Question 56 AEL01 - Assistant Engineer - Limited

The Correct Answer is B **Why Option B ("Dirt") is correct:** Dirt, specifically solid particulates (like wear debris, dust, metal filings, and silt), is the most common and damaging contaminant found in governor hydraulic fluid. Governor systems, especially those operating under high precision and using small clearances (like servo valves and spool valves), are highly susceptible to damage and sluggish operation caused by these hard particles. Unlike moisture, which can be mitigated or tolerated to an extent, dirt directly causes abrasive wear, erosion of components, and silting/sticking of control valves, making it the primary contaminate affecting reliability and function. **Why the other options are incorrect:** * **A) Moisture:** While water (moisture) is a significant contaminant that can cause corrosion, reduce lubricity, and lead to fluid degradation, it is generally considered the *second* most common contaminant after solid particulates (dirt) in hydraulic systems, particularly those that are well-maintained. Dirt is the universally dominant ingress and operational contaminant. * **C) Acid:** Acidic contamination occurs primarily due to fluid oxidation (breakdown of the oil base) or thermal degradation. While highly damaging when present, acid formation is a secondary consequence of fluid breakdown rather than a routine, most common ingress contaminate like dirt or moisture. * **D) Air:** Air is almost always present in hydraulic fluid (dissolved or entrained) and causes issues like foaming, oxidation, and spongy system response. However, air is typically classified as an *unwanted condition* or *gaseous contaminant* rather than the leading *physical or chemical contaminate* that causes component failure. Dirt (solid particulates) is the leading cause of wear and damage.