Pump flow rate
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Dear experts: I have a pump with a rated flow rate of 23 m3/h and a head of 113 m. In actual use, the valve can only be opened to 1/3 of its full position; under these conditions the flow rate is 12 m3/h and the head is 112 m. The fluid is clean water at room temperature, and there is no sign of blockage. However, when the outlet valve is slightly opened, the motor overloads and shuts down (the motor has a power of 22 KW, with an inlet diameter of DN80 and an outlet diameter of DN65). I would appreciate it if you could help me understand the reasons for this deviation. Thank you!
Please provide the pump outlet diameter and the pipeline diameter
This pump has low efficiency; you should check the performance test report – it appears that the motor is undersized; 45 Kw is required
I proposed increasing the motor power and enlarging the impeller diameter; I also examined the pump’s performance curve, and it seemed that the requirements could be met, but in practice this was not the case. Moreover, this manufacturer is also one of the best in China for producing water pumps. Both pumps, one in use and one as a backup, have developed problems (there are roughly 6 branch pipes for distributing water from the main pipe), so I am seeking help and discussing this matter with everyone.
Distance from the water tank to the pump inlet is 1500 mm; the pipe diameter is DN150/DN80, with the outlet having a diameter of DN65. There is also a return pipe with a diameter of DN50 (opening degree of 1/5).
Is there a diameter change at the pump’s outlet? Can the return line be tried to be fully closed?
This post was last edited by henglinkou on 2020-10-17 at 12:51. When you say the pump is in operation with a flow rate of 12 m3/h, is that the total flow rate? Does it include the amount of reflux? How was the head of 112m determined? It is likely that you calculated it based on the outlet pressure during operation, which is incorrect. The head during operation = (pump outlet pressure – pump inlet pressure) / density/g; it seems that your inlet pressure is negative. The pump has sufficient power; I can verify this using my calculation sheet. The problem with this pump is likely that the head rating was set too high; when the outlet valve is opened wide, the pump operates far outside its normal range, which causes the motor to trip. This is a problem of the design institute, not the pump manufacturer’s. Link to my pump calculation sheet: https://bbs.hcbbs.com/thread-1764877-1-1.html
The outlet has a diameter change, and the return pipe was tried to be completely closed, but with little effect.
You need to first provide the details of your process settings: the actual flow rate required by the process and the actual delivery height at the site. Based on what you’ve described, it is preliminarily judged that there is an issue with the pump selection. Either the flow rate is too high, or the head is too high, or both are excessively high
You need to first provide the details of your process settings: the actual flow rate required by the process and the actual delivery height at the site. Based on what you’ve described, it is preliminarily judged that there is an issue with the pump selection. Either the flow rate is too high, or the head is too high, or both are excessively high
1. Is there back pressure on the inlet? 2. Is the outlet pipe too large after the diameter change? By how many sizes is it larger compared to the pump outlet?