Well Water VOlume

Discussion in 'Irrigation' started by jkinchla, Sep 18, 2001.

  1. jkinchla

    jkinchla LawnSite Member
    from MA
    Messages: 74

    I have a customer who installed a new 0.75 HP submersed pump in a shallow well. The well guy promised 12 GPM at 50 psi for the irrigation system. Now that the pump has been installed, we only have 7 gpm at 40 psi, but I am testing at the spigot that is closest to the water flow into the house.

    I'm sure the well guy will say that the spigot is reduced, therefore we will have less water. However, the same spigot produced 5-6 gpm at 40 psi before the pump was changed to the new one. Thus, I don't believe that the well guy is delivering as promised. Does anybody know how much more water I can expect from the well once I am going straight off a 1" line into the irrigation system? Also, I need to put on a filter and I know that will reduce flow - but by how much? I need 10 GPM at 40 PSI to be comfortable.

    Thanks for your help!
  2. HBFOXJr

    HBFOXJr LawnSite Bronze Member
    Messages: 1,712

    Get the make and model of the pump along with the depth the pump the pump is below the surface. Consult with a supply house for the pump or manufacturer direct.

    If the pressure switch is set for 20psi on and 40 psi off you may not get an accurate flow test. I've seen it a million times. Your only running on tank pressure reserve if those are the settings.

    Gotta get the pump running continously to really check it and you should get somewhat close on a bibb. Set the pressure switch to 45-65 and you'll do better if the pump guy is reliable.

    A good Meyers or Goulds 3/4 horse will do 12 gpm if not real deep. Maybe 15 gpm if shallow in well.
  3. greasemonkey

    greasemonkey LawnSite Member
    Messages: 57

    well, I don't think that 10 gpm @ 40 psi is unreasonable, but to be sure you really need to do the math. Around here when we do a well system, we ask that the customer supply a copy of the well paperwork that they're required to submit to the local authorities (I don't know which ones). It gives info like how deep the pump is and the drawdown depth and other info that will help us to figure out how much water we can get. We also look at how long, and what size the pipe is running from the well head to the connection point. you also really need to pay attention to the pressure switch. If it's set to cut in @ 20 psi and out @ 40 than you're never going to know how much water you can really get. There's two screws in the pressure switch (if you take the cover off the pressure switch, there's usually a little sticker that tells you wich one is which), one that raises both the cut in and cut out pressure, never mess w/ this one b/c the cut in pressure has to be the same as the pressure tank's pre-charge pressure. The other screw raises the cut-out pressure only and is the one you want to adjust. make sure its set to cut out above the opperating pressure for your system. If it isn't than the pump will cycle excessivley and you'll get erratic watering. There's usually a boiler drain right near the pressure tank that you can hook a pressure gague up to if there isn't one installed in the tank "T"

  4. HBFOXJr

    HBFOXJr LawnSite Bronze Member
    Messages: 1,712

    Every pump manufacturer publishes a pump curve for each pump. It is a graph showing pressure on one axis and volume on the other. They publish them for several depths that the pump is best designed to work in.

    With accurate depth and model info you don't even need to do a flow test. The manufacturers chart will tell you what you need to know.

    A flow test is needed when lacking any information about the well and pump.

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