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Thread: well water, underground plastic tank...can it be pressurized?

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  1. #1
    DIY Junior Member Dolphin's Avatar
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    Default well water, underground plastic tank...can it be pressurized?

    Hi all, great forum... I have just taken over a property with a new well system. It services 4 residential properties, just being finished. I have general plumbing knowledge, but never worked on a well system...
    I was trying to grasp the well design...I think its improperly controlled and plumbed. Here is the set-up...
    Well pump feeds above ground in well house via 2" PVC pipe.... it feeds four 60 gallon pressurized bladder tanks (which are plumbed to act a single unit)....
    in addition, this 2" PVC feed goes down into the underground storage tank, about 1700 gallons, it appeared a poly tank when I saw it installed. Surely not metal.
    There is an additional water pump, which pulls water up from the under ground storage tank and discharges into the bladder tank loop, which in turn, pressurizes the underground storage tank. The check valves all seem to be in the right place.

    A few questions....

    1) Assuming I do not run the above ground pump (it could be there for fast fill of water trucks).....the way the system is controlled now, the well pump is controlled by a pressure switch on the bladder tank loop....set at about 50 lbs. However, this well water feed also fills the underground poly storage tank.... so the underground storage tank will have the same pressure as the bladder tank loop. Which forces the underground storage tanks "overflow" to release water by the well house. My initial question is... are underground poly tanks meant to be pressurized ? I would think, NO! ??

    2) Assuming I have the above correct.... I would think the most sensible control scheme would be..... the well pump should be controlled by a float switch in the underground storage tank. (there is a wire coming up from the storage tank which must be a float switch) The well pumps sole purpose should be to keep the underground storage tank full, till the float switch engages, but never under pressure. I would have to re plumb to accomplish this.

    3) The above ground pump near the bladder tanks should be controlled by a pressure switch on the bladder tank loop. It's sole purpose should be to pressurize the bladder tanks with water up to 50 lbs. of pressure.

    In other words, two separate control loops, which function independent of each other. Is this the "ideal" control scenario? Or can a single well pump pressurize the bladder tank, as well as the underground storage tank? As I see no way the underground poly storage tank won't constantly be pressurized every time the well pump comes on. Which is creating a lot of overflow, and some some water percolating up through the earth above the storage tank, as the overflow drain pipe size was undersized vs. the well pumps capacity. I am confused why it was plumbed and controlled by this method, seems bizarre to me... this was an experienced well driller which is why I am thinking I am missing something.

    Any input would be greatly appreciated, TYIA

  2. #2
    Moderator valveman's Avatar
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    The 1700 gallon storage tank cannot be pressurized. There is an additional pump in the storage tank that pressurizes the water in to the bladder tank loop. With the well pump working from a pressure switch, there should be a float valve or a float switch operating an electric valve to fill the storage tank. If the storage tank is overflowing, then the float valve or float switch is not working or not set at the proper level.

    There are several ways to set up the control scenario for a system like this. I would probably set the pressure switch on the well pump to operate at a higher pressure than the booster pump. Ie; well pump at 40/60 and the booster pump at 30/50. I would also have the electric tank fill valve tied into the pressure switch for the booster pump. When the well pump cannot satisfy the demand by itself, the booster pump comes on at 30 PSI. I would tie the booster pump in with the float switch for the electric valve, so the storage tank stops filling while the booster pump is running. This will give you the combined total volume of the well pump plus the booster pump for peak demands.

    When the peak demand is satisfied, the well pump will be able to increase the pressure to 50 PSI, which shuts off the booster pump and opens the electric valve to refill the storage tank. When the storage tank is full the float switch closes the electric valve. Then when there is no more demand, the well pump increases the pressure to 60, and the well pump is also shut off.

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    DIY Senior Member VAWellDriller's Avatar
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    What is the capacity of the well pump? Since it's only 4 houses, if your well yield and pump is good for anything over 15 - 20 gallons / minute, you can easily just do away with the 1700 gallon tank totally; install 1 pressure tank and a cycle stop valve. I build a lot of systems like this for anywhere between 2 and 100 houses. On just a few houses, I use the well pump, small pressure tank, and a CSV. When I get over 12 connections, they are considered public water systems governed by our state health department. There are more regs on water storage, peak flow, etc. Normally systems are engineered to pump directly to nonpressurized storage with the well pump and then have two centrifugal pumps (with two seperate pressure switches), drawing from the storage to pressurize a tank and the system. The well pump is controlled by BW liquid level controls, and but it is also plumbed and valved so that if there is a problem with either the booster pumps or the storage tank, you can open a valve and turn a switch and have the well pump pressurize the system and run off one of the pressure switches. If you have the capacity of the well, I would just simplify the whole system. If you have to use the underground tank, you need to re-plumb it so it's not pressurized.

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    DIY Junior Member Dolphin's Avatar
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    thanks guys for sharing your knowledge and thoughts.... Yes, the water demand is very low, it will prob. remain that way for the foreseeable future.... as VAWD suggests in his post...the four 60 gallon pressurized tanks is more than sufficient for the next several years. I do NOT have any specs on the well pump, the installer left NOTHING. However, it seems the well pump builds up pressure in the four tanks sufficiently...I will confirm this.

    1) What is an acceptable period of time for these tanks to reach pressure? 5-10 minutes?

    2) I can close a manual valve feeding the underground storage tank. Now the well pumps role will be to ONLY pressurize the four 60 gallon bladder tanks, which feed the properties. This raises one other question.....
    With the pressurized tanks fully charged, I assume there needs to be a check valve to PREVENT water from back feeding down the well. I don't see a check valve above ground to prevent this... or maybe a check valve system is built into the well pump below ground?

    3) That underground storage tank is full... is that OK? Should I install a valve that can gravity pour some bleach down into storage tank occasionally? The summers get HOT, and while the tank is underground, it only takes a small amount of growth in the above ground piping to turn the storage tank full of growth, I would think......or should I attempt to drain the storage tank?

    Valveman, your strategy makes perfect sense. And currently, there is NO electric valve that shuts off flow to the storage tank via a flow switch..... this represents the overflow condition. thx for sharing that.... makes perfect sense. For now, if the well pump + pressurized tanks is more than sufficient, it makes sense to remove the storage tank from the equation. In the future, when demand increases, I can install an electric valve to prevent storage tank overfill and add a 2nd pressure switch to control the booster pump. Its nice to know the future control strategy.... much appreciated.
    TYIA

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    Moderator valveman's Avatar
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    It all depends on the size of the well pump. If the well pump will produce the volume and pressure needed, then I would drain and disconnect the storage tank and booster pump.

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    DIY Junior Member Dolphin's Avatar
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    Valveman, I fully agree.... I am pretty confident the well pump is sufficient... I will investigate that in the next day or two...

    Assuming it is, should there be a check valve on the outlet side of the well pump, to prevent pressurized water going back down the well, when the well pump is off of course.... or do all modern well pumps have back flow prevention built into them?

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    Moderator valveman's Avatar
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    There has to be a check valve down the well on the pump, and that is the only check valve needed.

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