For how long is LO heated in the settling tank during the purification process?

The correct answer indicates that the lubricating oil (LO) is heated in the settling tank during the purification process for 24 hours. This duration is significant because it allows sufficient time for the oil to separate from impurities and contaminants that may be suspended in it. The heating process helps in reducing the viscosity of the oil, which enhances the effectiveness of settling and separation.

Maintaining the oil at an elevated temperature for this length of time promotes the settling of solids and facilitates the removal of water and other impurities. Thus, the decision to heat the LO for 24 hours is based on the need to ensure a thorough purification process before the oil is filtered or returned to use. The other durations, while they may seem plausible, do not align with standard industry practices regarding effective oil purification.