The so-called wear-resistant centrifugal pump flow adjustment is actually changing the working point of the centrifugal pump, which can be achieved by changing the pipeline characteristic curve and the pump characteristic curve. According to the characteristic curve of the wear-resistant centrifugal pump, the flow rate drops rapidly as the head increases, and the shaft power decreases slowly as the flow rate decreases. The six commonly used methods for flow adjustment of wear-resistant centrifugal pumps are as follows:
1. Variable speed adjustment
The principle is to change the position of the characteristic curve of the pump by changing the rotational speed of the centrifugal pump, thereby changing the operating point.
As shown in the figure, when the rotation speed is nA, it is large, when the rotation speed is reduced to nC, the performance curve of the pump moves down, the working point is C, the flow rate is reduced, and the head is reduced.
2. Adjustable diameter
After the impeller is turned, the performance of the 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. Bypass return adjustment
This adjustment method is to open the bypass valve of the pump, and a part of the liquid returns from the discharge pipe of the pump to the suction pipe, thereby reducing the discharge pipe flow. This method is more suitable for vortex pumps. This is because the head of the vortex pump rises sharply when the flow rate is reduced, and the shaft power increases instead. When increasing the flow rate, the shaft power drops slightly.
5. Throttle adjustment
For 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.
6. Outer diameter adjustment of cutting impeller
If the outer diameter of the centrifugal pump impeller is reduced, the performance at the same speed can be changed, and the head can be changed.
As shown in the figure below, at rated speed, when the outer diameter of the impeller is D2, the operating point is 1. When the outer diameter of the impeller is D’2, the characteristic curve of the pump moves down, the operating point is 2, and the head decreases.
This adjustment method has no additional energy loss and is an economical method, but it is only suitable for use when the centrifugal pump changes to a small flow operation for a long time.
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.
