Question 43 QMED01 - Junior Engineer

The Correct Answer is A. **Why Option A is Correct:** Option A describes the standard, best practice procedure for installing and seating new spiral packing (or rope packing) in a centrifugal pump stuffing box. 1. **"first tightened, and then backed off"**: This initial tightening compresses the new packing firmly into the stuffing box, ensuring it conforms to the shaft and the box walls. Backing it off slightly releases excessive initial pressure, preventing immediate overheating or scoring of the shaft upon startup. 2. **"start pump"**: The pump is started to allow the packing to run under operating conditions (pressure, temperature, speed). 3. **"while running under normal conditions; tighten evenly and slightly, over time"**: Packing requires a period of "running in" (or seating). During this time, the gland nuts are tightened incrementally and *evenly* (alternating sides) while maintaining a necessary slight leakage (weep). This gradual, controlled tightening ensures the packing is sufficiently compressed to minimize leakage without generating excessive frictional heat, which would destroy the packing and potentially damage the shaft sleeve. **Why Other Options Are Incorrect:** * **B) loosened until the gland clears the stuffing box:** Loosening the gland until it clears the stuffing box is too loose. This would result in massive leakage, the inability to hold pressure, and the complete failure of the sealing function. * **C) tightened an additional 10% to compress the packing:** Specifying a fixed, small percentage like "10%" is arbitrary and usually insufficient or inaccurate for seating new packing. New packing requires significant initial compression followed by gradual tightening during run-in, which cannot be accurately quantified by a simple percentage adjustment applied once. Over-tightening new packing initially leads to rapid overheating and failure. * **D) left in that position:** If the nuts are simply left in the position they were in during the initial installation (before the pump was run), the packing will likely leak excessively or, if initially compressed, will generate too much heat upon startup, leading to premature failure. New packing must always be seated and adjusted under running conditions.