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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?


    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
    Billington Heights, NY
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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.

  3. #3
    Join Date
    Aug 2009
    Prattville, Alabama
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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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