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boiler in a vacum

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anthony_12
anthony_12 Member Posts: 9
in Strictly Steam
TRUE OR FALSE "A STEAM BOILER IN A VACUUM IS NOT A GOOD THING"[NO VACUUM PUMP IS INVOLVED}

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  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
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    vacuum question

    when steam condenses, it develops a vacuum. this usually at the end of a burner cycle, and will persist until the main vents have let the air back into the pies, rads, and boiler steam chest.

    if you are seeing a vacuum at other times, then you may have:

    1. a vacuum system, or

    2. a plugged pigtail/faulty gauge.--nbc
  • Jamie Hall
    Jamie Hall Member Posts: 23,282
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    Generally speaking,

    false.  What harm is it going to do?  In fact, some steam systems in the old days deliberately ran a vacuum at some points in the cycle.



    As NBC notes, though, nowadays the vacuum shouldn't be very deep, nor last very long.  Not because it is bad for the boiler -- it isn't -- but it usually indicates a problem somewhere else in the system.  Unless... you have a system intended to run that way, and they are out there.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Ted_4
    Ted_4 Member Posts: 92
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    Maybe yes, maybe no

    A steam boiler that runs a vacuum in a system not designed for vacuum risks sucking make-up water in through the check valve, producing a flooded boiler.  I've seen this happen in two-pipe systems with zone valves that shut off all the mains when there is no call for heat.  The fix is to install a vacuum breaker above the water line to relieve the vacuum.

    One-pipe systems with main and radiator vents should never run a vacuum.

    See "The Lost Art" for details on vacuum systems.
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