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Regulation Of Multistage Centrifugal Pumps

Views: 0     Author: Site Editor     Publish Time: 2021-06-28      Origin: Site


The principle of multi-stage centrifugal pump is the same as that of a ground centrifugal pump. 

When the motor drives the impeller on the shaft at high speed, the liquid filled in the impeller is thrown from the center of the impeller along the flow path between the blades under the action of centrifugal force. Around the impeller, As the liquid is affected by the blade, the pressure and speed increase at the same time, and it is directed to the impeller at the next level through the flow of the guide shell. In this way, all the impellers and guide shells are passed one by one, further increasing the pressure energy of the liquid.. After each impeller is superimposed step by step, a certain lift is obtained and the underground liquid is lifted to the ground. This is the working principle of the stainless steel multistage pump.

The main characteristics of multistage centrifugal pumps:

1. Vertical structure, import and export flange on the same centerline, compact structure, small area, easy to install.

2. The vertical structure pump adopts the mechanical seal of the assembly structure to make the installation and maintenance more safe and convenient, and ensure the reliability of the seal.

3. The motor shaft of the multistage centrifugal pump is directly connected with the pump shaft through the coupling.

4. Horizontal pump with extended shaft motor, simple structure, easy to install and maintain operation.

5. The overflowing parts are made of stainless steel, which does not pollute the medium and ensures a long service life and beautiful appearance.

6. Low noise and low vibration. Adopt standardized design, good versatility.

What are the adjustment methods of multistage centrifugal pumps?

The two most commonly used methods are introduced:

1, Valve throttle

The simplest way to change the centrifugal pump flow is to adjust the opening of the pump outlet valve, while the speed of the multistage centrifugal pump remains unchanged(usually the rated speed). The essence is to change the position of the pipeline characteristic curve to change the pump's operating point. The intersection of the pump characteristic curve Q-H and the pipeline characteristic curve Q-Кh is the limit operating point of the pump when the valve is fully open. When closing the small valve, the local resistance of the pipeline increases, and the pump working point moves to the left, and the corresponding flow decreases. When the valve is closed, it is equivalent to infinite resistance and zero flow. At this time, the pipeline characteristic curve coincides with the longitudinal coordinates. It can be seen that when the flow is controlled by closing the small valve, the water supply capacity of the multistage centrifugal pump itself will not change, the lift characteristics will not change, and the resistance characteristics of the pipe will change with the change of Valve opening. 

This method is simple to operate, continuous flow, can be freely adjusted between a certain maximum flow and zero, and no additional investment, applicable to a wide range of situations. However, the throttle regulation is to consume the excess energy of the centrifugal pump to maintain a certain amount of supply, and the efficiency of the centrifugal pump will also decline, which is not economically reasonable.

2, Frequency conversion speed regulation

The deviation of working conditions from the high efficiency zone is the basic condition for the speed regulation of water pumps. When the rotation speed of the multistage centrifugal pump changes, the valve opening remains unchanged(usually the maximum opening), the characteristics of the pipeline system remain unchanged, and the water supply capacity and lift characteristics change accordingly. Under the condition that the required flow rate is less than the rated flow rate, the speed of frequency conversion speed regulation is smaller than that of the valve throttle, so the water supply power required for frequency conversion speed regulation is also smaller than that of the valve throttle. 

Obviously, compared with the valve throttle, the energy saving effect of frequency conversion speed regulation is very prominent, and the horizontal multistage centrifugal pump is more efficient. In addition, the frequency conversion speed adjustment is not only conducive to reducing the possibility of cavitation of centrifugal pumps, but also can extend the booting/stopping process by pre-positioning the lift/speed reduction time, so that the dynamic torque is greatly reduced. Thus, the destructive water hammer effect was eliminated to a large extent, and the life of the water pump and pipeline system was greatly extended.

The multi-stage centrifugal pump adopts the high-efficiency energy-saving hydraulic model recommended by the country, which has the advantages of high-efficiency energy conservation, wide range of performance, safe and stable operation, low noise, long life, and convenient installation and maintenance. By changing the material, sealing form of the pump and increasing the cooling system, hot water, oil, corrosive and abrasive media can be transported. Different multi-stage centrifugal pump manufacturers produce different multi-stage centrifugal pump models. Multi-stage centrifugal pumps combine more than two pumps with the same function. The fluid channel structure, which is represented by the first-stage dielectric pressure outlet, is connected to the second stage. The second stage of the media outlet is connected to the third stage of the inlet, and such a series of mechanisms forms a multistage centrifugal pump. The significance of multistage centrifugal pump is to increase the setting pressure.

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