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Performance Characteristics and Operation of Axial Flow Pump

Jun. 17, 2020

Axial flow pump performance characteristics

1. The axial flow pump is suitable for large flow and low head.

2. The H-V characteristic curve of the axial flow pump is very steep, and the shut-off head (when flow Q=0) is 1.5~2 times of the rated value.

3. Unlike centrifugal pumps, the smaller the flow of the axial flow pump, the greater the shaft power, so the valve should be opened to start.

4. The high-efficiency operating area is very small, and the efficiency drops sharply on both sides of the rated point.

5. The impeller of the axial flow pump is generally immersed in the liquid, so there is no need to consider cavitation, and there is no need to irrigate the pump when starting.


Axial pump operation and flow regulation

Axial flow pumps generally do not use outlet valves to adjust the flow rate. They are commonly used to adjust the flow rate by changing the speed of the impeller, adjusting the inlet guide vanes of the pump, or changing the installation angle of the blades.

1. Variable speed adjustment

Similar to the centrifugal pump, the axial flow pump can obtain multiple performance curves by changing the rotation speed, so that the working point is maintained in the high efficiency area. Variable speed adjustment has been used more and more in large axial flow pumps due to the convenience of adjustment.

2. Inlet guide vane adjustment

Axial pumps can be equipped with guide vanes at the inlet, and the guide vanes can be used to change the preselected intensity of the inlet flow to achieve the change of the pump characteristic curve. The guide vane adjustment is suitable for the occasion where the flow rate changes in a small range and the head changes in a large range.

3. Blade installation angle adjustment

The adjustment of the blade installation angle is equivalent to changing the specific speed of the pump. It is suitable for occasions requiring a large range of flow rate change and a small range of head change. The semi-adjustable blade type needs to be disassembled for each adjustment, so it is suitable for fewer occasions. The vane fully adjustable axial flow pump is equipped with hydraulic or mechanical adjustment mechanism. The hydraulic adjustment mechanism is derived from the turbine blade adjustment structure, which has the advantage of large output torque, but the oil system is complicated, and it is generally used for large axial flow pumps with a power of more than 2500kW. Mechanical adjustment mechanisms are generally used for axial flow pumps with power below 2500kW. Due to the complicated adjustment mechanism and the relatively poor reliability of blade mounting angle adjustment, it is gradually being replaced by variable speed adjustment.

The above information is provided by axial flow pump manufacturers.

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