Deep well pump installation: vertical-turbine vs. submersible decision + sizing

When you have a deep well

A "deep well" — for pump-spec purposes — is anywhere the pumping water level is below the practical lift of a surface pump. Practically, that means the pumping water level is more than ~25 ft below ground (suction lift is theoretically capped at ~33 ft atmospheric, and real pumps can pull at most 25–28 ft accounting for friction + NPSH margin).

Two pump styles serve deep wells:

1. Vertical line-shaft turbines — motor on the surface, long line shaft drives bowls + impellers immersed in the well 2. Submersible turbines — motor + bowl assembly together, dropped into the well below the pumping water level

Each has its place. The decision depends on well depth, capacity, head, and operating environment.

Vertical line-shaft turbine (VLT)

The classic deep-well pump:

• Surface motor (electric or engine), accessible for maintenance
• Pump bowl assembly at the bottom (typically 30–50 ft below pumping water level)
• Line shaft connecting the two through the column pipe
• Discharge via the column pipe to surface piping

Best for:

• Wells 100–600 ft deep (up to ~1,000 ft with multiple shaft sections)
• High flow (500–10,000+ gpm)
• Where surface motor accessibility matters (frequent monitoring, oil-lubed bearings)
• Long-life installations (40+ year service is common with proper maintenance)

Trade-offs:

• Long line shafts wear over time → bearing replacement at the column-bowl interfaces
• Larger surface footprint (the motor sits above ground)
• Vibration sensitivity (long shaft = lateral vibration mode at certain rotational speeds)
• Specialized installation crew required

Submersible turbine

Newer (1960s+) but now dominant:

• Sealed motor + bowl assembly drops to the well bottom
• No line shaft (motor is direct-coupled to bowl)
• Power via cable from surface to motor
• Discharge via column pipe to surface

Best for:

• Wells deeper than 600 ft
• Moderate flow (50–3,000 gpm)
• Smaller well diameter (4"–10")
• Limited surface space

Trade-offs:

• Motor inaccessible — any failure requires pulling the entire pump
• Sensitive to power quality (cable + motor are 200+ ft below surface, hard to troubleshoot)
• Requires special low-NPSH motor (cooled by surrounding water)
• Cable splicing in field is a critical skill

Sizing the pump rate

Determine the well's safe yield first. From the well driller's pump test:

• Static water level: depth to water with no pumping
• Pumping water level: depth to water during sustained pumping (at the well's safe yield)
• Drawdown: difference (= pumping level - static level)
• Specific capacity: pumping rate ÷ drawdown (gpm/ft of drawdown)

Specific capacity tells you what the well CAN sustain. Don't size the pump above that — you'll pull air, dewater the well, or violate water-rights limits.

Typical example:

• Static level: 80 ft
• Safe yield: 200 gpm at 50 ft drawdown
• Pumping water level: 80 + 50 = 130 ft

The pump must sit at least 30 ft below the pumping water level — typical: 160–180 ft below ground.

Sizing the pump head (TDH)

Total head includes:

TDH = pumping_water_level + discharge_pressure_at_surface + column_friction + surface_piping_friction

Worked example:

• Pumping water level: 130 ft (= 56 psi static lift)
• Discharge pressure required at surface: 50 psi (= 115 ft)
• Column friction (250 ft of 6" column at 200 gpm): 5 ft
• Surface piping friction: 8 ft

TDH = 130 + 115 + 5 + 8 = 258 ft

Pump must develop 258 ft TDH at 200 gpm. Required power (assuming 70% pump efficiency, 92% motor):

BHP = (200 × 258 × 1.0) / (3960 × 0.70) = 18.6 hp
Motor input = 18.6 / 0.92 = 20.2 hp → spec 25 hp standard frame

Pump submergence — the critical install spec

The pump bowl must be deep enough below the pumping water level that:

1. Suction is always flooded — even at the well's drawdown maximum 2. Cooling flow is guaranteed across the motor (submersibles) 3. Vortex prevention — no surface air pulled into the bowl

Minimum submergence above the pump bowl (per HI 9.8):

S_min ≈ D + 2.3 × D × F^0.5

Where F is the Froude number based on inlet velocity. For a standard 6" submersible pump at 200 gpm, S_min is typically 5–10 ft above the bowl.

In practice: pump centerline 30+ ft below the maximum-drawdown pumping water level. This margin handles seasonal drawdown variation + droughts.

