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Cavitation refers to the phenomenon that as the installation height of a centrifugal pump increases, the pressure inside the pump decreases. The lowest point of pressure within the pump is usually located slightly downstream of the inlet of the pump’s impeller blades; liquid rushes towards the center of these bubbles at high speeds, resulting in high-frequency, intense pressure fluctuations. This phenomenon is known as cavitation. Cavitation primarily occurs at the blades and shrouds on the outer edge of the impeller, as well as at the volute or diffuser; it does not occur at the blade inlets. For example, it occurs on the front side of the blade near the front cover plate at the blade inlet when the flow rate is greater than the design value. When the pressure at the impeller inlet drops to the saturation vapor pressure of the liquid being pumped at its operating temperature, the liquid undergoes partial vaporization. The resulting bubbles then move with the liquid from the low-pressure area to the high-pressure area. In the high-pressure area, these bubbles rapidly collapse and condense; the surrounding liquid rushes toward the space formerly occupied by the bubbles at extremely high speeds, generating intense shock waves. These shock waves impact the impeller and pump casing, causing noise and vibrations. Due to the repeated impact forces over a long period of time, as well as the chemical corrosion caused by trace amounts of dissolved oxygen in the liquid, the local surfaces of the impeller develop scars, cracks, and even sponge-like damage. Causes of cavitation in water pumps: The fundamental reason for cavitation is that the inlet pressure is lower than the saturated vapor pressure at the temperature at which the fluid is being transported. When a centrifugal pump is in operation, the pressure of the fluid decreases from the pump inlet to the inlet of the impeller; the liquid pressure is lowest near the blades. Thereafter, as the impeller does work on the liquid, the pressure rises rapidly. When the pressure near the inlet of the impeller blades is less than or equal to the saturated vapor pressure at the liquid’s transport temperature, the liquid vaporizes. At the same time, gases dissolved in the liquid may also escape, forming many bubbles. When the bubble moves with the liquid to a region of higher pressure within the flow channel, and the external liquid pressure is higher than the vaporization pressure inside the bubble, the bubble collapses and dissolves, forming a cavity. In an instant, the liquid around it rushes toward the cavity at extremely high speeds, causing the liquids to collide with each other and resulting in a sudden surge in local pressure (which can reach several hundred atmospheres). This not only hinders the normal flow of the fluid, but more seriously, if these bubbles collapse near the wall of the impeller, the liquid acts like countless small projectiles, continuously striking the metal surface at a high frequency (some cases reaching 2000–3000 HZ), causing the metal surface to crack due to impact fatigue. If the bubbles contain certain reactive gases (such as oxygen), they can utilize the energy released during bubble condensation (with local temperatures reaching 200–300°C) to form thermocouples and induce electrolysis, thereby causing electrochemical corrosion of the metal and accelerating the rate of its degradation. The phenomenon in which the aforementioned vaporization, condensation, and impact of a liquid generate high-pressure, high-temperature, and high-frequency impact loads, resulting in a combined effect of mechanical spalling and electrochemical corrosion damage to metallic materials, is known as cavitation. Factors affecting pump cavitation: Factors that influence liquid pressure and saturated vapor pressure can all affect the occurrence of cavitation. ①Structural parameters of the water pump inlet: these include the shape of the impeller’s suction inlet, the width of the blade inlet edge, the position of that edge, as well as the shape of the front cover. ② Operating conditions of the water pump: these involve factors such as the pump’s flow rate, head, and rotational speed. ③ Installation location of the water pump: this includes the hydraulic losses in the pump’s suction pipeline as well as the installation height. ④Environmental factors: These include the atmospheric pressure at the location where the pump is installed, the properties of the fluid itself, and the operating temperature of the fluid. Reasons for cavitation in centrifugal pumps: 1. The liquid level in the tank is too low, allowing air to be drawn in; 2. The flow velocity and the resistance in the suction pipeline are too high; 3. The pump is installed at too great a height; 4. The temperature of the fluid being pumped is too high; 5. The suction pipeline or the seal (in the case of seals without a liquid seal) is not properly sealed, allowing air to enter. Severe consequences of cavitation in pumps: Cavitation