Question 54 OSE02 - Assistant Engineer - OSV

The Correct Answer is C **Why Option C is Correct:** Option C states that "O-rings should be lubricated with a silicone-based grease." This is the proper procedure for reassembling pneumatic components. O-rings require lubrication for several critical reasons: 1. **Ease of Assembly:** Lubrication allows the O-rings to slide smoothly into their grooves and mating surfaces without pinching, tearing, or twisting (nicking/spiraling). 2. **Sealing Integrity:** Lubricant helps establish the initial seal and fills microscopic imperfections, ensuring airtight operation. 3. **Preventing Sticking/Wear:** In pneumatic systems, movement can cause friction. A suitable grease minimizes wear and prevents the O-ring from sticking to metal surfaces, which is crucial for the reliable operation of fast-acting valves like those found in propulsion control systems. 4. **Material Compatibility:** Silicone-based greases are non-reactive and highly compatible with standard elastomer (rubber) O-ring materials (such as Buna-N or Viton) and are generally safe for use in pneumatic systems, as they do not swell the seals or contaminate air lines excessively. **Why the Other Options are Incorrect:** * **A) O-rings should be lubricated with penetrating oil.** Penetrating oils (like WD-40) are thin, highly volatile, and often contain solvents or petroleum distillates that are incompatible with common O-ring elastomers. They can cause the rubber to swell, weaken, or deteriorate over time, leading to seal failure. Furthermore, they do not provide the lasting barrier and lubrication necessary for dynamic seals. * **B) O-rings should be lubricated with desiccant powder.** A desiccant is a substance used to absorb moisture (e.g., silica gel). Using powder, especially desiccant powder, on O-rings would create excessive friction and grinding, accelerating wear and potentially damaging the sealing surfaces. Desiccants have no lubricating properties and are entirely unsuitable for use on O-rings. * **D) O-rings should not be lubricated by any means.** This is incorrect, especially for dynamic seals or during initial assembly. While some static seals in extremely specific non-lube applications might avoid grease, proper lubrication is standard practice for nearly all O-rings, especially those in precision control systems, to ensure longevity, ease of assembly, and reliable sealing.