How to determine centrifugal pump issues by listening to sounds on-site?

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How to determine centrifugal pump issues by listening to sounds on-site? I. Cavitation noise: This is the sound produced when a water pump experiences cavitation, typically manifesting as a popping or cracking sound. II. Loose noise: This is the sound produced by the loosening of rotor components on the shaft. Such sounds are often periodic. When components such as the impeller or bushing of a circulating water pump become loose on the shaft (with a gap of even 1–3 millimeters), a clunking or knocking sound is produced. If the pump shaft is bent at this time, the collision noise will be louder, as the impeller and shaft sleeve tend to hang downward on the shaft, resulting in a gap forming below the shaft. But when the convex surface at the bend turns upward, it hits the impeller, causing it to move upward; before the impeller has finished moving upward, the convex surface of the pump shaft turns downward again, pushing the impeller to move downward. Thereafter, the convex surface of the pump shaft turns upward again, striking the impeller and causing it to move upward, thus producing a periodic sound. It must be pointed out that water pumps operating under such conditions are very dangerous; in addition to air leaking into the pump due to the swinging of the rotor components, more serious issues can arise such as cracks in the impeller and fractures in the pump shaft (at the edges of the mating surfaces). 　In some rolling bearing spacers, due to not being pressed against the bearing, intermittent knocking sounds against the shaft can be heard during operation. Due to the large gap between the spacing sleeve and the shaft, when it is not pressed axially, this gap will appear below the shaft. But accidental factors can also cause the gap to move upward; due to its own weight, the spacer sleeve falls downward, producing a slight knocking sound against the shaft. III. Abnormal noises at low flow rates – This mainly applies to volute pumps. The noise at low flow rates is similar to cavitation noise, but in some cases it is louder, as if stones were hitting the pump casing. This is mainly a design issue related to the position of the pump tongue. IV. Abnormal noises in rolling bearings 1. In newly installed rolling bearings, excessive radial tension during assembly can make it difficult for the rolling elements to rotate, resulting in a low-level humming sound. At this time, the bearing temperature will rise. 　　2. If the oil level in the bearing housing is insufficient, the rolling bearings will emit a steady whistling sound during operation. 　　3. When the gap between the rollers and the cage is too large, a relatively loud whooshing sound may be produced during operation. 　　4. When peeling occurs on the raceway surfaces of the inner and outer rings or on the surface of the rolling elements in a rolling bearing, intermittent impacts and vibrations will occur during operation. 　　5. If the rolling bearing is damaged (including a broken separator, cracked rolling elements, or cracked inner and outer rings), there will be cracking noises during operation.