Feedback control of thermal actuator on heating system valve - has wax-filled actuator heated by signal from bridge with feedback resistance inputs

摘要

A thermal actuator for control of a flow valve in a heating system is designed with a built-in feedback facility. The valve stage has a poppet (7) coupled to a valve stem (8) that is used to control the flow from inlet (3) to outlet (4). The valve stem has an extension (11) that is supported (29) on a frame and has a coil spring (25). The valve stem terminals (19) in the housing of the thermal actuator, the internal volume of which is fitted with wax. The surface of the housing is wound with heating coils (22) that are controlled by the output of a bridge circuit that compares feedback resistor values (R1,R2) with reference values.