What is the problem with the reduced flow rate in a DA-type multi-stage pump? How to solve it? [Solved]
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This post was last edited by lee2033 on 2019-12-23 at 17:12. It is a DA-type multi-stage pump with a rated head of 114 meters and a power rating of 11KW–2. After installation (replacing the original faulty pump of the same model), it operated normally for 4 to 5 days, after which the water flow rate decreased; the flow at the outlet (the end of the water outlet pipe) became much lower (estimated to be about half). The motor’s rated current is 22A; the current when the pump is in operation is around 13A, and it can reach 17A at times. However, the water flow remains low. =Update = (I just checked the performance curves of pumps; it seems that for many pumps, flow rate is inversely proportional to head, while power increases as the head decreases and the flow rate increases.) Can it be understood that in actual use, when the flow rate is low and the head is high, the current is low, while when the flow rate is high and the head is low, the current is high? Looking back at the condition of this pump, could it be that the actual operating head is too high, which results in a low water flow rate, and this is reflected in a lower motor current as well? ) There are no abnormal noises or vibrations during the operation of the pump itself; however, when it stops running, the temperature at the motor end of the coupling seems to be a bit high (higher than the temperature of the motor’s casing), while the side of the coupling related to the pump is cool. I’m not sure if this is related to the issue. What could be the reason, and how can it be resolved? I hope the experts can give me some advice. Thank you!
Is there a filter on the inlet pipeline? If so, check it
There is no filter; is it suspected that the pipeline is blocked?
Is it operating in a superwork state in 4~5? Check the insulation of the motor to see if its insulation level has decreased
Concerned that the pump’s inlet may get blocked, leading to cavitation in the pump
Please check whether there are any problems with the motor bearings, and check if the motor speed has decreased.
Thank you. May I ask how to measure the motor speed?
What problems might occur with the motor bearings? From the operating conditions, it seems there is no radial vibration or abnormal noise. Is it the axial thrust causing some problem? If there is a problem with the bearing, will the current be high?
Thank you for your reply. Do you mean that it’s possible that the motor was overloaded during the first 4 or 5 days of use, which led to a decline in its performance?
Is the inlet blocked?； ； Has the motor speed decreased? ； ； ； Is the outlet valve opened wider? ； ； Is cavitation occurring due to the medium temperature being too high?
There is no filter in the water inlet pipeline. Separated the pipeline at the pump inlet from the pump itself, opened the gate valve on the inlet pipeline, and took a quick look; the water flow seemed fine, with no signs of blockage. I can’t think of any other way to check the water inlet pipeline either.