Submersible Pumps: Types, Specifications & How to Choose for Your Borehole or Project

If your water source is underground, your pump needs to be underground too. Submersible pumps operate fully submerged — inside a borehole, a sewage wet well, a flooded construction site, or a mine sump. They push water upward instead of pulling it, which eliminates suction limits and makes them the only practical choice for extracting water from depths beyond 8 meters.

Across Africa, the Middle East, and Central Asia, submersible borehole pumps are the backbone of water supply. Every rural water scheme, every urban borehole, every irrigation system drawing from groundwater depends on a submersible pump. Selecting the wrong pump size, wrong motor rating, or wrong material means either a pump that cannot deliver enough water, or one that fails prematurely in harsh borehole conditions.

This guide covers every type of submersible pump, how they work, how to size them, what materials to specify, and how to select the right pump for your borehole or project.

How Submersible Pumps Work

A submersible pump is a sealed unit containing a motor and pump in a single assembly that operates completely submerged in the fluid it is pumping. Unlike surface pumps that create a vacuum to "pull" water up (limited to ~8 meters of suction lift by atmospheric pressure), submersible pumps sit below the water level and "push" water to the surface. This push-based mechanism has no theoretical depth limit — submersible pumps can operate at depths exceeding 500 meters.

Key components:

Motor — a hermetically sealed electric motor, either water-filled (water-cooled, lubricated by clean water) or oil-filled (cooled and lubricated by dielectric oil). The motor is positioned below the pump section so that water flowing past the motor provides cooling. Motor ratings typically range from 0.37 kW (0.5 HP) for small domestic boreholes to 250 kW+ (335 HP+) for large municipal and industrial installations.

Pump section — a series of impellers (stages) stacked vertically inside diffuser bowls. Each stage adds pressure (head). The more stages, the higher the pump can push water. A borehole pump lifting water from 200 meters depth may have 30–50 stages, while a drainage pump lifting water from 5 meters may have only one or two.

Intake screen / strainer — filters out sand and particles before they enter the pump. Critical for borehole pumps where sand ingress is the primary cause of premature failure.

Power cable — waterproof submersible cable that runs from the motor up to the surface control panel. Cable must be sized correctly for the motor current and the cable length (voltage drop increases with distance).

Drop pipe / riser pipe — the pipe that carries water from the pump to the surface. In borehole applications, this is typically HDPE pipe (for smaller installations) or galvanized steel pipe (for larger installations). The pipe must be sized to maintain acceptable flow velocity (1.5–3.0 m/s for HDPE, up to 3.5 m/s for steel).

Types of Submersible Pumps

Borehole / Deep Well Submersible Pumps

The most important pump type for water supply in developing economies. Designed to fit inside a drilled borehole and lift water from depths of 30 to 500+ meters.

Available diameters:

The 4-inch borehole pump is the workhorse of African water supply. It fits the most common borehole casing sizes (5" and 6"), provides flow rates adequate for community water systems and small-to-medium irrigation, and is the most cost-effective and widely available size.

Materials:

• Stainless steel 304 — standard for clean water boreholes. Corrosion resistant, suitable for pH 6.5–8.5.

• Stainless steel 316 — for aggressive water chemistry (high chloride, high TDS, low pH). Required for coastal areas and saline groundwater.

• Cast iron — lower cost for non-corrosive, clean water applications. Limited lifespan in aggressive water.

• Technopolymer / engineered plastic — lightweight, corrosion-proof impellers used in some manufacturers' economy ranges. Suitable for clean water with low sand content.

Motor types:

• Water-filled (rewindable) — motor cavity filled with clean water. Can be rewound locally if the motor burns out — a significant advantage in Africa where replacement motors may take weeks to arrive. Most common in 4" and 6" borehole pumps across developing markets.

• Oil-filled (encapsulated) — motor cavity filled with dielectric oil. Better protection against moisture ingress. Cannot be rewound — must be replaced entirely when motor fails. Common in European and US manufactured pumps.

• Sand-resistant / sand-fighter — specialized designs with floating impellers and wear rings that tolerate sand content up to 50–100 g/m³. Essential for boreholes in sandy aquifers (common across the Sahel, North Africa, and parts of the Middle East).

Sewage / Wastewater Submersible Pumps

Heavy-duty submersible pumps designed to handle raw sewage, wastewater with solids, and industrial effluent. They operate in sewage wet wells, lift stations, and wastewater treatment plants.

Key design features:

• Vortex impellers — create a swirling flow pattern that moves solids without the solids contacting the impeller. Passes soft solids up to 80mm diameter. Lowest clogging risk.

• Channel (single-channel) impellers — one or two large open passages allow solid particles to pass through. Passes solids up to 100mm diameter. Used for raw sewage with rags and debris.

