Working principle of chemical centrifugal pumps and analysis and treatment of common faults

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This post was last edited by Aggregated Cat_IEB8P on 2020-6-28 at 16:51. Centrifugal pumps are one of the commonly used mechanical devices in the chemical industry. They have a high failure rate in actual production, and can easily lead to serious production shutdowns; as a result, many chemical companies pay great attention to the maintenance of these pumps. Working principle of centrifugal pumps: Generally, a centrifugal pump consists of components such as an axis, impeller, bearings, and pump casing. When the centrifugal pump is powered on, the motor drives the impeller to rotate at high speed. As the impeller rotates, a very large centrifugal force is generated; under the influence of this force, the pressure of the liquid increases significantly. This in turn causes the blades to rotate at high speed, and the liquid is forced away from the impeller as a result of the centrifugal force. Common faults of centrifugal pumps and their solutions 1. Motor-related faults: Rotor imbalance fault: The main cause of this fault is an offset in the center of gravity of the rotor components. A rotor consists of a shaft along with several rotating disks, and it is very easy for the center of gravity of these disks to shift during operation, which in turn causes the rotor’s center of gravity to shift as well, ultimately leading to rotor imbalance. Eccentric rotor faults: Typically, they manifest as either misalignment of the stator or misalignment of the rotor, and both of these conditions can cause frequency vibrations. Therefore, after such faults occur, they usually manifest primarily as a condition of rotor excitation force, which is closely related to the load, but not related to the rotational speed. 2. Abnormal noises and vibrations – The main factors that cause centrifugal pumps to produce abnormal noises and vibrations are the following two. In terms of hydraulic performance, the first possibility is that the centrifugal pump draws in debris into its internal structure, causing the impeller to become clogged or damaged; in such cases, it is necessary to stop the machine immediately and carry out prompt cleaning ； Subsequently, the flow rate of the centrifugal pump fluctuated significantly, causing pressure changes, which in turn led to abnormal noises and unusual vibrations. Finally, an excessive suction lift leads to quite severe cavitation at the inlet of the impeller; in other words, the water flowing over the impeller forms bubbles in the low-pressure areas, and these bubbles are destroyed in the high-pressure areas. This results in certain impacts, which are quite severe, and vibrations will show abnormal patterns as a consequence. If such a situation occurs, the installation height of the centrifugal pump should be reduced. In terms of mechanics, the first possibility is that there’s an abnormality in the rotation of the rotor within a centrifugal pump or motor; in other words, an imbalance has occurred ； Subsequently, the foundation bolts of the centrifugal pump became loose, which led to abnormal vibration ； Another issue is the misalignment between the centrifugal pump and the motor; the solution is to correct this alignment ； Finally, since the impeller has not been balanced, correction measures also need to be taken. 3. Mechanical seal failure: Mechanical seal failures can be primarily divided into two types, namely failure of the stationary and rotating rings, and failure of the elastic elements. Factors leading to the failure of the rotating and stationary rings are directly related to the high temperature of the medium inside the centrifugal pump, which affects the seals used there. If an eccentric rotor fault occurs, it is necessary to adjust the load appropriately before conducting relevant tests to identify the cause of the fault. The embedded structure became loose or even detached, thereby causing failure of the stationary and rotating rings. The hardfacing method using cemented carbide should be employed to address this fault. The pump heats up relatively quickly, which significantly increases the likelihood of pump leakage. This phenomenon is particularly prone to occur when the pump vibrates or pulsates. After such failures occur, it is very likely that the graphite rings inside the stationary and rotating rings will break or even fall off, ultimately leading to the failure of these rings. After long-term operation of the centrifugal pump, the maintenance staff failed to carry out maintenance tasks according to the scheduled maintenance schedule; as a result, the compression ratio of the elastic components exceeded normal levels. This easily led to damage to the stationary ring of the friction pair, and in severe cases, it caused failure of both the stationary and moving rings. Failure modes of elastic elements: The failures of elastic elements are usually fracture or loss of elasticity. Generally, the cause of failure is severe vibration generated by the centrifugal pump during operation, or a vacuum condition. If the above situation occurs, the probability of component failure will **increase**. In addition, fracture failures may also be caused by improper heat treatment methods or weak welding, in which case it is necessary to replace the faulty elastic element immediately. For the failure to fire, the primary cause is the presence of certain scale in the cracks of the components; it is also possible that improper handling during heat treatment leads to this failure to fire. Therefore, such faults can be addressed through cleaning methods, with softened water typically being used as the cleaning agent. In summary, centrifugal pumps are used in many production processes within the chemical industry. When a centrifugal pump fails, it is necessary to identify the underlying causes in order to take appropriate action, and regular maintenance is also very important.