In preparation for getting a tug-barge unit underway, if enough time has elapsed since the last main engine shutdown, it may be necessary to blow down the engine's cylinders to expel any accumulated water or oil. What statement concerning cylinder blow down is true?
• Purpose of cylinder blow down on a large diesel before start • Role of fuel delivery during a safety check rotation of the engine • Function of cylinder test valves / indicator cocks in detecting and venting water or oil
• Ask yourself: During a safety blow down, do you want any combustion to occur, or are you only checking/clearing the cylinders? • If there is water or excess oil in a cylinder, what must be open so it can escape safely instead of causing hydraulic lock or damage? • Think about which combination (fuel on/off, cocks open/closed) best lets you SEE and VENT anything in the cylinders while the engine turns slowly.
• Verify whether fuel delivery should be ON or OFF during an inspection rotation meant only to clear and check cylinders. • Check the primary purpose of indicator cocks: are they used open or closed when you want to vent and visually check for water/oil? • Eliminate any option that would allow pressure to build in a closed cylinder while water might be present, or that would risk the engine firing during the test.
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