Questions about centrifugal pumps
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Three centrifugal pumps were purchased for the project, with the following specifications: the medium is 31% hydrochloric acid containing 2% fine solid particles, with a density of around 1200; the flow rate is 20 m3/h, and the head is 58 meters. The manufacturer specified the pump model as KJF80-50-400W, with an associated motor power of 15 KW. After installation, the system was tested with water; the current was around 12A when there was no load, but it rose to 30A–32A under load. The pump tripped when the flow rate exceeded 10 M3/H. I would like to ask, what exactly is the reason? ! ! Thank you
It’s a selection issue; if there is an overcurrent, it means the motor chosen was not suitable for the application. But calculated based on shaft power, 15KW is sufficient; how could there be an overcurrent? If your flow rate is only 20 cubic meters, a pump with an inlet diameter of 65 is sufficient; there’s no need to choose one with an inlet diameter of 80. You can try other pumps.
The medium does make a difference, right? The density of 32% hydrochloric acid is 1.159
The shaft power is around 11 kW; even with a density of 1.3, 15 kW would be sufficient
The motor size should not be too small; the calculated shaft power is only 7 KW, so a 15 KW motor is sufficient.
1. Check for process issues: Is there any diversion? Is the flow not passing through the flow meter? Is the flow rate too high? 2. Is the setting current of the thermal relay too low, below the rated current? Check for electrical issues: 3. Is the pump rotating properly, and are there any signs of jamming? 4. Is the flow meter accurate?
The current is around 12A when it’s not under load, and the rated power is 15KW; I think the problem lies with the motor
1. The motor may be faulty. 2. The pump may be stuck, or there may be a deviation in the concentricity between the pump and the motor. 3. Influence of the medium’s density.
In short: 1. Motor power of the pump: First, calculate the shaft power. Using an efficiency of 0.6, Pa = HQρ/102η = (58x20x1200)/(3600x102x0.6) = 6.32 kW; therefore, a motor power of 15 kW is more than sufficient. 2. Current under full load: Assuming the motor operates at full capacity and the supply voltage is 380 V, with standard coefficients applied, I = P/(√3*U*cosφ*η) = 15x1000/(1.732x380x0.9x0.8) = 31.7 A. It can be seen that the current is already relatively high. In summary, there should be no problems with the pump; it is recommended to check whether the control parameters for the pump motor in the MCC are set correctly