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  1. #1
    Gold Member
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    Apr 2012
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    Pomona Park Florida
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    Yanmar EX450

    Default Another well question

    I have a 4" steel cased well towards the back of my property. It evidenly hasn't been used in a number of years. There was a mobile home there at one time, the well is on my side, the septic system on the neighbors. I'd like to use the well for garden irrigation, but it's 500 feet from my nearest electicity, and there is no pump in the well. I just dropped a string and a weight, and the water table is at 16', and we are really in a dry season. I have a good Multiquip 3" trash pump powered by a 8hp Honda. Specs say the pump will handle 25' of suction lift. Talked to a local well driller the other day, and he advised that if the water table is 16-17' it would work fine. I have no idea how deep the well is.
    Here come the questions:
    If I put a drop pipe down in the well and plumb the pump to it using PVC and aflexible piece between the pump and the plastic, will this pump enough water for irrigation? If so, should that drop pipe be 3" or 2" ? ID of the casing is 4". How long does that drop pipe need to be? Let's say I drop 20' of 2" pipe in the well, (or would 3" be better?) can I use the 20' suction hose that fits the pump onto that, or would that be too much head?

  2. #2
    Platinum Member
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    Default Re: Another well question

    If your pump will do 25 ft lift then that it is was it can do. If the water drops below 25ft during your draw down then the pump will probably not be able to pull properly. What you don't know is, as you stated, the depth of the well, also you know the static water level is at 16' but the dynamic level may vary greatly from that level. What is your Multiquip pump gpm capability? Most pumps of that nature are not adjustable therefore it will draw water at the spec'ed gpm. If the well recharge rate is less than that, then the dynamic water level will drop. If it drops below the head capability of the pump it will cavitate. Your pump may very well function at more than 25' of lift but not at spec levels. It may also be harder on the pump and will long term damage it.

    For the cost involved I would get a section of drop pipe and measure the flow(could just use the pumps spec flow) for a period of time, say 5-10 minutes and then measure the water level in the well. Using a 5 gal water bucket and measuring how long it takes to fill and then doing the math would work but has inherent errors in it as well. Do this at 5-10 minute intervals for however long you would use it for irrigation and determine the wells capacity to stay up with the draw down. Watching it as frequently as I recommend will keep the pump from cavitating and burning up if the water level drops below the pumps lift capability.

  3. #3
    Gold Member
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    Apr 2012
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    Pomona Park Florida
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    Yanmar EX450

    Default Re: Another well question

    Pump is a model QP3TH, rated @396gpm, @ 3600rpm. 25'lift, 95' head max pressure 41.1psi.
    Let's talk about draw down. Not far from the well, is a drainage ditch with just a little water in it. I'm assuming that the water level in the ditch and the water level in the well is the water table level. Assuming that the pump will actually move 300 gpm, and knowing that water seeks it's own level, how much draw down would happen in a 4" pipe?

  4. #4
    Elite Member
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    Apr 2000
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    3,675
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    Grayson County, TX
    Tractor
    Kubota B2710

    Default Re: Another well question

    I would have to be one heck of a well to produce 396gpm.
    Alan L., TX
    South of Bugtussle
    North of Mustang
    On the banks of Buck Creek
    We don't rent pigs.

  5. #5
    Gold Member
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    Apr 2012
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    Pomona Park Florida
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    Yanmar EX450

    Default Re: Another well question

    As you can probably tell from my two previous posts, I know very little about wells. I certainly don't need 300 gpm to irrigate my sweet corn. I just assumed that you throttled the pump speed back to get what was a reasonable amount of flow.

  6. #6
    Veteran Member hunterridgefarm's Avatar
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    Jul 2005
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    Western NC
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    Kubota L3130DT, Kubota L185DT, JD LX277

    Default Re: Another well question

    You can check the deth of the well by continuing to lower the string with the weight until it hits the bottom of the well. If the water level is 16 ft from the top of the casing mark off the 16 ft and measure the string. A 6 inch casing has about 1 and 1/2 gallons of water per foot so 100 foot of casing would be 150 gallons. A 4" casing would most likely be around 1 gallon +/-.

