The shielded pump keeps tripping

This post was last edited by Shutong on 2021-2-19 at 21:41. I’ll talk about something I encountered twenty years ago; the situation may not necessarily correspond to the one described by the original poster. At that time, the pump was a Dalian Empire shielded pump used for transporting liquefied gas; the motor had high temperatures, and the pump experienced significant vibration. Upon shutdown for inspection, it was found that the motor bearings were worn, as well as the thrust plates and shaft sleeves. Cause analysis: During startup or operation, the pump runs out of liquid or experiences cavitation, which results in a lack of lubrication for the bearings or insufficient lubricant levels. This leads to poor lubrication of the bearings on the motor side, and dry friction between the bearings and the shaft sleeves as well as between the bearings and the thrust plates, causing wear of the components. Additionally, the presence of gas inside the pump causes fluctuations in the liquid pressure at the pump’s inlet and outlet, which leads to increased pump vibration and pulsations in the axial force. This accelerates the wear of the bearings as well as increases the risk of brittle fracture. Remedial measures: (1) Since the liquid medium being transported is prone to vaporization, it is necessary to thoroughly cool the pump and remove air from it before starting it up, so as to ensure a stable and sufficient flow of the medium after startup and to enable proper lubrication of the bearing components. (2) When maintaining the pump body, care should be taken to clean the small holes in the FB end cover, to prevent the lubricant from failing to pass through due to blockages in these holes or insufficient flow, which could lead to dry friction and damage of components such as bearings. (3) During maintenance, carefully inspect the shaft, bearings, bushings, keys, etc. for any defects such as damage or burrs. (4) Regularly inspect the pump inlet filter to prevent insufficient pump flow due to clogging of the filter, which could lead to cavitation and vibration fluctuations. (5) Thoroughly clean the reverse circulation pipeline flanges during each maintenance session to prevent blockages.

A high current trip is most likely due to low flow

Why does the current increase during idling?

1. Check whether there is an issue with the liquid level setting of the suction tank; this could be caused by cavitation. 2. Compare the design flow rate and pressure of the shielded pump to determine whether it is operating under overload conditions

Why is the current high despite low flow?