Question 57 QMED03 - Oiler

The Correct Answer is B **Explanation for Option B (Correct Answer):** The correct procedure for performing a bottom blow on a boiler equipped with a typical two-valve system (Blow Down Valve and Guarding Valve) involves opening the valve furthest from the boiler pressure vessel *first*, and closing it *last*. This valve is commonly referred to as the guarding valve or the slow-opening valve (the second valve away from the water drum). The specific instruction asks which valve is "spun open quickly." In standard boiler operating practice, the two valves are typically handled as follows: 1. **Guarding Valve (Slow-opening/Outboard valve):** This valve is opened *fully* and *first* (often relatively quickly if it's a quick-opening type, or fully cranked open if it's a slow-opening gate/globe valve) and remains completely open for the duration of the blowdown. Since it is the valve further from the drum, it acts as the primary isolation barrier when the blow is complete. 2. **Blow Down Valve (Quick-opening/Inboard valve):** This valve (closest to the drum) is then opened and closed rapidly to execute the blowdown. However, in the context of operational safety and standard procedures, the valve that must be ensured open **first** (and often referred to as the valve that is "spun open quickly" before the blow commences) is the Guarding Valve (B). This ensures that the pressure is only moderated by the inner valve (D) during the actual blowdown process, minimizing erosion damage to the guarding valve seat and ensuring the guarding valve is readily available as the secondary isolation device when the blow is finished. Once the guarding valve is fully open, the operation is then controlled by the inner blowdown valve. If the question implies which valve is fully opened *before* the rapid blow begins, it is the guarding valve (B). **Why other options are incorrect:** * **A) All valves are to be opened slowly:** This is incorrect. While the guarding valve (if it is a screw-type valve) may be opened carefully, the actual *blowdown* procedure relies on the rapid opening and closing of the inner valve (the blowdown valve, D) to achieve the necessary pressure surge and scouring action to remove sludge and sediment. * **C) Skin valve (last valve prior to overboard opening):** While this valve is the final boundary to the overboard discharge, it is often equivalent to the Guarding Valve (B) in a two-valve system, particularly in marine contexts. However, if a third valve existed (e.g., an additional outboard valve), the operational principle still requires the valve closest to the drum (D) to control the flow and the next valve out (B) to be fully open first. In a standard two-valve setup where B is the outermost valve, B is the correct choice. If the system has a dedicated "skin valve" separate from the "guarding valve," standard procedure still dictates that the valve opened and closed quickly for the blow itself is the inner valve (D), not the outermost valve (C). In the context of the available options, B represents the non-controlling valve that is opened first and fully. * **D) Blow down valve (first valve closest to water drum):** This valve is the valve used to *control* the duration of the blowdown. It is opened and closed *rapidly* (a quick snap open and shut) to execute the blow, but it is opened *second*, after the guarding valve (B) is fully open. Opening this valve first would expose the guarding valve seat to full erosion damage under throttling conditions, which violates proper procedure.