Well pump sizing

Discussion in 'Pumps and Tanks Well Forum & Blog' started by ollllo, Feb 23, 2013.

  1. ollllo

    ollllo New Member

    Messages:
    3
    Location:
    United States
    Hi all new to the forum and hoping that I can get some answers here. I just purchased a piece of land in west Texas. There is a new well on property. Previous owner had a well drilled about two weeks ago.

    Basically all I have is a 5" pvc pipe sticking out of the ground cemented in. Well is 80' deep, surface of the water in the pipe is 46' from the top. So 34' of water in 5" pipe. Well guy says it only produces 5gpm. That seems low to me, but that is what he said and I am in far west Texas.

    I am gonna build a well house and I want to install a pump and pressure tank and possibly a storage tank as well, do to low gpm on well.

    I can install the pump and such I just don't have a clue what size pump and pressure tank I need to supply water to a 2 bedroom one bath cabin/house. Any help from this forum would be appreciated.
  2. VAWellDriller

    VAWellDriller New Member

    Messages:
    170
    Location:
    Richmond, VA
    Buy a 1/2 hp 10 gpm pump, install at approximately 75' depth, put a dole 5 gpm flow restrictor on the inlet side of a 40 gallon bladder tank. That's the cheapest setup, won't over pump the well, and will give you all you need for a cabin.
  3. ollllo

    ollllo New Member

    Messages:
    3
    Location:
    United States
    Thanks VAWellDriller. Talked with an old rancher at work today. He basically told me the same thing. I didn't know you could restrict the outflow of a pump.

    Thanks again
  4. valveman

    valveman Moderator Staff Member

    Messages:
    4,380
    Location:
    Lubbock, Texas
    I would use a CSV1A instead of the Dole valve. The CSV will restrict the flow to matchg the amount being used. So if you only use 5 GPM, the CSV works like a 5 GPM Dole valve. But for short periods of time the CSV will let you have more than 5 GPM when needed, so the shower pressure won't be low. Also with the CSV you can use as small as a 4.5 gallon size tank.
  5. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    3,828
    Location:
    NW Ontario, Canada
    Well guy may be conservative in his estimate or maybe didn't take the time for a thorough test. The well may open up over time and produce more. My well was initially rated as 5 GPM, mainly because that is the minimum needed to get a building permit and financing.

    I agree with valveman WRT to the CSV versus the dole valve. If you find that the well is overdrawn, install a Cycle Sensor.

    http://www.cyclestopvalves.com/prod_sensor.html
  6. VAWellDriller

    VAWellDriller New Member

    Messages:
    170
    Location:
    Richmond, VA
    I like CSV's and install them on about 90% of new residential wells I drill, but I would think twice about installing one when the well is BOTH low yielding AND has a very small amount of storage capacity......in these cases of low yield and low storage, I don't install a system that is capable of overpumping the well.....maybe I'm a little conservative, but I've found that approach to work quite well. I hate cycle sensors and pumtecs....I guess they have their place, but I always thought that some water was better than no water, so if you setup to not overpump the well in the first place, you never face those periods of timeout.
  7. valveman

    valveman Moderator Staff Member

    Messages:
    4,380
    Location:
    Lubbock, Texas
    With a 5 GPM Dole valve, if you are using two, 3 GPM showers at the same time, the pressure gets really low (bad). With a CSV the pump would be producing 6 GPM, so the shower pressure is very good. With a well recovery rate at 5 GPM, and having enough standing water in the well to give 50 gallons of storage, the 6 GPM draw will not pump the well off for 50 minutes. As long as both showers do not run for 50 minutes, the well can keep up.

    Even with a draw of 10 GPM, because of the 50 gallons stored in the well and 5 GPM recovery rate, the well can maintain 10 GPM for 10 minutes. When trying to use 6 or 10 GPM with a 5 GPM Dole valve, the pressure would suuuuck. But with the CSV, the pressure will remain constant and strong. Only if you run two showers for longer than 50 minutes or 10 GPM for longer than 10 minutes would a Cycle Sensor be needed. But if you pump the well dry, the Cycle Sensor will shut off the pump, wait 10 minutes or whatever time was programmed into the Cycle Sensor, then it would restart the pump. This will save the pump and get you back in water as soon as possible.

    The CSV allows you to use the stored water in the well to supply peak demands for short periods of time. The CSV will also act like a Dole valve when you need water for long periods of time, like for sprinklers. Just don’t turn on more than 5 GPM when sprinkling. The Cycle Sensor protects the pump in case you have peak demands for longer than the well can supply.

    I have a well that only produces 9/10’s of a GPM. But there is about 100 gallons of water stored in the well. I use a 10 GPM pump with a CSV and a 4.5 gallon pressure tank. The 100 gallons stored in the well has always handled peak demands, and even when I have a house full of people the well has never pumped dry. I can handle a peak demand of 10 GPM for 10 minutes or a demand of 5 GPM for 24 minutes, even though the well only makes 9/10’s of a GPM.

