Proceedings Of The Marine

SUM 2014

Proceedings magazine is a communication tool for the Coast Guard's Marine Safety & Security Council. Each quarterly magazine focuses on a specific theme of interest to the marine industry.

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68 Proceedings Summer 2014 www.uscg.mil/proceedings A nswers Engineering 1. Note: Unloading an air compressor at start-up reduces both the starting current and the amount of time that it takes to come up to operating speed. Unload- ing may be accomplished by a pneumatic, hydraulic, magnetic, or centrifugal type pilot device ftted to the suction valves of the compressor. A. holding the discharge valve open Incorrect answer. Unloader mechanisms are generally ftted to the suction valves, not the discharge valves. B. the use of a pre-charged accumulator Incorrect answer. Pre-charged accumulators are not used for unloading. C. holding the suction valve open Correct answer. This action prevents compression from being achieved, thus unloading the compressor. D. temporarily discharging to the air receiver Incorrect answer. This action would not unload the compressor, as this is the resulting status of the compressor after the unloading period is over. 2. Note: Equalization of the power factor of two alternators is accomplished by equalization of the reactive power, which in turn is accomplished by equalization of the magnetic feld strengths, which in turn is accomplished by adjusting the voltage settings of both units in opposite directions until the power factors are equalized. A. Voltage settings of both units are adjusted in opposite directions. Correct answer. This is the correct procedure as described in the note above. B. Governor speed settings of both units are adjusted in opposite directions. Incorrect answer. This is the procedure for equalizing the kilowatt load of two alternators in parallel, not the power factor. C. Voltage settings of both units are adjusted in the same direction. Incorrect answer. This is the procedure for raising or lowering the bus volt- age, not equalizing the power factor of two alternators in parallel. D. Governor speed settings of both units are adjusted in the same direction. Incorrect answer. This is the procedure for raising or lowering the bus frequency, not equalizing the power factor of two alternators in parallel. 3. Note: Wet cylinder liners are subject to waterside cavitation erosion due to harmonic cylinder vibrations that cause vapor bubbles in the coolant to form and collapse. The resulting pitting is most pronounced near the middle of the thrust side of the liner. A. throughout the lower one-half of the liner Incorrect answer. B. throughout the upper one-half of the liner Incorrect answer. C. at TDC opposite the thrust side of the liner Incorrect answer. D. near the middle of the thrust side of the liner Correct answer. This the expected pitting pattern as described in the note above. 4. Note: The appropriate action to take should facilitate quick and safe entry into the hazardous atmosphere in response to an emergency. The gages should indicate a full cylinder and the gages should read within 200 psi of each other. A. Replace the defective gages with a new pair from the spare parts inventory. Incorrect answer. This action does not facilitate quick entry. B. Replace the air cylinder. Incorrect answer. This action does not facilitate quick entry. C. Assume that the lower gage reading is correct. Correct answer. By taking this action, the chance is minimal that the assumed pressure is lower than it actually is, and the wearer may safely exit the space before running out of air. D. Take the average of the two gages as the correct pressure. Incorrect answer. By taking the average of the two pressures, there is a good chance that the assumed pressure is lower than it actually is, and the wearer may actually run out of air prior to exiting the space. Summer2014_22.indd 68 5/13/14 9:46 AM

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