Problems with water pump flow rate and energy consumption
Thread Content
A question regarding pump flow rate and energy consumption. First question: For a pump that is operating properly, the flow rate can be controlled either by switching the inlet valve or by switching the outlet valve. Which valve should be used for this purpose? Second question: If the inlet valve is closed, the flow rate decreases, and energy consumption should also decrease. If the outlet valve is closed, the flow rate decreases as well – does energy consumption also decrease in that case?
Whether it’s a centrifugal pump or a reciprocating pump, I’ve never heard of them being adjusted using imported valves; my knowledge is limited, so I’m waiting for those with more expertise to give me some guidance.
The first is the outlet valve, the second one is not
Advice from the design institute: 1. Although adjusting the inlet and outlet valves will change the operating conditions. But the principles of the two are different. 2. Adjusting the inlet valve only changes the pump’s curve; closing the inlet valve reduces both the head and the flow rate. It may no longer meet the process requirements. Additionally, closing the inlet valve reduces local losses, making cavitation more likely to occur. It makes the pump’s operation unreliable. 3. Adjusting the outlet valve changes the pipeline curve: by closing the outlet valve, the flow rate decreases while the head increases, which will certainly meet the process requirements. And problems such as cavitation will not occur. In summary, there are hardly any centrifugal pumps that use inlet valves for regulation; otherwise, their operation is unstable. Although it saves energy, the drawbacks outweigh the benefits.
In the case of a centrifugal pump, reducing the outlet valve opening does not necessarily save energy; it is necessary to consider the power curve of the rated impeller
Thank you. May I ask, by adjusting the outlet valve – if the outlet valve is closed tighter, reducing the flow rate – will the energy consumption decrease?
The design institute reminds you that the view from the 5th floor is one-sided. Based on my many years of experience, when looking at the power curves provided by manufacturers, it can be seen that for all centrifugal pump manufacturers, the power increases as the flow rate increases. So, it is almost certain that by closing the outlet valve, the flow rate decreases and the power also decreases.
@Uppchao – there are always exceptions to everything; don’t be so absolute. It’s necessary to consider the pump’s power curve. For example, for the pump model in the attachment, whose impeller diameter is 150 mm, its power curve has a peak. If the rated operating point of the pump you choose lies to the right of this peak, reducing the valve opening increases the power. I’ve calculated the power values for nearly 2,000 pump models from Sulzer and Grundfos, and it’s not the case that the maximum power always occurs at the end of the curve; it also depends on how the pump manufacturer designs it. There is a design method called overload-free design, and only with such a design does the power curve rise gradually.