OS fitting on one pipe steam

keith123

Anyone ever see this ? 

DanHolohan

https://heatinghelp.com/systems-help-center/the-development-of-one-pipe-hot-water-heating-and-the-os-fitting/

keith123

It looked familiar to me. I vaguely remembered it from your seminar but never seen one in the flesh. I was confused on why it would be on a one pipe steam main. It’s one way to protect the main vent. 

The steam guy must’ve stolen it from the hot water guy 

Steamhead

Maybe they were using it to keep water from splashing up into the vent.

DanHolohan

I don’t think we will ever know.

mattmia2

What does the rest of the piping look like? This isnt a "we saw huge pipes and assumed it was steam but it was actually gravity hot water so we bought a boiler with steam trim and tried to make it work" is it?

Waher

The bulbous bulge is to help the flow of condensate slip past air/steam without creating turbulence. Someone posted a picture of a similar fitting connected to a radiator valve recently. I think those tees were meant for use on multi-story risers in one pipe steam systems where the radiators were directly off the riser. Someone used the same type of tee at the main vent to try and protect the main vent from potential water hammer.

DanHolohan

https://heatinghelp.com/systems-help-center/the-o-s-fitting/

dko

Maybe one the reasons why the old green painted hoffman 75 lasted so long

Interesting use of the fitting!