During the dry season or low tide in winter, the water level of the river drops, and how does the centrifugal pump fail to pump water?

In the development of a new pump type or product inspection, a water pump plant must perform a performance test to obtain the working performance of the water pump and indicate its operating parameters on the nameplate so that the user can select the water pump as a technical basis. Guidance role. In addition, in the product manual, there are also several performance curves drawn to allow users to use the pump, the use of conditions has changed, as the technical basis for the pump performance adjustment.
The performance curve of the pump is obtained through experimental methods. At the rated speed, the flow rate of the pump is changed by operating the opening degree of the gate valve, and the operating parameters such as lift, power, efficiency, and allowable vacuum height of the pump are all changed accordingly. The change law of this kind of mutual relation, comprehensive draws several curves to express, this is the water pump performance curve. Take the flow-head curve as an example to illustrate the change of the lift of the centrifugal pump with the flow rate. When the flow rate Q is 0, the head H reaches a maximum value, and when the flow rate increases from small to large, the head decreases from large to large. When the flow is small, the head is relatively high; when the flow is slowly increased, the head is gradually reduced. In addition, the flow rate—allowed to suck up the vacuum height curve—is within the same working range as the former.
In agricultural production, we install water pumping to pump highland irrigation, which is based on the actual terrain elevation (vertical height), and then consider the additional pipeline along the road and local loss head, and finally determine the pump lift. In the winter dry season or low tide, the water level of rivers has dropped, and the conditions for the use of water pumps have changed. In essence, the height of the actual surface elevation has increased. According to the performance curve, if the gate valve on the outlet pipe is closed down, that is, when the flow rate is reduced, a higher head can be obtained and the performance of the pump can be adjusted. At this time, the centrifugal pump can draw water.