Question 8

The Correct Answer is C **Why option C ("taking a light cut in a lathe") is correct:** An eroded globe valve disk (which is often conical or spherical) needs a precise, smooth, and geometrically correct sealing surface to function properly. The most reliable and accurate way to restore this surface is by using a lathe. By mounting the disk in a lathe and taking a light, precise cut, the machinist can remove the damaged material, ensuring that the critical sealing angle or radius is maintained perfectly, resulting in a leak-tight seal when the valve is reassembled. **Why the other options are incorrect:** * **A) sandblasting with lightweight grit:** Sandblasting is a cleaning or surface preparation method. It will make the surface rough and uneven, destroying the precise finish required for a tight seal. * **B) dressing the seat with crocus cloth:** Crocus cloth is a very fine abrasive material primarily used for polishing or removing very minor imperfections. While sometimes used on valve seats, it is insufficient to repair deep erosion on the disk itself and cannot maintain the critical geometry needed for sealing. * **D) scraping with a bastard file:** A bastard file is a coarse tool intended for rapid material removal, not precision finishing. Scraping the disk with a file would create an irregular, non-uniform surface that would guarantee leakage. Precision valve components require machining methods, not hand filing.