is a phenomenon specific to hydraulic machinery, and it can lead to many serious consequences. ① Cavitation reduces the performance of the pump. It disrupts the energy conversion between the impeller and the fluid, resulting in a decrease in the pump’s performance; in severe cases, it can even cause the flow of liquid to stop and the pump to cease functioning. ② Cavitation causes noise and vibration in the pump. When bubbles burst, the liquid collides with each other as well as with the wall surfaces, generating noises of various frequencies. In severe cases, a ‘cracking’ explosive sound can be heard inside the pump, simultaneously causing vibration in the unit. The vibration of the unit further causes more bubbles to form and collapse; these interactions lead to intense cavitation resonance, forcing the unit to shut down, otherwise it will be damaged. ③Cavitation causes erosion and damage to the components through which fluid flows. In centrifugal pumps, the areas that are damaged by cavitation first appear near the inlet of the blades, and then extend to the outlet of the impeller. Initially, pitting appears on the metal surface; subsequently, the surface develops grooves, honeycomb-like patterns, and fish-scale-like cracks. In severe cases, this can lead to holes in the front and rear covers of the blade or impeller, or even to the rupture of the impeller itself, resulting in serious accidents. Therefore, cavitation severely affects the safe operation and service life of the pump. ④Cavitation is also a major obstacle to the development of hydraulic machinery toward higher flow rates. The higher the fluid flow rate, the lower the pressure, which makes cavitation more likely to occur. Solutions to cavitation in centrifugal pumps: Based on the analysis of the factors affecting cavitation, we can identify the following solutions to this problem in centrifugal pumps: ① Improve the structural parameters at the pump inlet. 1) Modify the design of the impeller and optimize its structural parameters in order to reduce the conditions that lead to cavitation ； 2) Blades and other components through which water flows should be made of materials with good cavitation resistance ； 3) Reducing the pressure loss ∑h in the suction pipe. The suction pipeline system includes bottom valves, water strainers, pipes, elbows, etc.; ensuring a proper design for the installation of these components helps to minimize losses, which is also an important way to prevent cavitation in the water pump ； 4) Reduce the required net positive suction head of the pump itself; to this end, the diameter of the impeller’s suction inlet can be increased appropriately, or drainage without a foot valve can be employed. This approach is suitable for the design and manufacturing phase of centrifugal pumps; however, it is rarely used in actual production facilities. ② Installing an inducer wheel at the pump’s suction inlet proves to be very effective in improving the cavitation resistance of centrifugal pumps and addressing cavitation issues. Moreover, it has a simple structure that makes it easy to manufacture and install, is convenient for operation and maintenance, and has a low cost. It can be installed and tested without affecting production, making it particularly suitable for widespread use in production sites. ③Proper design of the suction piping and adjustment of the installation height. 1) Under conditions permitting installation, minimize the suction height of the pump as much as possible. This allows for a larger allowable net positive suction head during pump operation. Under normal circumstances, when the installation height is between 2 and 3.5 meters, cavitation in the pump is reduced. 2) To reduce the density of well water—specifically mine water containing coal dust and sediment—sedimentation treatment should be carried out before discharging the mine water, in order to decrease its density and thereby mitigate cavitation in pumps. 3) Reduce the average flow velocity of water entering the pump suction inlet. Although this method can completely eliminate cavitation problems, it is rarely used in production sites. This is because adjusting the pump’s suction piping and installation height involves a large amount of work and high construction costs, and is also constrained by the construction environment; thus, it can only be carried out when the plant is shut down or undergoing major maintenance. Meanwhile, due to process constraints, such adjustments will also affect subsequent processes, resulting in a chain reaction. ④Optimizing process operating conditions: When process conditions permit, changing operating parameters such as the pump’s flow rate, head, rotational speed, and the operating temperature of the medium can prevent cavitation from occurring. However, due to limitations in process conditions, optimizing the process operating conditions has significant limitations; in most cases, the effects are not notable. Therefore, this method can be used as an auxiliary method for solving cavitation problems.