O-S Fitting

The Northern Electric building had a one pipe gravity system for its 8 floors. The heated water would go to the top floor ceiling and spread out along the outside walls. There would be a pipe going down which would have two O-S tee (like monoflow) for each radiator on each floor. Each down main one would connect to a large return going into the boiler room building which was adjacent to the U shaped main building. As it was converted to multi use rental units, I installed Danfoss thermostatic valves on the radiators by moving them 10 inches from the O-S tee.