• Grinder / cutter impellers — a cutting mechanism at the inlet shreds solids, rags, and fibrous material before pumping. Used for sewage pumping where long fibrous material (wipes, rags) would clog other impeller types.

Materials: Cast iron body with hardened steel impeller. Internal coatings (epoxy, ceramic) for abrasion resistance. Stainless steel shaft. Silicon carbide or tungsten carbide mechanical seals for abrasive environments.

Typical applications: Municipal sewage lift stations, wastewater treatment plant influent pumping, industrial effluent, food processing waste, and combined stormwater/sewage systems.

Drainage / Dewatering Submersible Pumps

Portable, lightweight submersible pumps for removing clean to moderately dirty water from flooded areas, construction excavations, basements, and temporary applications.

Characteristics: Single-stage impeller, lower head capacity (typically 10–30 meters), high flow rate relative to size, designed for portability and intermittent duty. Automatic float switch turns pump on/off based on water level.

Typical applications: Construction site dewatering, basement flooding, pond/tank emptying, emergency flood response, and temporary water transfer.

Slurry Submersible Pumps

Specialized heavy-duty submersible pumps designed to handle abrasive slurries with high solids content. Used in mining, dredging, and industrial applications.

Materials: High-chrome white iron (27% Cr) or rubber-lined impellers and wear plates. Extra-heavy-duty shaft seals. Agitator at the intake to keep settled solids in suspension.

Typical applications: Mine dewatering (acid mine water), dredging, tailings pond management, sand/gravel extraction, and industrial sludge pumping.

How to Size a Submersible Pump: The 5 Essential Parameters

Getting the pump size right is the difference between a system that delivers reliable water for 10–15 years and one that fails within months. These are the five parameters you must determine before selecting a pump:

1. Required Flow Rate (Q)

How much water do you need, measured in m³/h (cubic meters per hour) or l/s (liters per second)?

Guideline for borehole water supply:

• Single household: 0.5–1.5 m³/h

• Small community (50–200 people): 2–5 m³/h

• Medium community (200–1,000 people): 5–15 m³/h

• Small town (1,000–5,000 people): 15–50 m³/h

• Urban distribution: 50–200+ m³/h

• Irrigation (per hectare, drip): 5–15 m³/h

• Irrigation (per hectare, sprinkler): 15–40 m³/h

Critical rule: The pump flow rate must not exceed the borehole yield (the sustainable pumping rate of the aquifer). Over-pumping collapses the water table, draws air into the pump, and causes cascading damage. Always size the pump to match the tested borehole yield, not the maximum pump capacity.

2. Total Dynamic Head (TDH)

The total pressure the pump must overcome to deliver water to the destination, measured in meters. This is the most important sizing parameter.

TDH = Static head + Dynamic water level drop + Friction losses + Delivery pressure

• Static head — the vertical distance from the pump installation depth to the highest delivery point (e.g., top of a storage tank)

• Dynamic water level drop (drawdown) — how much the water level falls when the pump is running. Determined by the borehole pump test. A borehole with a static level at 30m and a dynamic level at 45m has 15m of drawdown.

• Friction losses — pressure lost due to friction in the riser pipe and surface distribution piping. Depends on pipe material, diameter, length, and flow velocity. Smaller pipes = higher friction. Always calculate this — it can add 10–30% to the head requirement.

• Delivery pressure — the pressure required at the outlet point (e.g., 2–3 bar for a pressurized distribution network, 0 for gravity feed into an open tank).

Example: Borehole with dynamic water level at 80m, surface piping to a tank 20m above ground, friction losses 12m, delivery pressure 0 (open tank). TDH = 80 + 20 + 12 = 112 meters.

3. Borehole Diameter

The pump must physically fit inside the borehole casing with clearance for cooling water flow around the motor. A 4" pump requires a minimum 5" casing (6" recommended for better cooling and easier installation/removal).

4. Water Quality

Sand content, pH, temperature, TDS (total dissolved solids), and chemical composition determine the pump material and type. High sand content requires sand-resistant designs. Aggressive water chemistry requires stainless steel 316 or higher alloy construction.

5. Power Supply

Verify the available voltage (380V/415V three-phase is standard for industrial pumps in Africa and ME), frequency (50Hz), and power supply reliability. For off-grid or unreliable grid locations, consider solar-powered submersible pumps with variable frequency drives (VFDs) and battery or tank storage.

Motor Specifications for Africa and Middle East

Always specify 50Hz motors for Africa and Middle East projects. A 60Hz motor installed on a 50Hz supply will run at 83% speed, delivering significantly less flow and head than rated. This is a common and costly mistake in regions where both frequencies exist.

Installation Best Practices

Pump setting depth — install the pump at least 3–5 meters below the dynamic water level to ensure the pump remains submerged during operation. Never install above the dynamic water level — the motor will overheat without water flow for cooling.

