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  1. #1
    Join Date
    Apr 2009
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    massachusetts
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    Leak testing with nitrogen

    I always thought nitrogen stayed the same pressure in a system even if ambient temps change from one day to another.Do you guys see this to be true?

  2. #2
    Join Date
    Nov 2000
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    Nitrogen is subject to pressure changes at varying temperatures, just not as much as refrigerants and other gases are.
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  3. #3
    Join Date
    Apr 2009
    Location
    massachusetts
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    Got it,If I put in 300psi and return in a day or two and temps are ten degrees of each other,what do you think 5psi give or take?

  4. #4
    Join Date
    Mar 2007
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    3,108
    Quote Originally Posted by burto View Post
    Got it,If I put in 300psi and return in a day or two and temps are ten degrees of each other,what do you think 5psi give or take?
    I think at this point, you know as much about the system as you would if you had done nothing at all. Do a real leak test, or at the very least pull a vacuum and see if it holds. Don't be lazy.

    "There is no greater inequality than the equal treatment of unequals."

    -Thomas Jefferson

  5. #5
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    Dec 2011
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  6. #6
    Join Date
    Sep 2008
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    Western PA
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    http://hvac-talk.com/vbb/showthread.php?t=846662

    Here's a good thread on the topic.

    If I remember right, there's also a calculator that will allow you to compute what your target pressure should be, given known conditions.

  7. #7
    Join Date
    Oct 2011
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    Chicagoland Area
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    4,593
    300psi? A little overkill maybe?
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  8. #8
    Join Date
    Jul 2012
    Location
    Athens, GA.
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    143
    Here is a snippet about ideal gas law that will answer you question.

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  9. #9
    Join Date
    Feb 2010
    Location
    In a boiler room
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    I recently used this formula for a system that required me to document a standing 24 hour pressure test at 600 psi. I pumped it up and ended up with 604 psig on my digital Testo. Also took temp reading. Wasn't able to come back next day, ended up being 5 days and pressure was at 608 psig. I don't remember the temp change, it wasn't much, but using the forumla, it showed that 608 was right where I needed to be.

    Jim Bergman wrote an excellent article for RSES on how to calculate the pressure change for standing pressure tests. It is in the RSES Journal Archives.

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