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dave_141 Member Posts: 12
How does a steam boiler get into a vacuum and what can I do about it?


  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,573

    anytime a chamber full of steam condenses, it leaves a vacuum.i think they use this principle in canning food.
    in the case of the boiler,when do you see this vacuum? old vapor systems would continue steamming at below atmospheric pressure as the coal fire burnt up the last of its fuel.they had special air vents with a disk covering the outlet to prvent air coming back in.
    some of these were still on my system up until a year ago because of my then steam ignorance.
    you may have some similar on yours,but how and when do you see this vacuum?also see if [on a gravity return system] if you have a check-valve which should not be there.
    if you have proper venting i don't see how the boiler could develop a vacuum.
    lastly i believe that dan's book on steam[available here] goes over vacuum problems.good luck--nbc
  • Jamie Hall
    Jamie Hall Member Posts: 20,868
    does it work?

    As Nicholas said, older steam systems were intended to pull a vacuum. Nothing wrong with it, by itself -- if anything, it might reassure you that there are no leaks! If the system is otherwise working OK, not to worry. On the other hand, if you need more venting or if you are having water level problems, get and read Dan's book...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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