Mechanical equipment installation

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Effects of operation of a pump at low flow rates: Cause analysis. The flow rate of a centrifugal pump can be adjusted continuously using various methods. Under normal circumstances, it is most efficient for the pump to operate at its rated conditions; however, sometimes, due to certain reasons, the pump operates at low flow rates, which can lead to the following negative effects. Effects of operating a centrifugal pump at low flow rates: (1) Reduced efficiency and increased power consumption. Centrifugal pumps are generally designed so that their peak efficiency occurs around the rated operating point. If a centrifugal pump operates at low flow rates, its efficiency drops rapidly. Generally, the lower the flow rate of the same pump, the lower its efficiency; therefore, operating it at low flow rates is very uneconomical. Under normal circumstances, it is necessary to reequip with a suitable, efficient small pump at this time. Effects of centrifugal pumps operating at low flow rates (2): Increased vibration and noise, which lead to environmental pollution, damage to pump components, and reduced service life of the pump. At the design operating point, since the flow direction is consistent with the blade direction, the separation loss, shock loss, and vortex loss are relatively small, approaching zero. However, when the pump operates in the low-flow range, it deviates from its design point, which leads to increased flow separation losses, shock losses, and vortex losses in the pump’s flow-related components. These losses are accompanied by significant hydraulic noise and mechanical vibration. Effects of centrifugal pump operation at low flow rates (3): The backflow inside the pump increases significantly, leading to increased heat generation; this raises the temperature of the liquid within the pump, causing the pump body to heat up. This affects the mechanical properties of the pump’s components, and it also deteriorates the pump’s cavitation performance, further impacting the pump’s suction conditions. Effects of centrifugal pump operation at low flow rates (4): The radial force on the centrifugal pump increases, worsening the stress conditions on the pump’s rotor. As the pump operates outside its designed operating point in the low-flow range, the flow velocity of the liquid within the vortex chamber decreases. However, according to the analysis of the velocity triangle, the exit velocity of the liquid from the impeller increases instead; as a result, the liquid cannot converge, which leads to shock waves and an increasing pressure, thereby generating radial forces.