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To choose a submersible borehole pump, you need to determine the required flow rate, the pressure to be delivered at the point of use and the total dynamic head (TDH). Here is the method in three steps.
1 - Indicative flow rate / pressure table by number of occupants and watering
The number of occupants to be supplied and the area to be watered give a first order of magnitude for the flow rate (in m³/h) and the useful pressure (in bar): from 2 m³/h and 3.2 bar for 1 to 6 occupants up to 6 m³/h and 5.0 bar for 10 to 20 occupants.
View the indicative flow rate / pressure tableValues by number of occupants and area to be watered.
2 - Determining the pressure
To determine the pressure that the submersible pump must deliver at the point of use (tap), you must calculate the TDH (total dynamic head), expressed in metres of water column (mWC), in bar or in kg/cm². Reminder: 1 bar = 10 metres of water column. To calculate the TDH of a submersible pump, all values must be expressed in mWC.
TDH = Hr + Pc + Pr
| Term | Meaning |
|---|---|
| Hr | Static head: height between the water level and the point of use. |
| Pc | Head losses in the discharge pipework and friction points. |
| Pr | Residual pressure (mWC), the pressure that must be available at the taps or for watering. |
Determining water pressure · Calculating the TDH
3 - Example of a TDH calculation for a borehole pump
Installation intended to supply running water to a home of 4 people and a garden of 800 m².
- The pump is submerged at 60 m (depth between the pump intake and the borehole head, at ground level): Hr = 60 m.
- Head losses and friction in the pipework: Pc = 10 m WC.
- Residual pressure at the tap of 3.5 bar: Pr = 35 m WC.
TDH = 60 + 10 + 35 = 105 m WC
You therefore need to choose a pump that delivers 3 m³/h at 105 m (1.50 kW or 2.20 kW depending on the pump’s flow curve).
Schematic diagram of a 4-inch borehole pump installation with a pressure tank
