Why does a magnetic pump lose its magnetism?
The fundamental cause of demagnetization in a magnetic pump is that the temperature of its internal permanent magnet exceeds the material’s tolerance limit. Once this critical temperature is surpassed, the magnet’s magnetism undergoes irreversible attenuation or even complete loss.
In simple terms, high temperature is the direct culprit behind demagnetization, while various improper operating conditions and practices serve as the underlying factors that contribute to elevated temperatures.
How is high temperature generated?
During operation, a magnetic pump relies on the transported medium to lubricate and cool the internal friction pairs (e.g., sliding bearings) and to dissipate heat generated between the inner magnetic rotor and the isolation sleeve due to eddy current effects. Any factor that disrupts this cooling cycle or induces abnormal friction will cause a rapid temperature rise.
The main causes of demagnetization
Idling or dry operation
This is the most common cause. When there is no medium or insufficient medium in the pump, it operates in idle mode. During this state, internal components lose lubrication and cooling, causing temperatures to rise rapidly and resulting in rapid demagnetization of the magnets.
The rotor or impeller is jammed.
If the transported medium contains iron filings, welding slag, fibers, or other solid particulate impurities, these may become lodged between the inner magnetic rotor and the impeller. In such cases, the inner rotor ceases rotation, while the outer magnetic rotor driven by the motor continues to rotate at high speed, generating intense traction and friction between them that instantly produces substantial heat, leading to demagnetization.
Operating under conditions that deviate from the rated operating parameters
- Long-term operation at low flow rates: When the pump operates below its rated flow rate, the internal circulation of cooling medium becomes insufficient to effectively dissipate heat.
- Cavitation phenomenon: When the pump inlet pressure is too low or the medium temperature is excessively high, the liquid vaporizes to form bubbles. The rupture of these bubbles disrupts fluid continuity, leading to pump cavitation and flow interruption, which subsequently induces dry friction and elevated temperatures.
Part wear or design defects
- Bearing wear: Wear in sliding bearings or thrust bearings can cause friction between the inner rotor and the isolation sleeve, leading to high temperatures.
- Cooling channel blockage: The lubricating and cooling channels inside the pump are blocked by debris, preventing normal circulation of the cooling medium.
- Design flaws: Some pumps may have design defects such as insufficient cooling return flow, resulting in poor heat dissipation performance.
5. The medium temperature is too high
Directly conveying fluids exceeding the allowable temperature range of the magnetic pump (particularly its magnet materials) will also degrade magnet performance and ultimately lead to demagnetization.
How to prevent and manage it?
preventive measure
- Strictly prohibit idling: Ensure the pump is fully primed before startup and equipped with a liquid level protection device.
- Filter medium: Install a filter at the pump inlet and clean it regularly to prevent impurities from entering the pump.
- Standard operating procedures: Ensure the pump operates within its rated conditions, avoiding prolonged operation at low flow rates or with the outlet valve closed.
- Regular maintenance: Periodically inspect the wear condition of wear-prone components such as bearings and replace them promptly.
processing scheme
Once demagnetization occurs, the performance of the magnetic pump will significantly deteriorate (e.g., insufficient pressure or flow rate) or even cease operation entirely. Since demagnetization is irreversible, the only solution is to replace the internal and external magnetic rotor assemblies with new ones. During replacement, appropriate magnetic material (e.g., neodymium-iron-boron or samarium-cobalt) should be selected based on actual operating conditions (e.g., temperature and medium corrosiveness).
Two Contraindications for Magnetic Pump
In practical applications, the two most critical prohibitions for magnetic pumps are: strictly avoiding idle operation (dry friction) and preventing the entry of ferromagnetic particles or other impurities into the pump.
1. Empty rotation (dry friction) is strictly prohibited.
The cooling and lubrication of the sliding bearings in a magnetic pump rely entirely on the transported medium. If idling occurs or the medium runs out, the bearings will lose lubrication and cooling, causing a rapid temperature surge. This not only rapidly damages the sliding bearings but also prevents the dissipation of internal eddy heat, leading to permanent magnet demagnetization at high temperatures, failure of the isolation sleeve, or even complete equipment failure. Furthermore, when the outlet valve is closed, continuous pump operation must not exceed 2 minutes.
2. The entry of ferromagnetic particles and solid impurities is strictly prohibited.
Magnetic pumps require extremely high purity of the medium; ferromagnetic impurities or hard particles are strictly prohibited from entering both the magnetic drive unit and bearing friction pairs. Such contaminants not only cause severe wear on sliding bearings and isolation sleeves but may also lead to jamming of internal and external magnetic rotors. When a rotor becomes jammed, the driving and driven components of the magnetic drive automatically disengage to protect the pump; however, this process generates significant eddy current losses and magnetic losses in the alternating magnetic field, resulting in permanent magnet overheating and failure. Therefore, when handling media containing solid particles, a filtration device must be installed at the pump inlet.
