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Additive/ Subtractive Pressuretrols?

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Robert O'Brien
Robert O'Brien Member Posts: 3,541
edited February 2021 in THE MAIN WALL
Why make both?
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  • Jamie Hall
    Jamie Hall Member Posts: 23,322
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    Very different histories to the two lines.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,541
    edited February 2021
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    Jamie Hall said:
    Very different histories to the two lines.
    Yielding the same results
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  • Jamie Hall
    Jamie Hall Member Posts: 23,322
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    Robert O'Brien said:


    Jamie Hall said:

    Very different histories to the two lines.
    Yielding the same results



    Well, actually not quite. The line which produced today's vapourstats -- now including higher pressure range subtractive pressuretrols -- has a different fundamental mechanism (and initially used mercury, not mechanical, switches). It is not quite as robust, but has much better precision and slightly better accuracy. The mercury switch ones were far superior in that regard, as well as longevity -- provided they weren't overpressured at some point -- but ... well... mercury was deemed by Those Who Know to be the Worst Thing That Ever Happened.

    It's a little like saying a Ford and a Mercedes yield the same results. They do. But they aren't the same.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England

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