How to Choose the Right Submersible Well Pump for Your Project

how-to-choose-submersible-well-pump

One of the first questions customers ask us is:

“Which submersible well pump do I need?”

The question sounds simple, but a reliable answer cannot be based on horsepower, well depth, or pump diameter alone.

A 15 HP pump may deliver high flow at a relatively low head, while another 15 HP pump may deliver much less water at a much higher pressure. The motor power may be the same, but the hydraulic performance can be completely different.

Before recommending a pump, our engineers normally ask about the project first:

① How much water is required?

② What is the dynamic water level?

③ Where must the water be delivered?

④ What pipe will be used?

⑤ Does the water contain sand or corrosive substances?

⑥ What voltage and frequency are available?

⑦ How many hours will the pump operate each day?

These details are more useful than simply asking for a certain horsepower.

The right pump is not the largest model available. It is the pump that can deliver the required flow and pressure under the actual operating conditions without excessive energy consumption, unstable operation, or premature wear.

Don’t Start with the Pump — Start with the Project

Many buyers begin by looking through a pump catalogue.

They compare:

① Motor power

② Pump diameter

③ Maximum head

④ Maximum flow

⑤ Price

This is understandable, but it often leads to the wrong selection.

The numbers shown in a catalogue are usually maximum or nominal performance values. They do not automatically represent the conditions at which the pump should operate continuously.

Before comparing models, define what the pump must do.

Start with the application:

① Agricultural irrigation

② Municipal water supply

③ Industrial process water

④ Mining water supply

⑤ Livestock water systems

⑥ Residential or commercial groundwater supply

⑦ Tank filling

⑧ Pressure boosting

The application affects more than flow.

For example, an irrigation pump may operate for several hours during the irrigation season. A municipal pump may run every day and require higher reliability, standby capacity, and remote control. A mining application may involve sand, long pipelines, difficult maintenance access, and fluctuating water levels.

Two projects may require the same flow rate but need completely different pumps.

The selection process should therefore begin with the project conditions—not with a pump model.

Understand How Much Water You Really Need

Required flow rate is one of the first parameters used in pump selection.

It may be expressed as:

① Cubic metres per hour — m³/h

② Litres per second — L/s

③ Litres per minute — L/min

④ Gallons per minute — GPM

The important question is not:

“What is the largest flow this pump can produce?”

The useful question is:

“How much water does the system actually require?”

For irrigation projects

Flow demand may depend on:

① Irrigated area

② Crop type

③ Irrigation method

④ Number of sprinklers or irrigation zones

⑤ Available irrigation time

⑥ Seasonal water demand

A field requiring 400 m³ of water per day does not automatically need a 400 m³/h pump.

If the irrigation system operates for eight hours, the basic average requirement would be approximately:

400 m³ ÷ 8 hours = 50 m³/h

Additional allowance may be required for system losses or future expansion, but adding a large safety margin without calculation may cause oversizing.

For industrial and municipal projects

Consider both average and peak demand.

Confirm:

① Normal hourly consumption

② Maximum short-term demand

③ Number of operating hours

④ Storage-tank capacity

⑤ Whether another pump operates in parallel

⑥ Expected future expansion

A storage tank can often reduce the required pump flow because the pump does not need to match every short-term demand directly.

Do not ignore the well yield

The required flow must also be compared with the amount of water the well can sustainably provide.

For example:

① The system requires 80 m³/h.

② The well can sustainably provide only 55 m³/h.

Installing an 80 m³/h pump will not create more groundwater.

Instead, the dynamic water level may continue to fall. The pump may eventually operate with insufficient submergence, poor motor cooling, unstable flow, or dry-running conditions.

The final selected flow should be compatible with both:

① The system demand

② The sustainable well yield

Know the Well Before Choosing a Pump

“Well depth” is useful information, but it is not enough for selecting a submersible well pump.

