10gpm or 7gpm pump ?

Discussion in 'Pumps and Tanks Well Forum & Blog' started by Arky217, Oct 7, 2013.

  1. Arky217

    Arky217 New Member

    Messages:
    43
    Location:
    Arkansas
    New well; recovery rate, according to driller, is 5gpm. 115' deep, 50' static water level.
    Going with a Gould 1/2hp, 230V, 2 wire submersible pump.
    Pump will hang 100' deep; 60' from well to pressure tank at house.

    1st pump: Gould 10GS05422C, 10gpm, recommended range 3-16gpm.
    (Flowchart shows maximum pumping depth at 3gpm to be 210')
    At 100' depth, flowchart shows 12gpm.
    However, the performance chart for 100' depth at 30 to 50psi
    shows 10.5gpm at 30psi, 7.5gpm at 40psi, and a blank at 50psi.

    2nd pump: Gould 7GS05422C, 7gpm, recommended range 1.5 to 10gpm.
    (Flowchart shows maximum pumping depth at 1.5gpm to be 290')
    At 100' depth, flowchart shows 11gpm (which is slightly out of the recommended range).
    Performance chart for 100' depth at 30 to 50psi
    shows 9.7gpm at 30psi, 8.7gpm at 40psi, and 7.6gpm at 50psi.

    Not sure why the 1st pump is slightly out of the performance chart,
    but interpolating from the other figures, it would seem that at 50psi, the gpm would be
    between 4 and 5gpm, still within the recommended range.

    I'm thinking that the 1st pump would be sufficient. (The 1st pump is also $54 cheaper)

    The question is, which pump should I get and why ?

    Thanks,
    Arky
  2. Texas Wellman

    Texas Wellman In the Trades

    Messages:
    524
    Location:
    SE Texas-Coastal
    Are you remembering to add in your pressure to the head chart? 50 psi = 115 ft of head + the 100' of static once the well draws down. You need to be looking at the 200 ft of head line, not the 100 ft line.

    The 7 GPM pump is more expensive because it has more stages. You have a little bit of a tricky situation because your well is going to draw down once you start using water. The 10 GPM pump will give you better performance at first but will drop off once the well draws down to 100'. The 7 gpm won't quite give you as much at first but as the well draws it will beat the other pump.

    I might go with the 10 GS because at some point you're going to run out of water in the well. Having a pump that won't beat the well output would be a plus in this situation. The 7 GPM will outpump the well eventually and you could damage the pump.

    If I were you I would also look at a system to detect if the pump goes dry to kick it out to protect it.

    Good luck.

  3. valveman

    valveman Moderator Staff Member

    Messages:
    4,418
    Location:
    Lubbock, Texas
    You didn’t say what size casing you have, but 65’ of standing water is like having 100 gallons of water in storage. I would set the pump at 112’, and use a 10 GPM, 3/4HP pump. It can pump 10 GPM at 50 PSI until the water level drops to 112’. This way you can utilize the 100 gallons stored in the well and not be lacking for water in the house.

    You can use 10 GPM for 10 minutes, or 7 GPM for more than 15 minutes, before you pull the well down. This should be long enough to handle peak loads in the house.

    A CSV would turn that pump into a variable flow pump. So when you are only using a 3 GPM shower, the CSV makes it a 3 GPM pump and you won’t pump the well down. But when you need to run two or more showers at the same time, the CSV will let you do that until the storage in the well is depleted. http://www.cyclestopvalves.com/simple/home.php

    You will need a dry well protection relay like the Cycle Sensor just incase you use up all the water in the well. http://www.cyclestopvalves.com/prod_sensor.html
  4. Arky217

    Arky217 New Member

    Messages:
    43
    Location:
    Arkansas
    Thanks for the replies.
    I should have added that the well diameter is 6".
    Also, I will be using a 44 gal. pressure tank, drawdown at 30-50psi is 15 gal.
    Another thing, the useage will be minimal, one bath, just 2 people, no continuous usage such as lawn watering, etc.
    Even though I plan on throttling the usage with a valve to 5gpm at the output of the pressure tank,
    I expect that I won't ever even come close to pumping dry.
    That is unless the recovery rate of the well drops or the static water level goes way down,
    which I don't anticipate since the well was drilled in the dryest part of summer.

