From Curves to Real Performance: How to Keep Pumps Operating at Their True Duty PointBy: Dr. Hossein Ataei FarAbstract:Efficient pump operation ...

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From Curves to Real Performance: How to Keep Pumps Operating at Their True Duty Point
By: Dr. Hossein Ataei Far

Abstract:
Efficient pump operation is essential for reducing energy consumption and improving reliability in water and wastewater facilities. This article presents a system-based approach to operating centrifugal pumps at their intended duty point by integrating hydraulic system management, Best Efficiency Point (BEP)–centred operation, variable-speed control, routine verification of the real operating point, and structured asset care practices. The study emphasizes that pump performance is governed by the interaction between the pump curve and the actual system resistance and that changes in network hydraulics, suction conditions, and operating strategy primarily cause long-term deviations from the design condition.
Application of the proposed operational framework demonstrates that maintaining pumps at 90% or more of BEP flow, supported by variable-speed drives and proper pump scheduling, leads to more stable hydraulic operation and improved mechanical reliability. Regular verification of flow, pressures, and power consumption enables early detection of system fouling, blockages, and off-design operation. The results indicate that systematic monitoring of specific energy consumption (kWh/m³) provides a reliable indicator of duty-point deviation and energy performance. Overall, the integrated approach enables sustained operation close to the duty point, resulting in lower energy use, reduced hydraulic and mechanical stress, and extended asset life for water and wastewater pumping systems.

### Introduction
In water and wastewater facilities, a centrifugal pump does not operate at a fixed point defined by the manufacturer. Instead, it functions at the intersection of its performance curve and the actual system resistance. Therefore, the priority is to control the operating point through the system, not only through the pump. Maintaining clean and hydraulically stable pipelines, valves, wet wells, strainers, and other hydraulic structures ensures that the real system curve remains close to the original design condition.
The pump should operate as close as possible to its Best Efficiency Point (BEP). For most water and wastewater applications, a practical and widely accepted operating range is approximately 90 to 105 percent of the BEP flow. Operating within this range provides the best balance between energy efficiency, hydraulic stability, and mechanical reliability.
Flow and pressure should be regulated primarily through variable-speed drives rather than throttling. Variable-frequency drives (VFDs) allow the pump to respond to actual demand while maintaining the operating point within the efficient zone. Permanent throttling increases system losses and pushes the pump away from its optimal operating condition.
The real duty point should be verified regularly. Measured flow rates, suction and discharge pressures, and power consumption should be used to determine the actual operating point. Design values and commissioning data alone cannot accurately represent long-term operation because hydraulic conditions change over time.
Maintaining proper suction conditions and overall network hydraulics is essential. Suction lines, screens, wet wells, and pipelines must be kept clean to prevent hidden cavitation, unstable inlet conditions, and gradual efficiency loss caused by fouling, scaling, biofilm growth, or partial blockages.
The number of operating pumps also affects efficiency. In most pumping stations, a single pump operating near its efficient range is more energy-efficient and reliable than multiple pumps running lightly loaded or far from their optimal operating point.
For routine performance monitoring, a simple and practical indicator is specific energy consumption in kilowatt-hours per cubic meter pumped. Trending this value provides a direct signal of how efficiently the pumping system is operating relative to its duty point.

Alignment with Leading Pump Manufacturers
Major pump manufacturers such as KSB, Xylem–Flygt, Ebara, Sulzer, Grundfos, and others consistently recommend similar operational principles for water and wastewater facilities. These include BEP-centered operation, system-based pump selection and evaluation, use of variable-speed drives, proper wet-well and suction design, and continuous performance monitoring. Collectively, these measures are recognized as the most effective way to achieve high efficiency and long equipment life.

Key Message for Utilities
Efficient pump operation is not only a matter of hardware. It results from combining manufacturer technology, proper operational strategy, and structured asset care programs. When applied together, these elements allow pumps to operate continuously close to their duty point and BEP, resulting in lower energy consumption, higher reliability, and longer asset life.

References:
1. KSB SE & Co. KGaA. The sweet spot – How to keep your pump operating near its Best Efficiency Point (BEP). KSB Know-how Portal.
https://www.ksb.com/en-ca/software-and-know-how/know-how/ksb-canada-blog/best-efficiency-point
2. Xylem – Flygt. Pump Station Design – Engineering & Expertise Manual. Xylem Water Solutions.
https://www.xylem.com/siteassets/brand/flygt/flygt-engineering--expertise/manual_pumpstationdesign_20241018_master_en_lowres.pdf

Please review this post prepared by Eng. Nana Yaw Osei-Poku here:
[LinkedIn Post]
https://www.linkedin.com/posts/nana-yaw-osei-poku-cheme-llb-mph-65a1b7373_processengineering-chemicalengineering-pumpcurve-activity-7422974790925205504-PAm5?utm_source=share&utm_medium=member_desktop&rcm=ACoAAEBDhzIBsyuiuDI0-eiNhRpHh9ad-Axkqtk

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