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What's this thing attached to my radiator? Has 2 screws.


According to everything I've read on this website, my system is all sorts of f'd up.

This pdf doc on page 40 "TWO-PIPE WET RETURN SYSTEM WITH NO TRAPS" shows what my system looks like the most except that I'm missing the Main Vent.

It's a 2 pipe radiator that's vented with Hoffman 40's except for R2 Bath.
It has a vertical pipe with 2 screws on it. Anyone know what this is?

There are no traps in the radiator return... just an elbow.
It's a mix between 1 pipe and 2 pipe.
The uninsulated steam section is probably causing extra unnecessary condensate.
There are zero main vents...

I suspect that the wet return is clogged on the right side.

The diagram I drew only shows the west side.
The east side is more or less the same but they heat up just fine.


  • Jamie Hall
    Jamie Hall Member Posts: 23,310
    I love that radiator!

    But with no vents on things, it's not going to heat. No surprise there. Which leads me to wonder just a teeny weeny bit... are your really quite sure this thing isn't -- or wasn't -- gravity hot water?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • ventedTwoPipe
    ventedTwoPipe Member Posts: 2
    I have no idea. I bought this house a month ago. It was built over 100 years ago.

    I think the stem with the 2 screws can clue us in to what it used to be... Perhaps its a bleeder for hot water but it's connected to the bottom and not the top.

    There are some main steam pipes that newer without insulation, maybe the main vents were taken out along with the old pipes?
  • dopey27177
    dopey27177 Member Posts: 887
    If this is a two pipe steam vapor or steam system the master vent valve will be at or near the boiler. It will be part of the dry return piping.

    Pictures of the piping system and near boiler piping is needed to determine what you have, additionally can you name the radiators because that will be helpful in making some determinations.

  • motoguy128
    motoguy128 Member Posts: 393
    edited November 2020
    The section missing insulation and probably the run before it are likely full of water and need to be repitched. Water will block the flow of steam and cause hammering.

    Valves integrated in the radiators is really something special. The EDR has to be really high on those for their seize with all the pins. Looks like a boiler turned insistently out.

    Maybe that pipe hot water and early radiator designs left an air pocket to act as a compression tank for expansion. One screw is to check level cold, the other check level hot. How does the level of the screws compare to the height of the entering pipe.

    I’m guessing the system runs without traps and the boiler always needs to have slightly less output than the radiators and MUST always run at low pressure (ounces)