    With the mentioned above, is there any valid reason not to use pump number 1 ?

    Thanks again,
    Arky
  5. VAWellDriller

    VAWellDriller Member

    Messages:
    170
    Location:
    Richmond, VA
  6. valveman

    valveman Moderator Staff Member

    Messages:
    4,418
    Location:
    Lubbock, Texas
    Restricting the flow to 5 GPM before or after the pressure tank will leave you out of pressure in the house if you try to run the equivalent of two, 3 GPM showers at the same time. With a 5 GPM recovery and 100 gallons stored in the well, you could run 6 GPM to showers for at least 100 minutes, so I wouldn’t use a restrictor. I would just use a Cycle Sensor to protect the pump and shut it down if you do use more water than the well can produce.

    Also the tank that holds 15 gallons can be a problem. If you have used enough water to almost deplete the well just as you shut off the faucets, the well maybe pumped dry while trying to replenish the 15 gallons in the tank before the pump can shut off. A CSV will restrict the pump to 1 GPM when refilling the tank, so it won’t pump the well dry during tank refill. The CSV will work fine with the 44 gallon (15 gal draw) tank, but with the CSV a 4.5 gallon size tank is really all you need.
  7. masterpumpman

    masterpumpman New Member

    Messages:
    729
    Location:
    Virginia Beach, VA
  8. Arky217

    Arky217 New Member

    Messages:
    43
    Location:
    Arkansas
    Thanks again for the replies; after reading them, a couple more questions come to mind.

    About a throttling valve, I see now the advantage of having it on the input to the tank
    to keep the pump from pumping faster than the well's recovery rate.
    (I mentioned on the tank's output because that was the driller's advice.)
    Are there any other reasons to have it on the tank's input rather than the output ?
    (other than water usage limited to 5gpm, which won't matter in my case)
    Other than limiting water usage, is there any downside to using a throttling valve ?

    About the larger tank vs a csv valve.
    I can certainly see the advantage of the csv under typical home water usage for the average family
    which may include long or simultaneous showers, lawn watering, car washing, etc.
    However, with my conservative water usage, I don't think the advantage would come into play very often.
    The larger tank, however, would limit the pump start/stop cycles quite a bit.
    For instance, if the tank were full (15 gal of water), we could probably take two showers and flush the commode without the pump starting.
    Actually, with 50 feet of water from the static level to the pump ( about 70 gal), I probably won't use 70 gal all day.
    I've been on city water where I currently live for the last 10 years and my monthly usage is around 1500 gal (50gal/day).

    Even taking the above in consideration, I guess a throttling valve at the tank's input would still be a good idea
    just in case I ever had an occasion to need to use a lot of water at once (fire or such).

    So, considering the above info, is there really any reason for me to get the more expensive ($54 more) pump ?

    Thanks,
    Arky
  9. VAWellDriller

    VAWellDriller Member

    Messages:
    170
    Location:
    Richmond, VA
    The reason to put the throttling valve on the input is so you can have instant demands over 5 gpm in the house, that are covered by the drawdown of the tank. IE...flush the toilet while someone is in the shower...the flow might be 6-7 gpm while the toilet is re-filling. The disadvantage of installing a throttling valve is that you won't utilize the storage capacity of the well. If you're only going to use 50 gal/day, you can save your money on the pump and probably don't need the throttling valve either.
Similar Threads: 10gpm 7gpm
Forum Title Date
Pumps and Tanks Well Forum & Blog Berkeley well pump 3/4 10gpm pump Aug 4, 2008
Pumps and Tanks Well Forum & Blog $880 for Redjacket 1HP 7GPM pump? Jun 1, 2007

Share This Page