By using a pot of mercury and a submerged pipe, this device separated the water in the system from the water in the expansion tank. Honeywell called it the Heat Generator and it allowed open hot water systems to operate under pressure, and at higher temperatures, but still remain safe. This was a major advance in hot-water heating in that it allowed the hot-water people to compete with the steam people, whose prices were usually less. The patent dates to October 22, 1907. Thanks to Gerry Gill for sharing this with us.
This document contains the manufacturer's instructions for the HB Smith Series M450L Mills Water-Tube Boiler for automatic firing with oil or gas (Steam, Vapor, or Water ...
This document contains the jacket assembly instructions for the HB Smith Series 45 Mills Boiler (circa 1979).
This document contains the combustion chamber assembly instructions for the HB Smith Series 45 Mills Water-Tube Boiler for automatic firing with oil or gas (Steam, Vapor,...