Centrifugal pumps are facing problems
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Question: For a standard centrifugal pump with a flow rate of 15 cubic meters per hour, a head of 114 meters, and a motor power of 18.5 KW, the no-load current of the motor is 8.5 A. During water operation tests, when the pump was started with the outlet valve closed, the motor current was 31 A and the outlet pressure was 15.5 Kg/cm². When the outlet valve (DN40) was turned two turns, the current increased to 40 A and the outlet pressure dropped to 14 Kg/cm². With the outlet valve fully open, the current was 44 A and the outlet pressure was 13 Kg/cm². Is there something wrong with this pump? I earnestly request advice from experts.
The head is 114 m, and the head at the shut-off point should be around 125 m, which corresponds to approximately 12.5 kg of pressure. If there is no pressure at the inlet, the shut-off head of the pump, at 155 m, is significantly too high. It is recommended to carry out appropriate machining based on the outer diameter of the impeller, or to contact the manufacturer to have the impeller replaced.
Is this pump normally used for pumping water?
To determine whether there is a problem, you should compare it with your design parameters; based on the operating conditions mentioned above, it seems that your pump has a relatively high output.
Before making any further judgments, could you please tell me what the inlet pressure of this pump is? The pump pressure is equal to the outlet pressure minus the inlet pressure. Additionally, check the pump’s factory test performance curve.
What is the inlet pressure of this pump? It affects the outlet pressure.
Problems with a pump can be attributed either to mechanical faults within the pump itself (such as vibration, temperature, etc.) or to its performance parameters (such as head, current, flow rate). If there are no issues, then everything is fine
Based on the data you provided, consider the following issues: 1. The inlet pressure is high; as a result, the outlet pressure will naturally increase significantly. However, according to the data, the pressure at full open condition remains quite high, indicating significant backpressure. There is an issue with the pump selection – the point corresponding to the rated flow rate should be located in the high-flow region. Also, is the rated head you have designed reasonable? 2. The inlet pressure is close to atmospheric pressure: In this case, there is an issue with the pump selection, as the required head is clearly too high ； As for traffic, there is no data available to make a judgment. 3. Check whether the pressure gauge is functioning properly, and verify that the rated head and flow rate indicated on the nameplate are correct ；
If the density of the medium designed is lower than that of water and it is used for pumping water, such a situation will inevitably occur.
Since the designed medium has a density lower than that of water and is used for pumping water, such a situation is bound to occur.
If a pump for pumping water is to be designed, the motor power should be 22 KW. If a medium with a lower density than water is used for pumping water, overcurrent will inevitably occur; the rated current of the motor is around 34 A