. Power, heating and ventilation ... a treatise for designing and constructing engineers, architects and students . Thermostat in Casing. the latter is closed as will be described later. When the tempera-ture again drops, valve D is thrown in the opposite direction bythe expansion strip, cutting off the pressure, from the reservoirand exhausting the air from the steam valve, thus allowing it toopen under the action of a spring provided for this purpose. Fig. 161 shows the thermostat with the casing in place. The Powers Thermostat operates on a somewhat differentprinciple, the metal strip being
. Power, heating and ventilation ... a treatise for designing and constructing engineers, architects and students . Thermostat in Casing. the latter is closed as will be described later. When the tempera-ture again drops, valve D is thrown in the opposite direction bythe expansion strip, cutting off the pressure, from the reservoirand exhausting the air from the steam valve, thus allowing it toopen under the action of a spring provided for this purpose. Fig. 161 shows the thermostat with the casing in place. The Powers Thermostat operates on a somewhat differentprinciple, the metal strip being replaced by an expansion consists of two corrugated circular pieces of metal joined at 240 HEATING AND VENTILATING PLANTS the edges and supported and stiffened by flat steel springs asshown in Fig. 162. The interior of this hollow disk contains a vol-atile liquid having a boiling point of about 55°, and which is un-der a pressure of about 4 pounds per square inch at a temperatureof 70°. Any change in temperature of the surrounding airproduces a corresponding change in the pressure within the disk,. Fig. [65. Fig. 166 Fig. 165. Johnson Hot-Air 166. Johnson Pneumatic Valve. thus increasing or diminishing its thickness. Fig. 163 shows thePowers thermostat in section. A is the expansion disk, M amovable flange attached to a flexible diaphragm and operatingthe valve /. L is the exhaust valve, and H and / the pipe con-nections with the pressure reservoir and with the steam valve ordiaphragm. When the temperature rises the disk A expands, pressingagainst M and thus opening the valve /. This allows the air topass from H into / through the chamber K, and thus admits thepressure to the steam valve and closes it. When the temperaturefalls, the disk contracts and the valve / is closed by the actionof a coil spring. The air pressure is relieved from the steam SPECIAL DEVICES 241 valve through the small exhaust valve L. Fig. 164 shows thethermostat as it appears
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