Ways to change pumps’characteristic curves

• Regulate speed

Figure a is the characteristic curve of a pump at different speeds ((n₁> n₂> n₃), device characteristic curve R and similar parabola H-KQ^2. We will know from the figure that if we don’t change the device characteristic curve, the working point after speed change may deviate from the best efficiency working point. Only when the device characteristic curve is as close as possible to the similar parabola after speed changing, will the working point after speed changing keep high efficiency. Speed regulation is suitable for big power pumps and applications where head changes dramatically.

• Regulate through impeller trimming

Impeller diameter trimming will only make the characteristic curve move downwards, figure b shows the working points of different impeller diameters, of which the situation is similar to that of the speed regulation.

• Regulate through changing impeller vane angle

Changing impeller vane angle is suitable for axial or mixed flow pumps. Impeller vanes of axial and mixed flow pumps can be regulated. Usually, when the vane angle is not changed much, max efficiency under each angle changes little. Plus, for axial flow pumps, when the impeller vane angel changes, the pump’s head will not change much, but the flowrate will change a lot. For mixed flow pumps, head and flowrate will change dramatically after the impeller vane angle changes.