Some of the common issues that can occur when a pump is in operation include the following:
Abnormal noises are often one of the first signs of a problem. These sounds can be caused by loose components, such as the rotor or shaft, which may produce rhythmic or periodic noises. For example, if the impeller or sleeve becomes loose on the shaft (with a clearance of 1–3 mm), it can create a buzzing or impact sound. If the pump shaft is bent, the noise becomes more severe due to the impeller and sleeve potentially shifting vertically. As the bent part of the shaft rotates, the impeller moves up and down, creating a repetitive sound. This condition is very dangerous, as it can lead to further damage, such as impeller cracking or even pump shaft fracture at the point of contact.
Another cause of abnormal noise is the rolling bearing's spacer bushing. If it is not properly pressed into place, it may collide with the shaft during operation, resulting in intermittent knocking sounds. This is especially likely if there is a large gap between the bushing and the shaft, allowing for misalignment and occasional contact.
Low flow is another common issue. It can manifest as an unusual noise, similar to cavitation, but sometimes louder, resembling the sound of stones hitting the pump casing. This is often related to the design of the pump’s tongue position.
Rolling bearings can also generate different types of abnormal noises. For instance, if the radial tightening force during assembly is too high, the bearing may produce a low hum, especially when the temperature rises. Insufficient lubrication can result in a whistling sound, while excessive clearance between the rolling elements and the spacer can cause a loud humming noise. If the raceway or rolling elements are damaged, the bearing may emit intermittent shocks or a crackling sound.
Impeller damage or improper installation can prevent the pump from delivering water effectively. This may happen if the pump isn’t fully primed before starting, or if there is a significant leak. Blockages in the flow path—such as the bottom valve, impeller passage, or debris in the system—can also restrict flow. Additionally, if the pump is installed too high above the water source, or if the speed is too low (common in belt-driven systems), the pump may not function properly. In parallel centrifugal sewage pumps, if the outlet pressure is lower than the main line pressure, water may not be discharged.
Incorrect motor rotation can also cause the pump to run in reverse, leading to poor performance.
High bearing temperatures are often caused by low oil levels, which reduce the amount of lubricant reaching the bearing. Poor-quality oil, contamination, or emulsification can also contribute. If the oil ring fails to rotate, the bearing may lose its lubrication supply. Inadequate cooling water can further increase temperatures. Damaged bearings or excessive pressure from the bearing cover, which reduces radial clearance, can also lead to overheating.
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