Question 43

The Correct Answer is B **Explanation of Correctness (Option B):** Option B is correct because O-rings used in pneumatic (air-operated) control systems, especially those involving rubber or synthetic elastomers, must be lubricated upon reassembly. This lubrication serves several crucial purposes: 1. **Facilitates Assembly:** Lubrication allows the O-rings to slide easily into their grooves without tearing or twisting. 2. **Sealing:** It ensures a proper, initial air seal, preventing leakage. 3. **Protection:** It protects the rubber material from drying out or degrading prematurely due to contact with dry air or friction during operation. 4. **Material Compatibility:** Silicone-based grease is specifically recommended for pneumatic systems because it is generally inert, compatible with standard elastomers (like Buna-N or Viton) used for O-rings, and does not degrade the plastic or metal components of the valve. **Explanation of Incorrect Options:** **A) O-rings should be lubricated with desiccant powder.** Desiccant powder (a drying agent) is used to remove moisture from air lines, not as a lubricant. Applying desiccant powder would increase friction, potentially damaging the O-rings, and would not provide a fluid seal. **C) O-rings should be lubricated with penetrating oil.** Penetrating oil is designed to free rusted or seized parts. It is thin, often contains solvents, and is generally not compatible with elastomers. It could cause the O-rings to swell, degrade, or dissolve, leading to immediate system failure. **D) O-rings should not be lubricated by any means.** This is incorrect. While some specialized sealing materials or static seals might tolerate no lubrication, dynamic seals (like those found in moving valves) in pneumatic systems require lubrication to function correctly, prevent damage during assembly, and ensure longevity and proper sealing under pressure.