Pump Efficiency & Best Efficiency Point
⏱️ Estimated Reading Time: 10 min
🗓️ Last Updated: 29 August 2025
What is Pump Efficiency?
Pump efficiency is a measure of how effectively a pump converts mechanical input energy into hydraulic energy to move a fluid. In simpler terms, it tells us how much of the supplied energy is being used to do useful work — pumping fluid — and how much is being wasted through heat, noise, or mechanical losses.
For example, if a pump receives 10 kW of power and delivers 7 kW worth of hydraulic energy, its efficiency is 70%. The remaining 30% is lost due to internal friction, turbulence, or component inefficiencies. Higher efficiency means lower energy consumption, reduced wear and tear, and better overall system performance.
These energy losses often appear in the form of unwanted heat or noise. Since the primary purpose of a pump is to transport fluid efficiently from one point to another, any energy diverted to heat generation, vibration, or excessive noise is considered “wasted” energy.
Why is Pump Efficiency Important?
In a nutshell, a pump that works better helps you save money. When moving fluid in a system, a highly inefficient pump will waste energy, leading to higher electricity costs to power the pump. Additionally, there are the costs associated with maintenance. An inefficient pump will wear out faster than an efficient pump, resulting in a loss of revenue (since production is halted because the pump is not working), additional labour and time spent resetting the pump, and additional spare parts required annually.
How is Pump Efficiency Calculated?
Pump efficiency (η) is defined as the ratio of hydraulic power output to mechanical power input:
η = (Phyd / Pinput) × 100
This is the formula to calculate the pump efficiency where:
- η = Pump efficiency (Pump efficiency (unitless, expressed in percentage)
- Phyd = ρ × g × Q × H (kW) – This is the output power delivered to the fluid by the pump
- Pinput = This is the power supplied to the pump shaft (kW)
Hydraulic power (Phyd) is dependent upon Fluid density (ρ), Gravitation acceleration (g), Flow rate (Q) of the pump and Pump head (H).
To learn about how Hydraulic and Input Power of the pump is calculated visit the page Calculating Pump Efficiency.
Efficiency of Different Pump Types
Pumps can broadly be divided into two main categories based on how they move fluids: centrifugal pumps and positive displacement pumps. Each category has distinct efficiency characteristics, which are crucial for selecting the right pump for a given application. To know more about pumps, follow Classification of Pumps page.
Centrifugal Pump Efficiency
In centrifugal pumps, efficiency is defined as the ratio of the hydraulic power delivered to the fluid (flow rate × developed head × fluid density × gravity) to the mechanical power supplied to the pump shaft. Because these pumps rely on imparting velocity to the fluid, their efficiency is highly dependent on operating near the Best Efficiency Point (BEP). When operated too far left or right of the BEP, efficiency drops sharply due to recirculation, turbulence, and increased hydraulic losses.
Centrifugal pump efficiency typically ranges between 60% and 90%, with larger pumps generally achieving higher values. However, efficiency also varies with system head, impeller design, wear over time, and fluid viscosity. In applications where flow demand fluctuates, centrifugal pumps may experience efficiency penalties if not carefully matched to the duty point.
Positive Displacement Pump Efficiency
In positive displacement (PD) pumps, efficiency has a different meaning. Since PD pumps move a fixed volume of fluid per cycle, their theoretical efficiency is close to 100%. In practice, however, efficiency is reduced by internal leakage (slip), frictional losses, and energy consumed in valve operation.
The overall efficiency of a PD pump is primarily influenced by its volumetric efficiency (ηᵥ), which accounts for internal leakage and compressibility losses. It can be expressed as the ratio of actual delivered flow to the theoretical flow:
ηv = (Qactual ÷ Qtheoretical) × 100
This is the formula to calculate volumetric efficiency where:
- ηv = Volumetric efficiency (unitless, expressed in percentage)
- Qactual = Actual flow delivered by the pump (m³/s or L/s)
- Qtheoretical = Theoretical flow based on pump displacement or geometry (m³/s or L/s)
Positive displacement pumps generally maintain high efficiency across a wide pressure range, making them suitable for high-viscosity fluids or applications requiring constant flow regardless of pressure fluctuations. Typical efficiencies range from 70% to 95%, depending on pump type, operating conditions, and wear. Unlike centrifugal pumps, their efficiency is less sensitive to system head but more influenced by clearances, speed, and fluid properties.
