Why Does The Head Of A Centrifugal Pump Decrease With Increasing Flow Rate?

Sep 24, 2024

The reason why the head of a centrifugal pump decreases with increasing flow rate can be explained from multiple aspects. The following are some of the reasons summarized by Lutsee Pump Industry technicians, the manufacturer of centrifugal pumps. We welcome discussion and correction.
1. Impeller characteristics:
The impeller speed and blade shape of a centrifugal pump are important factors that affect changes in head and flow rate. The relationship between head and flow rate can be expressed by the formula H=KQ ², where H is head, K is constant, and Q is displacement (flow rate). This formula indicates that the head is proportional to the square of the flow rate. However, when the flow rate exceeds a certain value, the resistance experienced by the impeller and the friction of the fluid also increase accordingly, resulting in a decrease in head.
2. Principles of Fluid Dynamics:
As the flow rate increases, the flow velocity of the fluid inside the pump also increases, resulting in increased frictional resistance between the fluid and components such as the pump body and impeller. This resistance will consume some energy and reduce the head of the pump.
3. Pump design and working conditions:
Centrifugal pumps have an optimal operating point (i.e., the optimal efficiency point) during design, which corresponds to a specific flow rate and head. When the flow rate of the pump exceeds this optimal operating point, the head of the pump will begin to decrease. In addition, the actual working conditions of the pump (such as inlet pipe resistance, outlet height, etc.) can also affect its head.
4. The principle of conservation of energy:
During the operation of the pump, energy is conserved. When the flow rate increases, although the input power of the pump also increases accordingly, the effective energy (i.e. head) that the pump can transfer to the fluid will decrease due to the increase in internal friction and resistance.
In summary, the reason why the head of a centrifugal pump decreases with increasing flow rate is mainly due to the combined effects of impeller characteristics, fluid dynamics principles, pump design and working conditions, and energy conservation principles. In practical applications, in order to maintain the efficient operation of centrifugal pumps, it is necessary to control their flow rate and head reasonably, and avoid letting the pump work for a long time under conditions beyond its design range.