DIESEL ENGINE SPEED,DOE-HDBK-1018/1-93Diesel Engine FundamentalsFUEL CONTROLS, AND PROTECTIONHigh crankcase High crankcase pressure is usually caused by excessive blow-by (gaspressure - pressure in the cylinder blowing by the piston rings and into thecrankcase). The high pressure condition indicates the engine is in poorcondition. The high crankcase pressure is usually used only as an alarmfunction.SummaryThe important information in this chapter is summarized below.Diesel Engine Speed, Fuel Controls, and Protection SummaryA mechanical-hydraulic governor controls engine speed by balancing engine speed (mechanical flyweights) against hydraulic pressure. As theengine speeds up or slows down, the weights move the hydraulic plungerin or out. This in turn actuates a hydraulic valve which controls thehydraulic pressure to the buffer piston. The buffer piston is connected tothe fuel rack. Therefore, any motion of the buffer piston will control fuelto the cylinder by adjusting the position of the fuel rack, which regulatesthe amount of fuel in the injectors.Most mid-sized to large diesel engines have (as a minimum) the followingprotective alarms and trips.Engine overspeed alarm/tripHigh water jacket temperature alarmHigh exhaust temperature alarmLow lube oil pressure (alarm and/or trip)High crankcase pressure alarmME-01Rev. 0Page 40
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