Centrifugal pump, help needed.
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This post was last edited by moonkingta on 2017-1-14 16:21. A centrifugal pump with a head of 55 m, a flow rate of 5 m3/h, and an open impeller. Equipped with a 4Kw motor, with a speed of 2950 r/min and a rated current of 8.1A. After startup, the overcurrent ranges from 8.8 to 9.0 A; the current decreases after the outlet is opened, sometimes dropping to 7.8 A and sometimes to 8.3 A. What could be the reason? Please, experts, help analyze it. January 14: No significant issues were found during the inspections over these two days. It was decided to cut the impeller by 10 mm, and normal operation was restored after another trial run. Without the outlet connected, the current is 5.2A after startup; once the outlet is connected, it is around 7.1A. It is likely caused by an overly small gap between the impeller and the pump casing.
The current for a 4kw motor is 8.2; is your rated current 8.1? Is the motor power correct?
It’s not specified in detail, because when the pump starts, the current is high due to the load on the motor; at that time the outlet valve is closed, so the power required by the pump shaft is low and the current should decrease somewhat. Once the outlet valve is opened, the current rises back to its rated value. If the load changes during operation, the current will also fluctuate.
At startup, the inlet is fully open while the outlet is closed, resulting in a high instantaneous current, which then decreases. This is the general situation. What I’m describing is that after the initial high current during startup, the current still exceeds the rated value, but it decreases once the outlet valve is opened.
That’s right; the motors from Jiamusi have it marked that way on their nameplates.
The motor is too small; if it’s a new pump, it’s necessary to contact the supplier as soon as possible. If it goes on for too long, it might cause trouble!
The old one has been in use for five years.
The pump was replaced after 5 years of operation; generally, its performance declines over such a period. The motor you chose is too tight-fitting, and it causes overflow at the slightest problem – it’s better to use a 5.5Kw motor. You can check if there are any problems with the pump and pipes.
This phenomenon of yours is a bit strange. However, another possibility is that your measuring instrument isn’t accurate – for example, if your ammeter has a large range, it may not give accurate readings at low current levels