The return trap is like a mechanical condensate pump. This 1943 piece about Sarco Alternating Receivers and Lift Traps from the Sarco Company does a nice job of explaining how it works.
Here is the original Installation and Operating Instructions and Parts List for The H.B. Smith Company's Oil Fired Cast Iron Hot Water Boilers (No. OHB-13W). This is esti...
The Henry Ford Museum in Dearborn, MI has an interesting hot-water heating system. Take a look at the radiators below. They are from the Shaw-Perkins Manufacturing Compan...
We estimate that this cast-iron boiler catalog from The Peerless Heater Company in Boyertown, PA is from the 1980s or 1990s.