Pump efficiency describes how effectively a pump converts input energy into useful output.
In simple terms:
Input energy = power supplied to the pump shaft
Output energy = hydraulic power delivered to the fluid
Pump efficiency is expressed as:
Efficiency = Water Power ÷ Shaft Power
The higher the efficiency, the less energy is wasted as heat, vibration, or internal losses.
Pump speed plays a critical role in how a centrifugal pump performs.
Rather than focusing on physical size, engineers often use specific speed — a dimensionless value that helps predict pump behaviour across different designs.
Specific speed helps determine:
Expected efficiency range
Flow and head characteristics
Suitability for different applications
Risk of premature wear or failure
In practice, it allows designers and operators to compare pumps of different sizes while predicting performance with confidence.
Overall pump efficiency is made up of three key components:
Hydraulic efficiency – How effectively energy is transferred to the fluid, influenced by impeller design, vane shape and spacing.
Volumetric efficiency – Losses caused by internal leakage through wear rings, balancing holes and clearance gaps.
Mechanical efficiency – Losses from bearings, seals, packing and other rotating components.
As internal clearances increase and mechanical components wear, overall pump efficiency declines — reinforcing the importance of correct pump selection and ongoing maintenance.
One of the most critical design elements is the cutwater (or tongue) in the volute.
This feature controls flow into the pump throat. Optimal clearance between the impeller and cutwater:
Minimises pressure pulsations
Reduces internal recirculation
Maintains stable efficiency
When an impeller is trimmed excessively, clearance increases, internal recirculation rises, and efficiency drops.
Maintaining correct clearances is essential to long-term performance.
Yes — pump efficiency and the performance curve are closely linked.
General efficiency trends:
Low specific speed (<500): Low efficiency
Mid-range (≈2000–3000): Peak efficiency
High specific speed (>3000): Efficiency declines gradually
Understanding where a pump operates on its curve helps identify whether inefficiencies are design-related or operational.
Pump efficiency directly affects power consumption.
Power demand increases with flow and head
For the same duty point, higher efficiency = lower energy input
Improving efficiency:
Reduces energy costs
Lowers heat and wear
Extends pump life
Improves system reliability
Efficiency isn’t just a performance metric — it’s a cost control tool.
Efficient centrifugal pump operation depends on:
Correct pump selection
Operation near best efficiency point (BEP)
Proper internal clearances
Ongoing maintenance
Small efficiency improvements compound into meaningful energy and maintenance savings over the life of the pump.