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Thread: Overdrawing a shallow well?

  1. #1
    Homeowner JVance's Avatar
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    Default Overdrawing a shallow well?

    I am trying to troubleshoot some issues with the well in our new house (we have a few, but this would seem to be the logical first issue to tackle). We live on a coastal island, have a shallow well (34' deep), Goulds 1HP jet pump (set to 30/50 PSI start/stop pressure) and 120 gallon tank. The pump sucks a fair amount of air, as observed through the clear housings of the filters between the pump and the tank. From what I've read, air is not friendly to a jet pump, but it nonetheless moves enough volume of water and does not lose its prime.

    There is no information scribed for gpm on the placard in the well-head, so I don't know what flow the well is rated; but, I am concerned that this pump may be overdrawing the well. There generally appears to be more air in the filter housings at lower tank PSI (e.g. when the pump is capable of moving more gpm), and less air at higher tank PSI (e.g. when the flow is reduced). Do these observations suggest the pump may be overdrawing the well? If so, would restricting the discharge flow be the solution? What then is a recommended flow restrictor/regulator, aside from partially closing the ball-valve between the pump and tank?

    Thanks in advance for your advice!

  2. #2
    DIYer, not in the trades LLigetfa's Avatar
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    A shallow well jet pump cannot possibly overdraw a 34 foot deep well. The laws of physics forbid it. Could it be that it is setup for deep well operation and you omitted that detail? If it is a shallow well pump and the footvalve is set deep enough, then the air must be from a suction side leak, not from overdrawing.

  3. #3
    Homeowner JVance's Avatar
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    Absolutely not set up as a deep well.

    I pulled the placard, cleaned it off and found some more info. Casing depth is 25 feet; screen interval is 25 to 35 feet; gravel interval is 24 to 36(?) feet; static water level is 7 ft; and, the yield was estimated to be 5 gpm (1/2 to 1/3 the rating of the pump???).

    Could it be a leak on the suction side? Maybe...but with the amount of air I'm observing, if there was a leak between the pump and the foot valve, there would be no way the system would hold any pressure. There are times the pump is moving water and there is no air visible in the filter housings, then 10-15 seconds later, ~1 liter of water is displaced by air. If that much air can get in through a leak under vacuum, then what's stopping the tank from bleeding down under 40-50 psi of pressure?
    Last edited by JVance; 12-11-2011 at 07:28 PM.

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    DIYer, not in the trades LLigetfa's Avatar
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    Some people have topside checkvalves and those would prevent a suction side leak from leaking under pressure. If you are sure there is no other checkvalve and it holds under pressure then it's entirely possible the footvalve is not set deep enough and you are overdrawing the well.

    I would set the footvalve lower so that the pump cannot lift as fast from the greater depth when the level drops under heavy draw. I would also raise the min and max on the pressure switch slightly to reduce the GPM the pump produces.

  5. #5
    In the Trades Texas Wellman's Avatar
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    There should be no filters between the pump and tank. Pipe it straight in.

    Install a throttle valve between the pump and tank. Start with the valve wide open (have a pressure gauge at the pump). When you hear the pump "lose out", close the valve back. Close the valve until the pump picks back up. Once the pump picks back up slowly, slowly open the throttle valve until you find the balance.



    Quote Originally Posted by JVance View Post
    I am trying to troubleshoot some issues with the well in our new house (we have a few, but this would seem to be the logical first issue to tackle). We live on a coastal island, have a shallow well (34' deep), Goulds 1HP jet pump (set to 30/50 PSI start/stop pressure) and 120 gallon tank. The pump sucks a fair amount of air, as observed through the clear housings of the filters between the pump and the tank. From what I've read, air is not friendly to a jet pump, but it nonetheless moves enough volume of water and does not lose its prime.

    There is no information scribed for gpm on the placard in the well-head, so I don't know what flow the well is rated; but, I am concerned that this pump may be overdrawing the well. There generally appears to be more air in the filter housings at lower tank PSI (e.g. when the pump is capable of moving more gpm), and less air at higher tank PSI (e.g. when the flow is reduced). Do these observations suggest the pump may be overdrawing the well? If so, would restricting the discharge flow be the solution? What then is a recommended flow restrictor/regulator, aside from partially closing the ball-valve between the pump and tank?

    Thanks in advance for your advice!

  6. #6
    Homeowner JVance's Avatar
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    Quote Originally Posted by Texas Wellman View Post
    There should be no filters between the pump and tank. Pipe it straight in.
    1) I don't want sediment in the tank, 2) the filters are plumbed in parallel so the resistance has been halved, and 3) it's not the cause of the problem.

    Suffice to say, if no filters were plumbed between the pump and the tank, I would not be aware of this problem...


