A combination gas valve (or combination gas control) combines in a single unit all manual and automatic control functions required for the operation of gas-fired heating equipment. In other words, a single valve replaces the various individual pilot line and main line gas controls. A gas-pressure regulator is usually optional.
Many manufacturers of gas controls offer a complete line of combination gas valves; each valve is designed for a different kind of installation or application. Usually these valves will differ on the basis of the controller voltage or voltage source, valve application or function, required Btu capacity for the installation, and type of gas used.
Honeywell manufactures a line of standardized and interchangeable gas control components. A complete preassembled combination gas control can be ordered from the factory or one can be assembled in the field from a variety of different standardized components in order to meet the needs of a particular installation. This add-on feature also allows field replacement of a defective component without removing the complete valve from the installation. A number of possible combinations are illustrated in Figures 5-45 and 5-46.