Sand settling — after drilling, the borehole must be properly developed (surged and flushed) to remove fine sand before the pump is installed. Installing a pump in an undeveloped borehole guarantees premature failure from sand abrasion.

Check valve — install a non-return (check) valve on the pump discharge to prevent water in the riser pipe from flowing back through the pump when it stops. Backflow causes the pump to spin backward, damaging the motor and impellers.

Motor protection — install a motor protection relay (overload, dry-run, phase failure protection) in the surface control panel. Dry-run protection is essential — if the water level drops below the pump intake, the motor overheats and burns out within minutes.

Cable protection — secure the submersible cable to the riser pipe at regular intervals (every 3 meters) using cable ties or clamps. Loose cable can wrap around the pipe during installation, causing damage and making pump retrieval difficult.

Submersible Pump vs Surface Pump: When to Use Which

For any water source deeper than 8 meters, a submersible pump is the only practical option. Surface pumps (including jet pumps) cannot physically lift water from greater depths due to atmospheric pressure limitations.

Which Submersible Pump for Which Application?

Supply from Kasko Makine

Kasko Makine supplies the complete range of submersible pumps for water supply, sewage, dewatering, and industrial applications:

Borehole pumps: 3", 4", 6", 8", 10", and 12" diameter. Stainless steel 304 and 316 construction. Water-filled and oil-filled motors. Flow rates from 0.5 to 500+ m³/h. Heads from 20 to 500+ meters. Sand-resistant models available. 50Hz standard.

Sewage pumps: Vortex, channel, and grinder impeller types. Cast iron body, stainless steel shaft. Solids passage up to 100mm. Automatic level control. DN 50 to DN 300 discharge.

Drainage pumps: Portable and fixed installation. Clean water and dirty water models. Float switch control. Flow rates from 5 to 100+ m³/h.

Solar submersible pumps: DC and AC solar-compatible models with controllers and MPPT tracking. For off-grid boreholes and irrigation.

Complete water supply packages: Submersible pump + motor + control panel + HDPE riser pipe + HDPE distribution pipe + fittings + valves — everything needed to commission a complete borehole water system, shipped together.

All pumps supplied with performance curves, motor data sheets, installation manuals, and warranty certificates. Third-party inspection available on request.

FAQ SCHEMA

Q: What is a submersible pump and how does it work?
A: A submersible pump is a sealed unit containing a motor and pump that operates fully submerged in water. Unlike surface pumps that pull water up (limited to ~8 meters), submersible pumps push water upward from below, with no theoretical depth limit. They use multi-stage centrifugal impellers to progressively build pressure, lifting water from depths of 30 to 500+ meters.

Q: How do I choose the right submersible pump for my borehole?
A: You need five parameters: required flow rate (m³/h), total dynamic head (TDH — including borehole depth, drawdown, friction losses, and delivery pressure), borehole casing diameter, water quality (sand content, pH, TDS), and available power supply (voltage, frequency). The pump flow rate must not exceed the tested borehole yield to prevent over-pumping.

Q: What is the difference between 4-inch and 6-inch borehole pumps?
A: A 4-inch pump (100mm diameter) fits inside 5"–6" borehole casings and delivers 1–25 m³/h — suitable for community water supply and small irrigation. A 6-inch pump (150mm) requires 8" casing and delivers 5–80 m³/h — used for municipal water supply, large irrigation, and industrial applications. The 4-inch pump is the most common and cost-effective size for water projects in Africa.

Q: What material should a borehole pump be made from?
A: Stainless steel 304 is standard for clean water with normal pH (6.5–8.5). Stainless steel 316 is required for aggressive water — high chloride content, high TDS, low pH, or coastal/saline groundwater. Cast iron is lower cost but limited to non-corrosive clean water. For boreholes with high sand content, specify sand-resistant pump models with floating impellers and hardened wear rings.

Q: How deep can a submersible pump work?
A: Submersible pumps can operate at depths exceeding 500 meters. The depth is determined by the number of impeller stages (more stages = more head capacity) and the motor power. A typical 4-inch borehole pump can reach 200–300 meters with the appropriate number of stages. For very deep boreholes, 6-inch or larger pumps with high-stage counts are used.

Q: Why do submersible pumps fail in boreholes?
A: The most common causes are: sand abrasion (borehole not properly developed before pump installation), dry running (water level drops below pump intake — motor overheats), voltage problems (undersized cable causing voltage drop, wrong frequency), and incorrect sizing (pump flow exceeds borehole yield, causing drawdown below the pump). Proper sizing, sand-resistant materials, motor protection relays, and correct installation prevent most failures.

Request a submersible pump quotation — send us your borehole depth, dynamic water level, required flow rate, and delivery head to info@kaskomakine.com or WhatsApp +90 (537) 521 13 99. We respond within 24 hours and deliver to water projects across Africa, the Middle East, Central Asia, and beyond.