Submersible Well Pump Selection

A deep well submersible water system is used to supply domestic water automatically to the plumbing system of a home or building from a private well. The complete pumping unit is submerged in the well below water level.

Basic System Components

• pump and motor
• pressure switch
• pressure tank

Submersible Well Pumps (depths to 1100 feet or more)

• Submersible Pumps get their name because the entire unit, including both pump and motor, are submerged in the well during operation.
• They are powered by dependable 2 or 3 wire Submersible motors.
• A Submersible Pump works by passing water up through a series of STAGES, each stage consisting of an IMPELLER, a DIFFUSER and the BOWL in which they are seated.
• The width of the impeller determines pump capacity (GPM). The diameter determines pressure PSI.
• The number of stages in a submersible pump determines how high the pump will push the water.
• Submersible pumps offer a number of advantages to the homeowner:
  • Greater pumping depth.
  • Higher Capacity and Pressure.
  • Greater Efficiency. All the water pumped by the well is delivered to the service outlets. This reduces power consumption and lowers operating costs.

Preliminary Considerations

• How much water will be required for daily use?
• Can the well produce enough water to meet daily requirements?

WELL CAPACITY

• Determine how much water will the well produce in GPM (gallons per minute) by:
  • Well driller's log
  • Use of an older cleanout pump to determine flow rate.
    • Never use a new pump for this service.
    • After cleanout pump operates for 30 minutes at free flow, fill a 5-gallon bucket and make a note of the time it takes to reach capacity.
      • Gallons of Water / Seconds X 60 = GPM (Gallons per Minute)
      • GPH ( Gallons per Hour) = GPM X 60
    • If at any time during the 30 minutes of free flow water fails to flow, pump should be turned off immediately. Wait 3 to 4 hours, lower pump deeper into well, and throttle (use a gate valve) pump back by closing valve 1/4 turn.
    • The above procedure should be repeated until water flows continuously for 30 minutes. Not doing so could result in dry running and destruction of the pump.
    • The pump should never be closer than 10 feet to the bottom of the well.

Submersible Pump Sizes

• 5 – 7 GPM Series:
  • For low-capacity wells where a higher series would "over-pump" the well, causing pump failure.
• 10 – 13 GPM Series:
  • For average-capacity wells. These are the most popular choices in farm and home applications.
• 20 to 27 GPM Series:
  • For more than normal high-capacity wells: ranches, dairy farms, light irrigation, and light industrial water systems.
• 35 to 85 GPM Series:
  • Usually not used in residential domestic water applications. For very high capacity wells and/or very deep wells. For irrigation and industrial water systems where higher water volume is needed.

DEPTH OF WELL

• Well driller's log
• Tie a heavy weight to a string, lower into well until it reaches bottom, and measure this distance.

Water Pumping Level

• The Water Pumping Level is defined as the standing water level in the well when the pump is operating, and the water being pumped out equals the water entering the well.
• This level is generally several feet lower than the water level in the well when pump is not operating. It should be understood that pump setting depth does not determine pump performance.
• The main criterion is the Water Pumping Level not the depth to water.
• The depth of the pump below this water level is of no significance in relation to gallons and pressure delivered by the pump.

2-WIRE VS. 3-WIRE Submersible Pump Motors

• In a 3-wire pump motors,
  • The motor’s starting components are in a “control box” that is located above ground in the well house or basement.
  • 3-wire pump motors are equipped with high-starting torque motors, which is sometimes needed to break free mineral deposits that may adhere to the pump's moving parts.
  • If anything ever needs to be tested because of a problem, it is easier to test (and replace, if needed)
  • The starting components are above ground in the control box.
• In a 2-wire pump motors
  • All the motor starting components are located in the motor, down in the well.
  • If the pump gets locked up due to sand or grit, the biac switch will kick the motor in a reverse direction then back in the forward direction to try to break the pump loose. If it can’t the pump the pump and motor must be pulled and serviced.
  • Should not be used where abrasives or heavy water scale are present.
  • If there is a problem with the start control, the 2-wire pump must be pulled and serviced

Construction Materials

• Cast-iron basic construction represents good value and is useful in many applications.
• Thermoplastic construction provides excellent value and corrosion resistance.
• Stainless steel construction has superior corrosion resistance.

Pump Capacity Required

• The water system should have enough capacity to satisfy the family needs, particularly during periods of heaviest demand.
• The amount of water needed depends in three factors:
  • Number of people
  • Number of fixtures in the home
  • Peak demand Periods
    • Peak demand periods usually occur during morning and evening hours when most or all of the family is at home and the demand of water is the heaviest. These are the times when the most outlets are being used at the same time.
    • Peak demand periods usually involve 7 to 10 minutes of maximum water usage (showers, dishwasher, etc)
• To make sure your system will provide adequate capacity, you can use either or both of these methods:
  • Fixture Method:
    • One gallon for every fixture in the home
  • Seven Minute Peak Demand Method:
    • 1 bathroom in the home 7 GPM
    • 1-1/2 bathrooms in the house 10 GPM
    • 2 to 2-1/2 bathrooms in the house 14 GPM
    • 3 to 4 bathrooms in the house 17 GPM
    • 5 to 6 bathrooms in the house 25 GPM
  • Values given are average and do not include higher or lower extremes
  • Peak demand can occur several times during the morning and evening hours.
  • Additional requirements: farm, irrigation and sprinkling are not shown, These values must be added to the peak demand figures if usage will occur during normal demand periods.

Pump Pressure Required

• In addition to enough capacity, there must also be enough pressure to properly service the home.
• Discharge pressure is made up of:
  • Vertical Elevation: The pressure needed to raise the water vertically from the pumping level to the highest outlet in the home. (Measure in feet. Convert to PSI)
  • PLUS
  • Friction loss: The Friction loss in all pipe and fitting between the tank and the outlet. (Expressed in PSI)
  • PLUS
  • Service pressure. Pressure required at the outlets (Expressed in PSI)
• The most commonly used Discharge Pressure is 30/50 PSI. This means that the pump will cut-in when the pressure in the system falls to 30 PSI. And cut-out when the pressure reaches 50 PSI. This provides enough pressure to service most homes adequately.
• When selecting a pump, always use the lower or cut-in pressure, because that represents Peak Demand conditions.
• Pressure switches are adjustable in the field to accommodate unusual conditions.
• For example. An older home with corroded pipes and fittings or rusty fixtures may require extra pressure to overcome the additional friction loss caused by these conditions.
• Increased discharge pressure may also be required if vertical elevation is greater than normal; for example, a three story home or a home located a great distance from the pump.

Selecting A Submersible Well Pump

• Some of the factors involved in selecting which type of pump to use include:
  • Replacement situation (What kind of pump is being replaced?)
  • Maximum pumping depth
  • Well diameter
  • Judgment, experience and customer preference will also play a part in the final pump type selection. Other factors could be cost, future water usage projections and cost and ease of service.