Pump Efficiency Explained: Importance, Factors, and How to Optimization
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.
For a pump, the “wasted” energy can take many forms, including producing too much noise or heat. Noise and heat, which are typically undesirable forms of energy for a pump moving fluid from A to B, are categorized as “wasted” energy. All pumps offer different levels of efficiency; if you’re using Centrifugal Pumps, our guide on Achieving Maximum Efficiency for your Centrifugal Pump may be useful.
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 labor 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
Where:
- Phyd = ρ × g × Q × H (in Watts)
- ρ = Fluid density (kg/m³)
- g = Gravitational acceleration (9.81 m/s²)
- Q = Flow rate (m³/s)
- H = Head (m)
For example, if a pump receives 10 kW of input power and produces 7 kW of hydraulic output power, the efficiency is:
η = (7 / 10) × 100 = 70%
A higher efficiency indicates better energy utilization and less energy lost as heat, noise, or internal friction.
What Influences the Overall Efficiency of a Pump?
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 Best Efficiency Point (BEP)?
The Best Efficiency Point (BEP) is the precise operating condition (flow rate and head) where a pump achieves its maximum hydraulic efficiency – typically the “sweet spot” at the center of its performance curve. 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).
Why BEP Matters More Than You Think: The Hidden Costs of Off-Design Operation
The Best Efficiency Point (BEP) isn’t just a theoretical ideal—it’s the make-or-break factor in pump reliability, energy costs, and total ownership expenses. Most engineers focus on flow and head requirements but underestimate how severely operating away from BEP impacts real-world performance. Here’s why it deserves your full attention:
1. Energy Waste: The Silent Budget Killer
Every 10% deviation from BEP typically increases energy consumption by 2-5%. This seems minor until you realize:
- A 100 HP pump running continuously at 70% efficiency (vs. 85% at BEP) wastes $15,000+ annually (at $0.10/kWh
- Low-flow operation (below 40% of BEP) can halve efficiency due to recirculation losses
- Oversized pumps (common in 60% of installations) often operate at 50-60% efficiency when they could achieve 80%+
Real-World Example:
A municipal water plant saved $92,000/year simply by trimming impellers to shift operation closer to BEP.
2. Mechanical Consequences: How Off-BEP Operation Destroys Pumps
Radial Forces & Vibration:
At BEP: Hydraulic forces on the impeller are balanced → < 0.1 mm shaft deflection
Off-BEP: Unbalanced radial loads cause:
- 300% higher bearing loads (leading to premature failure)
- Shaft deflection exceeding 0.5 mm → seal misalignment
- Vibration spikes (2x-5x normal levels), accelerating wear
Cavitation & Suction Problems
Below 60% of BEP flow: Fluid recirculates violently, causing:
- Vapor bubble collapse (1,000+ bar microjets erode impellers)
- Noise levels exceeding 100 dB (indicates severe inefficiency)
- Pitting damage that reduces efficiency by 1-2% per year
Seal & Bearing Failures
| Operating Condition | Bearing Life | Seal Life |
| At BEP | 60,000 hrs | 5+ years |
| 30% of BEP | 8,000 hrs | 6 months |
3. The “Hidden” Costs You Never Accounted For
Maintenance Domino Effect
1. Off-BEP operation wears bearings 5x faster
2. Worn bearings increase shaft vibration
3. Vibration destroys mechanical seals
4. Seal failure floods bearings with process fluid
5. Result: 3-4x more downtime than BEP-operated pumps
Production Losses
- A single pump failure in a refinery can cost $500,000/day in lost production
- 90% of premature failures trace back to chronic off-BEP operation
Valve & Piping Damage
Throttling valves (used to force pumps off-BEP) experience:
- Cavitation damage in pressure-reducing applications
- 50% higher erosion rates due to turbulent flow
4. The Efficiency-Reliability Tradeoff Myth
Many assume that sacrificing some efficiency for flexibility is acceptable. Reality:
- A pump at 85% efficiency (BEP) may have a MTBF of 10 years
- The same pump at 65% efficiency often sees MTBF under 3 years
- Net result: The “savings” from flexible operation vanish into:
– 3x more spare parts inventories
– 2x more labor hours for repairs
– Unplanned downtime costs
Data Point:
Chemical plants operating within ±10% of BEP report 62% lower maintenance costs than those running at 50-70% of BEP flow.
5. How Industries Are Solving This
Oil & Gas:
– Use parallel pump systems to keep each unit near BEP
– Implement auto-trimming impellers that adjust to demand
HVAC:
– Variable primary systems with VFDs that track BEP in real time.
Water Treatment:
– AI-driven pump optimization adjusts speeds to maintain 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
Action Step:
- Audit your 3 highest-energy pumps for BEP deviation
- Measure vibration, amp draw, and efficiency at current flow
- Prioritize the unit with the biggest gap
Understanding the ‘Preferred Operating Region’ (POR)
The Preferred Operating Region (POR) is the recommended range for pump operation, typically spanning 70% to 120% of BEP. Since exact BEP operation isn’t always practical, the POR ensures:
- High hydraulic efficiency
- Minimal vibration and internal stresses
- Extended pump service life
What is the ‘Allowable Operating Region’ (AOR)?
The Allowable Operating Region (AOR) defines the broader range where a pump can function without severe damage. While efficiency declines, the pump remains operational within acceptable reliability standards.
What Happens Outside the AOR?
Operating beyond the AOR leads to:
- Excessive wear on seals, bearings, and impellers
- Higher maintenance costs due to frequent repairs
- Potential rapid failure at extreme flow rates (far left or right of the curve)
How Can I Optimize Pump Efficiency?
To maximize efficiency and approach BEP:
- Select the right pump size – Oversized or undersized pumps operate inefficiently.
- Adjust speed (RPM) – Slower speeds on larger pumps often improve efficiency.
- Consult experts – Pump specialists (especially pump manufacturers) can recommend high-efficiency models tailored to your needs.
Pump Performance Curve Chart
Use below pump performance curve to find safe operating range for the pump.