Why does long-term operation of a centrifugal pump at low flow rates cause the pump shaft to bend?
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Why does long-term operation of a centrifugal pump at low flow rates cause the pump shaft to bend?
When operating at low flow rates, deviating from the pump’s designed operating conditions leads to an increase in hydraulic radial and axial forces, resulting in shaft bending. This phenomenon is more pronounced in single-volute pumps, while it has a lesser impact on double-volute and vane pumps, as their radial forces can be automatically eliminated – though not completely – and are therefore much smaller than those in single-volute pumps.
What force is required to bend the shaft by that much? Is it a bit exaggerated?
When the pump operates at low flow rates, it experiences significant vibration; prolonged operation can lead to damage to the bearings, and in severe cases, the pump shaft may bend.
When the pump operates at low flow rates, it may enter a vacuum state; the fluid distribution within the impeller’s flow channels becomes uneven, which leads to a deterioration in the overall dynamic balance of the impeller. The irregular movement of the impeller causes the top end of the shaft to move irregularly as well, and the centrifugal force acting on that top end is much greater than normal. Operation over long periods inevitably results in issues with the shaft’s straightness, leading to bending.
It is estimated that your flow rate is below 30% of the designed value; this leads to erosion, axial movement and vibration. Over time, the dynamic balance is lost, and it’s strange if the shaft doesn’t bend