The pump does not deliver flow
Thread Content
As shown in the figure, during operation of the material transfer pump at the bottom of the tower, when pump A is started alone, the inlet static pressure is 0.1 MPa; after it starts operating, the pressure rises to 0.48 MPa. As the outlet valve is gradually opened, the pressure drops to around 0.13 MPa, and the flow rate is about 1/4 of the normal value. At the same time, the pump produces loud abnormal noises (similar to those associated with vacuum conditions), and there is significant vibration. When the outlet valve is slowly closed to a small opening, the pressure returns to normal and the pump operates normally. The behavior of pump B during operation is the same as that of pump A, but its flow rate is about 3 times that of pump A when it is in operation. When the two pumps operate simultaneously, the flow rate meets the requirements. When the pump is operating normally, the working pressure is around 0.44 MPa. The two pumps, AB, were disassembled for inspection; there was no blockage in the impeller flow, no significant corrosion, and the ring clearance was normal. Among them, there is a common inlet pipeline for AB; the direction of this pipeline is perpendicular to the ground, with the inlet pipeline for B located above the inlet of pump A.
The outlet pipeline is too large in diameter.
This equipment and pipelines have been in use for several years; they worked normally before and this kind of issue has never occurred
The NPSH of the two pumps cannot be guaranteed to be exactly the same by the manufacturer; it’s possible that the NPSH of pump A is 0.5 meters lower than that of pump B, and this is when the situation you described can occur. Also check the filter at the inlet. Is the installation height of pump B the same as that of pump A?
It was working normally before, and the problem only appeared now. As mentioned above, first check the filter to see if there is an excess or deficiency in the flow rate at the inlet. If the filter is fine, then check whether the inlet pipeline is unobstructed Was the pipeline purged when coming out from the bottom of the tower? Is the opening degree of valves and similar devices too small?
If the flow rate is not adequate and the pump does not produce any metallic grinding noises, the first thing to consider is to refill the pump and ensure that all air has been removed before starting it again; air should be released from the highest point of the pump’s outlet. If that doesn’t work, the next step is to check the inlet filter. If the filter is fine, then other possible causes need to be considered, such as low inlet pressure or a small diameter in the inlet pipe. When both pumps are running, the inlet pressure of pump B is higher than that of pump A; in this case, pump B has an advantage. If pump B is running and you want to switch to pump A, pump A will definitely experience vacuum conditions once it starts up, and pump B, which was previously operating normally, will also experience some pressure fluctuations. I really can’t find the cause; I’ve checked everywhere else, and I’ll consider removing the pump to inspect the impeller as a last resort. Also, I’m not sure about the medium of the pump, the temperature, and the inlet pipe diameter; could you provide that information?
The inlet of pump B is on top, so how can it have an advantage? If it’s just a T-shaped tee, then pump A below is the one that has an advantage
“It’s the common inlet pipeline for AB; the direction of this pipeline is perpendicular to the ground. The inlet pipeline for B is located above the inlet of pump A. My understanding is that the distance from the inlet of pump B to the common main pipeline is smaller than the distance from the inlet of pump A to the same main pipeline. Is my understanding correct, teacher?