Regarding the circulating water pump
Thread Content
The company’s power station uses circulation pumps, with two such pumps operating in parallel. One of the pumps is manufactured by Kaiquan; its performance parameters are as follows: flow rate of 110 m3/h, head of 45 m, rated current of 58 A, power of 30 KW, and rotation speed of 1475 revolutions per minute. The pump’s inlet and outlet connections have a diameter of DN125, while the pipeline inlet has a diameter of DN200 and the outlet also has a diameter of DN200; the main pipeline has a diameter of DN250. The other pump is manufactured by Nanfang Pump Industry; its performance parameters are flow rate of 100 m3/h, head of 50 m, rated current of 58 A, power of 30 KW, and rotation speed of 1475 revolutions per minute. Again, the pump’s inlet and outlet connections have a diameter of DN125, with the pipeline inlet and outlet both having a diameter of DN200, and the main pipeline having a diameter of DN250. Currently, there is a problem: when the outlet pressure of the pumps is 0.54 MPa, the current drawn by both pumps already reaches their rated value of 58 A. When the outlet pressure is adjusted to 0.5 MPa or 0.45 MPa, the current exceeds this rated value significantly, reaching 65 A to 70 A. The outlet valve for these pumps is a butterfly valve, and its opening degree is very low – only about one-fifth of the full opening range. What could be the cause of this? Is it due to an issue with the pipe diameters, or is it a problem with the pumps themselves?
Pump inlet 125, outlet 200? How about the other way around?
The head decreases while the flow rate increases. Supercurrent is completely normal
But I haven’t yet reached the desired head; it’s higher than the rated head. The outlet pressure of the pump is currently 0.54 Mpa.
The inlet pipeline of the pump is DN200 and then changes to DN125, matching the pump’s interface flange; the outlet changes from DN125 at the pump’s interface flange to DN200；
Your problem is that you haven’t understood the relationship between the opening degree of the pump’s outlet valve and the rated current. In this case, the rated current should be used as a reference point; the opening degree at which the current reaches this rated value is the opening degree at which the pump operates properly. Keep in mind that the degree to which the valve is opened is not a reference for your operations; the criterion should be meeting the specified rated current. Regardless of the number of pumps or their capacity, the adjustment is the same. For reference.
The problem now is that if the outlet pressure of the pump is adjusted to match the pressure and head, the current value increases. We are not concerned with the opening degree of the valve; we are only interested in the relationship between the pump’s outlet pressure and the current.
The outlet pressure of the pump is related to its flow rate; currently, the outlet pressure of the pump has not reached the desired level, which indicates that the flow rate is insufficient
Your problem is that you haven’t understood the relationship between the opening degree of the pump’s outlet valve and the rated current. In this case, the rated current should be used as a reference point; the opening degree at which the current reaches this rated value is the opening degree at which the pump operates properly. Keep in mind that the degree to which the valve is opened is not a reference for your operations; the criterion should be meeting the specified rated current. Regardless of the number of pumps or their capacity, the adjustment is the same. For reference.
I have also encountered this issue; there are no problems with the pipe diameter or the pump itself, but the pump supplied by the manufacturer is too large. The solution is to adjust the valve opening or cut the impeller.
This post was last edited by CHANGBAISHI on 2021-1-13 09:14. If it’s not a problem with your operations, then it’s a problem with the system design. It is sufficient to meet the normal pump production parameters; other issues are separate topics. It might be caused by an excessive amount of water returning from the user. As for meeting the requirements regarding flow rate, pressure, and rated current, the factor of the flow meter must be taken into account. Due to the errors associated with flow meters, as well as the operating conditions of these devices, they cannot be used as a means to measure usage conditions. However, if the operating pressure of the flow meter used for controlling the total return flow can be controlled, relatively accurate measurements can be obtained. The problem now might be that it is difficult for your system pressure to reach the conditions required by the flow meter for measurement. The key problem lies in the insufficient system pressure, caused by users increasing the return flow without restraint. It is a system operation issue. For reference.