Borehole Pumps

A borehole pump is a system of five parts – pump end, submersible motor, control box, cable and rising main – and getting it right depends on four measurements: casing diameter, pumping water level, borehole yield and the power supply on site. This guide takes you through each one, with the specifications that matter, worked examples and current South African price ranges for everything from a 3-inch 230V kit to a 200mm three-phase irrigation pump.

What makes up a borehole pump system

A submersible borehole pump is not one product. Five components work together, and a fault or mismatch in any one of them takes the whole installation down. Understanding what each part does is the fastest way to buy the right thing – or to find out what has actually failed.

Around these sit the accessories that make an installation safe and serviceable: a stainless steel safety rope that carries the weight, a non-return valve, a waterproof cable splice kit, cable ties to the rising main, and dry-run protection by control box, probe or float switch.

Never pump more than your borehole yields. Every borehole has a sustainable yield – the rate at which water flows back in. Pump faster than that and the water level drops to the pump, the motor loses its cooling, and it runs dry. Have a yield test done by your driller before you buy, and size the pump below the tested yield. A bigger pump will not produce more water from a small borehole; it will simply fail sooner.

Step 1 – Borehole diameter sets the pump size

Borehole pumps are described by the casing they fit: 3-inch (80mm), 4-inch (100mm), 6-inch (150mm) and 8-inch (200mm). Measure the internal diameter of your casing – not the drill bit size – and remember the pump has to pass down the full depth of the hole with the cable and cable guard alongside it.

If the casing is tight, has shifted, or the hole is not straight, drop down a size. A 3-inch pump in a 4-inch hole is a perfectly sound installation; a 4-inch pump jammed half-way down is an expensive retrieval.

Step 2 – Work out the total head

Head is the height, in metres, the pump must lift the water against – plus the losses along the way. It is the single most important number in selection, and the one most often under-estimated.

1. Use the pumping water level, not the static level. The water drops while the pump runs. Your driller's yield test gives the drawn-down level; design on that.
2. Set the pump depth. A commonly recommended rule is at least 3 m below the pumping water level, so the pump stays submerged, and at least 3 m above the bottom of the hole, clear of silt. Where possible, set it above the screens.
3. Add the vertical rise from the borehole head to the tank inlet, including the height of any tank stand and any rise in the ground between the two.
4. Add friction loss in the rising main and delivery pipe. On long runs this adds up quickly – a larger pipe is almost always cheaper than a larger pump.
5. Add outlet pressure if you are pumping direct into the house rather than a tank. Every 1 bar of pressure at the tap is 10 m of head.

A worked example: a pumping water level of 40 m, a tank on a 5 m stand at the house where the ground is 5 m higher than the borehole, and about 5 m of friction in the pipe run. Total head = 40 + 5 + 5 + 5 = 55 m. If the household needs 5 000 litres a day and the pump runs 8 hours on a timer, the required flow is 5 000 ÷ 8 = 625 litres per hour, or about 0.65 m³/h. You are looking for a pump whose performance table shows at least 0.65 m³/h at 55 m, with margin – and a borehole whose tested yield comfortably exceeds it.

Read the curve, not the headline. A pump's "maximum head" is the shut-off point, where it produces pressure but no water. Always select from the performance table at your actual head and flow.

Step 3 – Choose the supply voltage and motor

Single-phase or three-phase

Single-phase 230V borehole motors in our range run up to 2.2 kW, which covers the great majority of domestic installations. Beyond that, or where a long cable run makes single-phase impractical, you move to 400V three-phase; larger 6-inch and 8-inch installations are also available on 525V. Three-phase motors draw less current for the same power, which means smaller cable and less voltage drop on deep holes.

Oil-filled or water-filled

Whichever you choose, check the motor's maximum submersion depth. Motors are rated for a maximum depth below the water surface – some oil-filled ranges, for example, are offered in versions rated to 100 m and to 200 m submersion. Setting a motor deeper than its rating shortens its life.

Motor cooling

A submersible motor is cooled by the water flowing past it on its way into the pump. Franklin Electric specifies a minimum cooling flow of 0.08 m/s past 4-inch motors and 0.16 m/s past 6-inch and 8-inch motors, with motors rated for full load in water up to 30 °C. In a wide borehole with a low pumping rate the water moves too slowly to cool the motor.

A flow inducer sleeve – a tube around the motor that forces water past it – is required when the borehole diameter is too large for the pumping rate, when the pump is set in or below the screens, when water enters from above the pump, or when the pump is used in open water.

Step 4 – Choose the control box and protection

Single-phase borehole motors need a control box on the surface containing the start and run capacitors. Beyond that, the choice is how much protection you want – and on a borehole, protection is what separates a pump that lasts years from one that burns out in a dry season.

Always match the control box to the motor's exact kW rating and voltage. A control box from a different kW rating will fit the wires but carries the wrong capacitors, and the motor will run hot and fail.

Step 5 – Size the cable

Cable is where borehole installations most often go wrong. Every metre of cable drops a little voltage, and a motor that starts on low voltage draws more current, runs hotter and fails early. The deeper the pump and the further the control box from the borehole, the thicker the conductor has to be.

• Measure the full run: from the control box to the borehole head, plus the depth to the motor.
• Size the conductor on the motor's current and that total length, using the motor manufacturer's cable tables.
• Single-phase motors need heavier cable than three-phase motors of the same power over the same distance.
• Join cable to the motor lead with a proper waterproof splice kit – never tape alone.
• Confirm the installation against SANS 10142-1 and have it done by a qualified electrician.

Installation essentials

• Safety rope carries the weight. Hang the pump on a stainless steel safety rope, not on the pipe or the cable.
• Tie the cable to the rising main at regular intervals so it cannot chafe against the casing.
• Fit a non-return valve so the column of water does not drain back through the pump when it stops.
• Protect against dry running with an intelligent control box, a level probe or a float switch.
• Keep the pump off the bottom and above the screens where possible; use a flow sleeve where you cannot.
• Earth the installation and protect the control box from direct sun and rain.

Solar borehole pumps

Where there is no grid supply, or running costs matter, a DC solar borehole pump runs directly from solar panels through an MPPT controller – no inverter, no batteries, water stored in a tank instead of electricity in a battery bank. Solar systems in our range run from 120 W to 1.2 kW, and complete systems start from about R6 400. Size the solar array at a minimum of 1.3 times the pump's rated power.

For deep, low-yield boreholes, a solar screw pump is often the better choice than an impeller pump. See the Difful 3DSS Solar Screw Borehole Pump guide for a full worked example.

Helical rotor borehole pumps

Surface-driven helical rotor pumps work on a different principle: a drive head at the surface turns a rotor at depth, which moves a fixed volume of water with every turn. They produce high head at low flow and suit low-yield boreholes and long-life agricultural installations. Discharge heads, pipes and a full range of head spares are available in the Mono and Orbit ranges.

Borehole pump price guide

Typical price ranges from our current range, including VAT. Prices vary with brand, kW rating and cable length, and every product listing shows its live price.

Price ranges are drawn from our listings at the time of writing and include VAT. Rising main, safety rope, cable and installation are extra unless a kit states otherwise.

Shop the borehole range

Frequently asked questions

Related ranges

• Borehole Pumps — the full borehole category
• Difful Solar Submersible Borehole Pumps — DC solar screw pumps
• Leo & Omega Submersible Borehole Combo Range 230V — matched domestic kits
• Leo & Omega Control Boxes — standard to intelligent