type of system?

zepfan

with a system that has cast iron rads,shutoff valves located at the top of the rad,with just a return union on the outlet,no trap.is this a vapor/vac.sytem?the system has vents located at the end of each return.also a radatior supply valve on a two pipe steam sytem can it be modulated to control the amount of heat the radatior puts out? i thought that on one pipe system this will effect the flow of condensate that returns to the boiler,but was unsure about a two pipe system.thanks to all. 

Steamhead

It's probably some sort of Orifice or Tudor system

but could be a Richardson or Kriebel system. The latter two use special return ells that look ordinary but have stuff in them that helps the system work.



You can adjust the radiator's output with the hand valve on this system. That, along with the absence of radiator air vents, was why Vapor systems like these became popular.



Post some pics of your system: boiler, piping around boiler including any strange devices you find there, vent locations and a few radiators. If you can find any original hardware with maker's names or trademarks, this will help us ID your system.