Ways to improve the cavitation resistance of water pumps

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Ways to improve the cavitation resistance of water pumps. The ways to enhance the cavitation resistance of centrifugal pumps can be analyzed from two aspects: one is to design the suction pipeline correctly and appropriately, so as to ensure that there is sufficient effective net positive suction head △Ha at the pump’s suction inlet； Another approach is to improve the structural parameters at the pump inlet, use materials resistant to cavitation, or employ an inducer at the pump inlet. 1. Measures to increase the effective cavitation head ΔHa: As analyzed above, increasing the pressure Pa on the liquid surface in the suction cylinder and determining the geometric installation height Hg of the pump appropriately can both increase ΔHa, thereby preventing cavitation. Therefore, in petrochemical plants, suction heads that raise the liquid surface above the pump axis are commonly used; in such cases, a negative value is used in the calculations to increase ΔHa. For example, heat oil pumps should have a suction head of at least 2 meters in height. Additionally, reducing the resistance losses in the suction piping, as well as lowering the saturated vapor pressure Pa of the liquid, can also help increase ΔHa. This can be achieved by using pipes with larger diameters, shorter lengths, fewer bends and valves, and by keeping the temperature of the liquid as low as possible. 2. Measures to enhance the pump’s resistance to cavitation: (1) Increasing the diameter D0 of the impeller inlet and the width b0 of the inlet edge, as well as improving the shape of the impeller inlet or suction chamber, can reduce the pump’s Δh. (2) Using a double-suction impeller. A double-suction impeller functions like two single-suction impellers working back to back; each half of the impeller handles half of the pump’s flow rate. For two pumps with the same flow rate Q, speed n, and suction specific speed C, the ratio of Δhr for a double-suction impeller to Ah for a single-suction impeller is approximately 0.63. Thus, double-suction impellers offer better resistance to cavitation. (3) Choosing an appropriate position for the blade inlet and the shape of the front cover plate. Tests on impellers with four different inlet edge positions (see Figure 2-13) show that the more the blade inlet edge extends toward the inlet, the better the resistance to cavitation. The larger the arc radius of the front cover plate, the better the resistance to cavitation. When this value is between 0.1 and 0.15, the cavitation head can be reduced by about 18%. (4) Using an inducer, which is installed in front of the first stage of the impeller, as shown in Figure 2-15. When fluid flows through the inducer, it does work on the fluid, increasing its energy, which effectively boosts the pressure of the fluid entering the subsequent impellers, thereby improving the pump’s suction capability. The design calculations for this are discussed later. (5) Using materials resistant to cavitation. When cavitation cannot be completely avoided due to operational constraints, it is necessary to use materials resistant to cavitation for manufacturing the impeller blades. Commonly used materials include aluminum-bronze 9–4, stainless steel, alloy cast iron, and high-nickel alloys. Experience shows that the higher the strength and toughness of the material, as well as its hardness and chemical stability, and the smoother the surface of the impeller flow channels, the better the resistance to cavitation.