Dept. Bull. 1136, U. S. Dept. of Agriculture PLATE 6 
| . —asenny, 
: A 2 ace iy, 
Y 
My 
S 
MALTY RIC 
ft 
SELF-CONTAINED THERMOSTATS 
A.—This instrument does not require compressed air for operation, but depends entirely upon the 
pressure changes produced by variation in the temperature of the bulb a. Increase in pressure, 
which is transmitted through the tube 6 to the diaphragm motor c, tends to press down the balanced 
valve d and its stem e. Such a tendency is resisted by the spring f, the pressure of which can be 
adjusted by the spring housing g for any desired temperature within the range of the thermostat. 
When the temperature of the bulb a rises above that for which the thermostat is set, the diaphragm 
motor starts to close the valve, thus throttling down the steam supply, and when the temperature 
drops the action is reversed. In dry-kiln work conditions are usually close enough to constant so that 
the valve does not need to open or to close entirely, remaining in a partially open position. The 
strainer h, which must be-cleaned occasionally, prevents chips and dirt from entering the valve and 
causing breakage. The union connection on the bulb is not necessary for dry-kiln work. The 
accurate working range for self-contained thermostats is usually about 40° to 50° F. 
B.—Operating upon the same principle as the one shown in A, this instrument differs from the 
other chiefly in having a sliding weight for temperature adjustment in place of aspring. Correspond- 
ing parts are correspondingly lettered in the two illustrations. The bulb a is made up of a number of 
cylindrical tubes, to increase the surface-volume ratio and thus make the thermostat faster in its 
response to temperature changes. 
