Abstract: This article analyzes the basic types and hazards of the failure of sliding bearings in magnetic pumps, identifies the reasons for the failure of sliding bearings, and summarizes the countermeasures to reduce the failure of sliding bearings in magnetic pumps.

Keywords: magnetic pump; Sliding bearings; failure

1. Overview of the application of magnetic pumps

A unit's 80000 tons/year catalytic dry gas to ethylbenzene/styrene unit uses 45 magnetic pumps produced by Shengda Yin Company in the United States for transporting toxic media such as benzene, ethylbenzene, and styrene. During the operation of the device, multiple failures of the magnetic pump sliding bearings occurred, which not only affected the safety of the pump operation but also reduced production efficiency. Similar magnetic pumps in the same industry often experience sliding bearing failures, which have a certain degree of universality.

2. The harmfulness of magnetic pump sliding bearing failure

The sliding bearing (Figure 6) of the magnetic pump is fitted onto the bearing body of the magnetic pump, and is matched with the shaft sleeve on the inner magnetic rotor. The material is mostly silicon carbide. Its flushing, lubrication, and cooling rely on its own medium to circulate flushing and lubrication. It introduces the high-pressure liquid flow from the back of impeller 2 into the isolation sleeve, with a portion of the liquid flow flowing into the balance hole on the back of the blade hole through the intermediate bearing 7, and a portion of the liquid flow passing through the gap between the isolation cover and the inner magnetic rotor.

Figure 1 Schematic diagram of magnetic pump structure

1. Pump body; 2. Impeller; 3. Pump cover; 4. Isolation sleeve; 5. Pump shaft; 6. Bearings; 7. Shaft sleeve; 8. Thrust ring; 9. Internal magnetic rotor; 10. External magnetic rotor; 11. Connecting frame; 12. Suspension body; 13. Transmission shaft

When the sliding bearing fails and fractures, small pieces of silicon carbide fragments will enter between the isolation sleeve and the inner magnetic rotor of the magnetic pump along with the flushing lubrication circuit medium. Due to the high hardness of silicon carbide, which is between the isolation sleeve and the inner magnetic rotor, high-speed rotation can cut open the isolation sleeve and inner magnetic rotor like a turning tool, posing great harm.

3. Analysis of Failure Causes of Sliding Bearings in Magnetic Pumps

3.1 Insufficient exhaust before starting the magnetic pump

Due to the internal flushing cooling system used in the magnetic pump, unlike the external flushing system which has a clear exhaust system, it is necessary to exhaust the residual gas in the pump before starting it. If there is gas in the pump, it will further reduce the flushing cooling effect, forming a vicious cycle, which will eventually lead to the fracture and failure of the sliding bearings of the magnetic pump.

3.2 Low flow operation of magnetic pump

The flow rate of the flushing lubrication circuit of a magnetic pump is usually 2% -3% of the design flow rate of the pump. When the actual flow rate is less than the design flow rate of the pump, the flow rate of the flushing lubrication circuit of the pump sliding bearing will also decrease. When the magnetic pump runs at a low flow rate for 3 minutes, it may cause an increase in the liquid temperature in the flushing chamber of the centrifugal pump. The increase in medium temperature will cause some flushing lubrication medium to vaporize, resulting in a series of faults such as dry friction of the pump sliding bearing, damage to the sliding bearing, demagnetization of the magnetic cylinder, etc.

3.3 Impurities in the medium

Due to process pipeline or operational reasons, some pumps contain impurities. For example, a certain pump (P113) contains a large amount of coke powder due to process reasons, and the service life of sliding bearings is about 50% lower than that of other pumps. At the same time, if the pipeline blowing before the device starts is not clean, it will also increase the failure rate of sliding bearings. Therefore, regularly checking and cleaning the inlet filter of the magnetic pump is one of the means to ensure the smooth operation of the magnetic pump.

4. Countermeasures to reduce the failure rate of sliding bearings in magnetic pumps

4.1 Add a magnetic pump anti dry rotation controller

The anti dry running power monitor is a load monitoring device based on measuring the motor current of the magnetic pump, which has both measurement and protection functions. It measures and displays the actual power in kilowatts (kW) or power percentage (%) of the pump motor, usually set at 30% of the rated current of the measured pump. When the operating current of the motor is lower than the set value, the monitor can automatically disconnect the magnetic pump motor. Avoid the operation of magnetic pumps due to low load or overload conditions.

4.2 Add a reflux pipeline to the outlet pipeline of the pump

For magnetic pumps that are prone to operating at low flow rates, in order to ensure long-term operation of the magnetic pump and prevent frequent tripping of the anti dry running controller, a reflux pipeline is added to the outlet pipeline of the pump, directly flowing back from the pump outlet pipeline to the pump inlet pipeline, ensuring that the pump operates within a safe protection zone. The method of adding a reflux pipeline has been validated in P120 (anti hydrocarbon material pump), and the service life of the pump's sliding bearings has been significantly improved by adding a reflux pipeline.

4.3 Strengthen daily inspections and do a good job in equipment management

The failure of sliding bearings in magnetic pumps is often related to temperature rise. Strengthening temperature rise monitoring of operating pumps can prevent 90% of equipment failures in magnetic pumps. By measuring the temperature of the pump body and medium, and combining it with the pressure gauge at the pump outlet, it can be determined whether the magnetic pump is working properly. Meanwhile, we also have the following measures to ensure the long-term operation of the sliding bearings of the magnetic pump.

① Regularly clean the inlet filter of the pump, check if there is any internal leakage, and do not allow ferromagnetic impurities, carbon powder accumulation, or other phenomena in the medium.

② Before starting up, fully exhaust the pump and ensure that the pipeline is unobstructed;

③ Before starting the pump, check the direction of the motor and do not allow any reverse rotation.

④ The heat pump is not allowed to be driven in a cold state to prevent thermal cracks in the sliding bearings. The damage rate of sliding bearings in heat pumps that start without preheating is over 60%.

4.5 Regularly inspect the magnetic pump

Due to the characteristics of silicon carbide bearings, they have high hardness and are not easily worn. When many sliding bearings have cracks, there is no significant change in the vibration of the magnetic pump due to lack of wear. Therefore, we need to regularly check the operation of the magnetic pump every six months to prevent malignant events such as damage to the isolation sleeve and inner magnetic rotor. Through our regular inspection of pumps, 95% of accidents can be eliminated in Mengya state.

5. Summary

Compared to ordinary centrifugal pumps, magnetic drive pumps have lower vibration and noise, and their faults are not as obvious as those of ordinary centrifugal pumps. Therefore, operators and maintenance personnel need to observe carefully for a long time in their work practice to eliminate equipment accidents in a critical state. At the same time, planned maintenance and regular sampling work also need to be done well to ensure the stable and long-term operation of the equipment.

2026 August 2nd Week Marginal Product Recommendation

MG-TEX Steel with PTFE Fiber Fabric Bearings:

This new material uses the PTFE fibre fabric overlay on steel backing, the fabric is with high load capacity and much longer operating life comparing with conventional 3-layer bushes.The metal matrix provides the bearing with excellent load-bearing performance and can transfer the heat generated during the operation of the bearing in time, while PTFE woven material is designed to be used in completely dry friction conditions. It has a lower friction coefficient and excellent wear resistance. Compared with traditional bearings, in addition to high load performance, it can completely eliminate oil and eliminate process maintenance, and it slides smoothly. There will be no "sticky" phenomenon.

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