Factors Affecting Overall Efficiency of a Pumps
Overall pump efficiency is what you would use to determine the amount of wasted energy loss throughout a pump, which can be defined as the ratio of the actual power output to the actual power input. There are three elements that influence and change a pumps overall efficiency:
- Mechanical: This is the efficiency used to calculate and identify the power lost in moving parts of the pump, such as bearings, stuffing boxes, mechanical seals etc. This can be defined as the ratio of theoretical power the pump requires to the actual power delivered to the pump itself.
- Volumetric: Volumetric efficiency is used to calculate and identify the liquid lost through balancing holes and wear rings. This also includes the clearances between the pump casing and impeller vanes for semi-open or open impeller designs. This can be defined as the ratio of the actual flow rate that the pump provides to the theoretical discharge flow rate.
- Hydraulic: This is perhaps the most important factor to consider, as it calculates & identifies the losses of liquid friction and other losses inside the volute and impeller. This can be defined as the ratio of useful hydrodynamic energy (in the form of fluid) to the amount of mechanical energy delivered to the rotor
What is Pump Best Efficiency Point (BEP)?
The Best Efficiency Point (BEP) of a pump is the operating condition—defined by flow rate and head—where the pump delivers maximum hydraulic efficiency. Often referred to as the “sweet spot” of a pump’s performance curve, BEP represents the ideal balance between energy usage, mechanical stress, and smooth fluid flow. At BEP:
- Fluid enters and exits the impeller without turbulent recirculation
- Radial forces on the shaft are perfectly balanced
- Energy losses from friction, leakage, and heat generation are minimized
Key Metric: BEP is usually expressed as % of flow rate (e.g., 100 GPM at 85% efficiency).
Understanding BEP is critical because operating a pump away from this point can increase energy costs, accelerate mechanical wear, and reduce service life.
Why Pump BEP Matters: Hidden Costs of Off-Design Operation
The Best Efficiency Point isn’t just theoretical—it directly affects pump reliability, energy consumption, and total ownership costs. Many engineers focus only on flow and head requirements but underestimate the consequences of operating away from BEP.
1. Energy Waste: The Silent Budget Killer
Operating away from BEP can drastically increase energy costs:
- Every 10% deviation from BEP typically increases energy consumption by 2–5%.
- Low-flow operation (below 40% of BEP) can halve pump efficiency due to recirculation losses.
- Oversized pumps, common in 60% of installations, often run at 50–60% efficiency instead of achieving 80%+ at BEP.
Real-World Example:
A municipal water plant saved $92,000/year by trimming impellers to operate pumps closer to BEP.
2. Mechanical Consequences – How Off-BEP Pump Operation Destroys Equipment
Operating a pump away from its BEP can cause serious mechanical problems. Key consequences include:
Radial forces and vibration: At BEP, hydraulic forces are balanced and shaft deflection is minimal (< 0.1 mm). Off-BEP operation causes unbalanced forces, increasing bearing loads by up to 300%, shaft deflection above 0.5 mm, and vibration spikes 2–5 times normal levels.
Cavitation and suction problems: Below 60% of BEP flow, fluid recirculates violently, creating vapor bubble collapse that erodes impellers, produces noise above 100 dB, and causes pitting that reduces efficiency by 1–2% per year.
Seal and bearing failures: Bearings and seals wear faster under off-BEP conditions. Lifespan drops dramatically—for example, bearings at BEP last ~60,000 hours, while at 30% of BEP they last ~8,000 hours; seals last 5+ years at BEP, but only 6 months at 30% of BEP.
3. Hidden Maintenance Costs
Maintenance Domino Effect:
- Off-BEP operation wears bearings 5x faster.
- Increased shaft vibration destroys mechanical seals.
- Seal failure floods bearings with process fluid.
- Result: 3–4x more downtime than pumps running at BEP.
Production Losses:
- A single pump failure in a refinery can cost $500,000/day.
- 90% of premature failures originate from chronic off-BEP operation.
Valve & Piping Damage:
Throttling valves used to force off-BEP operation experience cavitation and 50% higher erosion.
4. The Efficiency-Reliability Tradeoff Myth
Many assume sacrificing efficiency for operational flexibility is acceptable. Reality shows:
- Pump at 85% efficiency (BEP) → MTBF ~10 years
- Pump at 65% efficiency → MTBF <3 years
Hidden Costs Include:
- 3x more spare parts inventory
- 2x more labor hours for repairs
- Frequent unplanned downtime
Data Point:
Chemical plants maintaining ±10% of BEP report 62% lower maintenance costs than plants running at 50–70% of BEP.
