Historical Minute -- October 2013
“In 1882, Napoleon Williames of Philadelphia patented in this country the art of circulating exhaust steam by the mechanical reduction of pressure upon the heating system. This being the foundation patent, broad claims were allowed, and every system of vacuum heating using mechanically induced circulation is founded more or less on this patent.
“In 1891, a patent was issued to Willis E. Hall, which, broadly stated, in its subsequent use consisted of the application of a thermostatic valve (trap) to the Williames system, and it seems as if the clearest way to describe it, is to call it the Williames thermostatic system.
“Based solely on these two patents, with the addition from time to time of a few upon specific forms of thermostatic valves and special devices for better control of various features, a system of steam circulation was developed and sold in considerable quantity.”
—“A new system of vacuum return line exhaust steam circulation” by James A. Donnelly, The Heating and Ventilating Magazine, October 1904.