Magnetic Pump Performance Analysis

  Regarding the demagnetization issue of magnetic drive pumps discussed in the last session, in this session, Anhui Shengshi Datang will provide some protective measures. Improvement Measures for Magnetic Drive Pump Demagnetization 1. Improvement Approach When improving the demagnetization situation of magnetic drive pumps, the primary focus is on enhancing the cooling aspect of lubrication to prevent the vaporization of the friction fluid, which leads to dry friction. However, it is also necessary to consider that the conveyed medium may contain vaporizable and volatile substances. According to the law of energy conservation, the velocity of the conveyed medium can be comprehensively reduced, and the static pressure can be increased to enhance the vaporization degree of the medium, thereby effectively preventing vaporization due to excessive temperature. Based on this improvement approach, comprehensive enhancements can be made to the impeller and bearing areas of the magnetic drive pump. 2. Improvement Measures (1) The bearing of the magnetic drive pump needs to be changed from semi-hollow to fully hollow, and the return hole should be completely drilled through to become a through hole, effectively increasing the actual flow rate of the medium for cooling and lubrication. (2) During installation, it is essential to ensure that the rotation directions of the spiral grooves match each other. The function of the spiral grooves is to provide flushing and lubrication for the medium. Therefore, the rotation direction of the spiral grooves must be clearly indicated to ensure smoother flow of the medium. During high-speed rotation, some heat will be carried away, thereby enhancing the cooling and lubrication effects on the bearings and thrust rings and promoting the formation of a liquid protective film during friction. (3) The impeller section needs to be trimmed, but it must be ensured that the impeller efficiency remains unchanged. Trimming the impeller not only reduces the fluid flow velocity but also comprehensively enhances the vaporization degree of the medium through static pressure, improving the vaporization effect. At the same time, the operating range of the magnetic drive pump needs to be expanded to reduce the vibration impact of the process during operation. (4) A protection device needs to be installed in the magnetic drive pump. During operation, if any component is overloaded or the inner magnetic rotor gets stuck in the "bearing seizure" condition, the protection device can cause it to automatically disengage, providing comprehensive protection for the magnetic drive pump. Operational Considerations for Magnetic Drive Pumps To fundamentally resolve the demagnetization issue of magnetic drive pumps, in addition to comprehensive improvements, the following points must be noted during operation: 1. Before starting the magnetic drive pump, priming must be performed to ensure no air or gas remains inside the pump. 2. The bearings of the magnetic drive pump rely on the conveyed medium for cooling and lubrication. Therefore, it is essential to ensure that the magnetic drive pump does not run dry or that all medium is cleared, as this could cause bearing failure due to dry friction or a sudden significant temperature rise inside the pump, leading to demagnetization of the inner magnetic rotor. 3. If the conveyed medium contains particulate matter, a filter screen must be installed at the pump inlet to prevent excessive debris from entering the magnetic drive pump. 4. Components such as the rotor and crankshaft have strong magnetic properties. During installation and removal, the magnetic field scope must be fully considered. Otherwise, it may affect nearby electronic equipment. Therefore, installation and removal must be performed at a distance from electronic devices. 5. During operation of the magnetic drive pump, no objects should come into contact with the outer magnetic rotor to avoid damage and other issues. 6. The outlet valve must not be closed during the operation of the magnetic drive pump, as this could damage components such as the bearings and magnetic steel. If the pump continues to operate normally after the outlet valve is closed, this time must be controlled within 2 minutes to prevent demagnetization. 7. The inlet pipeline valve should not be used to control the flow rate of the medium, as this may cause cavitation. 