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Two pipe steam flood back issue

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I’ve been servicing a two pipe steam system for about a year now. I recently changed to a vapor stat on the system. It does have two steam traps that feed into a small receiver with a float and make up water line. As the system isn’t running frequently right now due to warm weather I keep getting called back to a flooding back issue where the system is literally so full of water it is coming out of the overflow on the receiver and causing the boiler to have pressure on the pressuretrol that is currently set to 7 psi and has a manual reset. I have the vaporstat set to 16 oz with a differential setting of 8 oz. This is a very large home in Minneapolis MN. Useless info, this system does have an addition added to the home that is hydronic. The hydronic water loop is run off two pumps and a heat exchanger on the wet steam return line.

This is my first time posting on here but any help would be great. Starting to lose faith in me here and I don’t blame them.

Comments

  • JohnnyGlocalstp
    JohnnyGlocalstp Member Posts: 10
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    I should add all the radiators are in wall hidden with a vent louvre to modulate output of the cavity. This makes it impossible to level anything as it’s all “built in” I’ll post a picture if I have one on this phone.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
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    Don't lose faith!
    Even 16 ounces pressure is high for a vapor system, and must be verified by a good low-pressure gauge, (0-3 psi), in case the pigtail is blocked.
    There must be an auto-fill on the system, which somehow is overfilling the boiler. Try valving it off, and watching for movement in the gauge glass. Over-pressure could be forcing the water out into the wet returns, temporarily starving the boiler. At the end of firing, the water should come back. If there is a horizontal element in the returns, at a level, a little above the waterline height, a lot of water can be hidden as it rises to attain a level influenced by pressure. An unstable waterline can subject the block to undue thermal stress.--NBC
  • JohnnyGlocalstp
    JohnnyGlocalstp Member Posts: 10
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    NBC thanks for your helpful comment. The system is definitely getting pressure. As I left it was running at 2 psi on the gauge. There is a pressuretrol set for high limit at 7 pounds. Do you think I should even turn down the vaporstat and if so what would you set it to for this two pipe steam system? I had it set to 7 ounces and it didn’t run enough to get enough heat in the system. The radiators are all 3/4” to 1” steel piped.
  • Jamie Hall
    Jamie Hall Member Posts: 23,428
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    Can you draw a diagram of this system? I'm concerned about the two traps and the receiver with make up water line arrangement. In general -- there are always exceptions -- a two pipe system should have traps on all the radiators (except some vapour systems) and either crossover traps from the steam mains to the dry returns or vents on the steam mains, and must have vents on the dry returns -- but should need no other traps anywhere. The dry returns should drop to the wet returns and then right on into the boiler. It the water feed is automatic, it should be from a float or probe on the boiler.

    So what is the arrangement here? Not saying it won't work, but we need to know a little more about the arrangement to figure out how it is supposed to work -- and then why it isn't.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
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    This system should be able to function on 2 ounces.
    See if you can trace the route air takes to escape from the system as the boiler begins to make steam, as a crossover trap, or air eliminator must be inoperative.
    Where is the heat exchanger in the returns? That could be the place for water to hide if it is at waterline height. The water for the hot water loop should come from a tapping on the boiler, as the returns often are too cool.--NBC
  • JUGHNE
    JUGHNE Member Posts: 11,074
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    If you have a heat exchanger for the hot water heat and if the hot water heat side has an auto fill PRV, you could have a leak in the exchanger and the PRV is filling your steamer.

    If the condensate receiver has an auto fill valve it could be sticking open part of the time. (is it also a feed pump?)

    If the boiler has a LWCO with feeder it could be adding water.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
    edited March 2018
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    Good thinking Jugne!!—NBC
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,613
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    @JohnnyGlocalstp , What @JUGHNE said is the most likely problem(s)
  • JUGHNE
    JUGHNE Member Posts: 11,074
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    Johnny, does this have a condensate pump or a feeder pump?
  • JohnnyGlocalstp
    JohnnyGlocalstp Member Posts: 10
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    It does have a condensate receiver and a condensate pump. I believe it is a blowing by receiver float.
    Shut the feed line off for the last two days and the system is staying balanced and at the right levels with the existing water.

