Q&A on Purification Technology Version [001]

⑴ Changing the pipeline characteristic curve involves adjusting the opening degree of the valves on the pipeline to alter the value of the resistance coefficient. This method is easy to use, but it results in low pump efficiency. ⑵ Changing the pump’s performance curve, such as by turning the impeller, or altering the pump’s speed – this method yields good pump efficiency, but it is not convenient to use; it is suitable for situations where the flow rate needs to be changed over a long period of time.

1. Changing the pipeline characteristic curve: The simplest way to adjust the flow rate of a centrifugal pump is by controlling the opening degree of the pump’s outlet valve; essentially, this involves changing the position of the pipeline characteristic curve in order to alter the pump’s operating point. 2. Changing the characteristic curve of the centrifugal pump: According to the law of proportionality and the law of modification, two methods can be used to alter the characteristic curve of the pump – by changing its speed or by modifying its structure (such as by reducing the outer diameter of the impeller). These methods enable the adjustment of flow rate (along with changes in head pressure). 3. Series and parallel connection methods for pumps: When a single centrifugal pump is not sufficient to meet the transportation requirements, these pumps can be operated in parallel or in series. By connecting two centrifugal pumps of the same model in parallel, the head change is minimal, but the total flow rate increases. The overall efficiency of the pumps in parallel is the same as that of a single pump ； When centrifugal pumps are connected in series, the total head increases while the flow rate remains roughly the same; the overall efficiency of the series-connected pumps is equal to that of a single pump

⑴ Changing the pipeline characteristic curve involves adjusting the opening degree of the valves on the pipeline to alter the value of the resistance coefficient. This method is easy to use, but it results in low pump efficiency. ⑵ Changing the pump’s performance curve, such as by turning the impeller, or altering the pump’s speed – this method yields good pump efficiency, but it is not convenient to use; it is suitable for situations where the flow rate needs to be changed over a long period of time.

(1) Throttling control. The principle of throttling control is to change the shape of the pipeline characteristic curve, thereby altering the operating point of the centrifugal pump. When the flow rate needs to be reduced while the pump is in operation, the discharge gate valve of the pump is closed, which increases the resistance of the gate valve. Since more energy is consumed in the gate valve due to its being closed partially, this regulation method results in high losses and poor economic efficiency; however, it is widely used in practice because of its simplicity. (2) Bypass return regulation. This adjustment method involves opening the bypass valve of the pump, allowing some of the liquid to flow back from the pump’s discharge pipe to the suction pipe, thereby reducing the flow rate in the discharge pipe. This method is more suitable for vortex pumps, as the characteristic curve of these pumps shows a sharp increase in head when the flow rate decreases, with the shaft power increasing instead; whereas when the flow rate increases, the shaft power slightly decreases. (3) Variable speed adjustment. The principle is to change the position of the pump’s characteristic curve by adjusting the speed of the centrifugal pump, thereby altering the operating point. This adjustment method incurs no additional energy loss, making it a relatively economical approach. But a variable-speed motor must be used. (4) Adjustment of the outer diameter of the cutting impeller. Reducing the outer diameter of the centrifugal pump impeller can alter the pump’s performance at the same rotational speed, thereby changing both the flow rate and the head. This adjustment method also incurs no additional energy loss, making it a cost-effective approach; however, it is only suitable for use when the centrifugal pump needs to operate at a low flow rate over an extended period of time.

I. Adjustment of the outlet valve opening In this method, the pump is connected in series with a control valve in the outlet pipeline; the actual effect is similar to that of using a new pump system. The maximum output head of the pump remains unchanged, but the flow rate curve becomes flatter.       II. Regulation via bypass valve: In this method, the valve is connected in parallel with the pump; the actual effect is similar to that of using a new pump system. The maximum output head of the pump changes, and the characteristics of the flow curve also change, with the flow curve becoming more linear.       III. Adjusting the impeller diameter This method does not use any external components, and the flow rate characteristic curve changes as the diameter changes.      Method 4: Speed control. Changes in the impeller speed directly affect the pump’s flow curve; the characteristics of this curve remain unchanged. When the speed decreases, the curve becomes flatter, and both the head and the maximum flow rate decrease.

Adjust the opening of the outlet valve, adjust the bypass valve, and adjust the impeller

⑴ Changing the pipeline characteristic curve involves adjusting the opening degree of the valves on the pipeline to alter the value of the resistance coefficient. This method is easy to use, but it results in low pump efficiency. ⑵ Changing the pump’s performance curve, such as by turning the impeller, or altering the pump’s speed – these methods result in better pump efficiency, but they are not convenient to use; they are suitable for situations where the flow rate needs to be changed over a long period of time.