Question 66 UFIV01 - Chief Engineer - UFIV

The Correct Answer is A **Explanation for Option A (Correct):** A high crankcase pressure shutdown is a critical safety trip designed to prevent catastrophic engine failure (usually resulting from an impending explosion due to overheating bearings or friction, leading to oil mist formation and ignition). When such a protective device (often a relief valve or diaphragm-based pressure switch) is activated, it triggers a non-self-resetting lockout. This ensures that the engine cannot be inadvertently restarted until the cause of the dangerous condition has been investigated and repaired, and the safety system has been manually confirmed as ready to operate again. Therefore, after the repairs are completed and the crankcase is closed, the engine fails to start because the high crankcase pressure detector's protective device remains in the tripped/locked position and must be manually reset before the starting interlocks are released. **Explanation of Incorrect Options:** * **B) The high crankcase pressure detector protective device must have its diaphragm replaced first before the engine can be restarted.** * While the detector may use a diaphragm, activation of the pressure switch rarely damages the diaphragm permanently unless the pressure was extremely severe or the device failed to trip correctly. Replacing the diaphragm is not a standard post-trip requirement; resetting the electrical or mechanical mechanism is. * **C) The high crankcase pressure detector protective device's pressure chamber must be evacuated with a vacuum pump first before the engine can be restarted.** * Crankcase pressure detectors respond to pressure relative to the surrounding atmosphere. They do not require a vacuum to function or to be reset. This step is completely irrelevant to the operation or resetting of the safety device. * **D) The high crankcase pressure detector protective device must have its switch lever replaced first before the engine can be restarted.** * Like option B, tripping the safety device does not typically cause damage requiring replacement of the switch lever. The mechanism is designed to trip and then be reset. Replacement would only be necessary if the component was physically broken, which is not the standard procedure following a safety shutdown.