Question 21 QMED03 - Oiler

The Correct Answer is B **Explanation for Option B (Correct Answer):** Option B states that the jacket water pressure should always be greater than the sea water pressure. This is a fundamental safety and operational requirement in heat exchangers (coolers) that separate two different fluid systems, especially when one fluid (sea water) is corrosive or harmful to the primary system (fresh jacket water). If a leak were to develop in the cooler tube bundle or shell, maintaining the higher pressure on the fresh jacket water side ensures that the fresh water leaks into the sea water system, rather than the corrosive sea water contaminating the critical engine cooling system (the jacket water). Contamination by sea water would introduce salts and corrosive elements that could damage the engine components, requiring expensive repairs. Therefore, maintaining $P_{\text{jacket water}} > P_{\text{sea water}}$ is standard engineering practice for protection. **Explanation of Incorrect Options:** **A) sea water temperature must never be warmer than 40°F:** This is incorrect. Sea water temperatures vary widely based on location and season, often reaching 80°F to 90°F (27°C to 32°C) or higher in tropical regions. The cooler is designed to handle this range, although higher temperatures reduce the efficiency of cooling. **C) jacket water pressure must always be less than the sea water pressure:** This is the opposite of the required safety standard (B). Allowing the sea water pressure to be higher risks contaminating the engine's fresh water cooling system if a leak occurs. **D) jacket water temperature must always be less than 60°F:** This is incorrect. Jacket water must operate at high temperatures (typically 170°F to 195°F, or 77°C to 90°C) to maintain optimal engine efficiency and prevent the formation of sulfuric acid (a corrosive byproduct of combustion). 60°F is far too cold for proper engine operation.