Which condition can negatively impact the lubrication system of an APU?

Contamination of lubricant is a critical condition that can negatively impact the lubrication system of an Auxiliary Power Unit (APU). Lubricants are essential for reducing friction and wear between the moving parts of the APU. When contaminants, such as dirt, water, or metal particles, are introduced into the lubrication system, they can compromise the lubricant's effectiveness. Contaminants can lead to increased wear on engine components, as they disrupt the film strength of the lubricant and create abrasive conditions that accelerate degradation. Furthermore, contaminated oil can cause the formation of sludge and varnish, which can clog filters and narrow passages, further impairing the lubrication system's performance.

Increased lubrication frequency, cooler operational temperatures, and efficient oil circulation generally contribute to maintaining a healthy lubrication system. Higher lubrication frequency can help ensure that fresh oil replaces degraded oil, while cooler temperatures can enhance oil viscosity and improve its performance. Efficient oil circulation optimizes the delivery of lubricant to necessary parts, helping maintain adequate lubrication and cooling.