A pump curve is the single most important tool for selecting and operating a pump correctly. It shows how a pump will perform at different flow rates and heads, allowing engineers to match system requirements with pump capabilities. Understanding pump curves — and especially the Best Efficiency Point (BEP) — is key to reliable, efficient pump operation.
A pump curve is a graph provided by the manufacturer that plots:
Horizontal axis (L/s, m³/h, or gpm)
Vertical axis (m or ft)
The curve shows the relationship between flow and head. As flow increases, head decreases — this is the fundamental trade-off in pump performance.
Key Elements
Head vs Flow Curve
The primary line showing pump performance
Best Efficiency Point (BEP)
Where pump operates most efficiently
Efficiency Contours
Bands showing efficiency across flow range
Power Curve
Brake horsepower (BHP) required at different flows
NPSHr Curve
Net Positive Suction Head required to avoid cavitation
Operating Range
The safe window recommended by the manufacturer
Best Efficiency Point (BEP)
BEP is the flow rate at which the pump runs at maximum efficiency. At BEP, the pump experiences:
Minimal vibration
Lowest radial thrust
Reduced wear on bearings and seals
Optimal energy consumption
Rule of Thumb
Pumps should operate within ±10% of BEP whenever possible.
Operating Away from BEP
Too Far Left (Low Flow, High Head)
- Excessive recirculation inside pump
- High vibration and radial load
- Seal and bearing failure
Too Far Right (High Flow, Low Head)
- Cavitation risk increases
- Motor/engine overload
- Reduced pump life
System vs Pump Curve
Every pumping system has its own system curve, which shows how much head is required for different flow rates.
Operating Point
Where the system curve intersects the pump curve
Proper Selection
Choose a pump where the operating point is close to BEP
Example
System Requirement: 60 L/s at 45 m TDH
Pump BEP
62 L/s, 44 mOperating Point
60 L/s at 45 mStatus
Very close to BEPResult: Efficient, reliable operation with minimal wear
Best Practices
Always review pump curve data, not just catalogue flow/head values
Select pumps to run close to BEP for efficiency and reliability
Check NPSHr vs NPSHa to ensure cavitation-free operation
For variable duty systems, use VSDs (variable speed drives) to keep operation near BEP
Avoid oversizing — bigger is not always better
Summary
Pump curves are essential for correct pump selection and operation. By understanding how head, flow, efficiency, power, and NPSH interact — and targeting operation near the Best Efficiency Point — engineers can achieve reliable, long-lasting, and energy-efficient pumping solutions.