What is the BEP and What Happens to a Pumping System When a Pump is Not Operated at the BEP?

The Best Efficiency Point (BEP) is the point at which a pump operates with peak efficiency. It occurs when the flow enters and exits the pump with minimal turbulence, separation, or other losses. This point is crucial because operating a pump close to its BEP minimizes wear and tear, enhancing pump reliability and extending its operational life. The BEP is represented as the apex of the efficiency curve (green line) on a pump performance graph, showing the relationship between head (vertical axis) and flow rate (horizontal axis).

Understanding the BEP

At the BEP, the hydraulic loads and flow patterns are balanced, resulting in optimal energy conversion from mechanical to hydraulic energy. This not only enhances the pump’s efficiency but also minimizes vibration, noise, and mechanical stresses. The pump experiences the least amount of radial thrust, which is critical for reducing shaft deflection and ensuring longer seal and bearing life.

When a vertical line is drawn from the BEP down to the pump curve (black line), the corresponding flow rate and head at the BEP can be determined. This point represents the most efficient point of operation, which is ideal for maintaining the pump’s longevity.

Preferred Operating Region (POR)

The Preferred Operating Region (POR) is a range of flow rates around the BEP, within which the pump operates efficiently without substantial degradation of hydraulic efficiency or reliability. The POR is essential for maintaining high operational performance and avoiding premature wear. ANSI/HI 9.6.3, a guideline for rotodynamic pumps, defines the POR based on the pump type (radial, mixed, or axial flow).

Operating within the POR ensures:

• Reduced wear on internal components
• Minimization of flow-induced vibrations
• Extended bearing and seal life
• Lower energy consumption

A typical POR range is located slightly to either side of the BEP on the pump curve. It represents a safe operating margin where the pump still functions efficiently, but the design service life of the pump remains unaffected by excessive hydraulic loads or mechanical stresses.

Allowable Operating Region (AOR)

The Allowable Operating Region (AOR) is a broader range outside the POR where the pump can still operate acceptably. The AOR defines the boundaries within which the pump can function without severe performance loss or mechanical damage. However, the further the pump operates from the BEP within the AOR, the higher the likelihood of decreased efficiency and increased wear.

The AOR is determined by factors beyond energy efficiency, such as:

• Hydraulic loads (bearing life, shaft deflection, thrust, etc.)
• Temperature rise in the pumped liquid
• Shaft and bearing housing vibration
• Audible noise levels
• Power limitations
• Net Positive Suction Head (NPSH) availability
• Risk of suction recirculation

These factors should be carefully considered with the pump manufacturer to ensure the pump is operating within its allowable range for the application at hand.

Consequences of Operating Outside the BEP

When a pump operates far from its BEP, whether at a lower or higher flow rate, multiple issues can arise:

1. Low Flow Rates: At low flow rates, the pump experiences higher radial loading, which can lead to excessive shaft deflection. This increased deflection results in seal wear, bearing stress, and potential impeller contact with the pump casing, accelerating failure. This is particularly problematic with rotodynamic pumps, where excessive radial thrust can distort shaft alignment.
2. High Flow Rates: Operating at excessively high flow rates can result in inadequate suction head, leading to cavitation. Cavitation is a damaging condition where vapor bubbles form and collapse violently within the pump, leading to pitting, noise, and significant damage to the impeller and other internal components. Furthermore, high flow rates increase the likelihood of suction recirculation, where a portion of the flow returns to the pump inlet, disrupting the normal flow pattern.
3. Vibration and Noise: Pumps operated far from their BEP often exhibit increased vibration and noise, leading to a higher risk of mechanical failure. The additional stress on bearings and seals causes premature wear, and the audible noise from the pump indicates inefficient operation.
4. Increased Power Consumption: As the pump moves further from the BEP, efficiency drops, resulting in increased energy consumption. This leads to higher operational costs and contributes to a shorter lifespan due to the excessive strain on the motor and mechanical components.

Impact on Pump System Performance

The efficiency and reliability of a pump are significantly impacted when it operates outside the BEP, both in terms of energy consumption and maintenance requirements. Prolonged operation outside the POR and AOR can lead to frequent maintenance interventions, unplanned downtime, and higher operational costs.

Figure 1 below illustrates a typical pump curve with the BEP at the highest efficiency point, and the POR and AOR ranges indicated:

• BEP: The point of highest efficiency
• POR: The preferred operating range, ensuring optimal performance with minimal degradation
• AOR: The acceptable operating range, where efficiency and reliability start to decline, but operation is still permissible.

Conclusion

Understanding and operating a pump within its BEP and POR is critical to maximizing efficiency and extending service life. Deviation from the BEP, either at low or high flow rates, can result in excessive wear, cavitation, increased power consumption, and mechanical failures. Working closely with the pump manufacturer to define the AOR for specific applications ensures that the pump operates safely and efficiently, reducing maintenance costs and improving overall system performance.

Incorporating these best practices will not only enhance the reliability of pumping systems but also optimize energy usage and reduce downtime, ultimately leading to significant cost savings.

WaterHygge can help you choose the right pump for all applications. Pump selections are made by technical sales engineers who are familiar with your process, ensuring that the equipment is designed to exceed your requirements. Our extensive experience suggests that we have likely delivered solutions for similar processes in the past. With our proven results, we can help you achieve your desired outcomes more quickly.

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