Choosing the right pump for an application is critical to achieving reliable performance, energy efficiency, and long service life. Poor selection can lead to excessive wear, cavitation, high operating costs, and frequent breakdowns.
This guide outlines the key steps in pump selection and the factors to consider when sizing a pump correctly.
Key Considerations
Application Type
Dewatering, irrigation, wastewater, slurry, firefighting, process water, etc.
Fluid Characteristics
Clean water, sewage, abrasive slurry, corrosive chemicals.
Power Source
Electric, diesel, hydraulic, or solar-assisted systems.
Mobility
Fixed installation (skid/base-mounted) vs portable (trailer/submersible).
Duty Cycle
Intermittent, standby, or continuous 24/7 operation requirements.
Environment
Urban (noise-sensitive), remote site, hazardous or explosive areas.
Key Parameters
To size a pump correctly, engineers calculate the Total Dynamic Head (TDH) and Flow Rate required.
Flow Rate (Q)
- Based on system demand (litres per second, m³/h, or US gpm)
- Must account for peak flow, not just average flow
Total Dynamic Head (TDH)
TDH is the total pressure a pump must overcome, calculated as:
Static Suction Head (Hs)
Vertical distance from fluid surface to pump centreline (positive for flooded suction, negative for suction lift).
Static Discharge Head (Hd)
Vertical distance from pump centreline to discharge point.
Friction Losses (Hf)
Resistance in pipes, bends, fittings, and valves throughout the system.
Pressure Head (Hp)
Pressure required by the system (e.g., sprinkler or process pressure).
Matching Pump Curves
Pump manufacturers provide performance curves showing head vs flow for each pump model.
Select a pump that operates near its Best Efficiency Point (BEP) for optimal performance.
Avoid running pumps at extreme left (low flow/high head) or right (high flow/low head) of the curve to reduce wear and risk of cavitation.
Power & Efficiency
Pump Efficiency
Expressed as a percentage, higher efficiency means lower operating cost.
Brake Horsepower (BHP) Formula
Where: Q = Flow (gpm), H = Head (ft), SG = Specific Gravity of fluid, η = Efficiency
Select the motor/engine size with a margin (10-15%) above calculated BHP.
Consider variable speed drives (VSDs) for electric pumps to match demand.
Example Calculation
Application: Irrigation Pump for Sprinkler System
- Flow required: 50 L/s
- Static suction lift: 3 m
- Static discharge head: 25 m
- Friction losses: 7 m
- Pressure required at sprinklers: 20 m
Select a pump that delivers 50 L/s at 55 m TDH and check the curve for efficiency and power requirements.
Best Practices
Always size for peak demand, not average.
Select pumps close to their BEP for longevity and efficiency.
Allow a safety margin on power requirements.
Consider future system expansion when sizing.
Verify pump material compatibility with the fluid.
Check NPSH (Net Positive Suction Head) to avoid cavitation.
Summary
Pump selection and sizing require balancing flow, head, efficiency, and system design. By carefully calculating TDH, matching pump curves, and considering power and fluid properties, operators can ensure optimal performance and reduced lifecycle costs.