Here are photos of a circa-1944 Perfex Series 155 Magic Dial Thermostat, as well as the instruction manual.
Honeywell Gas Valve Patent
Thanks to Gerry Gill for finding and sharing this patent.
And thanks to Tim McElwain for these comments about the patent, "It looks like the prototype for what became Honeywell’s Series 10 and Series 20 motorized valves. The Series 10 really caught on and was numbered the V-155 Motorized Gas Valve, it was used as a DPST Thermostat operated Valve with the old T-102 Chronotherm Thermostat. In later years the V-155 was reduced to a two wire SPST valve and labeled the V-855 Series 80. This is a very durable valve and still in operation on some old systems in the East Side of Providence to this day. The only maintenance is some “FINOL” oil (trade name from Honeywell) added to the valve once a year and it will work like a charm. The series 20 version was used on some old coal systems that had the concept of power to open and power to close (often called the stalled motor principle). It was not as popular as the V-155 for gas as it was a little more complicated to install the external system that went with it. Many of our newer controls today use the principle including White Rodgers motorized zone valves and zone dampers on warm air systems. We also see it on mod motors and some vent dampers." Timmie M. McElwain, President, Gas Appliance Service Training & Consulting and Gas Training Institute
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