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As I find interesting old patents, I will post them here...
Gorton Radiator Vent Valve - 1950 issueGorton Radiator Valves - 1955 issueGorton Steam Radiator Valves - 1965 issueHoffman Swivel Tube Connection - 1931 issueImprovements in Steam Radiators - 1877 issueHoffman Valve for Steam Heating Systems - 1904 issueHoffman Automatic Air Valve - 1908 issue
Hoffman Automatic Air Valve - 1918 issue
Hoffman Air Valve Lock - 1928 issue
Hoffman Thermostatic Steam Trap - 1931 issue
Hoffman Faceless Valve - 1935 issue
Hoffman Boiler Return Trap - 1935 issue
Hoffman Steam Trap - issue 1936
Hoffman Thermostatic Relief Valve - issue 1936
Hoffman Adjusting Means for Air Valves
Hoffman Adjustably Vents Air Valve - 1940 issue
If anyone finds other interesting ones, please post .. a great resource is www.google.com/patents