The main diesel propulsion engines on your uninspected fishing industry vessel are protected with a mechanical over speed trip mechanism similar to that shown in the illustration. Upon testing the trip setting, you discover that it is necessary to make an adjustment. Assuming that several adjustments may be necessary before the final setting is accurately achieved, what statement concerning adjustment is true? Illustration MO-0101
• Mechanical overspeed trip mechanism – how the spring tension and adjusting screw set the trip speed • Locknut function – why a locknut is used on an adjustment screw located on a vibrating, rotating machine • Safe working practice around rotating machinery – where your hands and tools can safely be when the flywheel is turning
• When you physically turn the adjustment screw shown in the illustration, would you want the flywheel and trip mechanism moving or stopped? Why? • If you expect to make several trial adjustments, what could happen to the setting during each test run if the locknut is left loose while the engine is operating? • Think about the purpose of a locknut on any adjustment: is it meant to be tight only once at the very end, or does it serve a safety and security role every time the machine is run?
• Look closely at the location of the spring, screw, and locknut relative to the flywheel and rotating parts in the illustration. • Decide whether hands/tools could safely reach that screw while the engine is running at or near overspeed. • Decide whether a loose locknut during engine operation could allow the screw to back out or change position due to vibration.
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