Selecting the right pump type is fundamental to achieving efficient, reliable operation. The wrong pump can lead to poor performance, high energy costs, frequent breakdowns, and premature failure.
The Key Question
What are you pumping, how much, how far, and under what conditions? Answering these questions guides you to the right pump type.
10 Key Questions
Before selecting a pump, answer these essential questions to define your requirements:
What are you pumping?
Clean water, sewage, slurry, chemicals, or solids-laden fluid?
What flow rate is required?
Litres per minute or cubic metres per hour?
What is the total head?
Vertical lift plus friction losses in the system.
What are the suction conditions?
Flooded suction or suction lift? How high above water?
What solids are present?
Size, type, and concentration of solids in the fluid.
What is the fluid temperature?
Hot fluids affect NPSH and material selection.
What is the pH and chemistry?
Acidic, alkaline, or corrosive? Material compatibility is critical.
What power is available?
Electric (single/three phase), diesel, hydraulic, or pneumatic?
Continuous or intermittent duty?
24/7 operation or occasional use? Affects motor and seal selection.
Fixed or portable installation?
Permanent installation or needs to be moved between sites?
Pump Types
| Pump Type | Best Applications | Key Advantages |
|---|---|---|
| Centrifugal | Clean water, high flow, moderate head | Simple, efficient, low maintenance |
| Self-Priming | Suction lift applications | No foot valve needed, handles air |
| Submersible | Deep wells, sumps, tanks | No priming, quiet, compact |
| Diaphragm | Slurries, chemicals, solids | Handles solids, runs dry, seal-less |
| Trash/Solids | Construction, sewage, debris | Large solids passage, rugged |
Suction Conditions
Understanding suction conditions is critical for pump selection. The wrong choice leads to cavitation, loss of prime, and pump damage.
Flooded Suction
Pump is below the water level. Liquid flows to pump by gravity.
- Most reliable configuration
- Standard centrifugal pumps work well
- No priming required
- Best efficiency and longest life
Suction Lift
Pump is above the water level. Must create vacuum to draw liquid up.
- Requires self-priming or auto-prime pump
- Maximum practical lift: 7-8 metres
- Reduces with altitude and temperature
- Prone to air leaks and loss of prime
Suction Lift Limits
| Condition | Max Practical Lift |
|---|---|
| Sea level, cold water (15°C) | 7-8m |
| Sea level, warm water (40°C) | 5-6m |
| 1000m altitude, cold water | 6-7m |
| High altitude + warm water | 4-5m |
Note: These are maximum practical limits. For reliable operation, design for 1-2m less than the maximum.
Rule of Thumb
When suction lift exceeds 5m, consider using a submersible pump instead. Submersibles eliminate suction lift problems entirely and often provide better reliability.
Selection Criteria
Consider these factors when choosing a pump:
Fluid Properties
- Clean water vs solids content
- Viscosity (thin vs thick)
- Temperature range
- Chemical composition / pH
System Requirements
- Required flow rate
- Total head (pressure)
- Suction conditions
- Continuous vs intermittent duty
Site Conditions
- Power availability
- Space constraints
- Environmental conditions
- Accessibility for maintenance
Operational Factors
- Energy efficiency goals
- Maintenance capabilities
- Spare parts availability
- Total cost of ownership
Sizing & Safety Margins
Proper sizing ensures reliable performance and long pump life. Include appropriate safety margins to handle real-world variations.
Flow Rate Margin
- Clean water: +10-15% margin
- Solids-laden: +15-20% margin
- Variable demand: +20-25% margin
- Critical application: +25-30% margin
Head Margin
- Known system: +10% margin
- New installation: +15-20% margin
- Long pipelines: +20% for friction losses
- Future expansion: Consider next pump size up
Avoid Oversizing
While margins are important, excessive oversizing wastes energy and can cause the pump to operate outside its efficient range. Aim for the pump to run at 80-110% of its Best Efficiency Point (BEP).
Motor Sizing
- Size motor for maximum power point on pump curve, not duty point
- Add 10-15% service factor for variable conditions
- Consider starting current and voltage drop for electric motors
- For diesel: allow 10-20% derating for altitude and temperature
Power Sources
Choose the power source based on availability, portability requirements, and operating conditions.
Electric Motor
Best For: Fixed installations with reliable power
- Lowest operating cost
- Quietest operation
- Minimal maintenance
- Single-phase (up to ~7.5kW) or three-phase
Diesel Engine
Best For: Remote sites, portable applications
- No mains power required
- Highly portable
- Good for intermittent use
- Higher maintenance requirements
Hydraulic Drive
Best For: Excavator/machine mounting
- Uses existing hydraulic power
- Submersible versions common
- Variable speed control
- Ideal for dredging applications
Pneumatic (Air)
Best For: Hazardous areas, mining
- Intrinsically safe – no sparks
- Can run submerged
- Simple and robust
- Requires compressed air supply
Decision Guide
Quick Selection Logic
- Pump above water level? → Self-priming or auto-prime
- Pump submerged? → Submersible pump
- Large solids or debris? → Trash pump or solids handling
- Chemicals or slurry? → Diaphragm or specialty pump
- High head, low flow? → Multistage centrifugal
- High flow, low head? → Axial flow or large centrifugal
Summary
Key Takeaways
- Match the pump type to your fluid properties and site conditions
- Consider suction conditions – they often dictate pump type
- Factor in total cost of ownership, not just purchase price
- Consult with pump specialists for complex applications