Rural Water Systems – Pumps

Now that you found water on your property, you’ll have to bring it to the surface.

If the water level is 30 feet down or less you can install a pump at grade.  This would also apply to water drafted out of a spring or pond.  Keep in mind that surface water is more susceptible to contamination than ground water.

A surface-mounted pump should be self-priming, which means it can draw water from the source even if the suction line is empty.

If the water level is below 30 feet, the pump will have to go down hole.  It has to do three things:

  • Lift water to the surface
  • Push it into the pressure tank(s)
  • Overcome friction in the discharge piping

Suppose you drilled your well to 480 feet.  You hit water at 420 feet and the static water level is at 360 feet.

You don’t want to install the pump at the bottom of the well.  Leave some room for accumulation of silt and sediment.  At least 20 feet.  That puts the pump at 460 feet.  Although the water level is 100 feet higher, the worst case is when you pull water too fast and drop the level down to the pump.

This brings up the concept of recharge rate.  Water enters the well through perforations in the casing.  You don’t want to draw water out faster than it flows in.  At least not for long.  Running a pump dry will destroy it.

Your driller can perform a test to determine the recharge rate.

The system pressure is controlled by a switch that turns the pump on and off automatically.  Typical pressure range is 40 to 60 pounds per square inch (psi).  On at 40, off at 60.  Greatest pressure is therefore 60 psi.  As you use water, the pressure in the system drops until the pump kicks in and refills the tanks.

The amount to allow for pipe friction depends on the water flow rate, pipe size, and length of discharge line (depth of pump plus distance from well to pressure tanks).  If the line is properly sized, this number will be small.  Start with 5 psi.

Summary of conditions for this example:

  • 460 foot lift
  • 60 psi to get into tanks
  • 5 psi pressure loss due to friction

Pumps curves are based on feet not psi.  To convert, multiply psi by 2.3 to get feet.

Total head = 460 + (60 × 2.3) + (5 × 2.3) = 610 feet

Round to 600 feet to keep things simple.  Here are curves for Goulds series 7GS pumps.

7GS Curves

Start on the y-axis at 600 feet and move to the right.  When you hit a curve read down to the x-axis.  A 7GS15 pump will give you about 5 gpm.  A 7GS20 will give you 8.5 gpm.  A flow rate of 5 to 10 gpm should be adequate for you and your horses.  Boarding facilities and farms require something larger.

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