Experiment on Determining the Characteristic Curve of Centrifugal Pumps ~ Problem Solving~
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I have a few questions for those who are more knowledgeable~ Please help me~ Thank you so much!! 1. Why does a centrifugal pump need to be started with the outlet valve closed, and why is the outlet valve used to regulate the flow rate? 2. Theoretically, analyze whether the head of the pump will change at the same flow rate when this pump is used to transport saltwater with a density of 1200 kg/m³ (ignoring the effect of viscosity), and what happens to the power consumption? 3. After the centrifugal pump starts, if the outlet valve isn’t opened, will the pressure keep rising? Why?
Close the outlet valve; at this point the flow rate is 0, and the required power is minimal. Flow rate and head are independent of density, but power increases as density increases. The third one is not quite clear. All of these you’re asking about are experiments in chemical engineering principles!
Yeah, it can’t be found on Baidu, so I’m coming to ask~ Thank you
First, the centrifugal pump is started with its outlet valve closed in order to achieve a zero-load start, which serves to protect the motor. If the valve is not closed, the starting current will be very high, and according to Joule’s law, this could damage the motor. Secondly, the head of a centrifugal pump is related to its flow rate; the pump comes with a head-flow curve when it leaves the factory. And when calculating shaft power, density, head, and flow rate need to be taken into account. Finally, the outlet pressure of a centrifugal pump represents the pressure energy it can provide. If the valve remains closed, its outlet pressure will stabilize at the head corresponding to zero flow rate (the head-flow curve). However, this situation can lead to an increase in the temperature of the material, damage to the mechanical seal, and vaporization of the material.
1. The centrifugal pump is started with the outlet valve closed in order to ensure a minimum starting current. 3. The pressure does not increase
Clydestone’s answer is correct! The view given in the answer to the second question about LPV is very easy to forget!
Third question: Once it reaches a certain level, the pressure stops increasing and remains at that level. Since there is a gap between the inlet and outlet of the centrifugal pump, once a certain pressure is reached, the water simply circulates between the inlet and outlet.
The second question is that the theoretical head of a pump has nothing to do with the density of the liquid; the same pump provides the same theoretical head regardless of the type of liquid it transports, and it depends only on the flow rate.