Centrifugal pump performance curve
Thread Content
Are the performance curves of ordinary centrifugal pumps different from those of centrifugal pumps equipped with variable frequency drives (flow-efficiency)? Figure 1 is the performance curve of a conventional centrifugal pump
In Figure 1, efficiency increases as the flow rate rises, and after reaching a peak, it decreases again as the flow rate increases
The underlined part in this image states that there is no change in efficiency before and after changing the rotational speed. Since changing the rotational speed of a variable-frequency pump means changing the flow rate, it follows that changes in flow rate do not result in any changes in efficiency. Therefore, the performance curve (flow rate–efficiency) would be a horizontal line?
Is there not a single sensible person?:'
1. Are you sure that the pump shown in Figure 2 of Chapter 2 is a centrifugal pump, and not a piston pump or a screw pump? 2. The higher the rotational speed of a centrifugal pump, the higher its efficiency
The law of cutting should have been called the law of proportionality in the previous chapter! Only when the speed is changed while the operating conditions remain unchanged is it called the proportional law. The constant efficiency mentioned in Figure 2 refers to the fact that the efficiency values at the two operating points before and after changing the rotational speed remain unchanged. It’s not all operating points after changing the speed; in such cases, an efficiency curve still exists, it’s not the relative curve ； If the rotational speed does not change much, the efficiency remains the same. Generally speaking, as the speed decreases, efficiency also decreases ； As the speed increases, efficiency may improve.
Changing the frequency causes the entire curve to shrink, and the extent of this shrinkage is determined by the scaling law shown in the second diagram. Pump efficiency is not a calculated value; it is determined after the pump is manufactured, and it should remain unchanged.
In the first graph, doesn’t the traffic efficiency performance curve increase as traffic volume rises, only to start declining after reaching its peak?
Efficiency changes; it is higher at high speeds. Look at the table: 12.5 cubic meters, 20 meters, rotation speed of 2900. It has a flow rate of 6.3 cubic meters, a head of 5 meters, and a rotation speed of 1450. The efficiencies of the two are 51% and 45% respectively. It’s better to have no books than to trust them blindly.
It refers to centrifugal pumps; take a look at those two screenshots: (