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Thread: Pump/driven well question

  1. #1
    DIY Junior Member drvnwell's Avatar
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    Default Pump/driven well question

    I recently punched a driven well to 41 feet with 2" galvanized pipe with 5' well point. My water table is at 19'(so 22' in the water). I have a question about pump/pipe sizing. I am going to use a 1hp shallow well pump that is rated at 15gpm. The pump inlet is sized at 1 1/4". Will there be enough suction from the pump if I reduce the 2" pipe to 1 1/4" at ground level? If this won't work, my other idea is to use a 1 1/4" pvc well point placed inside the 2" casing. I am concerned, though, that the draw will exceed the water that is replenished into the 2" pipe. Any thoughts would be appreciated.

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    Sprinkler Guy Wet_Boots's Avatar
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    Have you tried filling the point from a hose? There is supposed to be an equivalence between the flow of water you can pour into a point and the flow of water you can draw from it.

    Also, there is the matter of "developing" the point, to get fine particles away from clogging the screening. I had points where the soil was not even close to ideal sandy conditions, and I would occasionally have to spend time clearing the screen, by forcing water in, then pumping it out, and repeating the process for as long as it took for particles to stop accumulating in the 100-mesh strainer I had installed in the pump output.

    A water table at the 20-foot mark may limit what you can draw, using a shallow-well jet pump. Invest in a deep-well convertible jet pump, with a packer ejector assembly in the well, and you get past the depth limitations of the shallow-well jet pumps.

    By the way, what were you using to drive the well point?

  3. #3
    DIY Junior Member drvnwell's Avatar
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    After the point was driven, I flushed it with a hose. I could hear the water down to about 8-10 feet, but it didn't get any higher. I also back flushed the point with a clog buster for about 40 minutes. I had access to a 2" gas pump that was hooked up and run for about 25 minutes. After about 15 minutes the water ran relatively clear. It was pumping about 4gpm.

    I initially tried to wash the well with 2" pvc pipe. I got down to about 10' when I hit gravel. After more research I purchased a 6" auger and augered a hole down to the water table(19'). I was unable to go deeper as the sand was caving in on itself. I then proceeded by driving a well point another 21' using a modified post hole driver.

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    Well Drilling/Service justwater's Avatar
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    if you want to try the shallow setup... casing being 2" and 40+ feet is nice, just drop 30' of 1-1/4" pvc down the well with foot valve on bottom, plumb it into the pump. i would recommend a quality pump, dont go with a plastic cheapo. shallow pumps cant pull water deeper than 25, so it will never suck air having 30' of drop pipe. its only pump what the well will yield, so the garden hose test wetboots suggested is your next step imo.

    we were typing at the same time, so scratch my last sentence. the shallow well pump should work. its much less of a pita than the deepwell setup.. especially a couple years down the road.

    if you had good sand at 19', why didnt you start the screen there? im not a shallow sand well guy, never done one.
    Last edited by justwater; 10-09-2013 at 11:12 AM.

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    DIY Junior Member drvnwell's Avatar
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    My hole was augered to the water table(19'). I then dropped the well point in and went another 21'.

    So that is my plan. I will drop 1 1/4 inch pipe 30+ feet into the 2 inch and see what kind of flow I get. Two other questions:

    Is a foot valve preferred over a flow valve? If I have a flow valve near the pump I will be able to prime the supply line below the flow valve. I wouldn't be able to with a foot valve.

    Should the 1 1/4 inch pipe be sealed at the top of the 2 inch pipe?

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    DIY Senior Member Reach4's Avatar
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    Just a comment... may be too obvious. Mount the pump, and the pipe, to the pump as low as practical. If you raise the pump or pipe 2 feet higher, that is 2 feet less depth that you will be able to pump from.

    I am thinking that they will suggest sealing against dirt but to not seal against air. I am not sure.

    Also note that at higher altitudes, you will not be able to pump from as deep, if I understand correctly. I think shallow well pump depends on the atmospheric pressure to push the water up. That is not quite the case; it is the fact that at very low absolute pressures, water boils. But since the boiling point of water drops to 59F at 0.246 PSIA (fairly close to zero), comparing the absolute atmospheric pressure gives a close approximation. Here is a graph: What this says to me is that at Elevation AMSL 5,355 ft / 1,632 m -- the altitude of ABQ -- you could only pump from about 85% as deep as somebody in Florida.
    Last edited by Reach4; 10-09-2013 at 01:09 PM.

