Question 31 QMED04 - Boiler Technician-Watertender

The Correct Answer is C ### Explanation for C (Correct Option) **C) The specific gravity of the fuel.** determines the size of the ring dam (or gravity disc) required for a centrifugal purifier. The centrifugal purifier separates oil, water, and sludge based on differences in their specific gravities (or densities) when exposed to high centrifugal force. For efficient separation, the interface between the oil and water phases must be correctly positioned within the bowl. * The function of the ring dam is to physically define the outer boundary of the oil phase and the inner boundary of the water phase. * If the specific gravity of the fuel oil changes (e.g., due to temperature changes or switching to a different grade of fuel), the position of the interface changes. * To maintain the correct interface position for optimal separation (ensuring oil moves toward the center outlet and water/sludge moves toward the periphery/water outlet), a gravity disc (ring dam) with a corresponding diameter must be fitted. The correct diameter is calculated based on the specific gravities of the oil and water, and the operating temperature. ### Explanation for Incorrect Options **A) The viscosity of the fuel.** Viscosity primarily affects the flow rate and the temperature at which the purifier must operate to achieve optimal separation. High viscosity requires heating the oil to reduce its resistance to flow, thereby improving separation efficiency (Stokes' Law applies), but it does not determine the size of the gravity disc. **B) The quantity of water to be removed from the fuel.** While the purifier must handle the water present, the volume of water is handled by the overall capacity and throughput of the machine, as well as the design of the bowl's sludge/water space. The specific gravity difference, not the quantity of the dispersed phase, determines the interface position set by the ring dam. **D) The quantity of dirt to be removed from the fuel.** The amount of dirt (solids/sludge) affects the frequency of de-sludging/cleaning required and the size of the sludge space within the bowl. However, like water quantity, the amount of solids does not influence the position of the oil-water interface, which is solely dictated by the specific gravities of the two liquid phases.