1. Flow - head curve (H - Q curve); the three kinds of pump H - Q relationship curve is down, that is, the head with the increase of the flow rate decreases. This is because the flow through the pump increases, the flow rate is also increased, the loss of the pump also increases, so the head down. The change of Q - H curve of centrifugal pump is relatively flat, which indicates a smaller impact on the head flow changes in a wide range so it is suitable for the flow and lift often changes essentially the same occasion; axial flow pump Q - H curve is steep, and the saddle shaped turning point, which indicates only in the larger flow, head change is not too large, but too large or too small in the flow, head changes are large, at the same time, the axial flow pump head is generally higher than the centrifugal pump lift is low, so the axial flow pump for low lift and large flow and flow changessmall, between the mixed flow pump the Q - H curve between centrifugal and axial flow pump, so it is suitable for medium head occasions.
2. Flow - shaft power curve (N - Q curve), the N - Q curve of centrifugal pump is rising, that is, the pump shaft power is increased with the increase of flow rate, flow rate is zero, the minimum shaft power. Therefore, in order to avoid the pump start to make the motor overload, the centrifugal pump should be in the case of the closure of such as water pipe valve. In addition, the centrifugal pump operating in the case of less than the rated head, to pay attention to the motor overload.
The N - Q curve of the axial flow pump is decreased, that is, the shaft power decreases with the increase of the water quantity. According to the characteristics of axial flow pump should start in the case of open outlet valve. In addition, the axial flow pump operating at higher than its rated head, should pay attention to motor overload.
The Q - N curve of the mixed flow pump are relatively flat, namely the influence of flow rate on the shaft power is very small, so the mixed flow pump on the valve not essential.
3. Traffic - the efficiency curve (Q curve relationship between the changes of Q - ETA); ETA curve of centrifugal pump and mixed flow pump is relatively flat, especially on both sides of the maximum efficiency point, curve down is not obvious. It shows that the high efficiency of the centrifugal pump and mixed flow pump is wide, which is conducive to the regulation of the flow. Axial flow pump (refer to the fixed blade axial flow pump) Q - ETA curve is very steep, the curve on both sides of the highest efficiency decreased obviously. It shows that the high efficiency of axial flow pump is narrow, which is not conducive to the regulation of flow.