A proper well assessment should include:

① Total well depth

② Static water level

③ Dynamic water level

④ Well casing diameter

⑤ Well yield

⑥ Pump installation depth

⑦ Seasonal water-level variation

Static water level

The static water level is measured when the pump is stopped and the water level has recovered.

It indicates the natural groundwater level under non-pumping conditions.

Dynamic water level

The dynamic water level is measured while the pump is operating at a specific flow rate.

This is usually more important for pump selection because it represents the actual pumping condition.

Consider a 150-metre-deep well:

① Static water level: 28 metres

② Dynamic water level: 62 metres

③ Pump installation depth: 100 metres

The pump does not normally need to lift water from the full 150-metre well depth.

The hydraulic calculation should begin from the pumping water level, which in this case is approximately 62 metres below ground level.

Drawdown

Drawdown is the difference between the static and dynamic water levels.

In the example above:

62 m − 28 m = 34 m drawdown

Large drawdown may indicate:

① A relatively low-yield well

② Excessive pumping rate

③ Restricted groundwater recharge

④ Well-screen blockage

⑤ Changing aquifer conditions

The pump should not be selected without considering how the water level behaves during continuous operation.

Seasonal changes matter

A water level measured during the rainy season may be considerably higher than the level during the dry season.

Where seasonal variation is significant, confirm:

① Lowest expected dynamic water level

② Minimum required pump submergence

③ Distance between the pump and the well bottom

④ Motor cooling conditions

⑤ Dry-run protection requirements

Selecting a pump from one water-level measurement can create problems later if the groundwater level falls.

Well Diameter Is More Than a Fitment Question

The pump must physically fit inside the well casing, but clearance also affects installation and motor cooling.

Confirm the actual internal diameter of the well casing.

Do not rely only on the nominal casing size, especially where:

① The casing is old or deformed.

② Mineral deposits have reduced the internal diameter.

③ The well is not completely straight.

④ Cable guards increase the pump’s external dimensions.

⑤ Pipe couplings are wider than the pump body.

Adequate clearance is required for:

① Lowering the pump safely

② Removing the pump during maintenance

③ Routing and protecting the power cable

④ Allowing water to pass around the motor

⑤ Avoiding contact with the casing wall

For some installations, especially large-diameter wells, open reservoirs, or tanks, a cooling sleeve may be required to direct water past the motor.

A pump fitting inside the casing does not automatically mean the motor will receive sufficient cooling.

Don’t Ignore the Pipe System

The pump does not only lift water out of the well.

It must also move water through the complete discharge system.

This may include:

① Rising pipe inside the well

② Horizontal pipeline

③ Elbows and fittings

④ Check valves

⑤ Isolation valves

⑥ Filters

⑦ Flow meters

⑧ Pressure tanks

⑨ Irrigation equipment

⑩ Elevated storage tanks

All of these affect the required pump head.

Total Dynamic Head

A practical pump-head calculation normally includes:

① Vertical lift from the dynamic water level to the discharge point

② Required pressure at the outlet

③ Friction loss through the pipeline

④ Losses through valves and fittings

The general relationship is:

Total Dynamic Head = Vertical Lift + Required Pressure Head + Friction Losses

Example

Suppose a project has:

① Dynamic water level: 55 m below ground

② Storage tank inlet: 15 m above ground

③ Required pressure at the tank inlet: 1 bar

④ Estimated pipe and fitting losses: 12 m

The approximate head requirement is:

① Vertical lift: 55 + 15 = 70 m

② Pressure head: approximately 10.2 m

③ Friction losses: 12 m

Total Dynamic Head ≈ 92.2 m

A suitable safety allowance may be added where conditions are uncertain, but the pump should not be oversized without reason.

Pipe diameter can change the pump requirement

A small pipe creates higher water velocity and greater friction loss.

This can result in:

① Higher required pump head

② Increased energy consumption

③ Greater pressure loss

④ Higher risk of water hammer

⑤ Reduced delivered flow

A slightly larger pipe may cost more initially but can reduce operating costs over the life of the system.

