Some of the common issues that occur when a pump is running include the following:
One of the most frequent problems is abnormal noise. This type of sound usually originates from the rotor or shaft and may have a rhythmic pattern. For example, if the impeller or sleeve becomes loose on the shaft (with a clearance of up to 1–3 mm), it can produce a buzzing or impact sound. If the pump shaft is bent, the noise becomes more pronounced due to the tendency of the impeller and sleeve to shift downward. As the bent part rotates, the impeller may move upward or downward, creating periodic sounds. It’s important to note that this situation is very dangerous, as it can lead to severe damage such as impeller cracking or even pump shaft fracture at the point of contact. Additionally, the looseness may allow air to enter the pump, worsening the condition.
Another source of noise comes from rolling bearings. If the bearing spacer bushing isn’t properly pressed onto the shaft, it may collide with the shaft during operation, causing intermittent knocking sounds. This is often due to excessive clearance between the bushing and the shaft, which can result in the bushing shifting and hitting the shaft unexpectedly.
Low flow is another common issue. Abnormal noises, especially in the pump casing, are often associated with low flow. These sounds can resemble cavitation or even the sound of stones being dropped into the pump. This problem is typically related to the design of the pump's tongue position.
Rolling bearings can also produce unusual noises. New bearings might emit a low hum if the radial tightening force is too high, making it difficult for the rolling elements to turn smoothly. When the bearing temperature rises, this noise becomes more noticeable. If there is insufficient lubrication, the bearing may produce a whistling sound. A large gap between the rolling elements and the cage can cause a loud humming noise. If the raceway surfaces or rolling elements are damaged, the bearing may generate intermittent shocks and impacts. In cases of severe damage—such as a broken cage, cracked rings, or broken rolling elements—the bearing will make crackling or snapping sounds.
Impeller damage or lack of water during startup can prevent the pump from transferring energy to the fluid effectively. This may happen due to an improperly filled pump, serious leaks before starting, or blockages in the flow path, such as a clogged bottom valve, impeller passage, or loss of the inlet gate. High installation height, low pump speed (especially in belt-driven systems where pulleys don’t match or are too loose), or improper motor rotation direction can also lead to poor performance.
High bearing temperatures are often caused by low oil levels, which reduce the amount of oil reaching the bearing. Poor-quality oil, contamination, or emulsification can also contribute to overheating. If the oil ring fails to rotate, the bearing may lose its lubrication supply. Insufficient cooling water or damaged bearings can further increase temperatures. For rolling bearings, excessive pressure from the bearing cover can compress the radial clearance, reducing flexibility and leading to increased heat.
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