at any other time when necessary. One method of connecting 
the engine and pump exhaust with the steam main is shown on 
figure 7. 
Both low and high pressure mains should be drained at the far 
end through a gate valve to a suitable trap after the supply to the 
last coil has been taken off, as illustrated on figure 7. 
The steam main should pitch in the direction of flow 1 inch in 30 
feet at least and 1 inch in 10 feet where practicable. 
Where high-pressure steam is used a pressure regulating valve 
should be placed on the main to balance and control the pressures 
in the system. 
