Fault analysis of brushless DC water pump (magnetic isolation pump)



(1) The magnetic pump shaft is broken. The material used for the pump shaft of the CQB magnetic pump is 99% alumina ceramic. The main reason for the pump shaft breaking is that the shaft is twisted and broken due to the dry wear of the bearings during pump operation. When disassembling the pump for inspection, it can be seen that the bearings are severely worn. The main way to prevent the pump from breaking is to avoid idling the pump.

(2) The magnetic pump bearing is damaged. The material used for the bearings of CQB magnetic pump is high-density carbon. If the pump runs out of water or there are impurities inside the pump, it will cause damage to the bearings. If the coaxiality requirement between the inner and outer magnetic rotors of the cylindrical coupling cannot be guaranteed, it will directly affect the service life of the bearing.

(3) The magnetic pump cannot pump out liquid. The inability of a magnetic pump to produce liquid is the most common malfunction of the pump, and there are also many reasons for it. Firstly, check whether there is any air leakage in the suction pipeline of the pump, whether the air inside the suction pipeline is discharged, whether the amount of liquid filled in the magnetic pump is sufficient, whether there is any debris blocking the suction pipe, and whether the pump is reversed (especially after replacing the motor or repairing the power supply line). Also, pay attention to whether the suction height of the pump is too high. If the above inspection still cannot solve the problem, the pump can be disassembled for inspection to see if the pump shaft is broken. The dynamic and static rings of the pump should also be checked for integrity, and the entire rotor should be able to move slightly axially. If axial movement is difficult, check if the carbon bearing is too tightly combined with the pump shaft.

It is worth noting that the magnetic pump has been repaired several times and no problems have been found. It is important to pay attention to whether the magnetic coupling is working properly. Bearings, inner magnetic rotors, and spacers all generate heat during operation, which will increase the working temperature. On the one hand, it will reduce the transmitted power, and on the other hand, it will cause great trouble for magnetic pumps that transport easily vaporized liquids. The power transmitted by a magnetic steel decreases continuously with the increase of temperature. Generally, the decrease in its transmission capacity is reversible below the working limit temperature of the magnetic steel, while it is irreversible above the limit temperature. That is, after the magnetic steel cools down, the lost transmission capacity can no longer be restored. In special circumstances, when the magnetic coupling slips (loses step), the eddy current heat in the spacer will increase sharply, and the temperature will rise sharply. If not dealt with in time, it will cause demagnetization of the magnetic steel, causing the magnetic coupling to fail. Therefore, a reliable cooling system should be designed for magnetic pumps. For media that are not easy to vaporize, the cooling circulation system generally leads out the liquid flow from the impeller outlet or pump outlet, and returns to the suction port through the bearing and magnetic transmission part. For media that is easy to vaporize, heat exchangers should be added or the liquid flow should be directed to the storage tank outside the pump to avoid heat returning to the suction port. For media with solid or ferromagnetic impurities, filtration should be considered, and for high-temperature media, cooling should be considered, To ensure that the magnetic coupling does not exceed the operating limit temperature.

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