Here is a case study related to mechanical seal systems. Read it carefully; consider not only the mechanical seal needs, but the hydraulic requirements of the pump as well, before answering the questions.

Problem description: Two pumps, pump #1 and pump #2 run continuously and both draw liquid from the distillation tower. If the fluid level drops below a specified value, pump #2 draw-off control valve will begin to close in order to allow the fluid level in the Distillation Tower to rise. The draw off valve only modulates for a very short time and never fully closes as the tower fills rapidly when this valve begins to close. During this time the pump noise levels rise. The seal life in pump# 2 is far shorter than that of pump #1. The seal in pump #2 is of the unbalanced type.

Analysis of the failed seal shows the tiny cracks on the seal and damage of the O-rings. Production do not want to change to dual seals because of interchangeability between designs.