The pump and pipeline should be selected as one system.

Maximum Head Is Not the Operating Head

Pump catalogues often show a maximum head and a maximum flow.

These two values normally occur at different points on the pump curve.

A pump cannot usually deliver its maximum flow at its maximum head.

For example, a catalogue may show:

① Maximum flow: 100 m³/h

② Maximum head: 180 m

This does not mean the pump delivers 100 m³/h at 180 m.

At 180 m, the flow may be close to zero. At 100 m³/h, the available head may be much lower.

The actual requirement must be plotted on the pump performance curve.

The selected duty point should preferably fall within the manufacturer’s recommended operating range.

Avoid continuous operation:

① Too far to the left of the curve

② Too far to the right of the curve

③ Below the minimum recommended flow

④ Beyond the motor power limit

⑤ In an unstable hydraulic region

Operating far from the efficient range may cause:

① Higher energy consumption

② Excessive axial or radial loads

③ Vibration

④ Motor overload

⑤ Rapid bearing wear

⑥ Reduced service life

The pump curve is not only a sales document. It is one of the most important tools used in correct selection.

Bigger Isn’t Always Better

Oversizing is one of the most common causes of poor pump-system performance.

Some buyers choose a larger pump because they expect:

① More water

② Higher pressure

③ Better reliability

④ Longer service life

In practice, an oversized pump may create the opposite result.

An oversized pump may cause:

① Excessive drawdown in the well

② Frequent starting and stopping

③ Higher power consumption

④ Excessive pipeline pressure

⑤ Valve and fitting damage

⑥ Operation outside the efficient range

⑦ Increased water velocity

⑧ Higher risk of water hammer

⑨ Motor overload under certain conditions

⑩ Premature wear

An oversized motor does not correct an incorrect pump selection

A larger motor only provides more available power.

It does not automatically make the hydraulic selection correct.

If the impeller stages, flow range, or pump curve do not match the system, increasing motor power will not solve the basic problem.

Undersizing also creates problems

A pump that is too small may:

① Fail to deliver the required flow

② Fail to reach the required pressure

③ Run continuously without meeting demand

④ Operate at an unsuitable point on the curve

⑤ Overheat because of poor operating conditions

The objective is not to choose the largest or smallest pump.

The objective is to select the pump whose normal operating point matches the project.

Water Quality Can Change the Pump You Need

Groundwater may look clean while still containing substances that affect pump life.

Before selecting materials, confirm as much information as possible about:

① Sand content

② Chloride concentration

③ pH value

④ Water temperature

⑤ Total dissolved solids

⑥ Iron and manganese

⑦ Corrosive chemicals

⑧ Suspended solids

Sand and abrasive particles

Sand can wear:

① Impellers

② Diffusers

③ Wear rings

④ Bushings

⑤ Bearings

⑥ Shaft surfaces

⑦ Check valves

The severity of wear depends on more than the sand percentage.

It is also affected by:

① Particle size

② Particle hardness

③ Pump speed

④ Water velocity

⑤ Operating hours

⑥ Pump material

⑦ Hydraulic design

A pump described as “sand-resistant” is not immune to abrasion.

Where sand content is high, the correct response may include:

① Selecting a more wear-resistant pump design

② Reducing the pumping rate

③ Improving well development

④ Installing the pump farther above the well bottom

⑤ Inspecting the well screen

⑥ Monitoring sand concentration over time

Corrosive water

Material selection should reflect the actual water chemistry.

Common options include:

① Cast iron

② Stainless steel 304

③ Stainless steel 316

④ Duplex stainless steel

⑤ Bronze components

Cast iron is suitable for many normal groundwater applications and is often cost-effective.

Stainless steel may be preferred where:

① Corrosion resistance is important.

② Water quality must be protected.

③ Chloride levels are elevated.

④ The project requires cleaner internal surfaces.

⑤ Long-term appearance and material stability matter.

However, “stainless steel” is not one universal material.

