GB1201481A - Improvements in or relating to means for actuating valves and similar mechanical control devices - Google Patents

Abstract

1,201,481. Automatic temperature control systems. BRITISH THERMOSTAT CO. Ltd. July 3, 1968 [April 5, 1967], No.15556/67. Heading G3R. An actuator providing a mechanical output for the operation of a valve or similar mechanical control device comprises a temperature responsive member mechanically connected to the valve or other device, an electric heater associated with the temperature responsive member, and temperature sensing means in thermal relationship to the temperature responsive member and connected to control means to regulate the energy to the electric heater in accordance with one or more variables one of which is the temperature of the responsive member. A bellows member 2 actuating a valve 4 controlling a gas supply has a heater 9 supplied from an amplifier according to the temperature measured by an element 8. Another input to the amplifier is derived from a sensing element 10 responsive to a heat exchanger 7 output temperature. In the absence of an output from element 10 the bellows 2 assumes a position dependent on the set point of element 8 which is modified by the element 10 to open or close the valve 4 in accordance with the heat exchanger temperature. The system may be arranged to adjust the temperature of the heat exchanger in accordance with outside conditions, and a bridge or potentiometer circuit may be associated with the amplifier so that other features e.g. room or boiler temperature may be incorporated. Sensing elements 8, 10 may be temperature dependent resistors, thermocouples, transistors, or other temperature dependent devices. The system may be modified to control humidity or pressure, or it may be arranged to act at a remote control device by substituting a manually adjustable resistor for the element 10. The bellows may be replaced by a diaphragm, a bi-metallic element or other differential expansion device.