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Air Pressure Bellows

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  • 26-08-2015 4:46pm
    #1
    LCRS
    Registered Users Posts: 10 ✭


    Just posted this in Engineering then saw this sub so will chance you guys too! Any input welcome.

    I am trying to spec a bellows for a type of forge and the only reference to it I have is from an old book saying the air pressure needs to be at least "25 pounds to the superficial foot" with the option of increasing that. Now I have looked up the term "superficial foot" and it seems to refer to a measurement for timber - a square foot of timber one inch thick. Would anyone here be able to convert this to a more modern value? The term superficial foot may refer to a cubic foot but I am not sure as it is a pretty old book.

    If anyone could shed some light on this it would be greatly appreciated.

    Also if anyone is interested, the piece in the book is referring to a horse shoe nail maker in Dublin in 1864 who would first heat up the nail rod as normal in his everyday forge. After it came to a red heat it would be placed over the anvil and a very strong blast of cold air applied to it. This apparently INCREASED the heat of the nail as there was so much friction from the air. The author goes on to say that this could be compared to an "aerolith" at rest. "The air from the bellows moving past it the same velocity with which an aerolith in motion would, under ordinary circumstances, travel through the lower region of the atmosphere."

    Thanks for reading.


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    #2
    dlouth15
    Registered Users Posts: 1,169 ✭✭✭dlouth15


    It looks like in the context of pressure, superficial foot is simply square foot. This is from a glance at old books on construction on the internet which talk about "load per foot superficial". Since the load can't depend on the thickness of the thing on which the load is placed, "foot superficial" can only mean area.

    So the units are pounds per square foot. It's also a measure of volume, which is a square foot one inch thick but in the context of pressure it is just a square foot.

    Google does the conversion easily, just put "25 pounds per square foot into pascals" into the search engine and you get "1197.00647 pascals"

    Interesting story about the nail maker. I would not have thought you could get that sort of air velocity out of a bellows.


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