Magnetic pump

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1. Introduction to magnetic pumps: Like shielded pumps, magnetic pumps use static seals in place of dynamic seals, thereby eliminating leakage problems; hence they are particularly suitable for transporting valuable, toxic, flammable, or explosive liquids. Magnetic-driven centrifugal pumps are mainly used nowadays. Structure and working principle of magnetically driven centrifugal pumps: Magnetically driven centrifugal pumps operate by taking advantage of the ability of magnets to attract magnetic materials and the magnetic force that exists between magnets. As shown in the figure below, the motor is connected to the outer rotor, while the impeller is connected to the inner rotor; there is a separator sleeve between the inner and outer rotors. When the outer rotor rotates driven by the motor, the attractive and repulsive forces between the permanent magnets of the inner and outer rotors cause the inner rotor to rotate as well, thereby achieving the purpose of transporting liquid. 2. Maintenance of magnetically driven centrifugal pumps: 1) Disassembly method and sequence for magnetically driven centrifugal pumps: ① Remove the coupling guard, and retighten the fixing bolts in the pump base ； ②Make positioning marks on the coupling hubs; remove the motor anchor bolts and take out the motor. ③ Use a puller to remove the pump coupling, make marks on it, and drain the lubricating oil from the oil tank ； Loosen the pump bracket bolts, pull out the bracket portion horizontally, and place it flat in the maintenance area. Loosen the impeller back nut, then pull out the impeller. If it’s stuck, use pulling force or a pry bar to symmetrically pry it out. Finally, remove the spacer sleeve. ④With the pump cover lowered, loosen the bolts that hold the pump suspension in place, pull the suspension part out vertically, remove the bolts securing the inner bearing caps. Align the suspension horizontally, and tilt the pump shaft at the rear wheel end downward toward the cork, so that the rotor can be disengaged from the suspension ； ⑤Loosen the outer magnetic steel locking screw, then pull down the outer magnetic steel using force; this will also pull down the two bearings. ⑥Loosen the isolation sleeve fastening bolts and remove the isolation sleeve. Pull out the internal magnet together with the pump shaft and balance disk as a single unit. Remove the locking bolt at the end of the rotor, take off the retaining plate and pull out the bushing. Then, use pulling force to remove the inner magnet, take off the balance disc, and pull out the bushing at the impeller end. 2) Inspection of components: (1) The impeller of the pump body should be free from any scratches or corrosion. (2) The enclosures surrounding the inner and outer magnetic rotors should have no cracks, breaks, or holes. (3) After removing the isolation sleeve, it must be carefully inspected for any cracks; isolation sleeves made of metallic materials must undergo flaw detection to ensure they have sufficient strength and a proper safety factor. (4) The inner and outer surfaces of the bearings should be checked to ensure there are no cracks, and that the clearance between them and the shaft is within the specified range. (5) The shaft should be free from scratches and corrosion, and its straightness must meet the requirements specified in the manual. 3) Assembly: (1) When assembling the magnetic rotor with the power equipment, the maximum end face runout of the outer magnetic rotor relative to the isolation sleeve should not exceed 0.25 mm, and the maximum radial runout should not exceed 0.50 mm. It is also necessary to ensure that the clearance between the inner and outer magnetic rotors and the isolation sleeve meets the requirements specified in the manual. (2) For sliding bearings, the clearance between the thrust plate and the graphite bearings should comply with the specifications given in the manual; if no specific value is provided, this clearance should not exceed 1 mm. The radial clearance of the bearing should meet the specified requirements; if the clearance is too small, the pump is prone to shaft seizure and increased friction, which affects its efficiency ； An excessive clearance will accelerate bearing wear and vibration. (3) As for the impeller and throat ring, both are vulnerable components, and the fit clearance required for their assembly is relatively large; therefore, it is necessary to ensure that the throat ring clearance meets the requirements specified in the user manual during assembly. (4) After the external magnetic rotor is connected to the motor, its radial and axial runout should be less than 0.01 mm. (5) During the assembly process, it is not allowed to use hard tools or objects to strike the graphite bearings, the inner and outer rotors, the isolation sleeves, etc.