Use and Maintenance of Magnetic Drive Pumps

Usage Notes

(1) After installation, rotate the coupling by hand to check for any rubbing or contact.

(2) To prevent debris from entering the pump, a filter is installed at the pump inlet. The filter area is more than 3 to 4 times the cross-sectional area of the pipeline.

(3) Do not allow the pump to run without load.

(4) For pumps with high head, a check valve should be installed on the outlet pipe to prevent water hammer caused by sudden shutdown from damaging the pump.

(5) Pump startup procedure: Before starting, open the inlet valve to fill the pump with the liquid to be transported; close the outlet valve; perform a test run of the electric motor to check if the pump rotation direction is correct; after the pump starts, slowly open the outlet valve until the pump reaches a normal operating state, then adjust the outlet valve to the desired opening degree. Conduct a 5 to 10-minute trial run without any abnormalities, and then it can be put into operation.

Shutting down procedure: Close the outlet valve; cut off the power supply; close the inlet valve. If the pump is not used for a long time, clean the flow path inside the pump and cut off the power supply.

Maintenance Notes for Magnetic Pumps

(1) The pump shaft breaks. For the CQB type magnetic pump, the pump shaft is made of 99% alumina ceramic. The main reason for the pump shaft breakage is that the pump is running without load, and the bearings dry grind, causing the shaft to be twisted. When disassembling the pump for inspection, it can be seen that the bearings are severely worn. The main method to prevent the pump from breaking is to avoid the pump running without load.

(2) The bearing is damaged. The bearings of the CQB pump are made of high-density carbon. If the pump is cut off from water supply or there are impurities in the pump, it will cause damage to the bearings. If the coaxiality between the inner and outer magnetic rotors of the cylindrical coupling is not guaranteed, it will also directly affect the lifespan of the bearings.

(3) The pump fails to pump liquid. The pump failing to pump liquid is a common fault of the pump. There are many reasons for this. First, check if there are any air leaks in the suction pipeline of the pump, check if the air in the suction pipe has been discharged, whether the liquid volume in the pump is sufficient, whether there is any debris blocking in the suction pipe, and also check if the pump is reversed (especially after changing the motor or after the power supply line is repaired). Also, pay attention to whether the suction height of the pump is too high. Through the above checks, if the problem still cannot be solved, disassemble the pump for inspection to see if the pump shaft is broken, and also check if the moving ring, static ring, and the entire rotor can move axially slightly. If it is difficult to move axially, check if the carbon bearing is too tightly combined with the pump shaft.

It should be noted that if the pump has been repaired several times but no problem is found, attention should be paid to whether the working condition of the magnetic coupling is normal. Bearings, inner magnetic rotor, and spacer rings will generate heat during operation, which will cause the working temperature to rise. On the one hand, it will reduce the transmitted power, and on the other hand, it will cause great trouble for pumps transporting liquids that are prone to vaporization. The power transmitted by the magnetic steel increases continuously as the temperature rises. Usually, below the working limit temperature of the magnetic steel, the decrease in transmission capacity is reversible, but above the limit temperature, it is irreversible, that is, after cooling, the lost transmission capacity cannot be restored. In special cases, when the magnetic coupling slips (out of step), the eddy current heat in the spacer will increase sharply, and the temperature will rise rapidly. If not handled in time, it will cause demagnetization of the magnetic steel, and the magnetic coupling will fail. Therefore, magnetic pumps should be designed with a reliable cooling system. For non-vaporizable media, the cooling circulation system is generally led out from the impeller outlet or the pump outlet, passes through the bearings and the magnetic transmission part and returns to the suction inlet. For vaporizable media, an exchanger should be added or the liquid flow should be led to a storage tank outside the pump to avoid heat returning to the suction inlet. For media with solid impurities or ferromagnetic impurities, filtration should be considered. For high-temperature media, cooling should be considered to ensure that the magnetic coupling does not exceed the working limit temperature.

When considering whether the speed is sufficient, first check if the motor speed is normal. You can measure it with a speed meter. If the motor speed is normal, consider whether there will be a slip of the magnetic coupling.

(4) Insufficient head. The causes of this malfunction are as follows: there is air in the conveying medium, the impeller is damaged, the rotational speed is insufficient, the specific gravity of the conveyed liquid is too high, and the flow rate is too large.

(5) Insufficient flow. The main reasons for insufficient flow are: the impeller is damaged, the rotational speed is insufficient, the head is too high, and there are foreign objects blocking in the pipe, etc.