Setup evaluation for low yield deep well

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

  1. ChasM

    ChasM New Member

    Messages:
    2
    Location:
    Illinois
    Hi all - We would greatly appreciate any feedback on the following proposed well setup for a household of 2 having two bathrooms. We currently use about 125 gallon per day. Mainly we would like to know if this is a good setup for our situation but would welcome any suggestions to improve the overall design. Thanks in advance!

    The Well:

    500' - 6" diameter. The approximate yield is only .75 gpm with a 45' static water level.

    Proposed setup:

    A two wire 1-1/2 hp - 10 gpm Grunfos pump with a pumptec for protection. The pump is to be set at 440' deep using 10 gauge wire that will have a total run of 500' to the service box. The drop pipe is Schedule 80 PVC with brass couplings. The pressure tank has a true 25 gallon draw down at 30-50 psi. The tank will be located in a basement 40 feet from the well.
  2. valveman

    valveman Moderator Staff Member

    Messages:
    4,586
    Location:
    Lubbock, Texas
    Ok .75 GPM is 1,000 gallons per day, and the well should store close to 600 gallons. So I don’t see any problem with using 125 gallons per day, or even up to 1,000 gallons per day. I think you would like a 40/60 pressure switch setting better than 30/50. I would prefer a Cycle Sensor to a Pumptec, but what you are proposing will work.
  3. VAWellDriller

    VAWellDriller Member

    Messages:
    171
    Location:
    Richmond, VA
    Wire size is a little under for the length run you have proposed... Also, lots of people do it in this situation, but because of the high static, this pump will be starting with lots of upthrust way off the right of its curve. If its only two people and two bathrooms, you would have way more than enough by setting a 10 gpm 1 hp pump at 300' and you would be running the pump MORE along its designed head conditions. Because of the low yield, you will still need a device to protect against running pump dry.
  4. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,185
    Location:
    NW Ontario, Canada
    Smaller wire would soften the start a little. Starting against 40 PSI instead of 30 would help too. A CSV would also soften the start.
  5. VAWellDriller

    VAWellDriller Member

    Messages:
    171
    Location:
    Richmond, VA
    Maybe Valveman can correct me, but I don't think the csv will help with softening start to reduce upthurst.....the valve should be wide open when pump starts, flow will be wide open, and csv won't start to restrict until set downstream pressue is reached.

    I would put a 1hp, 10, a csv, and a 40/60 switch, save on the pipe, wire, pump, and energy.
  6. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,185
    Location:
    NW Ontario, Canada
    I was basing it on what valveman said in the past.
    http://www.terrylove.com/forums/showthread.php?45084-Pressure-tank&p=333632&viewfull=1#post333632
  7. valveman

    valveman Moderator Staff Member

    Messages:
    4,586
    Location:
    Lubbock, Texas
    I looked at those things as well. 480’ is max for that size wire with a 1.5 HP pump. But I agree with LL that, “the longest length of the smallest wire permissible will deliver a reduced voltage soft start”. So I would rather use 500’ of #10 wire than to step up to #8 and loose the soft start.

    I also agree with VA that the smaller pump will have less upthrust. But the 1 HP pump would only pump 50 PSI and about 5 GPM from 275’. That will reduce the stored water available from 600 gallons to 345 gallons. This still maybe enough to supply the house, but as the well production decreases over time, many people have to lower the pump at a later date. So I like to start off that way and not have to lower things later.

    A CSV can eliminate upthrust. You just need to use a small tank, like the 4.5 gallon size, and set the CSV the same as the start up pressure. That way as long as you don’t open up more water than say 10 GPM, the CSV acts like a 10 GPM Dole valve and holds enough backpressure on the pump to prevent upthrust.

    However, with the 1.5 HP pump, static of 45’, and a CSV setting of 40 PSI, there will be 228 PSI backpressure and 188 PSI of differential across the CSV. To handle differential pressure that high we would use two of the CSV1A valves in series. The first CSV would be set at about 130 PSI, and the second CSV would be set at the 40 PSI needed for the house. This way both CSV’s have less than 100 PSI differential and will last a long time. The friction loss of two CSV1A valves will also help prevent upthrust at wide open flow if needed.

    I also prefer the small pressure tank on weak producing wells. Many times people will use up the 345 or 600 gallons stored in the well just about the time they shut off all the faucets. Then the well pumps dry while trying to refill the 25 gallons in a large tank, because there is not 25 gallons left in the well. A low pressure safety switch will not catch this problem and the pump will melt down. With a CSV filling a small tank at 1 GPM, you won’t pump the well dry refilling the tank.

    I also agree you need a Dry Well protection device. I prefer the Cycle Sensor over the Pumptec for these situations. With a CSV or a Dole valve on the pump, the amps fluctuate so much that the pumptec thinks you are out of water, just from the normal amp drop that happens when restricting the pumps flow with a valve. The Cycle Sensor can show you the lowest amps produced while the pump is restricted to 1 GPM, then you can set it just lower than that and still be protected from an actual dry well condition.

    I know you would like the constant pressure from a CSV compared to the pressure constantly changing from 40 to 60 as you use water. With less than 600 gallons used per day, the difference in power consumption between a 1 HP and a 1.5 HP will be less than a couple of bucks per month.

    Or you can put in a 10 GPM Dole vale to limit the upthrust and let it cycle on and off with an 80 gallon tank that holds 25 gallons of water. You will just see the pressure going up and down between 40 and 60 anytime you are using water, and you have a possibility of pumping the well dry while the large tank is refilling.
  8. ChasM

    ChasM New Member

    Messages:
    2
    Location:
    Illinois
    Thanks everyone for the replies. They were exactly what I was looking for. I will discuss with my installer your suggestions and let you know the outcome.
  9. VAWellDriller

    VAWellDriller Member

    Messages:
    171
    Location:
    Richmond, VA
    I would generally agree with longest run of smallest wire, but I also like to stay within specs and meet code....in this case and most others you don't have to increase the whole run to do it correct....just bump up one run to #8, like the house to the wellhead.
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