    I use a gas pump for irrigation but not from a well. Pumps have more pushing power than pulling. My pump also has 25'lift of suction but I am not certain that is 25 foot of vertical lift.

    You could drop the suction hose down the pipe and fill the hose with water before connecting to the pump, even if your pump is self priming this would aid in getting the flow started. I would then have a short section of discharge hose and just see how long it would pump until the water table drops below the suction hose. You can quickly stop the pump once the flow stops, this way you won't burn the pump up. If your pump has a throttle, once the flow starts you can run it half to 3/4 throttle to slow the GPH down.

    My pump has 350 feet to pump/push the water before it gets to my irrigation lines. From this point my sprinkler heads are 75' to 125' away from my main 2" line. I run 5-6 sprinkler heads at 3/4 throttle with a 5hp pump.

    Here is a couple of pictures of how I T-ed of the main line.
    Attached Thumbnails Attached Thumbnails -t-2-jpg   -t-1-jpg  
    I suffer from MPD...Multiple Project Disorder

  7. #7
    Veteran Member
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    Default Re: Another well question

    To wrap up some of the replys and add a few.

    1. Determine the depth of the well and install your footvalve about 6' above the bottom. The footvalve goes on the bottom of the drop and is a checkvalve - only allows the water to flow one direction, up the pipe.

    2. Install pump and prime - that requires fillin the entire drop pipe and pump with water - usually done through a pipe plug on the pump outlet pipe. All air must be out of the the pump and pipe. I usuially spin the pump a turn or two to be sure there is no air bubble in it.

    3. Don't cound on a 26' suction - that is based at sea level and would require a pump and all intake plumbing to be in perfect condition.

    4. You say it is a trash pump - those usually move volume but don't produce much pressure. Is there a rating for the pumps "head"? YOu can determine what pressure the pump develops from that. I used to have the conversion formula in my head but it seems to have disappeared this morning.

    5. If you are using sprinklers, 30psi is about the lowest pressure you can use for reliable impulse sprinklers IME.

    Harry K

  8. #8
    Silver Member
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    Jun 2012
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    Mid, Michigan
    Tractor
    Kubota L3540 w/ LA514 FEL, 66" QA Bucket, 48" QA Forks, 7' RB, 18" Ripper, Ferris IS2000z ZTR

    Default Re: Another well question

    One random bit of trivia on wells. The larger your reservoir tank is in your house, the longer your well pump will last. Same holds true with upsizing the motor by a 1/4 hp. If they say 1/2 will do, pick the 3/4HP. Parents well pump lasted 34 years before failing. Otherwise these may only last 12-15 years. It's really not the running of a well pump that does it in but the starting up.

  9. #9
    Platinum Member
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    Piedmont Triad, NC
    Tractor
    Didn't intend to have a Deere fleet - it just happened 310C, F915 & 5200

    Default Re: Another well question

    Pump flow ratings are based on some set of conditions. Suction at 25 below the pump will decrease the flow, pressure at the outlet will decrease the flow. Either way, you will not get 396 gpm from your pump.

  10. #10
    Super Star Member Egon's Avatar
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    Nova Scotia, Canada

    Default Re: Another well question

    Quote Originally Posted by hosspuller View Post
    Pump flow ratings are based on some set of conditions. Suction at 25 below the pump will decrease the flow, pressure at the outlet will decrease the flow. Either way, you will not get 396 gpm from your pump.
    Yes, and you only have maybe a little more than five feet for drawdown before you lose suction. The twenty five feet will apply to perfect conditions which usually do not happen.

    Don't spend a lot of money on the trash pump hookup!
    Egon
    50 years behind the times
    Livin in a
    Worn out skin bag filled with rattlin bones

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