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  1. #1
    Join Date
    Jul 2018
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    Help with EPA universal test question, thanks.

    When should a low pressure system be leak checked according to ASHRAE
    guideline 3-1996?

    Answer:

    When the system rises from 1 mm Hg to a level above 2.5 mm Hg
    during vacuum testing

    I can't figure this out, doesn't the pressure lower if it goes from 1 mm hg to 2.5 mm hg? Why would you leak check a system where the pressure is dropping?

    Thanks for any insight into this.

  2. #2
    Join Date
    Mar 2013
    Location
    Billington Heights, NY
    Posts
    19,120
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    the vacuum decay test. you arent running the vacuum pump during that. it's when you're blanked off and seeing if there is a rise in pressure.
    This forum requires that you wait 20 seconds between posts. Please try again in 50 seconds.

    Experience - knowing when to get the hell out of the way and plug your ears. "Don't be a sissy. Turn it on!"

    Pecmsg - "NEST should only be used with 3-M filters to guarantee total destruction of the equipment!"

    Poodle Head Mikey - "the world is well populated with the unknowing and the uncaring and the stupid."

  3. #3
    Join Date
    Aug 2009
    Location
    Prattville, Alabama
    Posts
    3,227
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    Pressure is not dropping.
    The units "mm Hg" is referenced to absolute pressure, not atmospheric pressure (that would be "inches of Hg").
    So, the larger the measurement of mm Hg, the farther away from 0 psia (per square inch absolute), or the greater the pressure.

  4. Likes rjk_cmh liked this post

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