The Hutchison Vapor Heating System is very simple once you know how it works. There is no trap at the individual radiators. The returns are trapped at the boiler by means of the Hutchison trap-receiver and damper regulator combination. Here is a diagram from a 1923 edition of The Heating and Ventilating Magazine.
This chapter on hot water heating systems and piping was prepared by Professor F.E. Giesecke (Director of Texas Engineering Experiment Station in TX) for the The American...
Here are ratings for the Erie radiator from Jarecki Mfg Co Ltd. They were based in Erie, PA and their radiators appeared in issues of Domestic Engineering in the 1890s.
Brian Roberts & Paul Yunnie compiled this document that contains beautiful vintage advertisements and illustrations of radiators from the mid to late 1800s and early 1900...