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Return line in two pipe steam system

wam525wam525 Member Posts: 3
I've been trying to get rid of the water hammer noise in our 2 pipe steam system. I fixed a previous major remodel in the large kitchen where the radiators were moved and reconnected by a plumber with only hot water experience, so none of the pipes had proper slope. Now there is a residual occasional hammer on the other part of the house connected with a long sloped steam pipe. However the return line has no slope at all, and I'm wondering if it is needed for a return line. Also, about 50 feet from the boiler there is a strange pipe assembly connecting the steam and return lines (see picture). Could this be causing any water noise?
Thanks for any help for our c 1900 home.


  • nicholas bonham-carternicholas bonham-carter Member Posts: 8,269
    Do you have traps on the radiators, and crossover points? If so, they may need new innards.
    Keep the pressure down to a few ounces as well, to prevent water from backing up into the boiler.—NBC
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 7,541
    Those two pipes look like a loop seal. It is used to drain condensate from you steam line into the condensate return. The loop seal will fill with water to make a seal (loop seal) and as condensate drops into the loop seal it rises in the other pipe and enters the return pipe.

    You have to run your pressure low or the steam will blow the water out of the loop seal and cause hammering. That loop seal looks like it's maybe 5'? so you need to keep your pressure under 2psi.

    For the loop seal to work the condensate line is usually at a lower elevation than the return, don't know if yours is can't tell from the picture.

    Is that where the hammering is coming from?
  • Jamie HallJamie Hall Member Posts: 13,852
    A further comment on that loop seal. I see a drip leg on it. If you can get the cap off of that, check and see that the pipes are free of blockage. In fact, rinse them out.

    Ideally the return line would have some slope. It doesn't need much, and it can go either towards the boiler or towards a drip to a wet return. Whether it could be a problem with water hammer, though, depends on where the venting is. If -- as I suspect -- the mains vent into the return with crossover traps, and then are vented to the atmosphere at or near the boiler, then it is possible for there to be some water hammer in that return, but only near the beginning of a heating cycle. Otherwise, I would check everything for slope. The condensate must be able to drain to a wet return somewhere.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 7,541
    @Jamie Hall
    had a good idea that I didn't think of. If the hammering is in that location that loop seal could be plugged up. Especially where it only looks like 3/4" pipe

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