Reasons for frequent bearing wear in shielded pumps
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This post was last edited by yxmqh on 2009-12-14 at 14:15. Our company has several magnetic pumps and canned motor pumps in operation, and for one set of these pumps, the bearing detector frequently reaches the red zone. Each time maintenance personnel conduct inspections, they attribute this to severe bearing wear as the cause of the detector going into the red zone. The frequency of maintenance is roughly on a monthly basis; under normal conditions the bearings need to be replaced every 3–4 months, but in worse cases, replacement is necessary already after just 1 month. I would like to ask those among you who have expertise in equipment technology: what could be the reasons behind the frequent activation of the bearing detector in canned motor pumps, with severe bearing wear being the stated cause for such issues? ? ? Operating conditions: The medium for this pump is a mixture of phenol and water, with water being the predominant component. It is condensed water from the vacuum system that is collected and then returned to the system. This condensed water is pumped to a heat exchanger for cleaning; the heat exchanger is used alternately, and it suffers from severe scaling, so it is estimated that it needs to be cleaned every 5–10 days (this is a conservative estimate; it might take less time). Analysis: The cause of wear could be dirty material containing salt, or it might be due to insufficient lubrication resulting in dry friction between the bearings. Are there any other possible reasons?
Based on what you’ve described, the medium is likely the main cause; consider installing a fine filter at the inlet and cleaning it regularly
In addition to ensuring good filtering performance, you can also try replacing the bearings with more wear-resistant materials, such as ceramics or cemented carbides.
The main reasons for the frequent wear of the graphite bearings in shielded pumps are as follows: 1. The medium contains impurities, especially fine particles; it is not clean, since the lubricant for the graphite bearings in shielded pumps is the same medium that is being transported. 2. The pump often operates at a low liquid level, that is, in a condition of no liquid flow (or with an empty pump); it is strictly prohibited to operate a canned motor pump with no liquid present ； When it operates at a low liquid level, it greatly accelerates the wear of the graphite bearings. Corresponding handling method: 1. Use the fine filter proposed by LS to remove impurities from the medium, especially particles. 2. Install a interlock protection device for electrical appliances (i.e., an empty pump protection device) to automatically shut down the pump under low-load conditions. 3. It is recommended not to replace bearings with wear-resistant materials, as it’s better to replace the graphite bearings rather than the shafts! Moreover, the pump shaft of a canned motor pump often carries the rotor of the canned motor. For reference!
In reply to the person above: The liquid level can’t be low; under normal operation it’s at around 60-70%. This was confirmed through the glass panel on site. It seems that silicon carbide bearings are being used, and such bearings aren’t cheap. Based on its performance, this pump alone isn’t sufficient to meet the process requirements – often two pumps need to be operated simultaneously during cleaning. Could there be some issue with the pump itself that leads to severe bearing wear? For example, issues with the connections between various components or their spacing might not be meeting the required standards
If it doesn’t work, then change the type of pump; can’t a regular centrifugal pump be used?
The shielded pump we use is equipped with backwashing functionality. The manufacturer’s technical staff said that it is essential to ensure that the pump is filled with liquid before starting it, otherwise the lifespan of the bearings will be reduced
The shielded pump we use is equipped with backwashing functionality. The manufacturer’s technical staff said that it is essential to ensure that the pump is filled with liquid before starting it, otherwise the lifespan of the bearings will be reduced
Our factory also has many canned pumps. At the beginning of operation, the bearings of these pumps wear out quite severely; sometimes they need to be replaced every hour. The reason for this is poor cleaning before starting up, which results in impurities remaining inside the pipelines. In the end, we had no choice but to install a centrifugal pump, and it’s working well now.