Some issues regarding the frequent failure of shielded pumps

After reading the post above, I completely agree; the shielded pumps in our factory get damaged frequently during the start-up and shutdown of the installations, resulting in high maintenance costs. The main reason for this is *artistic changes and fluctuations. Although shielded pumps offer advantages such as leak-free operation and a low maintenance rate, they are highly affected by changes in operating conditions; their advantages become more prominent when the device is running properly. The inlet filter screen is crucial for shielded pumps; not only must the mesh size be chosen appropriately, but once signs such as low pressure, high vibration, or high temperature appear during inspections and maintenance, the pump must be stopped immediately for inspection. For the situation described by the poster, this can be avoided by reducing the size of the outlet or using only the smallest return line.

This can be avoided by reducing the outlet size or using only the minimum reflux line

Shielded pumps do have many advantages, but they can be easily damaged if the selection and operating environment are inappropriate. According to the poster, there should be no major issues with the pump selection; the damage was caused by improper use. Cooling of the canned pump is of utmost importance; if the cooling conditions are poor, the graphite bearings will be damaged within a short time (about 1 minute), which in turn leads to wear of other components. According to the factory instructions, ensure a minimum net positive suction head for the shielded pump during unloading.

Reply to 2# yxmqh: We use it for transporting phenol, and the liquid is free of impurities. So what are the requirements for the inlet filter screen?

Reply to 4# ZHANGZHANTJ: Hello. Our factory uses this pump to transport phenol, and the required liquid temperature is around 50-60 degrees. Therefore, we insulate the entire pipeline; the pump body is insulated using hot water, with no cooling water used. Could this have any impact? Also, how can we ensure an adequate minimum net positive suction head? I’ve read some information about a “automatic circulation pump protection valve” that can control the opening degree at the pump outlet based on the pump’s flow rate and pressure, thereby preventing sudden loss of pressure and potential damage to the pump. Since we are transporting phenol, which is a corrosive substance, I’m not sure whether such a valve can be used in this case

I have 40 shielded pumps in use, and none of them ever break down. The temperature of the bearings is very important; a temperature of 50 degrees in your case is probably not caused by a problem with the bearings. The bearings in my pumps reach around 100 degrees in temperature, while the boiling point of the material is 70 degrees. Therefore, it’s necessary to ensure an adequate minimum net positive suction head. Change the filter mesh from 100 mesh to 50 mesh, and control the outlet valve during discharge

For your liquid, as long as there are no particles, the mesh size of the filter can be smaller

The poster should take measures to prevent the pump from running dry, as this can lead to accelerated wear of the thrust disc, which is likely the main reason for the frequent failures of the pump

Shielded pumps use the material they transport to cool the motor and lubricate the bearings; therefore, they have a minimum flow requirement, and it is strictly prohibited to operate them with no fluid flow or in idle mode. Near the end of unloading, the tank is almost empty; the pump operates at high speed, and severe accelerated wear of the bearings leads to wear of the shielding sleeve, resulting in motor damage. Care should be taken when using shielded pumps for unloading; to avoid vacuum formation, the unloading is generally not completed completely. When the pressure gauge shows fluctuations, it indicates that little material remains, and the machine should be stopped. The pump shutdown time can be determined based on on-site experience. Using self-priming shielded pumps for unloading yields good results.

It is crucial that the pump does not run idle or at low flow rates; when the pump is in operation, it is necessary to ensure that there are no solid particle crystals inside, and it is best to clean it with a solvent when it is shut down.