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Several common adjustment methods of centrifugal pump flow

20 Jul 2021Email

Flow rate is one of the important parameters of centrifugal water pumps, which is very important for water pumps. In the use of centrifugal water pumps, it is sometimes necessary to adjust the pump flow rate. The correct flow rate adjustment method can promote the overall operation of the pump, so how to adjust the pump flow rate What are there?

centrifugal water pumps

1. Variable speed adjustment

Changing the speed of the centrifugal water pump can change the performance of the water pump, thereby changing the working point of the water pump. This method is called variable speed adjustment.

2. Adjustable diameter

After the impeller is turned, the performance of the centrifugal water pump will change according to a certain rule, so that the operating point of the water pump will change. We call the method of turning the impeller to change the working condition of the pump, which is called the variable diameter adjustment.

3. Variable angle adjustment

Changing the installation angle of the blades can change the performance of the water pump, so as to achieve the purpose of changing the operating point of the water pump. This way of changing the operating point is called variable angle adjustment of the pump.

4. Throttle adjustment

For centrifugal water pump devices with gate valves installed in the outlet pipeline, if the gate valve is closed for a small amount of time, local resistance is increased in the pipeline, and the pipeline characteristic curve becomes steep, and its operating point moves to the upper left along the Q-H curve of the pump. The smaller the gate valve is closed, the greater the increased resistance and the smaller the flow rate. This method of changing the operating point of the pump by closing the gate valve is called throttling adjustment or variable valve adjustment.

When the gate valve is closed, the local head loss of the pipeline increases, the characteristic curve of the pipeline system moves to the upper left, and the pump operating point also moves to the upper left. The smaller the gate valve is closed, the greater the local head loss and the smaller the flow rate. It can be seen that throttling adjustment not only increases the local head loss, but also reduces the water output, which is very uneconomical. However, due to its simplicity and ease of use, it is widely used in small water pump installations and water pump performance tests.

5. Valve adjustment

It is currently the most commonly used and most popular method of use. Install a regulating valve on the water pump discharge pipeline, and adjust the flow rate by changing the valve opening. The method is simple and reliable, but the power loss is large, the economy is not good, and the effect of small flow or small flow is not good.

6. Variable speed adjustment

By changing the speed of the pump impeller to adjust the flow rate, this method has very little additional power loss and is the most economical method. However, it is necessary to add a variable speed mechanism and a variable speed motor. The initial investment cost is relatively high. The constant pressure variable frequency water supply system and the central air conditioning cooling water (frozen water) circulation system are two typical examples of the application of variable frequency speed regulation in water centrifugal pump regulation. The method of changing the speed is most suitable for centrifugal pumps driven by steam turbines, internal combustion engines and DC motors. Frequency conversion can also be used to change the motor speed, and sometimes the speed can be adjusted by using a fluid coupling.

7. Bypass adjustment

Using bypass to adjust the flow rate can solve the problem of continuous operation of the centrifugal pump at a small flow rate, but the additional loss caused by the insufficient utilization of the split flow rate increases, and the process pipeline also increases.

8. Cutting the outer diameter of the impeller

By cutting the outer diameter of the impeller to adjust the flow of the centrifugal pump, the power loss is small, but the impeller cannot be recovered after cutting, that is, the flow can only be adjusted in the direction of small flow. Moreover, the cutting amount of the impeller is limited, and the flow rate adjustment range is limited. It is suitable for occasions that need to work under a small flow for a long time and the flow does not change much. For example: ⅠS150-125-315A single-stage single-suction centrifugal pump and IS150-125-315B centrifugal pump two types of centrifugal pumps are models obtained by cutting the diameter of the impeller of the IS150-125-315 centrifugal pump.

9. Replace the impeller

Changing the impellers of different diameters to adjust the flow of the pump. Power loss is small, but impellers of various diameters are required, and the range of flow adjustment is limited.

10. Block several impeller flow passages

Blocking several impeller channels (even numbers) reduces the flow of the water pump. It is equivalent to throttling regulation, but it is more energy-efficient than regulating valve throttling.

11. Adjust the exit angle of the blade

Adjusting the flow rate of centrifugal pumps by changing the outlet angle of the impeller blades is mostly used in axial flow pumps.

12. Cavitation adjustment

By changing the inlet pressure of the centrifugal pump (water level, suction valve), cavitation occurs in the centrifugal pump, the characteristic curve of the water pump is changed, and the method of changing the flow rate of the water pump. Practice has proved that if the cavitation adjustment is used properly, the damage to the flow parts of the centrifugal pump is not serious; on the other hand, it can automatically adjust the flow rate and reduce the power consumption of the pump. Cavitation adjustment methods are generally used in the condensate pumps of small and medium thermal power plants.

13. Increase or decrease the number of centrifugal water pumps

Adjust the flow rate of centrifugal pumps by increasing or reducing the number of centrifugal pumps in operation, supplemented by a suitable combination method

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