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In terms of mechanical component damage risks:

• For the impeller: When the pump is over-speeding, the circumferential speed of the impeller exceeds the design value. According to the centrifugal force formula (where is the centrifugal force, is the mass of the impeller, is the circumferential speed, and is the radius of the、leads to a significant increase in centrifugal force. This may cause the impeller structure to bear excessive stress, resulting in deformation or even rupture of the impeller. For example, in some high-speed multi-stage centrifugal pumps, once the impeller ruptures, the broken blades may enter other parts of the pump body, causing more severe damage.
• For the shaft and bearings: Over-speeding makes the shaft rotate beyond the design standard, increasing the torque and bending moment on the shaft. This may cause the shaft to bend, affecting the fitting accuracy between the shaft and other components. For instance, the bending of the shaft may lead to an uneven gap between the impeller and the pump casing, further aggravating vibration and wear. For bearings, over-speeding and low-flow operation worsen their working conditions. As the speed increases, the frictional heat of the bearings rises, and the low-flow operation may affect the lubrication and cooling effects of the bearings. Under normal circumstances, the bearings rely on the circulation of lubricating oil in the pump for heat dissipation and lubrication, but the supply and circulation of lubricating oil may be affected in a low-flow situation. This may lead to excessive bearing temperature, causing wear, scuffing, and other damages to the bearing balls or raceways, and ultimately resulting in bearing failure.
• For the seals: The seals of the pump (such as mechanical seals and packing seals) are crucial for preventing liquid leakage. Over-speeding increases the wear of the seals because the relative speed between the seals and the rotating parts increases, and the frictional force also increases. In a low-flow operation, due to the unstable flow state of the liquid, the pressure in the seal cavity may fluctuate, further affecting the sealing effect. For example, the sealing surface between the stationary and rotating rings of a mechanical seal may lose its sealing performance due to pressure fluctuations and high-speed friction, leading to liquid leakage, which not only affects the normal operation of the pump but also may cause environmental pollution.

• For the head: According to the similarity law of pumps, when the pump is over-speeding, the head increases in proportion to the square of the speed. However, in a low-flow operation, the actual head of the pump may be higher than the required head of the system, causing the pump’s operating point to deviate from the best efficiency point. At this time, the pump operates at an unnecessarily high head, wasting energy. Moreover, due to the small flow, the flow resistance of the liquid in the pump relatively increases, further reducing the pump’s efficiency.
• For the efficiency: The efficiency of the pump is closely related to factors such as flow and head. In a low-flow operation, vortexes and backflow phenomena occur in the liquid flow in the pump, and these abnormal flows increase energy losses. At the same time, the frictional losses between mechanical components also increase during over-speeding, reducing the overall efficiency of the pump. For example, for a centrifugal pump with a normal efficiency of 70%, in an over-speeding and low-flow operation, the efficiency may decrease to 40% – 50%, which means more energy is wasted in the pump’s operation rather than in transporting the liquid.

In terms of energy waste and increased operating costs:

Finally, the risk of cavitation increases: