Pump Selection

Factors to consider when selecting a borehole pump

  1. Available power source
  2. Total dynamic head

Available Power Source

The first and most basic factor to consider when selecting a borehole pump is to determine the available power source 220V Single phase of 380V Three phase, if you intend to use a 380V 3Phase pump make sure that your 380V three phase power source as three live lines a neutral line and an earth available.

Total Dynamic Head

The total dynamic head of the water system must also be considered when determining the size of the borehole pump to be installed.

The total dynamic head determines the various head losses that the pump must overcome.

Total Dynamic Head = Elevation Head + Friction Head Loss + Pressure Head

Elevation Head

Elevation head is the vertical distance which the water must be pumped, in other words the depth of the bore hole.

In situations where the water after reaching the top of the borehole must still be pumped up an incline to reach the top of a hill or fill a water tank on a stand remember to add these additional heights to the Elevation head.

Elevation Head = Depth of Borehole + Tank Height (If Applicable) + Any Additional Vertical Inclines (if Applicable)

Friction Head Loss

Friction head loss is the loss of pressure due to the flow of water through pipe and fittings. Friction head loss can be reduced by using a larger diameter pipe or by changing piping materials.

Friction head loss can also be compensated for by calculating the friction head loss using the following information and an Online Friction Head Loss Calculator

  1. Flow Rate in (m3/hr)     –     m3/hr = L/hour ÷ 1000        or        m3/hr = (L/Min x 60) ÷ 1000
  2. Pipe Diameter in (mm)2
  3. Pipe Length in (m)
  4. Pipe Material

After entering all information on the online calculator click the calculate button and enter the pipe friction loss result in (m) into the Total Dynamic Head Formula in place of the Friction Head loss.

Pressure Head

Pressure head is the maximum operating pressure of the water system converted from pressure (bar) to (meters of head)(m)

This is applicable only to water systems that get their pressure directly from the borehole pump, not for Water tank systems.
If you are pumping into a water tank or dam the pressure head in the Total dynamic head formula will be 0m

If you need 3bar of pressure for irrigation when the irrigation system is connected directly from the borehole pump, simply add 30m to cover the Pressure head.
or
for other required pressures add 10m of pressure head to the Total Dynamic Head formula for every 1bar of pressure required.

Finally it is important to consider the borehole output capacity as tested by the borehole driller so as not to have too large a pump and over-pump the borehole causing the pump to dry run.

Pump Selection Using a Pump Curve

In order to determine is the proposed borehole pump is properly sized, it is necessary to refer to he pump manufacturer’s performance curve or chart.

The total dynamic head and desire pump capacity are applied to the pump curve to determine proper pump selection based on required electrical power input and optimum efficiency.

To determine proper pump size, locate the point on the pump curve where the pump capacity and the total dynamic head intersect and select the pump which will provide the required capacity of water under the particular head conditions. If the point of intersection falls above the curve line, select the next highest pump size.