8. After the magnetic drive pump has been in continuous operation for a certain period, it should be appropriately stopped. After confirming that the wear on the bearings and thrust rings is not severe, disassemble them to inspect the internal components. If minor issues are found in any components, replace them immediately. In addition to the above considerations, here are some supplementary points: A. Root Cause: In-Depth Understanding of Demagnetization Mechanism The magnetic coupler of a magnetic drive pump consists of an inner magnetic rotor and an outer magnetic rotor. When the inner magnetic rotor overheats due to insufficient cooling and lubrication, or when abnormal conditions (such as dry friction or cavitation) cause a sharp temperature rise, once the Curie temperature of permanent magnet materials like NdFeB (typically between 110°C - 150°C) is reached, their magnetism will sharply decline or even permanently disappear. Therefore, the ultimate goal of all measures is to ensure that the inner magnetic rotor always remains below a safe temperature. B. Preventive Measures During Design and Selection (Source Control) The following aspects are crucial when purchasing or improving magnetic drive pumps: 1. Selecting Appropriate Magnetic Material and Protection Grade: a. Neodymium Iron Boron (NdFeB): High magnetic energy product, but relatively low Curie temperature and prone to corrosion. Must ensure complete encapsulation (e.g., stainless steel sleeve) and good cooling. b. Samarium Cobalt (SmCo): Slightly lower magnetic energy product, but higher Curie temperature (can exceed 300°C), better thermal stability, and more corrosion-resistant. For high-temperature conditions or applications requiring high reliability, SmCo magnets should be prioritized. c. Inquire with Suppliers: Clarify the magnet material, grade, and Curie temperature. 2. Providing Accurate Operating Parameters: During selection, it is essential to provide the manufacturer with accurate medium characteristics (including composition, viscosity, solid particle content, and size), operating temperature, inlet pressure, flow range, etc. This helps the manufacturer select the most suitable pump type, materials, and cooling flow path design for your needs. 3. Consider Installing a Temperature Monitoring System: a. Isolation Sleeve Temperature Monitoring: Install temperature sensors (e.g., PT100) on the outer wall of the isolation sleeve. Since the inner magnetic rotor temperature is difficult to measure directly, the isolation sleeve temperature is the most direct reflection. Setting high-temperature alarms and shutdown interlocks is the most effective automated means to prevent demagnetization. b. Bearing Monitoring: Advanced magnetic drive pumps can be equipped with bearing wear monitors to provide early warnings before severe wear leads to temperature rise.   C. Key Supplementary Considerations in Operation and Maintenance In addition to the mentioned priming, preventing dry running, and avoiding cavitation, the following should also be noted: 1. Minimum Continuous Stable Flow and Cooling Circuit: a. Magnetic drive pumps have a minimum continuous stable flow. Operating below this flow rate means the heat carried away by the internal medium circulation is insufficient, leading to temperature buildup. b. It is essential to ensure that the pump's cooling return line (if equipped) is unobstructed. This line not only provides bearing lubrication but is also a lifeline for cooling the inner magnetic rotor. This line must never be closed or blocked. 2. Avoid "Low Flow" Operation: Prolonged operation near the low flow point results in low efficiency, with most of the work converted into heat, similarly causing medium temperature rise and increasing demagnetization risk. Ensure the pump operates within its efficient range. 3. System Pressure and Net Positive Suction Head (NPSH): a. Ensure Sufficient Inlet Pressure: The mentioned increase in static pressure to enhance vaporization essentially means increasing the Available NPSH (NPSHa) to be significantly greater than the pump's Required NPSH (NPSHr). This is fundamental to preventing cavitation, as the vibration and localized high temperatures generated by cavitation pose a dual threat to magnetic drive pumps. b. Monitor Inlet Filters: For media containing impurities, the inlet filter must be cleaned regularly. Clogging can cause inlet pressure drop, inducing cavitation. 4. Contingency Plans for Abnormal Conditions: a. Power Interruption: If a factory experiences a sudden power outage followed by a quick restoration, be cautious as the medium in the system may have partially vaporized or the pump may have accumulated air. In such cases, follow the initial startup steps for inspection and priming; do not start directly. b. Hot Medium Transfer: When conveying easily vaporizable media, consider insulating the inlet pipeline and even cooling the pump body (e.g., adding a cooling water jacket) to ensure the medium remains in liquid state upon entering the pump. D. Deepening Maintenance and Inspection 1. Regular Disassembly Inspection: In addition to checking bearing and thrust ring wear, focus on inspecting the isolation sleeve and inner magnetic rotor surfaces. Any scratches or wear points may indicate poor cooling or misalignment. Check the magnetic strength of the inner magnetic rotor (using a Gauss meter), establish historical data records, and track its magnetic decay trend. 2. Management of Standby Pumps: The inner magnetic rotor of a magnetic drive pump stored as a long-term standby might experience slight demagnetization due to surrounding stray magnetic fields or vibrations. Regularly rotate the pump and alternate its use.