Cable sizing for submersibles

The submersible pump cable carries motor current through 200+ ft of well casing. Voltage drop matters:

• Maximum 3% voltage drop at FLA at the motor terminals
• Specification: use the manufacturer's cable-size table for your motor + cable run length

For a 25-hp 230V three-phase motor, 250 ft cable run:

• Motor FLA: ~64 amps
• Per Belden/Southwire submersible cable table: #4 AWG copper

Voltage drop calculation (sanity check):

V_drop = 2 × I × L × (R/L) per conductor
       = 2 × 64 × 250 × 0.000308 (Ω/ft for #4)
       = 9.85 V
       = 4.3% of 230V — slightly above the 3% target

For tight margins, upsize to #2 AWG: drops to 2.7%. The cable cost premium is usually $200–$500 — small relative to the consequences of marginal voltage at the motor.

Cable installation specifics

Splice carefully. The factory motor lead is 10–20 ft long. The drop cable splices to it inside the well. Use only manufacturer-approved heat-shrink splice kits rated for submerged service. Standard waterproof tape fails within months; bad splices are the #1 long-term failure cause.

Strain-relief. The cable's own weight pulls on the splice. Tie the cable to the discharge column pipe every 10–15 ft with cable ties or stainless straps. A 250-ft cable hanging unsupported pulls 60+ lb on the splice point.

Surge protection. A nearby lightning strike induces voltage spikes through long cables in well casings. Spec lightning arrestors at the controller for any rural / exposed installation.

Motor protection

Submersible motors burn out from:

1. Single-phase loss (most common, biggest bearing/winding killer) 2. Voltage too low (extended low voltage cooks the windings) 3. Locked rotor (sand binding, debris, mechanical jam) 4. Dry running (water level drops below the pump intake)

Standard protection package:

• 3-phase overload relay set to motor SF amps (not just FLA)
• Single-phase loss protection trip in <5 seconds
• Low-voltage trip
• Thermistor in the motor windings, wired to controller trip
• Low-water-level cutoff (electrode in the well casing or well-pump-controller pressure-monitor)

Skipping any one of these guarantees a motor failure within the first 5 years.

Common installation errors

Pump too high in the well. Drawdown exceeds expectations during summer; pump pulls air; impeller cavitates. Always size for the worst-case drawdown.

Wrong cable size. Voltage drop > 5% — motor never starts properly under load. Sometimes runs but slowly burns out windings.

No surge protection. First nearby lightning strike fries the motor + controller.

Splice not done with manufacturer kit. Splice fails after 6 months. Pull the pump (multi-day operation, $5,000+ in crane time) just to redo the splice.

Strain not relieved on cable. Cable separates from splice over time, motor disconnects.

Strainer or inlet screen omitted. Sand enters the pump bowls, accelerates impeller wear, creates premature rebuild.

Water-quality considerations

Deep-well water often contains:

• Sand: erodes impeller bowls. Spec sand-rated impellers (chrome iron) for sandy aquifers.
• Iron / manganese: deposits build on bowl interiors. Reduces capacity over time.
• Hydrogen sulfide: corrodes pump materials. Use stainless steel construction or coated bowls.
• Hard water (high Ca/Mg): scales the discharge piping. Periodic descaling required.

Get a water quality analysis from the well driller before specifying pump materials. Standard cast iron is fine for many waters; stainless or coated is needed for aggressive water.

Maintenance schedule

| Frequency | Task | |---|---| | Weekly | Pump operation check (start/stop, discharge pressure) | | Monthly | Voltage + amp readings vs. nameplate | | Quarterly | Vibration check (surface, vertical line-shaft only) | | Annually | Drawdown verification (still matches design?) | | 5 years | Pull pump for inspection + bearing replacement | | 10–20 years | Major rebuild OR replacement |

A well-installed deep-well pump should last 15–25 years with normal maintenance. Replace the bowls + impellers when capacity drops 20%+ from original.

How the calculator handles it

The Headloss Calculator handles deep-well system curves directly:

1. Enter pumping water level as the "static suction lift" (negative number) 2. Add column friction in the discharge piping section 3. Add surface piping friction 4. Add static head from ground level to discharge (water tank, distribution main, etc.) 5. Get the system curve → cross with the pump curve → confirm operation

For NPSH on submersibles: enter the depth-of-submersion as a positive head term in the suction-side calculation. NPSHa is usually huge for properly-installed submersibles.

References

• AWWA Manual M21 — *Groundwater.*
• AWWA C654 — *Disinfection of Wells.*
• Hydraulic Institute. *ANSI/HI 11.6 — Submersible Pumps for Hydraulic Performance, Hydrostatic Pressure, Mechanical, and Electrical Acceptance Tests.*
• Hydraulic Institute. *ANSI/HI 9.8 — Rotodynamic Pumps for Pump Intake Design.*
• Driscoll, F. G. *Groundwater and Wells,* 2nd ed. Johnson Screens.
• USGS Water-Supply Paper 1473 — *Theory of Aquifer Tests.*