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weight of water

Discussion in 'Commercial' started by Texas-Tech, Dec 30, 2017.

  1. Texas-Tech

    Texas-Tech Official Geezer*

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    We have a small process chiller cooling an MRI, JM Fluidics self contained unit. It sits on the roof of a 6 story hospital. Have had some alerts and always thought it was low on water, supply pressure only showed 30psi. Went out this past week and decieded to try and fill the loop and remove the air. When we were finished the supply pressure was at 70 and for the first time the return line actually showed 30 psi.

    Downstairs in the equip room there is a filter with a gauge on either side. They were reading 70psi and are now showing 130. It has to be from the weight of the water being pumped down from the roof. Is there a way to calculate the effect of the weight and height?
     
  2. pecmsg

    pecmsg Junior my ASS

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    2.31 or 3.21#’s per ft of elevation
     
  3. Chuck

    Chuck SSP

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    I think it’s the other way around. For every 2.3 ft rise you lose 1 psi, or gain if going down.
     
    Last edited: Dec 30, 2017
    HMD likes this.
  4. Ballvalve79

    Ballvalve79 It's only fire what could go wrong

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    .433 lbs of pressure for every foot of vertical rise.
     
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  5. Joeysmith

    Joeysmith New Member

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    .433 psi per foot plus the 30 psi I believe
     
  6. Chuck

    Chuck SSP

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    .433 psi per foot is also correct
     
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  7. Joeysmith

    Joeysmith New Member

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    Do you add the system pressure to that or not? Never really messed with anything like that.
     
  8. Chuck

    Chuck SSP

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    What does the pressure run on the return side of the pump and where is the expansion tank connected in relation to the pump?
     
  9. Zman

    Zman Hanging by a Thread

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    The "I know a Guy" State
  10. Zman

    Zman Hanging by a Thread

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    IMG_20171231_010004.jpg
     
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  11. Zman

    Zman Hanging by a Thread

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  12. Zman

    Zman Hanging by a Thread

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    But you can't Believe everything you Read! IMG_20171231_013138.jpg
     
  13. R/HVAC

    R/HVAC selfemployed

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    If the system has glycol in the loop that will change the specific gravity too.
     
  14. tuna

    tuna New Member

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    There is a maximum pressure the mri heat exchanger is rated for. The last mri I worked on I believe the max pressure was 90 psi +/-.

    You just need enough water pressure in the system to be 5psi or so at the highest point with everything running. I would also check the heat exchanger rating and make sure the pressure is less with pump on or off. The one I worked on earlier this year connected to an existing chilled water system. We didn’t have enough differential pressure to get the right flow. The engineer had us install a pump to get the correct flow. We installed the pump on the leaving side of heat exchanger to keep from adding pressure.
     
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  15. Texas-Tech

    Texas-Tech Official Geezer*

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    this is a 2 pump system, one circulates through the brazed plate evap and back into the tank, other pump circulates down into the process then back up to the tank. I believe the pipe size is 1 1/2"
     
  16. HMD

    HMD does it matter?

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    can't really check pressure drops with different gages.
    should use only one.
     
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  17. HMD

    HMD does it matter?

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    6 stories.
    10' per floor (swag)
    4# per floor (swag)
    4x6 =24, plus some cushion to get it over the top.............. 10#
    35# static water column should be enuff
     
  18. pecmsg

    pecmsg Junior my ASS

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    We guesstimate 12' per floor!
     
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  19. HMD

    HMD does it matter?

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    that'll work
     
  20. oroy54

    oroy54 New Member

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    I still guesstimate 1/2 pound per foot psi.