Optimal operating conditions of centrifugal pumps

Refer to the performance curve for the optimal operating conditions; generally, the minimum flow rate is 20% of the rated flow rate.

The optimal operating condition is generally the point where efficiency is highest; the current should not exceed the rated value. Prolonged operation at very low flow rates can lead to cavitation and damage to the seals, but operating at a flow rate close to the rated value should not pose any problems

This is also something I want to know. In current system design, the rated flow rate of many pumps is 2 to 3 times their operating flow rate. To meet future expansion needs, these pumps are required to operate at low frequencies for extended periods; especially since my system operates under negative pressure. Can such pumps function properly over a long time?

I don’t think there’s any problem, as long as it isn’t operating below the minimum flow rate. If it is variable frequency, there is no issue with power consumption.

Try to reply as follows: At what percentage of the rated flow rate is the discharge volume of the centrifugal pump at its optimal operating condition during operation? Or at what level of current is it optimal relative to the rated current? Considering solely the long-term stable operation of the pump, the optimal operating condition is its best efficiency point. At this point, efficiency is highest and vibration is minimal. There is no inherent relationship between this optimal operating point and the motor’s rated current. For a centrifugal pump operating for an extended period of time, what percentage of the rated flow rate is the minimum allowable flow rate? What happens if a pump operates at an extremely low flow rate for an extended period of time, or operates at a flow rate close to its rated value? Strictly speaking, the minimum flow rate of a centrifugal pump is closely related to the structure of the pump itself. When the operating flow rate of the pump is below the minimum discharge volume, it may lead to increased vibration in the pump, and cavitation may also occur due to the heating of the liquid being pumped, which results in vaporization. Based on experience, the optimal efficiency point generally corresponds to a flow rate of 30–40%. The recommended operating points are, in order, the flow rate at optimal efficiency, the rated flow rate; operation at extremely low flow rates is not recommended. The reason has been explained above. Finally, as a supplementary point, the rated flow rate is a parameter specific to the process, not a characteristic of the pump itself. In other words, the rated flow rate, along with motor power, etc., are determined by designers based on operational requirements; there is no inevitable one-to-one relationship between these values and the pump’s properties. For a pump, its characteristic flow rate represents the point of optimal efficiency, as well as the preferred operating range and the allowable operating range; for details on this relationship, refer to Figure 26 in API 610 (10th edition). In other words, once a pump is manufactured, these parameters remain fixed.