Building Better Pumping Systems: Optimizing New Designs

Selecting for Maximum Attainable Efficiency
The expected efficiency of a centrifugal pump can vary as a function of specific speed, the BEP rate of flow, and a wide range of construction and design features used in specific pumping applications. The theoretical values of maximum obtainable efficiency in Figure 2 provide an example for what can be achieved with reliable design and manufacturing practices.

Figure 2 shows that for a given specific speed, an increase in a pump BEP flow rate can result in superior efficiency. Similarly, for a given pump BEP flow rate, an increase in the design specific speed can achieve enhanced pump efficiencies, up to a point.

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As the system ages or operational requirements change, the head may need to increase. If the pump impeller was selected with some trim, the pump head may be increased by substituting an untrimmed impeller into the pump. This will increase the power requirements of the pump, so consider the cost effectiveness of specifying an oversized driver for initial duty. As the system ages or operational requirements change, the head generated by the pump may need to increase. If the pump impeller was selected with some trim, the pump head may be increased by substituting an untrimmed impeller into the pump. This will increase the power requirements of the pump, so consider the cost effectiveness of specifying an oversized driver for initial duty. Pumped liquid is another factor that can significantly affect pump efficiency and reliability. Corrosion, erosion and fouling will reduce pump efficiencies due to increasing surface roughness within the pump. Suggested solutions are shown in Table 2 below.

Table 2

Pump Design Speeds & Styles
Larger pumps will have higher initial costs than smaller, high-speed pumps, but tend to be more robust and lightly loaded resulting in significantly lower maintenance costs.