SS304, SS316, and duplex stainless steel have different levels of corrosion resistance. The correct choice depends on the actual water composition.

Do not specify the most expensive material automatically.

Do not select the cheapest material without checking water quality.

Motor and Electrical Conditions Must Match the Site

A hydraulically correct pump can still fail if the motor and electrical system are not properly matched.

Confirm:

① Voltage

② Frequency

③ Number of phases

④ Available transformer capacity

⑤ Cable length

⑥ Starting method

⑦ Number of starts per hour

⑧ Generator use

⑨ Variable-frequency drive requirements

⑩ Protection-panel configuration

Voltage and frequency

A motor designed for 380 V, 50 Hz should not be treated as equivalent to a 460 V, 60 Hz motor.

Voltage and frequency affect:

① Motor speed

② Current

③ Power

④ Pump performance

⑤ Cooling

⑥ Motor life

Always confirm the electrical supply before production or shipment.

Cable length

Long cables create voltage drop.

The cable size should be selected according to:

① Motor current

② Cable length

③ Starting current

④ Installation method

⑤ Allowable voltage drop

⑥ Local electrical regulations

A cable that is too small may cause:

① Difficult starting

② Low motor voltage

③ Higher current

④ Excessive cable heating

⑤ Reduced motor life

Motor protection

A reliable control system should normally consider:

① Overload protection

② Short-circuit protection

③ Phase-loss protection

④ Phase-sequence protection

⑤ Under-voltage protection

⑥ Over-voltage protection

⑦ Dry-run protection

⑧ Water-level control

⑨ Over-temperature protection, where available

⑩ Surge or lightning protection where required

For remote or critical installations, monitoring current, pressure, flow, and water level can help identify problems before a failure occurs.

Operating Hours Affect the Selection

A pump operating one hour per day does not have the same duty as a pump operating continuously.

Confirm the expected operation:

① Intermittent

② Seasonal

③ Daily duty

④ Continuous 24-hour duty

⑤ Emergency standby

⑥ Parallel operation

⑦ Duty-and-standby operation

For long operating hours, pay closer attention to:

① Pump efficiency

② Motor efficiency

③ Material durability

④ Bearing design

⑤ Motor cooling

⑥ Availability of spare parts

⑦ Ease of maintenance

A lower-priced pump may appear attractive at the purchasing stage, but a small efficiency difference can become significant when the pump operates thousands of hours per year.

For continuous or critical water supply, the system may also require:

① One duty pump and one standby pump

② Automatic changeover

③ Separate power supplies

④ Remote alarms

⑤ Spare motor or pump components

The purchase decision should reflect the cost of downtime, not only the cost of the pump.

Think About Installation and Maintenance Before Buying

A pump must eventually be installed, inspected, and possibly removed from the well.

These practical details are often considered too late.

Before purchasing, confirm:

① What type of rising pipe will be used?

② Can the lifting equipment handle the total suspended weight?

③ Is there enough space above the well for pump removal?

④ How will the power cable be secured?

⑤ Is a safety cable required?

⑥ Where will the check valve be installed?

⑦ Can the pump be removed without dismantling other equipment?

⑧ Are spare parts available locally?

⑨ Can the motor be repaired or rewound?

⑩ Is there a standby pump for critical applications?

Suspended weight

The lifting equipment must support more than the pump weight.

The total suspended load may include:

① Pump

② Motor

③ Rising pipe

④ Water inside the pipe

⑤ Power cable

⑥ Check valves and fittings

⑦ Safety cable

This total load can be considerable in deep wells.

Installation depth

The pump should be installed:

① Below the lowest expected dynamic water level

② With sufficient motor submergence

③ Far enough above the well bottom to reduce sediment intake

④ In a position that allows adequate motor cooling

⑤ Away from damaged or restricted sections of casing

Installing the pump as deep as possible is not always the best approach.

