The main method of pump flow control 1 to change the pipeline characteristic curve The most simple way to change the centrifugal pump flow is to use the pump outlet valve opening to control, its essence is to change the position of the pipeline characteristic curve to change the pump operating point. 2 changes in centrifugal pump characteristics According to the law of proportion and cutting law, change the pump speed, change the pump structure (such as cutting impeller diameter method, etc.) can change the centrifugal pump characteristics of the two curves, so as to adjust the flow (while changing the pressure Head) of purpose. However, for already working pumps, the method of changing the pump structure is less convenient and the versatility of the pump is reduced by changing the pump structure, although it is economically convenient at some times to regulate the flow1 and is rarely used in production . Here only analyze the change of centrifugal pump speed regulation method. When the pump speed is changed to adjust the flow rate from Q1 to Q2, the pump speed (or motor speed) drops from n1 to n2, and the pump speed is n2, the characteristic curve of pump QH and the pipeline characteristic curve He = H0 + G1Qe2 Curve does not change) to point A3 (Q2, H3), A3 is the new operating point after adjusting the flow through the speed. The adjustment method has the advantages of obvious regulation effect, quickness, safety and reliability, prolonging the service life of the pump and saving electric energy, and additionally reducing the rotational speed operation can effectively reduce the NPSHr of the centrifugal pump and keep the pump away from the cavitation zone and reduce the centrifugal pump The possibility of cavitation occurs 2. The disadvantage is the need to change the pump speed through the variable frequency technology to change the prime mover (usually the motor) speed, the principle of complex, large investment, and the flow adjustment range. 3 pump string, and even adjust the way When a single centrifugal pump can not meet the delivery tasks, you can use the centrifugal pump in parallel or series operation. In parallel with two centrifugal pumps of the same type, although the pressure head changes little, but increases the total delivery flow, the total efficiency of the parallel pump is the same with the efficiency of a single pump; when the centrifugal pump is connected in series, the total pressure head increases, Little change in flow, the total efficiency of tandem pumps with a single pump the same efficiency.