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What is the performance curve of the agricultural pump?
- Dec 08, 2018 -

What is the performance curve of the agricultural pump?


A curve that reflects the relationship between pump performance parameters (eg, flow, head, power, efficiency) is called the pump performance curve. Generally, when the pump speed is constant, the abscissa axis represents the flow rate, and the ordinate axis represents the indenter, power and efficiency, respectively, and the pump performance curve obtained by the test method.

The most commonly used agricultural pumps are single-stage centrifugal pumps, followed by axial and mixed-flow pumps. These three pumps have different configurations, different impellers, and different performance curve trends. Below we briefly analyze the changes in the three main performance curves of the three pumps.

(-) flow curve

It is customary to use English letters to represent curves. The curve of the centrifugal pump is relatively flat. In the small flow area, when the flow changes, the head changes little. When the flow reaches a certain value, the lift will gradually decrease. The curve of the axial flow pump has a steeply falling shape in the small flow region and has a saddle-shaped unstable working area. When the flow rate exceeds a certain value, the head rapidly decreases as the flow rate increases. The working area of the axial pump must be placed on the right side of the saddle-shaped unstable area to prevent the pump from running unstable. The Q-H curve shape of the mixed flow pump is located between the centrifugal pump and the axial flow pump. Typically, the curve of the mixed flow pump has no unstable saddle area.

(2) Flow rate - power curve

It is customary to use English letters to represent the Q~N curve. The power here refers to the shaft power. As the flow rate increases, the curve of the centrifugal pump gradually increases. When the flow rate is small, the power becomes small; when the flow rate is equal to zero, that is, when the gate valve is closed, the power is minimum. Therefore, the centrifugal pump is suitable for starting the brake. As the flow rate increases, the curve of the axial flow pump decreases. When the flow rate is zero, the power is the largest, which is 2 to 3 times the normal working power. Therefore, the axial flow path cannot close the gate valve. Therefore, the gate valve is not mounted on the outlet pipe of the axial flow pump. The curve of the mixed flow is relatively flat, that is, when the flow rate changes, the power variation is small, and the power machine is not overloaded because the flow rate is too large or too small. This is also the biggest advantage of mixing cockroaches.

(3) Flow efficiency curve

It is customary to use English letters and Greek letters to represent the Q~v curve. When the flow rate is zero, the efficiency of all pumps is equal to zero. As the flow rate increases, the efficiency gradually increases; when the flow rate increases to the design flow value, the efficiency is highest; when the flow rate continues to increase, the efficiency decreases. Therefore, the Q~v curve is like a part of a mountain with slopes on both sides and mountains in the middle. The slope of the Q~v curve of the centrifugal pump is slower, and the slope of the curve of the axial flow pump is steeper. The Q~V curve of the mixed flow pump is located between the centrifugal pump and the axial flow pump. If the Q~v curve is gentle near the highest efficiency point, it means that the pump has a wide effective working area. When the flow changes, efficiency does not drop too much. Conversely, if the Q~v curve is steep near the highest efficiency point, it means the pump. The efficient work area is small and the efficiency drops rapidly as the flow changes. In order to compensate for the defects of the axial flow pump, the blade is adjusted to the installation angle, and when the flow rate is changed, the blade installation angle is changed to maintain the efficiency of the water pump.


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