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Effectively reduce the pump in the operation of cavitation damage method (2)
Third, reduce cavitation damage in service pumps.
1. Inlet pool optimization
At the site of operation, it's important to observe where cavitation or other issues occur in the pump's inlet flow. If a strong vortex is visible on the surface of the pool, consider installing a vortex breaker to minimize its formation. Additionally, pay attention to the design of the nozzle and the overall shape of the basin. For example, ensure that the nozzle is positioned correctly and check whether air bubbles are entering the pump's suction pipe. Raising the water level in the pool can also help reduce or even eliminate cavitation. At the Jietai Pumping Station, after modifying the inlet structure, erosion was reduced by approximately 45%. Similarly, at Qilu Petrochemical, after addressing the inlet vortex issue, the flow stabilized from 8,500 m³/h to 9,700 m³/h and from 8,000 m³/h to 8,200 m³/h, respectively.
2. Pipeline configuration
The inlet piping should be designed to minimize losses. This includes reducing the number of elbows and valves, ensuring that no part of the pipeline rises above the pump’s inlet to prevent air accumulation. For instance, the Chishui Natural Gas Fertilizer Plant increased the diameter of the inlet pipe from 800 mm to 1,000 mm and added an exhaust line to address pressure drop issues caused by resistance, effectively solving the cavitation problem.
3. Adjusting pump flow
Wang Weidong from the Xinjiang Electric Power Design Institute pointed out that the original formula used in China for calculating resistance was based on Soviet standards, which often overestimates actual resistance. Using a more accurate formula can help avoid cavitation at high flow rates. Additionally, adjusting the pump’s performance by trimming the impeller can improve both cavitation resistance and operational efficiency. This method has been proven effective in practice.
4. Use of injection systems
An injection device operates similarly to a jet pump. High-pressure water from the pump outlet is directed into a chamber and then through an annular nozzle into the suction pipe. The high-pressure water mixes with the incoming fluid, increasing the energy level and helping meet the required net positive suction head (NPSH) margin. Wu Yu from Zhejiang University suggested that the backflow rate should be controlled between 2% and 5%. In Changsha, Zhang Dehuang applied a similar technique using a 1/2-inch tube to redirect water from the balance plate to the pump inlet, reducing the system’s NPSH by 0.5–0.8 meters. Guo Dilong from Wuhan University introduced a jet-centrifugal pump device, which is highly effective but generally not suitable for retrofitting existing pumps.
5. Air injection method
While air injection doesn’t prevent cavitation itself, introducing a small amount of gas can reduce the damage caused when vapor bubbles collapse. The gas acts like a protective layer, cushioning the runner walls. This technique is commonly used in turbines but is rarely applied in pumps due to challenges in controlling the gas supply. Sun Shou and Yan Jinwen from Wuhan University of Water Resources and Electric Power conducted research on this method and found promising results. However, they emphasized that proper gas flow, location, and injection method are critical. Improper application can lead to significant drops in flow, head, and efficiency, resulting in adverse effects.