What is Pump Efficiency and Why is it Important?
Pump efficiency, to put it simply, is how well a pump transfers useful energy from a hydraulic power source to the pump output. As an example, if an electric motor was to provide X amount of energy to a machine, and the output is 1/X (Half of X), then the efficiency of the machine is 50%. This is because 50% of the energy has not been used on the primary output of the machine, and as such is ‘wasted’ energy.
For a pump, this “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.
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) refers to the optimal operating condition on a pump’s performance curve, where it achieves maximum hydraulic efficiency. At BEP, fluid flows through the pump with minimal energy loss, ensuring peak performance and reduced wear.
What if I Cannot Reach the BEP?
Operating away from BEP does not necessarily cause immediate pump failure, but it may reduce efficiency and increase long-term wear. Pumps can still function effectively within certain limits, though sustained operation far from BEP is not recommended.
Understanding the 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 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.