5. How Industries Optimize Pump BEP
Oil & Gas:
- Parallel pump systems to keep units near BEP
- Auto-trimming impellers for variable demand
HVAC:
Variable primary systems with VFDs tracking BEP in real time
Water Treatment:
AI-driven pump optimization maintains BEP despite demand swings
Key Takeaways
1. BEP isn’t optional – it’s the foundation of pump reliability
2. Every 10% away from BEP costs 2-5% more energy + 3x maintenance
3. Low-flow operation is the #1 cause of premature failures
4. Solutions exist (VFDs, trimming, parallel systems) to stay near BEP
Understanding the ‘Pump Preferred Operating Region’ (POR)
A key question to ask; what is more important when selecting a pump efficiency or BEP?
For long-term performance and reliability, operating near the BEP is generally more important than maximum efficiency. However, another key concept the Preferred Operating Region (POR) needed to be understood.
Key points about POR:
- Typically spans 70% to 120% of the BEP flow rate.
- Operating within the POR ensures high hydraulic efficiency, low vibration, and balanced radial forces on the shaft.
- Helps extend pump service life and reduce maintenance costs.
- While exact BEP operation is ideal, POR allows practical flexibility for varying system demands without significantly compromising efficiency or reliability.
In short, the POR is the recommended operating range that keeps pumps running efficiently and safely even under fluctuating process conditions.
The ‘Allowable Operating Region’ (AOR)?
The Allowable Operating Region (AOR) of a pump is the broader range of operating conditions within which a pump can function without immediate or catastrophic failure, but not necessarily at optimal efficiency. It defines the limits beyond which pump operation becomes unsafe or can cause rapid damage.
Key points about AOR:
- Extends beyond the Preferred Operating Region (POR).
- The pump remains operational, but efficiency drops and mechanical stress increases.
- Operating near the edges of the AOR can lead to higher wear on bearings, seals, and impellers, increased vibration, and higher maintenance costs.
- Exceeding the AOR (far left or right of the pump curve) can result in rapid failure, cavitation, and severe mechanical damage
How to Improve Pump Efficiency/ Optimizing Pump Efficiency
To maximize efficiency and operate close to the Best Efficiency Point (BEP):
1. Select the Right Pump Size
- Avoid oversized pumps that operate far left of BEP (causing recirculation, cavitation, and excessive heat)
- Avoid undersized pumps that operate far right of BEP (resulting in inadequate flow and excessive energy consumption)
- Use accurate system curve calculations to match pump to application
- Consider future system requirements but avoid excessive safety margins
2. Implement Variable Speed Drives (VSDs)
- Adjust pump speed (RPM) to match exact system requirements
- Slower speeds on oversized pumps significantly improve efficiency
- Maintain operation near BEP across varying demand conditions
- Typically reduces energy consumption by 30–50% in variable flow systems
3. Conduct Regular Maintenance
- Monitor and replace worn impellers, wear rings, and bearings
- Maintain proper alignment and lubrication
- Check and repair seals to prevent efficiency losses
- Clean filters and strainers to reduce system resistance
4. Optimize System Design
- Minimize pipe friction losses through proper piping layout
- Eliminate unnecessary bends, restrictions, and valves
- Use appropriately sized pipes to minimize friction
- Consider parallel pumps for highly variable demand
5. Consult with Experts
- Pump specialists can recommend high-efficiency models tailored to your needs
- Manufacturers provide detailed performance curves for optimal selection
- Energy audits can identify efficiency improvement opportunities
- System analysis can identify mismatches between pump and system characteristics
6. Monitor Performance
- Install flow meters and pressure gauges to track operating points
- Use energy monitoring to identify efficiency degradation
- Compare actual performance to pump curve predictions
- Implement predictive maintenance based on performance data
7. Consider Retrofitting or Replacement
- Older pumps may benefit from modern high-efficiency components
- Sometimes complete pump replacement provides better ROI than continual repairs
- Newer designs often offer significantly improved efficiency characteristics
The most effective approach combines proper initial pump selection with ongoing monitoring and adjustment to maintain operation as close to BEP as possible throughout the pump’s lifecycle.
Pump Performance Curve Analysis
This interactive chart visualizes a pump’s performance by showing its head (pressure) and efficiency across different flow rates. The green shaded area represents the optimal operating range (80-110% of the Best Efficiency Point), while vertical lines mark the BEP (orange) and minimum safe flow (yellow). Users can adjust the BEP percentage and drag a slider to see how different flow rates affect the pump’s head and efficiency in real-time, with the red dot indicating the current operating point.