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Thanks to Gerry Gill for finding and sharing this patent for the Danfoss 1-PS valve. Note that the vacuum breaker is not yet a part of the valve. 

This literature from Danfoss about the RA thermostatic operators and RA valves is no longer in print. Thanks to Bill Burton of Danfoss for scanning it and sharing it with...

This Data for Heating Engineers and Architects for the Design of Vapor Heating Systems booklet is from The Trane Company, published in 1917.

This excerpt about Vapor Heating: The Donnelly Fractional Distribution System is from The Heating and Ventilating Magazine, December 1921.

Thanks to Gerry Gill for finding the patent for this ingenious device that combined a damper regulator with a pressure gauge, water gauge, safety device. It was issued to...

This booklet about the Doody System of Vapor Heating dates back to 1916. Thanks to Brian Reynolds and Frank "Steamhead" Wilsey for sharing this rare information with us. ...

Thanks to Frank "Steamhead" Wilsey for finding and sharing this one with us. Here are his comments about this piece from 1912: "As nearly as I can figure, the 'Doody Atta...

Here is a patent issued to O.G. Johnson for the Dunham Return Trap from April 2, 1922. Thanks to Gerry Gill for finding and sharing this patent with us.

This document outlines the Dunham Differential System for heating. Thanks to Frank "Steamhead" Wilsey for finding, scanning and sharing this rare information with us.

This brochure outlines Dunham's product offering in 1946. It outlines how the Dunham Differential Vacuum Heating System worked. It also highlights products including Dunh...