A diesel engine is equipped with the over speed trip assembly shown in the illustration. At the inspection, the counter weight was found to be tripping out at too high of an RPM. The adjustment to lower the tripping speed RPM was carried out by __________. See illustration MO-0101.
• centrifugal force vs spring tension balance in an overspeed trip • effect of changing spring compression on the RPM at which a weight can move outward • effect of changing counterweight mass on the trip speed
• At a given speed, what keeps the counterweight from flying out and tripping—centrifugal force or spring tension? Which one is trying to hold it in, and which one is trying to push it out? • If the device is now tripping at too high an RPM, do you want the counterweight to be able to move outward more easily or less easily? Which change to the spring or weight will help that happen? • If you made the weight lighter, would that increase or decrease the centrifugal force at a given RPM, and would that make the mechanism trip sooner or later?
• Identify which part in the illustration is the restraining force (look at spring #12 and its adjuster #13–#14). • Decide whether you must increase or decrease that restraining force to make tripping occur at a lower RPM. • Eliminate any option that would obviously make the weight need more RPM (more centrifugal force) before it can move out far enough to trip.
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