There is an inverse relationship between the head and the flow in the work of the pump, which is mainly reflected in the centrifugal pump. Specifically, when the head increases, the flow decreases; On the contrary, when the head is reduced, the flow rate will increase. This relationship can be visually expressed by the performance curve of the pump.
Analysis of the relationship between head and flow
Definition understanding:
Head: refers to the height of the pump can raise water, composed of suction head and pressure water head. The suction head is the height from the center of the impeller to the water surface, and the pressure head is the height from the center of the impeller to the height from which the water is pumped. The size of the head reflects the ability of the pump to overcome the gravity and flow resistance of the water.
Flow rate: refers to the volume of liquid transported by the pump in a unit time, usually expressed in cubic meters per second or cubic meters per hour. The size of the flow reflects the conveying capacity of the pump.
Inverse relationship:
In the centrifugal pump, because the water is thrown out by the centrifugal force in the impeller, when the head increases, it means that the water needs to overcome greater resistance to be lifted to a higher position, which will cause the speed of the water in the impeller to slow down, and then the amount of water passing through the impeller per unit time is reduced, that is, the flow is reduced.
Conversely, when the head is reduced, the resistance that the water flow needs to overcome is reduced, the water flow speed is accelerated, and the amount of water passing through the impeller per unit time is increased, that is, the flow rate is increased.
Performance curve:
The performance curve of the pump is a graph that describes the working state of the pump under different head and flow. The inverse relationship between head and flow can be visually seen through the performance curve. On the curve, with the increase of head, the flow rate decreases gradually. As the head decreases, the flow rate increases gradually.
Practical application:
When selecting and using the pump, it is necessary to determine the appropriate head and flow according to the specific working conditions and needs. If the head is too high and the flow is too small, it may cause the pump to not work properly or be inefficient; If the lift is too low and the flow is too large, it may waste energy or cause instability in the pipeline system.
In addition, it is also necessary to pay attention to the rated flow rate of the pump and the highest efficiency point. The rated flow rate refers to the flow value corresponding to the pump when working at the highest efficiency point. Operating at rated flow, the pump has the highest efficiency and the lowest energy consumption. Therefore, when selecting the pump, the operating point close to the rated flow rate should be selected as far as possible.
In summary, there is an inverse relationship between head and flow in the work of the pump. This relationship is of great significance for the understanding and selection of pumps.