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Two Pipe Gravity Return

Leo Member Posts: 770
Thank you guys for responding. One other question, there is no Hartford Loop now and the picture in the Lost Art doesn't show one. Does this system need one, does it have an adverse effect?



  • Leo
    Leo Member Posts: 770
    Two Pipe Gravity Return

    My boss is bidding on a job but he has never seen this type of system. It appears to be a Two Pipe Gravity Return like pictured on page 125 of The Lost Art. He wants to know how it works and what he should pay attention to so he doesn't inherit a horror story. The present system works fine, no complaints other than the owner wants to up grade the old boiler. This is an oil boiler and will remain oil. I am attaching a diagram he gave me.

    Thanks for any assistance,
  • 2 pipe air vent system

    Leo, the chief thing to remember is that you need a vaporstat to control this.

    Size it to the radiation, pipe it like the book says, make sure it's insulated, Clean the water, and watch that beauty work.

    Once it's up to temperature, there is steam in every pipe. No main vents are used (weren't invented yet, I don't think).

    After it is running a while, check the condition of each vent.

    No secrets on this one, she's pretty simple.

  • Ken_8
    Ken_8 Member Posts: 1,640
    That's a very nice system!

    To grossly oversimplify; this one's a piece of cake. Just be sure to size the boiler riser(s) as large as physically practical - and install a vaporstat.

    You already know the rules for BTU boiler sizing based on what's standing there now in EDR (radiation). Make sure the supplies and returns are all insulated (if not already) and take it from there. All return legs must be below the NOWL (SOP right?).

    We always replace the main and rad vents with new Gorton's. I urge you to as well.

    Other than that, this is an easy and straight forward replacement. Use the boiler manufacturer's piping methods, and the system should be better than ever.

    Any questiuons? You know where I am Leo.

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  • Steamhead
    Steamhead Member Posts: 16,736
    One of the simplest systems out there

    One of the biggest mistakes I've seen is to install vents on the return lines in this system. These returns do not handle air the way those in a Vapor system do. If you vent the returns on this system, more steam will get into them than they can handle, and they will BANG!

    Vent the steam mains the same way you would on a one-pipe system- calculate the amount of air in the mains to size your vents. The steam should fill the mains in about a minute- then all rads will get steam at about the same time.

    Using a Vaporstat will help keep steam in the radiators and not let it into the returns.

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    Steam, Vapor & Hot-Water Heating Specialists
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  • NEEDS one

    Even if you aren't in Hartford.

    They hadn't thought of it until 1919.

    No adverse effects, either.

  • Ken_8
    Ken_8 Member Posts: 1,640
    Since all the makers show it in the destruction (sic) manual...

    I suspect you would void the warranty without one. It is also in all mechanical codes I can think of.

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