Difful 3DSS Solar Screw Borehole Pump

The Difful 3DSS is a 3-inch brushless DC solar screw borehole pump built for deep, low-yielding boreholes. It uses a progressive cavity (helical rotor and stator) pumping element instead of impellers, which lets it push water up to 180 metres on as little as 120 watts of solar power. It runs directly from a solar array through its MPPT controller — no batteries, no inverter and no grid connection.

What the 3DSS is, and who it is for

Most solar borehole pumps are centrifugal: stacked impellers that spin water outward. They move good volume but lose output quickly as head rises, and they struggle on a borehole that recharges slowly. The 3DSS works on a different principle. A single helical rotor turns inside an elastomer stator, trapping a fixed volume of water in each cavity and walking it up the pump. That makes it a positive displacement pump, and it changes the performance in two ways that matter on a difficult borehole:

• High head from low power. A 210 W 3DSS reaches 77 m. Getting that from a centrifugal pump typically costs several times the array.
• Flatter output across the head range. Flow holds up as head increases instead of collapsing, so the pump keeps delivering at the bottom of a deep hole.

The trade-off is volume. The 3DSS is deliberately a low-flow pump — 1.2 to 2.2 m³/h. It is the right tool for household water supply, livestock watering, drinking water and small-area garden irrigation from a deep or slow-recovering borehole. For large-area irrigation, choose a higher-flow impeller series such as the 4DLR or 4DSC.

Choosing between screw and impeller: if your borehole is deep and slow, choose the screw-type 3DSS. If it is shallower and yields well, an impeller pump such as the Difful 3DPC will give you far more water for the same money.

3DSS range — models and specifications

Five models are stocked in the South African range. All share the same 3" body, 3/4" outlet and 2 m factory cable tail.

Difful also manufactures a 12 V 80 W model (3DSS0.5-28-12-80) and a 48 V 750 W variant (3DSS2.0-150-48-750). Both are available to order.

Performance table — head against flow

Find the row for the flow you need, then read across to see the head each model will still deliver at that flow. A dash means the model cannot reach that flow rate.

Reading this correctly matters. The "max head" figure in the specification table is the shut-off head — the point at which flow stops. Size from the performance table, not from max head. A 500 W 3DSS quoted at 109 m delivers roughly 1.0 m³/h at 78 m, which is the number to design around.

How to size a 3DSS for your borehole

1. Measure the pumping water level, not the static level. Water drops while the pump runs; design on the drawn-down level.
2. Add the vertical rise from the wellhead to the tank inlet.
3. Add friction loss in the rising main. Use 32 mm (1") pipe or larger — 3/4" pipe on a long run wastes a surprising amount of head.
4. Total the three figures. That is your total dynamic head.
5. Find your daily water requirement, then divide by realistic pumping hours. In most of South Africa, budget on 5–6 hours of full-output sun per day, not 12.
6. Pick the model whose performance table still shows your required flow at your total dynamic head — with margin.

A worked example: a household needing 2 000 litres a day from a borehole with a 70 m pumping level, plus 8 m rise to the tank and roughly 4 m of friction, has a total dynamic head of about 82 m. At 5.5 hours of good sun, 2 000 L requires roughly 0.36 m³/h. The 500 W 3DSS1.7-109-48-500 delivers around 0.8 m³/h at 82 m — comfortably inside its range, with headroom for a poorer day.

Solar array sizing

Difful specifies a minimum array of 1.3 × the pump's rated power. That margin covers panel temperature derating, dust, wiring loss and the fact that panels almost never produce their nameplate rating in the field. The array's open-circuit voltage must also stay under the controller's ceiling, or the controller will trip on over-voltage.

Panel configurations are indicative. Always confirm the actual VOC of the panels you are using at the coldest expected ambient temperature, since VOC rises as temperature falls.

Cable sizing

Voltage drop between the array and the controller is the most common cause of disappointing output on a solar pump installation. Difful publishes the following minimum conductor sizes by run length, in mm²:

Conductor cross-section in mm². Confirm against SANS 10142 and local wiring regulations before installation.

Construction and build quality

The MPPT solar controller

Every 3DSS ships with its matched DC controller. The controller does three jobs: it tracks the array's maximum power point so the pump makes use of weak morning and late-afternoon light, it soft-starts the motor to avoid mechanical shock, and it protects the pump.

Protection functions

• Dry-run protection — sensor-free, no separate probe required
• Pump stall protection
• Over-current protection (hardware and software)
• Over-voltage and under-voltage protection
• Open-phase protection
• High-temperature protection
• Automatic start and stop with float switch or water-level probe

Controller fault codes

What is in the box

Typical applications

• Off-grid household water supply — deep borehole to elevated tank
• Livestock watering — remote troughs with no grid connection
• Drinking water — rural and community supply points
• Small-area irrigation — gardens, orchards, tunnels and nurseries
• Deep, low-yielding boreholes where a centrifugal pump would run dry

Frequently asked questions

Pricing

Each 3DSS is supplied as a complete DC solar system — pump, brushless motor, MPPT control box and submersible borehole cable of the length shown. Prices include VAT and are subject to change; the online store always carries the current price.

Longer cable lengths and the 750 W and 1100 W models are available to order — send us your borehole depth and we will quote the right combination.