A deeper installation increases:

① Cable length

② Pipe length

③ Suspended weight

④ Removal difficulty

⑤ Installation cost

The depth should be selected according to water-level conditions and safe operating requirements.

Questions We Usually Ask Before Recommending a Pump

A useful pump recommendation requires complete information.

When contacting a supplier, prepare the following details.

① Application

What will the pump be used for?

Examples:

• Irrigation
• Municipal supply
• Industrial water
• Mining
• Residential supply
• Tank filling

② Required flow

Provide the normal required flow, not only the maximum expected flow.

State the unit clearly:

• m³/h
• L/s
• L/min
• GPM

③ Required head or discharge pressure

Where possible, provide:

• Vertical lift
• Pipeline length
• Pipe diameter
• Required outlet pressure
• Elevation of the discharge point

④ Total well depth

Provide the measured depth rather than the original drilling target.

⑤ Static water level

State when and how the measurement was taken.

⑥ Dynamic water level

Also provide the pumping rate at which the level was measured.

A dynamic water level without a corresponding flow rate is incomplete information.

⑦ Well casing diameter

Provide the internal diameter where possible.

⑧ Well yield

Confirm the sustainable pumping rate or available well-test data.

⑨ Water quality

Provide:

• Sand content
• pH
• Chloride
• Temperature
• Water analysis report, where available

⑩ Electrical supply

Confirm:

• Voltage
• Frequency
• Phase
• Starting method

⑪ Operating schedule

State:

• Hours per day
• Starts per hour
• Seasonal or continuous use
• Duty or standby requirement

⑫ Pipeline details

Provide:

• Vertical pipe length
• Horizontal pipe length
• Pipe material
• Internal diameter
• Number of major valves and fittings

With these details, the supplier can review the duty point, motor rating, materials, electrical requirements, and installation conditions.

Without them, the recommendation is largely an estimate.

Common Buying Mistakes

Many pump failures begin before the pump is installed.

They begin during selection.

① Choosing by horsepower alone

Horsepower does not define flow and head.

Always review the pump curve.

② Using total well depth as the required head

The pump normally lifts water from the dynamic water level, not from the bottom of the well.

Add discharge elevation, pressure, and friction losses separately.

③ Ignoring the well yield

A high-capacity pump cannot produce water that the aquifer cannot supply.

④ Selecting from maximum catalogue values

Maximum flow and maximum head are not the same operating point.

⑤ Forgetting pipeline friction

Long or undersized pipes can consume a large part of the available pump head.

⑥ Adding an excessive safety margin

A reasonable allowance is useful.

Doubling the required flow or head “to be safe” often results in oversizing.

⑦ Ignoring seasonal water-level changes

A pump selected from wet-season data may not remain submerged during the dry season.

⑧ Choosing materials by price alone

A low initial price can become expensive if corrosion or abrasion causes early failure.

⑨ Assuming all stainless steel grades are equivalent

SS304, SS316, and duplex stainless steel do not provide the same corrosion resistance.

⑩ Forgetting the electrical system

Incorrect voltage, insufficient cable size, or poor motor protection can damage a correctly selected pump.

⑪ Ignoring maintenance access

A pump that is difficult to remove may create high labour and downtime costs.

⑫ Buying without complete performance data

A quotation should identify more than model name and motor power.

Ask for:

• Rated flow
• Rated head
• Pump curve
• Efficiency
• Motor current
• Materials
• Pump dimensions
• Recommended operating range

A Practical Selection Example

Consider a hypothetical agricultural project with the following conditions:

① Required irrigation flow: 45 m³/h

② Total well depth: 140 m

③ Static water level: 32 m

④ Dynamic water level at 45 m³/h: 68 m

⑤ Discharge point: 8 m above ground

⑥ Horizontal pipeline: 600 m

⑦ Pipe internal diameter: 100 mm

⑧ Required pressure at the irrigation system: 2.5 bar

⑨ Water contains a moderate amount of fine sand

⑩ Power supply: 380 V, three-phase, 50 Hz

The selection should not begin with the 140 m well depth.