    Great thinking here —>
    JUGHNE said:

    If you have a heat exchanger for the hot water heat and if the hot water heat side has an auto fill PRV, you could have a leak in the exchanger and the PRV is filling your steamer.

    If the condensate receiver has an auto fill valve it could be sticking open part of the time. (is it also a feed pump?)

    If the boiler has a LWCO with feeder it could be adding water.

    The only problem is the hydronic loop is maintaining pressure. It does have its own relief as well. It’s never changed from 12-15 psi. The way it’s piped is the condensate return is piped trough the steam boiler in a big loop and has the heat exchanger for he hydronic loop in the middle converse the boiler. I think if it was leaking by I’d lose pressure in the hydronic loop or gain way more pressure than I’d need popping the relief.

    The receiver feed is a basic water line hooked to a float style valve internal to the receiver. No electronics at all.

    It’s funny because I am at another place with the EXACT same problem and we JUST put this float fill line into the receiver.

    A coworker mentioned when the boiler goes off for a while it’ll create a vacuum and could be drawing water through the condensate receiver float.

    Thanks everyone for the ideas!!
  • JohnnyGlocalstp
    JohnnyGlocalstp Member Posts: 10
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    This is the same style receiver/pump/make up float
    as the other house.
  • JUGHNE
    JUGHNE Member Posts: 11,074
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    I believe we would refer to that as a "feeder pump with receiver", rather than a simple condensate pump with its own float to switch on the motor.

    What controls the feeder pump?
    You could add the sight glass on the right side of the receiver tank to watch that level.

    I have heard of the vacuum problem and adding a vac breaker to the boiler may fix it.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
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    Is the pump controlled by the LWCO, or an internal float in the tank?
    A float type control will not know what the proper boiler water level is, or should be, and will tend to overfill, which is why we don’t like non-gravity systems. You may have to remove the pump, and repipe the returns as gravity.—NBC
  • JUGHNE
    JUGHNE Member Posts: 11,074
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    How about a wide angle of boiler, pump and controls.....with out the Borax? ;)
  • JohnnyGlocalstp
    JohnnyGlocalstp Member Posts: 10
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    I don’t know about removing the receiver as the return lines come in too high. I don’t have a picture but when I talk to the caretaker I’ll have her send me a photo. The photo I shared was another project with the same components and problems more or less. The McDonnell miller 150 controls the feeder pump with its float switches and interrupts the burner circuit.
    Here is a picture of the other single pipe system with the same flooding issue.
    Also thanks guys. I’m the “steam guy” at the shop and it’s nice to know I have some knowledgeable and helpful people out there in the world that got my back.
  • Danny Scully
    Danny Scully Member Posts: 1,426
    edited April 2018
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    Why the pump @JohnnyGlocalstp?
  • JUGHNE
    JUGHNE Member Posts: 11,074
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    Is the M&M 150 LWCO located on the other side of the boiler?
    It looks like an electronic probe type near the sight glass side.

    Is there a HW circ pump on the return under the equalizer?
    Is it pulling water out of the boiler to the exchanger and where does it return to the boiler?
    Could it be that when this pump starts the boiler level drops enough to add extra water to the boiler?

    And aren't the returns high enough for gravity return or is the feeder receiver needed because of slow return or small boiler water capacity for the connected system?
  • JohnnyGlocalstp
    JohnnyGlocalstp Member Posts: 10
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    > @JUGHNE said:
    > Is the M&M 150 LWCO located on the other side of the boiler?
    > It looks like an electronic probe type near the sight glass side.
    >
    > Is there a HW circ pump on the return under the equalizer?
    > Is it pulling water out of the boiler to the exchanger and where does it return to the boiler?
    > Could it be that when this pump starts the boiler level drops enough to add extra water to the boiler?
    >
    > And aren't the returns high enough for gravity return or is the feeder receiver needed because of slow return or small boiler water capacity for the connected system?

    All great questions! You’re seeing the watch dog on the actual boiler in question they don’t have that but they do have the 150 on the opposite side that turns the receiver feed pump on and the burner circuit off on a call for water. I like where you are going with the drop in available water when the pump comes on due to feeding the coil. I’ll let you know what I find.