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  1. #1
    Join Date
    Oct 2019
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    Chilled water pressure rising.

    Hi, in our plant we operate Trane centrifugal chillers CVHF910 which supply chilled water to cooling coils of 14 air handling units in 7 story building. Recently we noticed that chilled water pressure is rising for some reason, reached 160psi in and 140psi out at the evaporator / normal pressure is 90psi in/75psi out/. At the same time expansion tank pressure stayed the same, 45psi. We drained some water to bring the pressure back to normal. Stayed normal for couple of days and then started rising again. It is a mystery and I hope someone will clue me in what is going on.

  2. #2
    Join Date
    May 2012
    Location
    California
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    What is your make up water doing?

    Sent from my SM-G960U using Tapatalk

  3. #3
    Join Date
    Oct 2005
    Location
    USA
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    546
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    Quote Originally Posted by Marin View Post
    Hi, in our plant we operate Trane centrifugal chillers CVHF910 which supply chilled water to cooling coils of 14 air handling units in 7 story building. Recently we noticed that chilled water pressure is rising for some reason, reached 160psi in and 140psi out at the evaporator / normal pressure is 90psi in/75psi out/. At the same time expansion tank pressure stayed the same, 45psi. We drained some water to bring the pressure back to normal. Stayed normal for couple of days and then started rising again. It is a mystery and I hope someone will clue me in what is going on.
    Sounds like your pressure reducing valve is bleeding by. one way to find out is if your city pressure matches your loop pressure.


    Sent from my iPhone using Tapatalk
    RTFM!!!

  4. #4
    Join Date
    Aug 2006
    Location
    Mixing oil and fire with a big spoon.
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    6,893
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    Are your gages accurate?
    "Right" is not the same as "Wise".

    Don't step on my favorite part of the Constitution just to point out your favorite part.

  5. #5
    Join Date
    Oct 2019
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    Thread Starter
    Quote Originally Posted by jayguy View Post
    Are your gages accurate?
    Yes, they are accurate.

  6. #6
    Join Date
    Oct 2019
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    5
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    Thread Starter
    If PRV is passing it will pressurize expansion tank. The expansion tank pressure is 45psi. City pressure is 80-90psi.

  7. #7
    Join Date
    Feb 2016
    Location
    Louisburg Kansas
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    Unless you have significant leaks shut off the PRV isolation valve for a couple days and see what happens. Before doing that shut the system down and check the residual pressure and check it the same way again after the PRV is isolated a couple days.
    No man can be both ignorant and free.
    Thomas Jefferson

  8. #8
    Join Date
    Oct 2019
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    Thread Starter
    Quote Originally Posted by WAYNE3298 View Post
    Unless you have significant leaks shut off the PRV isolation valve for a couple days and see what happens. Before doing that shut the system down and check the residual pressure and check it the same way again after the PRV is isolated a couple days.
    Thanks, we will try that.

  9. #9
    Join Date
    Sep 2007
    Location
    edmonds wa
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    Might want to put on a water meter on the make up line, and then monitor that for any usage.
    UA Local 32 retired as of Jan 2020

  10. #10
    Join Date
    Oct 2019
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    Thread Starter
    Quote Originally Posted by buford View Post
    Might want to put on a water meter on the make up line, and then monitor that for any usage.
    Part of the mystery is that there is water meter between expansion tank and chilled water line and there was no make up water to the system. The reading of the water meter stayed the same for couple of months.

  11. #11
    Join Date
    Feb 2016
    Location
    Louisburg Kansas
    Posts
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    If you had no makeup for two months I would check the water meter. Aside from checking the expansion tank water level you need to know for sure you are not adding water to the system before you can go to the next troubleshooting step.
    No man can be both ignorant and free.
    Thomas Jefferson

  12. #12
    Join Date
    Sep 2010
    Location
    MO
    Posts
    15
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    Other possibilities, city supply can creep in the evenings with lower usage, any work performed recently? Possible cross connection.

  13. #13
    Join Date
    Nov 2011
    Location
    East Side
    Posts
    7,174
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    there's only a few possible causes.

    water pressure regulating valve failing.

    make up water bypass valve bleeding by.

    expansion tank bladder busted and/or tank water logged....as water expands, pressure goes up.

    pump dead heading, raising temperature and pressure.

    connection from other water system to CHW closed loop.

    chiller tube leak, causing refrigerant to bleed into system and raise pressure. (unlikely since you have low pressure machines)


    start eliminating possible causes.

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