Title: Thermostatic control for use in variable air distribution systems

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Abstract: Air flow volume in a delivery duct is sensed in the form of changes in duct pressure and the sensed pressure is fed back to a diaphragm assembly which is part of a thermostatic control located in the room to which hot or cold air is being delivered. Dependent upon the sensed pressure, the diaphragm assembly throttles a bleed opening in the supply line of a pneumatic actuator, which actuator determines the position of a damper in the duct to thereby control the volume of air flow in the duct. A bellows is also part of the thermostatic control and senses room temperature to establish a spring force on the diaphragm assembly and against which the sensed pressure must act. The bellows is adjustable to afford room temperature selection. The bellows and a compression spring act on a master lever, the compression spring reacts against the bellows force. The combination bellows-spring produces movement of the master lever in two opposite directions and this movement is utilized to activate a control for continuously switching the system between delivery of cold or hot air. The thermostatic control includes a second lever moved in response to the bellows-spring movement. The position of the second lever establishes a biasing force against which, in the diaphragm assembly, the sensed duct pressure must act in establishing the position of the damper. A cam arrangement is associated with this second lever and is effective to determine the position, and movement, of the lever so as to provide selection in the percent of available air capacity which is utilized and/or lever movement between maximum and minimum limits as desired.


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