    Install a throttle valve between the pump and tank. Start with the valve wide open (have a pressure gauge at the pump). When you hear the pump "lose out", close the valve back. Close the valve until the pump picks back up. Once the pump picks back up slowly, slowly open the throttle valve until you find the balance.
    Going shopping...

  7. #7
    Homeowner JVance's Avatar
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    Quote Originally Posted by LLigetfa View Post
    Some people have topside checkvalves and those would prevent a suction side leak from leaking under pressure. If you are sure there is no other checkvalve and it holds under pressure then it's entirely possible the footvalve is not set deep enough and you are overdrawing the well.

    I would set the footvalve lower so that the pump cannot lift as fast from the greater depth when the level drops under heavy draw. I would also raise the min and max on the pressure switch slightly to reduce the GPM the pump produces.
    There may be a top-side check valve, but if so, it's under ground somewhere between the well head and the well stub in the garage. At the well head, there is a 2nd pipe with a ball-valve that appears to tee into the well pipe as they go into the ground (I'm assuming this is for inspection/sanitizing). If I open this ball-valve when the tank is under pressure, there is no back-flow of water through this valve. Would this confirm there is a check valve between the pump and well, or does this 2nd pipe not connect to the well pipe (e.g. does it run parallel to the well pipe down the casing)?

  8. #8
    Moderator valveman's Avatar
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    The second pipe is probably making it into a "deep well jet pump". There should be a check valve on that jet assembly where the two pipes go together.

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    DIYer, not in the trades LLigetfa's Avatar
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    If there are two pipes from the well to the pump, it is setup as a deep well pump as Cary said in which case the injector/ejector/eductor is down the well.

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    Moderator valveman's Avatar
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    Quote Originally Posted by LLigetfa View Post
    If there are two pipes from the well to the pump, it is setup as a deep well pump as Cary said in which case the injector/ejector/eductor is down the well.
    Usually yes. But I have seen the ejector placed above ground and a check valve attached before you put a single pipe down the well.

  11. #11
    Homeowner JVance's Avatar
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    There is only one pipe that exits the well head that goes to the pump. The second pipe ends at the top of the well. From what's visible through the open ball-valve of that second pipe, it tees into the well pipe a few inches below the seal.

    Again, I'm assuming the purpose for this second pipe is for inspecting/sanitizing the well. It stops at the well head and doesn't go anywhere; otherwise trying to sanitize a well with a single, glued PVC pipe (and unknown check valves between the pump and well) would be fruitless...
    Last edited by JVance; 12-13-2011 at 02:10 PM.

  12. #12
    Homeowner JVance's Avatar
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    Fortunately, I shut off my pump before leaving home this morning. The pump was running, but the pressure in the tank had not changed for several minutes. The body of the pump was very hot and there was no air in the filters. To check if the pump was moving water, I closed then opened the ball valve between the pump and the tank; it produced no change in tone to indicate that the flow of water had been impeded by the ball-valve: the pump was not pumping any water. (side note: this explains the failure of a few PVC fittings threaded into the pump body; I thought that I had over-torqued them on assembly, but heat likely played a role in the threads failing)

    When I shut the pump off, there was no (audible) back-flow of water from the tank back through the pump and down the well, such as what I hear when there is air in the well pipe. This would seem to indicate that 1) the well pipe was free of air, and 2) I drew down the well far enough that the pump could not draw up the water. I'm beginning to think the root of the problem is that I have a crappy shallow well rated for 5 gpm yield, and a 1HP pump rated for 2-3x that flow. [edit: just got off the phone with the guy that drove this well...symptoms are consistent with too much pump for a low producing well. We may either throttle down the pump or drive another well (or both). They will be out to inspect the well tomorrow.]
    Last edited by JVance; 12-14-2011 at 07:04 AM.

  13. #13
    DIYer, not in the trades LLigetfa's Avatar
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    When you open the well, measure how far down the footvalve is. If you set the footvalve deep enough, the pump will not be able to draw it all the way down to suck air and therefore will become self-regulating. The higher it has to lift the water and the higher the pressure it pumps up to, the lower the GPM.

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    Homeowner JVance's Avatar
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    Quote Originally Posted by LLigetfa View Post
    When you open the well, measure how far down the footvalve is. If you set the footvalve deep enough, the pump will not be able to draw it all the way down to suck air and therefore will become self-regulating. The higher it has to lift the water and the higher the pressure it pumps up to, the lower the GPM.
    The foot valve would appear to be low enough.

  15. #15
    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by JVance View Post
    The foot valve would appear to be low enough.
    Low enough for what? Low enough to overdraw the well? How low is low enough?

    The laws of physics are immutable. You claim your well is 34 - 35 - 36 feet deep. A shallow well pump cannot pump down the water to that depth to suck air.

    http://www.terrylove.com/forums/show...uot-water-from

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