Understanding Deep Well Pump Basics
A deep well submersible pump is a specialized pump designed to operate entirely submerged in well water, typically at depths ranging from 30 meters to over 400 meters. Unlike jet pumps that sit above ground and use suction, submersible pumps push water upward, which makes them inherently more efficient for deep applications.
The pump assembly consists of three main components: the pump unit (multiple impeller stages), the submersible motor, and the discharge assembly with check valve. These components are lowered into the well as a single unit on the drop pipe.
Step 1: Determine Your Well Dimensions
The well casing diameter is the single most important physical constraint. Standard deep well submersible pumps come in these sizes:
| Pump Diameter | Minimum Casing ID | Typical Flow Range | Max Depth |
|---|---|---|---|
| 4 inch (100mm) | 4.5" (114mm) | 1-15 m3/h | 400m |
| 6 inch (150mm) | 6.5" (165mm) | 10-50 m3/h | 450m |
| 8 inch (200mm) | 8.6" (219mm) | 30-150 m3/h | 500m |
| 10 inch (250mm) | 10.75" (273mm) | 80-400 m3/h | 500m |
Critical rule: Pump OD must be at least 6mm smaller than the well casing ID to allow water flow around the motor for cooling. Insufficient clearance causes motor overheating and premature failure.
Step 2: Calculate Total Dynamic Head for Deep Wells
Deep well TDH includes several components that shallow well calculations sometimes miss:
TDH = Static Water Level + Drawdown + Surface Pressure + Friction Loss
- Static Water Level: distance from ground to water surface when not pumping
- Drawdown: how much the water level drops during pumping (typically 5-30m)
- Surface Pressure: required pressure at discharge (1 bar = 10.2m)
- Friction Loss: pipe friction over the full length of drop pipe + surface pipe
Example calculation: Well with static level at 80m, drawdown 15m, required surface pressure 3 bar (30.6m), friction loss 12m → TDH = 80 + 15 + 30.6 + 12 = 137.6m. Select pump rated for 145-155m head.
Step 3: Material Selection for Different Water Conditions
| Water Condition | Pump Body | Impellers | Shaft |
|---|---|---|---|
| Clean fresh water | SS304 | SS304 | SS304 |
| Hard water (high calcium/magnesium) | SS304 | SS304 or SS316 | SS316 |
| Sand/silt content up to 50g/m3 | SS304 | SS316 with wear rings | SS316 |
| Sand/silt content 50-150g/m3 | SS316 | Duplex SS with hard coating | Duplex SS |
| Brackish / saline water | SS316 | SS316 or Duplex | Duplex SS |
| High iron / acidic (pH less than 6) | SS316 | SS316 | SS316 or Duplex |
Step 4: Submersible Cable Selection
Undersized drop cable is one of the most common installation errors, causing voltage drop and motor burnout:
| Motor kW | Up to 50m depth | 50-100m | 100-200m | 200-300m |
|---|---|---|---|---|
| 1.5 kW | 2.5mm2 | 2.5mm2 | 4mm2 | 6mm2 |
| 3.0 kW | 2.5mm2 | 4mm2 | 6mm2 | 10mm2 |
| 5.5 kW | 4mm2 | 6mm2 | 10mm2 | 16mm2 |
| 7.5 kW | 6mm2 | 10mm2 | 16mm2 | 25mm2 |
| 11 kW | 10mm2 | 16mm2 | 25mm2 | 35mm2 |
Always use submersible-rated cable (PVC/XLPE insulated, water-blocking construction). Standard building wire will fail rapidly when submerged.
Step 5: Installation Best Practices
- Use a torque arrestor — Absorbs starting torque, prevents cable damage from twisting against the casing wall
- Install a check valve every 60-100m — Prevents water hammer and backflow that can spin the pump backward
- Set pump above screen level — Position the pump intake 3-5m above the well screen to prevent sand ingestion
- Use stainless steel drop pipe or high-pressure PE — Galvanized steel corrodes and contaminates water over time
- Install a flow sleeve if required — When casing diameter is large relative to pump, a sleeve ensures adequate motor cooling water velocity
- Test water quality before final pump selection — A simple water analysis (pH, TDS, iron, sand content) costs $50-100 and can prevent a $2,000 pump failure
Common Mistakes to Avoid
- Oversizing the pump — Causes frequent cycling, burnt motors, and excessive energy use
- Ignoring drawdown — Pump running at deeper-than-expected water level may cavitate or run dry
- Skimping on cable — Voltage drop leads to high current draw and premature motor failure
- Using wrong check valve type — Spring-loaded valves are preferred for vertical installations; swing checks can stick
- Insufficient well development — A new well should be properly developed (surge block, air lift) before pump installation
For expert assistance with deep well pump selection: NOVAPUMP provides free technical consultation including TDH calculation verification, material compatibility analysis, and cable sizing recommendations tailored to your well specifications.