Abstract: The mechanical seal of the axial flow pump in the loop reactor of a high-density polyethylene unit underwent modifications due to a series of failures including blackening of the seal oil, the presence of bubbles within the seal chamber, elevated pressure in the seal oil tank, and seal face wear caused by axial movement of the pump shaft. The sealing system was modified from a double mechanical seal with PLAN 32+PLAN 52 flush scheme to a triple mechanical seal with PLAN 32+PLAN 53C+PLAN 52 flush scheme. This paper compares the structure and operating principles of these two sealing schemes, expounds the advantages of triple mechanical seals and their potential leakage risks. Based on this analysis, it proposes routine maintenance and failure prevention measures for the modified mechanical seals.

Key words: high-density polyethylene (HDPE), loop reacto, axial flow pump, mechanical seals, flush plan