The basic fuel system, common to all Cat diesel engines, includes an engine driven fuel transfer pump,
a secondary fuel filter, unit fuel injectors and a fuel pressure regulator. Optional Caterpillar supplied fuel system components include flexible hoses, a manual fuel priming pump, and a duplex primary fuel strainer. A basic fuel system schematic is shown in Figure 1.
The engine driven transfer pump delivers fuel to the unit injectors via the secondary fuel filter. The pump is equipped with a pump-mounted safety valve and the fuel flow at rated rpm is listed in the technical data and varies with engine speed.
The unit injector, either mechanically or hydraulically actuated, combines the functions of pumping, metering and injecting into a single unit. It is located near the center of the combustion chamber in each cylinder head, between the
rocker arms. External manifolds supply fuel from the transfer pump to the injectors, eliminating the need for high pressure fuel lines. Fuel continuously circulates through the injectors, and the excess fuel that is not used for combustion cools the injectors and is returned to the fuel tank via the pressure regulating valve. This excess fuel also aids in the purging of air from the system.
The fuel delivery pressure to the injectors is controlled by a pressure regulating valve. The pressure regulator must be adjusted at the installation site in order to provide the proper fuel pressure to the injectors.
The manual fuel priming pump is recommended if no electrical priming pump is available. The manual pump
helps to bleed air from the fuel piping before initial engine operation and following engine maintenance such as filter element changes and injector replacement.
Caterpillar also recommends the use of a duplex primary fuel filter prior to the engine driven fuel transfer pump. This filter is available from Caterpillar via custom quote. When used, the duplex primary fuel filter is installed, remotely from the engine, in the fuel transfer pump suction piping.