Problems with the operation of mechanical pumps
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When the two pumps operate separately, the flow rate is low; the pumps vibrate significantly and produce abnormal noises. The outlet pressure remains constant at a certain level. When the outlet valve is closed, the pressure rises with slight fluctuations, until the valve is closed to a certain extent at which point the pressure becomes stable again, although the flow rate remains low； But when the two pumps operate simultaneously, the valve opening is small, the pressure is normal, and the flow rate is also normal – what’s going on here? You say there is a blockage in the inlet pipe, yet both pump units are operating normally. Please, someone knowledgeable, help explain this.
This post was last edited by WSRYLONG on 2018-7-13 at 10:15. When the pump operates alone, it operates within conditions of high flow rate and low head, which leads to cavitation; as a result, the pump experiences significant vibration and abnormal noises during operation. Please check whether the outlet pressure at this time is lower than the rated head; if so, it indicates that the analysis above is generally correct. When both pumps are operating simultaneously, with the valve open to a small degree, the pressure remains normal and the flow rate of each pump is also normal; thus, cavitation does not occur, and both pumps function properly.
When the two pumps operate separately, the flow rate is low; what is that value? And what is the flow rate when both pumps are run together? If only one unit is used, the traffic volume is 80; when both units are used, the traffic volume is 140. The flow rate is higher for a single pump or when it is operating alone. When the flow rate is high, the velocity of the liquid increases, and the pump is prone to cavitation.
When operating separately, one has a capacity of 2 tons and the other around 6 tons; when operated simultaneously, the combined capacity reaches 10 tons. The design parameters are a volume of 10 cubic units, a density of 0.8, a head of 24 m, and an outlet pressure of 0.3 MPa
The design parameters are a volume of 10 cubic units, a density of 0.8, a head of 24 m, and an outlet pressure of 0.3 MPa; when operating alone, the outlet pressure is around 0.15 MPa.
If two pumps cannot meet the design parameters when operating separately, it is astonishing that they can achieve those parameters when operated in parallel. After all, when pump units are connected in parallel, the pressure remains constant, but the flow rate is slightly less than the sum of the flow rates of the two pumps. I think the original poster still needs to conduct further analysis, regarding the operating characteristic curves of each pump, as well as those of the pumps when operated in parallel.
I’ve encountered this situation before; you really should check the entrance.
Personally, I think it’s caused by the pump not being able to operate under its designed conditions!