Expansion Tank Precharge Low

Discussion in 'Pumps and Tanks Well Forum & Blog. Water is life.' started by WellNewb, Jan 8, 2020.

  1. WellNewb

    WellNewb New Member

    Joined:
    Jan 4, 2020
    Location:
    NY
    Hey guys, injust received a new Amtrol expansion tank. The Precharge is supposed to be 38psi but when I tested it with 2 separate pressure guages, it measured 35.5psi.

    Is it possible that the charge is reading low because it's been in transit for a few days out in the cold weather and I should just trust that it's precharged to the correct amount?

    It's just weird that 2 separate pressure guages from different manufacturers would register 35.5psi.

    Thanks a lot!
     
  2. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    38 is unlikely to be the right amount either. City water, I presume. You want to set the air pressure to the same as the water pressure in your pipes when you have a faucet dribbling water. If that pressure varies during the day, I would try to set it to what it is max, if I knew that. Setting the air precharge to the same or 2 psi higher than the current water pressure will usually be near ideal.

    So why was the number lower than the published factory precharge? Maybe the Schrader valve slowly leaks. The valve cap should stop that if it is tightened normally. Maybe the unit was in stock for a long while, and air diffused out. Maybe you have two tire gauges that read a little low.
     
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  4. valveman

    valveman Cary Austin Staff Member

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    Occupation:
    Pump Controls Technician
    Location:
    Lubbock, Texas
    Just the change in room temperature can make that much difference. Nothing to worry about. If you have a gauge that reads decimals you are probably more accurate than the factory. This is why I always stay to the low side of a pre-charge. Too little is OK, too much is not.
     
  5. WellNewb

    WellNewb New Member

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    Jan 4, 2020
    Location:
    NY
    I have a well with a 40/60 pressure switch so the tank should be set at 38psi from what i understand.
     
  6. valveman

    valveman Cary Austin Staff Member

    Joined:
    Mar 15, 2006
    Occupation:
    Pump Controls Technician
    Location:
    Lubbock, Texas
    I would tell you 35 for the reasons above. You air pressure gauge will not read the same as the water pressure gauge.
     
  7. WellNewb

    WellNewb New Member

    Joined:
    Jan 4, 2020
    Location:
    NY
    I'll just leave it alone then. Thanks for the input. It's an unfinished basement so the temps vary from 45 in winter to 70ish in summer. If its 35.5 now, I imagine it may be closer to 38 in the summer.
     
  8. valveman

    valveman Cary Austin Staff Member

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    Occupation:
    Pump Controls Technician
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    Lubbock, Texas
    Yes that is how it works. Water temp makes a difference as well.
     
  9. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    Since you called it an expansion tank, I had incorrectly presumed city water.

    If your precharge pressure is a bit high, it is not a big deal as long as you don't have a lever on your pressure switch. The symptom of too high is a momentary pressure dip when the pump turns on.
     
  10. valveman

    valveman Cary Austin Staff Member

    Joined:
    Mar 15, 2006
    Occupation:
    Pump Controls Technician
    Location:
    Lubbock, Texas
    And tremendous water hammer when the tank bladder bottoms out.
     
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