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A canned motor pump is an mechatronic device that combines a canned motor with a mechanical pump. A shielded motor is one in which a shielding sleeve made of non-magnetic material is placed between the stator and rotor of the motor, thereby dividing the stator and rotor into two separate, isolated spaces. The purpose of doing this is to eliminate mechanical shaft seals (mechanical seals that rely on the fit between moving and stationary parts), in order to achieve a completely leak-free system. Shielded pumps use sliding bearings instead of rolling bearings, and the liquid being transported fills the space between the rotor and its bearings during operation, so no lubrication is required. The shielded pump operates smoothly with low noise. The amount of routine maintenance required is also very low. Due to its many irreplaceable advantages, the shielded pump is widely used in industries such as chemical processing, refrigeration, water supply and drainage, and the nuclear industry. As the number of uses and scope of application increase, the amount of damage also gradually rises. Taking the P1 series canned pumps used in ammonia refrigeration equipment as an example, the maintenance methods will be introduced. 1. General fault diagnosis and repair of shielded pumps: 1. The resistance value of the motor winding coils is normal ； The pump won’t start rotating. The reason is dry grinding caused by operation without fluid, which led to the seizure of the rotor shaft sleeve and the graphite bearings. Or jamming caused by other mechanical failures. The solution involves disassembling the shielded pump, cleaning the components, and locating the fault point. Repair or replace the parts. 2. The motor is fine, but the operating current is too high; the reason is insufficient liquid flow. There is dry grinding. Or there may be mechanical jamming and an improper tightening of the motor end cover. Treatment method. After decomposition. Clean and reassemble. 3. It generates a lot of noise during operation, and its operating current is also unstable. The reason is severe wear of components such as the rotor shaft sleeve thrust disc and graphite bearings. Disassemble the shielded pump. Clean and replace the worn-out components. An interference fit is used between the graphite bearing and the bearing end cover; the bearing end cover must be heated in order to remove or install the graphite bearing. Pay attention to the fit dimensions during assembly. Axial runout (0.5-1.5mm). In the machine direction (0.08–0.12 mm), the maximum wear amount shall not exceed 0.4 mm. If there are problems with the motor windings, then the shielded pump must undergo major repairs whenever there are issues with its motor. II. Major overhauls of shielded pumps are handled in two different ways. One possibility is that the shielding cover is undamaged; it’s only the motor that has a problem. Another case is where both the motor and the shielding sleeve are damaged. In either case, it is necessary to cut open the casing of the shielded pump motor and remove the motor stator in order to carry out repairs. In cases where the shielding sleeve is not damaged, efforts should be made to keep it intact during disassembly. To reduce maintenance costs and labor time. 1. Method for removing the motor stator: Disassemble the shielded pump and use a flat chisel to cut through the weld at the lower ring of the shielding sleeve. Use a lathe or cutting machine to cut along the original weld site on the motor housing. Place the positioning points correctly, and lift out both the positioning cover and the shielding sleeve from the motor (the ring welds on the shielding sleeve remain unchanged). Check whether stabilizing pins are installed between the motor housing and the stator. If any. Remove the nail firmly. Then heat the motor housing and lift out the stator. (An interference fit is also used for the assembly between the motor housing and the stator.) 2. Motor repair: There is not much difference between the motors used in shielded pumps and ordinary motors; the only requirement is that the insulation level must be higher. It can be manufactured according to the standards for H-class motors. It is best to use enameled wire from the QZY series and high-temperature resistant insulation materials, and manufacture the product strictly in accordance with the specifications of the original motor. To ensure the original motor’s performance. 3. Manufacturing of the shielding sleeve: For shielding sleeves that can no longer be repaired, they must be made anew. The fabrication of the shielding sleeve is key to the maintenance of shielded pumps. It is necessary to use high-quality stainless steel sheets with a relatively high nickel content that possess good corrosion resistance; the thickness of these sheets should be the same as that of the original shielding sleeve, and the cutting dimensions must be precise. Since the shielding sleeve is very thin, direct welding presents a challenge. If possible, it is best to use an automatic welding machine for welding. It can also be done by hand welding, but it requires a higher level of skill. The finished shielding sleeve should be rounded, pressurized, and leak-tested. The method I used was to apply pressure with nitrogen up to 1 MPa and then immerse it in water to check for leaks. This method is both simple and practical. 4. Initial assembly and adjustment: Clean the insulation paint and dirt from the stator, then apply a small amount of refrigeration oil to the inside and outside of the stator using a brush. Press the shielding sleeve into the stator. Install the upper and lower protective covers. Heat the motor housing, press in the stator, install the rotor, attach the upper retaining cover and asbestos gasket, and apply a small amount of refrigeration oil to the rotor shaft sleeve thrust disc and graphite bearings. Install the upper and lower motor end caps and the impeller. Adjustment is carried out, as the motor cover and the motor housing are already positioned. The concentricity is no longer an issue; here the main task is to adjust the left-right deviation, once the impeller can rotate smoothly by hand. Several positioning points can be welded between the motor housing and the upper positioning cover. 5. No-load test: Operate with power applied. Check the no-load current of the motor. Operating noise and smoothness (for a time of no more than three minutes). If there are no issues, the next step can be carried out. 6. Welding and pressure testing: Disassemble the shielded pump again. First, weld the seam between the motor housing and the upper positioning cover. Then weld the upper and lower ring welds of the shielding sleeve. Use a steel tube turned on a lathe, with an inner diameter 0.4 mm smaller than that of the shielding sleeve and a length 6 mm shorter than that of the shielding sleeve, as the support sleeve. Push it into the shielding sleeve, and then pressurization can be carried out. The method involves filling the motor’s wiring terminals with 1.2 MPa of nitrogen, and placing the repaired shielded motor in a water tank to test for leaks. If there are no leaks within two hours. Then it can be assembled. The maintenance of shielded pumps requires relatively high technical skills. But as long as it’s done carefully. It can still be done well.