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non-wet rotor circulators in small/efficient sizes?

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by pybyr, Aug 6, 2008.

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  1. pybyr

    pybyr Minister of Fire

    Joined:
    Jun 3, 2008
    Messages:
    2,301
    Loc:
    Adamant, VT 05640
    Hello all-

    in another thread, Kabbott raised the fascinating idea of putting a plate HX directly in the primary loop of a primary/secondary system (the HX will be my interface between the unpressurized storage tank and the boiler and heat loads) rather than having the HX “hanging off” a secondary; his approach, as he noted, would allow deletion of one circulator.

    http://www.hearth.com/econtent/index.php/forums/viewthread/21028/

    On the un-pressurized side of the HX, between the HX and the thermal storage tank, I am planning to use "back to back" circulators in opposite directions as has been pioneered by folks here and is being deployed by WoodNotOil.

    One factor that putting the HX in the primary may introduce is that my unpressurized loop between the HX and storage may be much more likely to siphon itself out, and/ or leave air in the circulators on the unpressurized side of things, which I know will spell trouble, fast, for wet-rotor circs.

    I know that the old-type circulators had separate motors, without wet rotors, but they were huge and electrically inefficient

    anyone know whether there are any current-technology, electrically-efficient, not too huge circulators that can prime themselves and that do not require being internally immersed in fluid 100% of the time?

    or, for that matter, I welcome any other suggestions on how it might be possible to avoid the unpressurized side siphoning dry and pulling air into the circulators

    I thought of zone valves, but from all I've read here and elsewhere, they apparently usually have small inside ports and introduce a lot of flow resistance, which I would like to avoid

    thanks

    Trevor

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  2. in hot water

    in hot water New Member

    Joined:
    Jul 31, 2008
    Messages:
    895
    Loc:
    SW Missouri
    No, a circulator is not designed to be self priming. Most will have a pressure number listed by the manufacturer.

    Grundfos UP series wants 1.3 psi or 3 ft. at 140F and 4 psi or 9 ft. at 190F

    NPSH net positive suction head is a calculation that take into account pressure and the type of fluid.

    This is one of the reasons un-pressurized OWF go through circs. especially when they use high head circs :)

    hr
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