    Also using a large pressure tank without a CSV, the well can be pumped dry while just filling the pressure tank. If the well was almost empty when you turned off the showers, the water needed to refill the pressure tank could cause the well to go dry before the tank gets refilled. With a CSV, the tank refills at 1 GPM, so the well doesn’t get pumped dry while refilling the pressure tank.

    I would only use a Dole valve if the well were filling a cistern. You would be surprised how much of the time a little water stored in the well can supply peak demand, without needing a cistern and additional booster pump. It just has to be set up to be able to use the well storage for peak demands and not pump dry refilling a pressure tank. (Ie. CSV)
  8. Texas Wellman

    Texas Wellman In the Trades

    Messages:
    522
    Location:
    SE Texas-Coastal
    I have a little different opinion, but here's a method I have found that will work well.

    Get a 1/2 HP convertible jet pump, like the goulds J series. Put a twin-line jet in the well, at least 20-30 ft under the water. Install a tail-pipe under the jet where the footvalve would normally go (with a footvalve on the end) about 34' long. The jet pump can never pump more than the well will produce.

    The tail-pipe will draw the water without penalty until the level starts to drop. Once the water level gets to about 28-30 ft (below the jet) the pump will only be able to draw what the well is producing. Your pump will never run out of water and it will be able to pump more water and then taper off as the level falls. You should be able to pump about 8-12 GPM depending on the water level and pump.

    If you need more info I'll be glad to help.
  9. VAWellDriller

    VAWellDriller New Member

    Messages:
    170
    Location:
    Richmond, VA
    Texas ---I like that a lot....well thought out!
  10. valveman

    valveman Moderator Staff Member

    Messages:
    4,380
    Location:
    Lubbock, Texas
    That is a good way to keep a customer from over pumping a well. But with a static water level of 46’, a pumping level of 70’, a ½ HP jet will only do 4.7 GPM at 30 PSI. That pretty low pressure and volume.

    Just because the well is a low producer doesn’t mean you can’t have good pressure. The system I described will give you full pressure and volume until the well really is dry. I find that most times people will be finished using water before the well runs dry, and they have good pressure until the minute they turn off the faucets. And a submersible is much less trouble compared to a jet pump.

    There are a lot of ways to skin a cat though.
  11. Texas Wellman

    Texas Wellman In the Trades

    Messages:
    522
    Location:
    SE Texas-Coastal
    It's a cabin. At 50' the 1/2 horse will do about 8 gpm, as the water drops to 70 it will still do about 5 gpm. Plenty. If you need more water just buy a bigger pump or go to a two-stage. It's also probably the cheapest option out there.

    The 1-HP J+ would do a good job for about $150-200 more than the 1/2 HP.
  12. valveman

    valveman Moderator Staff Member

    Messages:
    4,380
    Location:
    Lubbock, Texas
    I can see using a larger pump. The problem in my head with this set up is that water can only be drawn from a max of about 24’. When the water level pulls down to that depth, the pump stops pumping, gets hot, and melts down. At the very least, low NPSH could cause damage or just loss of prime from cavitations.
  13. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    3,828
    Location:
    NW Ontario, Canada
    TW is banking on the well not running dry, and that when the level drops to the max a jet pump can pull from, that it will still produce enough to prevent a melt-down.
  14. Texas Wellman

    Texas Wellman In the Trades

    Messages:
    522
    Location:
    SE Texas-Coastal
    I'm not sure if we're on the same page or not. The pump is a deep-well style. Put the jet in the well about 50-60', install a tail-pipe under the jet about 34'. If the well draws down it will only draw down to a maxiumum of 34' (really less). Once the well draws down below the jet the pump loses efficiency until the output of the well matches the draw of the pump. If the well only makes one GPM, the pump will only pump one GPM. If it makes 5 GPM, the pump will pump 5GPM. It's about as foolproof as you can get on a slow producer because the pump will eventually even out with the well production.

    BTW I've seen this set-up work many, many times with a packer style jet. With a packer style the tail-pipe is effectively not needed. I've seen wells that only make 1-2 GPM work fine this way.

  15. craigpump

    craigpump Member

    Messages:
    854
    Location:
    ct
    Your right TW that is a good way to do it, my father used to do tons of jet installations just like that when I was kid.
  16. valveman

    valveman Moderator Staff Member

    Messages:
    4,380
    Location:
    Lubbock, Texas
    I guess the deep well style jet is still circulating enough water through the jet to prevent cavitations? I know with a single pipe jet or and end suction centrifugal that restricting the suction can cause damage from cavitations.
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