DIESEL ENGINE SPEED,
Diesel Engine Fundamentals
FUEL CONTROLS, AND PROTECTION
High crankcase pressure is usually caused by excessive blow-by (gas
pressure in the cylinder blowing by the piston rings and into the
crankcase). The high pressure condition indicates the engine is in poor
condition. The high crankcase pressure is usually used only as an alarm
The important information in this chapter is summarized below.
Diesel Engine Speed, Fuel Controls, and Protection Summary
A mechanical-hydraulic governor controls engine speed by balancing
engine speed (mechanical flyweights) against hydraulic pressure. As the
engine speeds up or slows down, the weights move the hydraulic plunger
in or out. This in turn actuates a hydraulic valve which controls the
hydraulic pressure to the buffer piston. The buffer piston is connected to
the fuel rack. Therefore, any motion of the buffer piston will control fuel
to the cylinder by adjusting the position of the fuel rack, which regulates
the amount of fuel in the injectors.
Most mid-sized to large diesel engines have (as a minimum) the following
protective alarms and trips.
Engine overspeed alarm/trip
High water jacket temperature alarm
High exhaust temperature alarm
Low lube oil pressure (alarm and/or trip)
High crankcase pressure alarm