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    Sprinkler Guy Wet_Boots's Avatar
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    A foot valve is better than a check valve at the pump, for your drop pipe idea. You need to have a shut-off valve on the pump output, so you can open it gradually. There's a real possibility that you'll encounter cavitation with a wide-open output.

    What kind of variation is there in the water table level? A few feet deeper than 20, and a shallow-well pump won't function under any circumstances. Even as it is, a deep-well convertible with an injector assembly in the well is probably a better performer.

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    Well Drilling/Service justwater's Avatar
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    no need for shutoff on a shallow pump discharge as the pump should not cavitate.. doesnt need backpressure like a deewell jet pump. it will pull whatever water the well will allow with water level holding no lower than the ~25' mark. i do agree that the deepwell jet pump could likely outperform (so long as the well would give it), but if the gas pump seemed to work fine for their needs i would go with the shallow pump. deepwell jet pumps are a pain in 2" steel wells.. especially down the road.

    like reach said, seal the drop pipe to the top from dirt and critters.. airtight not necessary. and any more than 30' of drop pipe is just wasting money, remember pump cant pull deeper than ~25. hope it works out for you, good luck with it.

    **oh yea, with foot valve you should be able to fill from pumps discharge until the pump and drop pipe is completely full. foot valve is the way to go.. imo a 1" one. 1-1/4" foot valves barely fit. also sch. 40 pvc in 1-1/4 will be a tight fit at the bell end, i'd probably use 1 joint sch 20 with the narrower bell end on bottom with foot attached, then glue 10' of sch 40 into it coming out of the well... so you got wiggle room. of course i'm assuming you can get ahold of 20' sections with bell ends... if not i'd either find a thin coupling or use 1" sch 20. the tight fits arent a big deal initially but sometimes hard to get it all back out after being in a while.
    Last edited by justwater; 10-09-2013 at 05:31 PM.

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    DIY Junior Member drvnwell's Avatar
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    Thanks for the feedback guys!

    The suggestion to downsize to a 1 inch foot valve is a good idea. Will the 1 inch restrict the flow very much? My 1 1/4 inch pipe is assembled with internal slip couplings so it fits the 2" with room to spare. Another question comes to mind now that I've taken the recommendation to use a foot valve and that is, how is the supply line drained for the winter months?

    Wet_Boots, the Rio Grande river is less that 1/2 mile to my west. I don't think that the well will draw down too much. My biggest concern would be that the casing doesn't replenish as fast as it is being pumped out. Time will tell.

    I appreciate the knowledge.

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    Sprinkler Guy Wet_Boots's Avatar
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    If you were needing high pressure from your pump output, the shallow-well pump with a 20-foot lift, plus whatever your altitude factors in, along with suction-pipe losses, might disappoint you. Depending on what's available in the way of jet pumps, you might be able to cover your bases with a package deal, like some I've seen, that include a convertible jet pump, along with a bolt-on injector for shallow well use. The bolt-on injector isn't useful in a 2-inch pipe, but the convertible pump would be ready to work with a packer-type ejector that fits the 2-inch pipe.

  11. #11
    DIY Junior Member drvnwell's Avatar
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    Wet_Boots,

    That is my plan B if this doesn't work out. I have a shallow well pump already available so I am going to hook it up and see what I get. The jet pumps are supposed to be good down to 86 feet. I am planning on using the h20 for irrigation supplied by drip hose. If my flow isn't sufficient I will make the switch.

  12. #12
    Sprinkler Guy Wet_Boots's Avatar
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    Drip isn't too demanding, so far as pressure goes. It's the rotor heads that need higher pressure. You're still close to being up against physical limits, depending on the exact amount of lift. Near to sea level, a pump can start cavitation around 25 feet of suction vacuum. Avoid any flow restrictions in the suction line, short of the necessary foot valve.

    In fact, strictly for shallow well jet pump use, you could probably skip the drop pipe and foot valve, and gain a few feet of water leeway. The drop pipe and foot valve does nothing to cancel out the physical limitations of water lift. Only a deep-well injector accomplishes that. Expect to spend awhile on the priming, for which the outlet shutoff valve will be invaluable, keeping it near to closed until the prime takes hold.

    As for wintertime, you only need to top the point with a tee and a plug.

  13. #13
    DIY Junior Member drvnwell's Avatar
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    So I got everything set up with a 1hp shallow well pump and 30' drop pipe with a foot valve. Everything is working great. I am getting about 4 1/2 gallons/minute. I let it run for over three hours and it just chugged away with no disruption in flow. I wanted to say thanks to everyone for the advice. You guys made my life much easier than it could have been had I not pursued the knowledge this board has to offer. Thanks!!

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