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Thread: Circulator pump location

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  1. #1
    DIY Junior Member ShockHazard's Avatar
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    Nov 2012
    North East Pennsylvania

    Default Circulator pump location

    The boiler I'm working on has the circulator on the outlet of the boiler, essentially pushing the water through the heaters rather than pulling it.
    Is this ever legit?

    I've never seen it this way, but don't know why not.

  2. #2
    In the trades Dana's Avatar
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    Jan 2009


    It's totally legit (preferred, in fact), so long as the expansion tank & air scoop is between the boiler and the pump.

    Books have been written advocating that system architecture. It's nicer to the pump, and allows the air scoop to purge air somewhat better than some other configurations.

    On some low mass boilers (particularly those with higher head) it's sometimes better to pump toward the boiler making it the high-pressure point on the system to reduce flash-boil sizzle to not lose heat-transfer efficiency.

    More here.
    Last edited by Dana; 11-02-2012 at 03:22 PM.

  3. #3
    In the Trades dwindle's Avatar
    Join Date
    Nov 2012
    North East Pennsylvania


    Almost every one I've ever worked on had it as the very last thing in the line.
    I always assumed is was so in case of a break, it would suck in air rather than pump out water and run the boiler dry.

    Unfortunately, this one is before the expansion tank, so I suppose I'll be moving it.

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    Sep 2004
    New England


    All boilers today have low pressure cutouts that shut them down with an uncompensated leak. A circulator run dry will fail fairly quickly, at least most of them use the water to lubricate their bearings. Having the expansion tank before the pump helps to ensure the pump stays full of water and not create microbubbles or water flashing to steam.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    Master Hot Water Mpls,MN BadgerBoilerMN's Avatar
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    Mar 2011


    Nice drawing Dana! All low-mass boilers, including electric boilers, should be pumped-to for the reasons mentioned. It is the position of the expansion tank and air-eliminator that is most important, most properly, always on the low pressure side of the pump. This maintained the point of no pressure change.

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