The explanation of the “optimal efficiency point of pumps” in API610

The optimal efficiency should be related to the piping/backpressure system; the optimal efficiency point is a point determined jointly, while the rated flow rate point is merely a characteristic of the pump.

In accordance with API610 requirements, the pump’s operating point should preferably fall within the range of 80–120% (the flow rate at the best efficiency point), and the rated flow rate should be within the range of 80–110% of that best efficiency point flow rate; generally, the rated flow rate is 1.05–1.1 times the normal flow rate. This requirement is mainly to balance energy conservation and operational reliability. I didn’t find the statement mentioned by the original poster, that “the optimal efficiency flow rate should be between the rated flow rate and the normal operating flow rate,” in the standards.

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According to API610, version 11, section 6.1.13, the optimal efficiency point of the pump should be located between the rated flow rate and the normal flow rate.

This doesn’t belong to the API documentation; it’s just a technical discussion. I didn’t put the entire API standard here. A discussion on centrifugal pumps would hardly be appropriate without referring to API610, as it is currently the highest standard for the manufacturing and design of centrifugal pumps.

Furthermore, according to API610 version 11, the preferred operating range of the pump should be between 70% and 120% of the flow rate at the optimal efficiency point

Oh, I see. I’ve been using version 10 here; it hasn’t been updated yet. According to version 11, it can be understood that the normal flow rate lies within 70% of Qbep, while the rated flow rate does not exceed 1.1 times Qbep. Because after the pump has been operating for a certain period of time, the flow-related components wear out and its performance declines; at this point, the Qbep value or the rated value becomes the operating point at which the pump can still maintain sufficient output and efficiency. But in reality, almost no one does this, because it results in the selection of a pump with excessive specifications, leading to higher costs and no advantage in bidding; however, the costs over the entire life cycle are low. In China, few companies take into account the costs over the whole life cycle – as long as the price is low during bidding, that’s sufficient.

For pumps with a fixed speed, the optimal efficiency point of the pump is an inherent characteristic of the pump itself, and it is independent of pipeline design, operation, and process conditions. In other words, once a pump is manufactured, unless it is a variable-speed drive pump, its optimal efficiency point is fixed. For pump manufacturers, unless production is custom-made (which is technically possible but too costly), production is carried out in series (similar to standard components); therefore, it is unlikely to create pumps that can operate at their optimal efficiency point across the entire flow range and pressure range. Once the process design conditions are determined, the pump’s rated operating point (which generally refers to flow rate and head; efficiency is not part of the design parameters provided to the manufacturer) as well as its normal operating point are also established. Only after that is it possible to determine the suitability of the pump in terms of flow rate, head, and efficiency. That is, the rated operating point is determined first, and then the pump is selected. In terms of head and flow rate alone, manufacturers generally offer multiple pump types to choose from. API 610 requires that the \"optimal efficiency flow rate point be between the rated flow rate point and the normal operating flow rate point.\" ”Essentially, this requires pump manufacturers to take energy consumption into account when selecting pumps; that is, the optimal efficiency point should not lie outside the rated flow rate and normal operating flow rate points, as in such a case, from a design perspective, the operating point will never be at the optimal efficiency point.

Does anyone have a template for the pump data sheet in version 11?