Tank air pressure for non bladder water tank

Discussion in 'Pumps and Tanks Well Forum & Blog' started by DonL, Jan 1, 2012.

  1. DonL

    DonL Out of the Trades

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    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: Jan 1, 2012
  2. LLigetfa

    LLigetfa DIYer, not in the trades

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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: Jan 1, 2012
  3. valveman

    valveman Moderator Staff Member

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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. LLigetfa

    LLigetfa DIYer, not in the trades

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    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.
  5. DonL

    DonL Out of the Trades

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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 ¾ of the way up from the bottom of the tank.


    Can I assume the tank should be ¾ full of water, or is that not correct ?
  6. cacher_chick

    cacher_chick Test, Don't Guess!

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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.
  7. LLigetfa

    LLigetfa DIYer, not in the trades

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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. DonL

    DonL Out of the Trades

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

    DonL Out of the Trades

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    I do have a water Softener.

    I don't see why that would mater, But I guess that it does ?
  10. LLigetfa

    LLigetfa DIYer, not in the trades

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    I explained it in my first post but will try again with different words. Water flow through an obstruction is limited by the obstruction much more than air is through the same obstruction. If you've ever had a glass shot out of your hand at a sink that is spitting air and water, you'd understand what I mean.

    A softener backwash is flow limited by an orifice. On many softeners, they use power only to turn a clock through the various cycles. The rest is done with water pressure. If the power were to fail during the backwash, the well pump stops and the level in the pressure tank starts to drop. If the air is jacked so much that there is enough pressure in the tank after all the water has been expelled, it will be chased by a burst of air. The air behind the water will have a voilent boiling action in the resin tank which can drive the resin into the head and the drain if there is no top basket.

    I know this first hand because my WellMate precipitation tank is supercharged to provide drawdown that rivals a bladder tank. I have never had the misfortune of a power failure during a backwash, but the iron in my water wreaks havoc on the AVC and when it stops working, the air will pass through to the iron filter on every cycle. The greater flow rate on the iron filter will drop the level in the precipitation tank and blow media up into the head and down the drain.
  11. Texas Wellman

    Texas Wellman In the Trades

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    Don,
    Forget about all the other replies and listen to mine. I have been doing this for well over 20 years, I probably know more about what kinds of set-ups we have here than anybody else.

    For various reasons, all the tanks in our area have remained galv. hydro-pneumatc. Most everywhere else the bladder tank is the std.

    Here, an AVC is designed to use the suction port of a jet pump to suck in a tiny little wisp of air every time the pump starts. I don't like them because most either fail within a few months or even not work right brand new out of the box.

    If you don't have a schraeder valve on the side of your tank, get one. Turn the pump off (be mindful that by doing this you could lose the prime in the pump). Open a spigot somewhere close to the tank. Start adding air. I like to use a clip-on style chuck that allows you to add air hands-free. Add air until you see the water start to spurt out of the spigot. Hopefully your spigot is plumbed at a low point of the tank. Close the valve when the air starts sputtering out. Keep adding air for about 5 minutes or so. Remove the air chuck and turn on the pump. Hopefully once the pump pressures up the tank you'll have at least 1/2 air to water. If you get too much air, don't worry, it will naturally exit after a few days. You might hear it sputtering out.

    By doing this you can at least double the draw down of your 120 gallon tank and extend the time between draining.

    Good Luck.
  12. cacher_chick

    cacher_chick Test, Don't Guess!

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    I have a submersible pump with the bleeders in the well, so that every time the pump runs it sends a slug of air to the tank in front of the water. My air volume control releases excess air from the tank.
  13. Tom Sawyer

    Tom Sawyer In the Trades

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    Yes, yes and once again YES
  14. ballvalve

    ballvalve General Engineering Contractor

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    All fine and good, and I usually remove the air release valve on the plain tank associated with a submersible pump. Then I use a air inducer system ABOVE ground right next to the tank, and adjust the nipple length between the check valve with schrader valve and the bleed off valve to give a shot of air that does not 'overload' the tank.

    Then, one may still pressurize the tank with a compressor to a few pounds under cut in pressure to add much to draw down amount. ...And when you forget to add air with the AC, as most do or will from many times to time, You still do not end up with a water logged tank.

    But I start to think that a GOOD diaphragm tank is really the best way to go in the long run - but never a "bladder tank".

    2 interesting notes: One well I have makes water with much air in it, and so the tanks never water log without any air maker. Another well I have feeds a 3000 gallon tank, and flows to a 8 stage booster pump that feeds a plain 80 gallon pressure tank. I always wondered why it too, never water logged, until 2 of us with radios monitored the flow - turns out that at the outlet of the 3000g static tank there is a small SUCTION leak - lets air in only when the pump sucks from the tank, but no water out when static. Suction leaks are odd things that few discover. And in this case is a very good 'problem'.
    Last edited: Jan 1, 2012
  15. DonL

    DonL Out of the Trades

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    I don't have a schraeder valve, but next time I drain my tank I will install one, and do as You suggest.

    I have been draining my tank about every 4 months and it seems to work fine. But maybe could do better.

    Every time that I have used an AVC, I end up having to drain the tank every 4 months anyway.

    I do like the larger tank, In case of a power failure I have a little more reserve.


    Thank You for your Input.
  16. LLigetfa

    LLigetfa DIYer, not in the trades

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    How do you coordinate that with the PoCo? Do they give you advance notice? Around here it seems the power always goes out when my tank is just about empty.

    If you supercharge the tank, depending on where you draw from there may be very little water left in it to use to reprime the pump. As Texas wellman said, there is a risk of losing prime doing that.
  17. DonL

    DonL Out of the Trades

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    No advance notice, But I can run my pump off of my generator if needed. Fill the water tank and shut it off.

    I guess it is about a 50-50 chance that it would be empty or full, when the power fails.

    I always keep water on hand to re-prime the pump, and do not rely on the water in the tank for priming.
  18. LLigetfa

    LLigetfa DIYer, not in the trades

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    When I was running galvanized tanks, I would raise them up so that the pump was lower than the tank. Also, the house was hooked to the side, up off the bottom so there was always water that could be drawn from the drain cock for priming.

    Now with a sub, priming is of no concern. WRT power outages, my pump is 240V and my genset is 120V so no joy there. Never had an outage last more than a few hours.
  19. DonL

    DonL Out of the Trades

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    The water inlet to the tank is above the pump outlet and the water Outlet is at the bottom of my vertical tank that sits on a slab outside.

    During a Hurricane, we may loose power for a day or 5.

    My water tank is over 20 years old but seems solid.

    It may be about time to invest in a new one.
  20. Texas Wellman

    Texas Wellman In the Trades

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    Unless your tank is leaking, I wouldn't replace it. They were way better made 20-30 years ago. If you do get ready and want to replace it, let me know. I can probably make you a good deal installed.

    Last edited: Jan 2, 2012
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