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Thread: Glycol and wet rotor circulator breakdown

  1. #1
    DIY Member luc's Avatar
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    Default Glycol and wet rotor circulator breakdown

    Hi everyone,
    We have a wet rotor circulator on the glycol side of the heat exchanger on our outside wood furnace that is down again. The circulator was burning hot and it seems to me that the rotor was sticking. These small wet rotor circulators are supposed to be really good but we used several during the past 5 years. This one is still on the waranty.

    The circulator runs non stop during the winter season.

    We used distilled water for the glycol solution in the furnace.

    The circulator has a cast iron pump housing and is made for a closed system. If I am not mistaking the furnace is an open system. Could this be the cause of the breakdown?

    Luc

  2. #2
    In the Trades Bob NH's Avatar
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    Is the circulating fluid exposed to air or is the glycol side sealed? Some wood furnaces operate at atmospheric pressure because it is diffucult to control the temperature and pressure.

    If oxygen can get into the system then you will have problems with a cast iron circulator.

  3. #3
    DIY Member luc's Avatar
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    Thanks Bob for your answer.

    The outdoor furnace is non-pressurized. It is atmospheric vented. I guess a bronze or stainless housing circulator would better then a cast iron housing circulator? Also, is it normal that the water is black in the tubing?

    Luc

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    It shows that the water is picking up rust. It will be worse if you don't have a sealed system and an oxygen barrier (if you had say some plastic pipe like PEX in there). In a closed system, it reaches an equilibrium, in an open one, it continues to get worse.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    DIY Member luc's Avatar
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    I contacted the manufacturer of the outdoor wood furnace and they have been using cast iron circulators for years without any major problems. They use rust inhibitors in the water solution. They told me that our pump was installed incorrectly or that we had a cavity problem.

    If it was a cavity problem, the water going through the pump would make some noise? The pump was very quiet when it was running. The impeller looked OK when we changed the pump.

    I don't think that the pump was installed incorrectly. The installation was done by a qualified contactor.

    My guess is that the pH of the glycol solution might be related to the sticking of the rotor. We took the pH a few weeks ago and it was between 6 and 7. We added some chemicals to bring it up.

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    Don't remember the exact spec, but one boiler I had a long time ago did say you should replace the working solution periodically (maybe 5-years?). I do not know if that is a generic requirement, or specific to that unit. While the antifreeze itself doesn't wear out, the additives (similar but not identical to a car's antifreeze) do get used up.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  7. #7
    In the Trades Bob NH's Avatar
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    Quote Originally Posted by luc View Post
    The outdoor furnace is non-pressurized. It is atmospheric vented. I guess a bronze or stainless housing circulator would better then a cast iron housing circulator? Also, is it normal that the water is black in the tubing? Luc
    Copper corrosion products can be black.

  8. #8

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    is the pump installed in a position with the rotor in the verticle position??if so it is in wrong.air can get trapped in the rotor housing........as far as cavity,i think you mean cavitation,this can happen if there is not enough straight piping on both the upstream and the downstream sides of the circulator

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