It should be reviewed in the following order.

① Confirm the flow

The required duty flow is 45 m³/h.

The well test shows that this pumping rate is sustainable.

② Calculate the vertical lift

Dynamic water level: 68 m below ground.

Discharge elevation: 8 m above ground.

Vertical lift:

68 + 8 = 76 m

③ Convert the required pressure

Required pressure: 2.5 bar.

Approximate pressure head:

2.5 × 10.2 = 25.5 m

④ Estimate friction losses

The 600 m pipeline, fittings, valves, and rising pipe must be calculated.

Assume the estimated total friction loss is 18 m.

⑤ Calculate the approximate TDH

76 + 25.5 + 18 = 119.5 m

The initial duty point is therefore approximately:

45 m³/h at 120 m head

⑥ Review the pump curve

The selected pump should deliver approximately 45 m³/h at 120 m within its recommended operating range.

Do not select a pump only because its maximum head exceeds 120 m.

⑦ Review the motor

Confirm that the motor power is sufficient at the required duty point, including the manufacturer’s power margin.

Also confirm voltage, frequency, starting method, and cable size.

⑧ Review the sand conditions

Because the water contains fine sand, review:

• Abrasion-resistant components
• Pump installation height above the well bottom
• Well development
• Allowable sand concentration
• Inspection frequency

⑨ Confirm the installation

Check:

• Pump diameter
• Well casing clearance
• Rising-pipe rating
• Cable length
• Check-valve arrangement
• Motor cooling
• Lifting capacity

This example shows why well depth and horsepower alone cannot provide a reliable selection.

Final Pump Selection Checklist

Before approving a submersible well pump, confirm that all of the following information has been reviewed.

Hydraulic conditions

① Required flow is clearly defined.

② Dynamic water level is known.

③ Well yield is sufficient.

④ Total Dynamic Head has been calculated.

⑤ Friction losses are included.

⑥ Required outlet pressure is included.

⑦ The duty point is shown on the pump curve.

Well conditions

① Total well depth is confirmed.

② Well casing internal diameter is confirmed.

③ Pump installation depth is defined.

④ Seasonal water-level changes are considered.

⑤ Pump submergence is sufficient.

⑥ Distance above the well bottom is sufficient.

Water quality

① Sand content is known.

② Water temperature is acceptable.

③ Corrosion conditions have been reviewed.

④ Pump materials match the water quality.

⑤ The selected design is suitable for the expected solids.

Electrical conditions

① Voltage is confirmed.

② Frequency is confirmed.

③ Phase is confirmed.

④ Cable size is calculated.

⑤ Starting method is suitable.

⑥ Motor protection is included.

⑦ Dry-run protection is considered.

Installation and operation

① Rising-pipe pressure rating is adequate.

② Check valves are correctly arranged.

③ Lifting equipment can support the suspended load.

④ Motor cooling is adequate.

⑤ Expected operating hours are known.

⑥ Maintenance access is available.

⑦ Spare-parts availability has been considered.

⑧ Standby capacity is considered for critical applications.

Choosing a Pump Is a System Decision

A submersible well pump should not be selected as an isolated product.

Its performance depends on the complete system:

① The well

② The groundwater level

③ The required flow

④ The pipeline

⑤ The discharge pressure

⑥ The water quality

⑦ The electrical supply

⑧ The control system

⑨ The installation method

⑩ The operating schedule

When these conditions are clearly defined, pump selection becomes much more reliable.

When they are ignored, even a high-quality pump may operate inefficiently or fail earlier than expected.

If you are preparing a new groundwater project, send SLAPK the following basic information:

① Required flow

② Required head or pipeline details

③ Total well depth

④ Static and dynamic water levels

⑤ Well diameter

⑥ Water analysis

⑦ Voltage and frequency

⑧ Daily operating hours

Our engineering team can review the complete duty conditions and recommend a pump based on the project—not simply on horsepower or catalogue limits.