【011】Working Principle of Magnetic Pump - Anhui Wanfulong Pumps and Valves

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This post was last edited by sean816 on 2015-11-20 at 16:48. Working principle of magnetic pump: A magnetic pump consists of three components: the pump itself, the magnetic drive unit, and the motor. The magnetic drive of the key component consists of an outer magnetic rotor, an inner magnetic rotor, and a non-magnetic isolation sleeve. When the electric motor drives the external magnetic rotor to rotate, the magnetic field can penetrate the air gap and non-magnetic materials, causing the internal magnetic rotor connected to the impeller to rotate synchronously. This enables contactless transmission of power, thereby converting dynamic sealing into static sealing. Since the pump shaft and internal magnetic rotor are completely enclosed by the pump body and isolation sleeve, the problems of leakage are completely resolved. This eliminates the safety risks associated with the leakage of flammable, explosive, toxic, and harmful substances through the pump seals in the oil refining and chemical industries, thereby ensuring the physical and mental health of workers as well as safe production. I. Working principle of magnetic pump: n pairs of magnets (where n is an even number) are arranged in a systematic manner on the inner and outer magnetic rotors of the magnetic drive, so that the magnets form a complete and interconnected magnetic system. When the inner and outer magnetic poles are in opposite polarities, that is, when the displacement angle Φ between the two poles is 0, the magnetic energy of the magnetic system is at its lowest ； When the magnetic poles rotate until like poles face each other, that is, when the displacement angle Φ between the two poles equals 2π/n, the magnetic energy of the magnetic system is at its maximum. When the external force is removed, due to the mutual repulsion between the poles of the magnetic system, the magnetic force will cause the magnet to return to the state with the lowest magnetic energy. Thus, the magnet moves, causing the magnetic rotor to rotate. II. Structural Features 1. Permanent Magnets: Permanent magnets made of rare-earth permanent magnet materials have a wide operating temperature range (-45–400°C), high coercivity, and strong anisotropy in their magnetic field direction; they do not lose their magnetism even when like poles are brought close to each other, making them an excellent source of magnetic fields. 2. Insulating sleeve: When a metal insulating sleeve is used, it is placed in a sinusoidally varying magnetic field; eddy currents are induced in the cross-section perpendicular to the magnetic field lines, which are then converted into heat. The expression for the eddy current is: . Among them, Pe–eddy current ； K—constant ； n—Rated speed of the pump ； T – Magnetic driving torque ； Pressure inside the F-separator sleeve ； D – Inner diameter of the spacer sleeve ； The resistivity of a material ； —The tensile strength of the material. Once the pump is designed, n and T are determined by the operating conditions; to reduce eddy currents, considerations must be given to F, D, etc. Using non-metallic materials with high resistivity and high strength to manufacture the isolation sleeve yields a very significant effect in reducing eddy currents. 3. Control of cooling lubricant flow rate: When the pump is operating, a small amount of liquid must be used to flush and cool the gap area between the internal magnetic rotor and the isolation sleeve, as well as the friction pairs of the sliding bearings. The flow rate of the coolant is usually 2%-3% of the pump’s designed flow rate, and the annular gap between the internal magnetic rotor and the isolation sleeve generates high heat due to eddy currents. When there is insufficient cooling lubricant or when the flushing holes are clogged, it will cause the temperature of the medium to rise above the operating temperature of the permanent magnets, resulting in the internal magnetic rotor gradually losing its magnetism and thus rendering the magnetic drive ineffective. When the medium is water or a water-based liquid, it is possible to maintain the temperature rise in the annular gap area at 3-5℃ ； When the medium is a hydrocarbon or oil, the temperature rise in the annular gap area can be maintained at 5-8°C. 4. Sliding bearings: The materials used for the sliding bearings of magnetic pump include impregnated graphite, filled polytetrafluoroethylene, and engineering ceramics. Due to the excellent heat resistance, corrosion resistance, and friction resistance of engineering ceramics, the sliding bearings in magnetic pumps are often made from such materials. Due to the brittleness of engineering ceramics and their low coefficient of expansion, the bearing clearance must not be too small to avoid shaft seizure. Since the sliding bearings of magnetic pump are lubricated by the medium being transported, different materials should be used to manufacture the bearings depending on the type of medium and the operating conditions. 5. Protection measures: When the driven component of the magnetic drive operates under overload conditions or when the rotor gets stuck, the primary and driven components of the magnetic drive will automatically separate, thereby protecting the pump. At this point, the permanent magnets in the magnetic drive are subjected to the alternating magnetic field generated by the driving rotor, which results in eddy current losses and magnetic losses; these factors cause the temperature of the permanent magnets to rise, leading to failure of the magnetic drive. III. Advantages of magnetic drive pumps Compared with centrifugal pumps that use mechanical seals or packing seals, magnetic drive pumps have the following advantages. 1. The pump shaft has been changed from a dynamic seal to a closed static seal, completely preventing medium leakage. 2. No separate lubrication or cooling water is required, reducing energy consumption. 3. It changes from coupling-driven transmission to synchronous dragging, with no contact or friction. It features low power consumption and high efficiency, as well as damping vibration effects, which reduce the impact of motor vibrations on the pump and the impact of cavitation vibrations in the pump on the motor. 4. During overload, the inner and outer magnetic rotors slip relative to each other, providing protection for the motor and pump. IV. Operating Precautions 1. Preventing Particle Entry (1) Ferromagnetic impurities and particles must not enter the magnetic drive and bearing friction pairs. (2) After transporting media that are prone to crystallization or precipitation, it is necessary to rinse the pump promptly (fill the pump chamber with clean water after stopping the pump, and then drain it completely after running for 1 minute) in order to ensure the service life of the sliding bearings. (3) When transporting a medium containing solid particles, filtration should be performed at the inlet of the pump flow tube. 2. Prevent demagnetization (1) The magnetic torque should not be designed to be too small. (2) It should operate under specified temperature conditions; it is strictly prohibited for the medium temperature to exceed the limits. A platinum resistance temperature sensor can be installed on the outer surface of the magnetic pump’s isolation sleeve to monitor the temperature rise in the gap area, so as to trigger an alarm or shut down the pump when the temperature exceeds a set limit. 3. Prevent dry friction (1) Idle operation is strictly prohibited. (2) It is strictly prohibited to evacuate the medium. (3) With the outlet valve closed, the pump shall not operate continuously for more than 2 minutes to prevent the magnetic drive from overheating and failing.