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Thread: Tank air pressure for non bladder water tank

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  1. #1
    Jack of all trades DonL's Avatar
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    Default Tank air pressure for non bladder water tank

    I was wanting to get a experts view on how much air pressure needs to be added to a empty Water storage tank.

    After draining all of the water from the tank, How much Air pressure should I have in the tank ?

    And what percentage of the tank would have water , When the pump fills it and the pump turns off ?


    Thanks, Have a Happy New Year.


    P.S. Sorry for leaving out, Tank 30 feet above sea level, 120 Gal tank, 40/60 switch setting.


    DonL
    Last edited by DonL; 01-01-2012 at 10:04 AM. Reason: P.S.
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    DIYer, not in the trades LLigetfa's Avatar
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    I am a DIYer, not an expert but from my experience maintaining my hydropnuematic tank, will add my two cents.

    Tank manufacturers have their own idea as to where the air level sits by how and where they locate the air volume control. Since it varies by manufacturer, I would have to say there is not one right answer for all scenarios. The theoretical ideal for max drawdown would have the tank nearly empty at kick-in. That however could become an issue if you have a softener or filter backwashing and the pump cannot keep up with the draw. Air may get interspersed in the stream and could blow resin or media into the head and into the drain.
    Last edited by LLigetfa; 01-01-2012 at 11:51 AM. Reason: typo

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    Moderator valveman's Avatar
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    If you have an Air Volume Control (AVC), it doesn't matter how much air you add, because it wll come out untill the float on the AVC is up. Usually just draining the tank completely, and not adding any more air, will give you the correct amount.

    You can pre-charge a standard type tank if you remove the AVC, or pump the air up to 35 with a 40/60 switch, while the water level is above the AVC.

  4. #4
    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by valveman View Post
    Usually just draining the tank completely, and not adding any more air, will give you the correct amount...
    Doing that on my WellMate tank results in very little drawdown. Over time the micronizer will increase the volume to what the AVC maintains but that is a slow process so anytime I drain the tank, I will use my air compressor to restore the air level to what the AVC does to maximize my drawdown.

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    Jack of all trades DonL's Avatar
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    I forgot to mention that I did remove the AVC and plugged the ports.

    I never could get them to last , or work. On the Old Pump or the one I have installed now.

    The AVC did not have a float, It was mounted about of the way up from the bottom of the tank.


    Can I assume the tank should be full of water, or is that not correct ?
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    Test, Don't Guess! cacher_chick's Avatar
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    My tank has the float-style AVC about 1/2 way up the side of the tank, so that's all the air that it could hold.

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    DIYer, not in the trades LLigetfa's Avatar
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    My understanding is there are two types of AVC. One style only lets air out and works in conjunction with a submersible and a bleeder/snifter. The other kind takes air in and works with a piston or jet pump. Any I've seen were about half way up the tank.

    The more air in the tank, the more drawdown. If the AVC is not working, the more air, the less often it needs to be topped up. If you don't have a softener or backwashing filter, I see no downside to having more air.

  8. #8
    Jack of all trades DonL's Avatar
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    Quote Originally Posted by cacher_chick View Post
    My tank has the float-style AVC about 1/2 way up the side of the tank, so that's all the air that it could hold.

    So how full is your tank with water ? When your pump shuts off ?
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