consists of a multi-hole spray tip, a valve seat, and a
hydraulic lock, preventing the cam from retarding
needle valve extending the full length of the nozzle and
during injection. Fuel is directed by a passage in the
head to its seat, which is supported by a spring. The
advance housing end plug to the pressure side of the
high pressure is conducted from the fuel line to the
advance piston. The piston moves the cam
spray tip immediately above the valve seat. When the
counterclockwise (opposite to the direction of pump
valve needle is lifted vertically from its seat, fuel is
rotation). The spring-loaded side of the piston balances
the force of the power side of the piston and limits the
maximum movement of the cam. Therefore, with
In both the distribution pressurized type and the
increasing speed, the cam is advanced and, with
unit injection type of fuel injection systems for diesel
decreasing speed, it is retarded.
engines, the pumps and injector nozzle are operated by
cam-actuated mechanisms similar to the valve lifting
DISTRIBUTION PRESSURIZED INJECTOR
mechanisms of internal combustion engines.
NOZZLE.--The distribution pressurized types have
either a high-pressure pump that discharges fuel in a
UNIT INJECTOR SYSTEM.--The unit injector
common header to which each fuel injector nozzle is
system combines the pump and the nozzle in one hous-
connected by tubing, or individual high-pressure
ing. There is one unit injector per cylinder (fig. 4-47).
pumps for each cylinder connected to the fuel injector
The fuel first passes through a primary filter
nozzle by tubing. In either case, the injector nozzle does
located between the fuel tank and the transfer pump,
not furnish the pressure necessary to overcome the
which may be of either the gear or the vane type. On the
cylinder pressure and spray the fuel into the cylinder,
discharge side of this pump is a secondary filter. Both
but only meters and times the fuel injection. A
filters have a drain cock at the bottom of the housing for
spring-loaded bypass valve on the header or on the line
removing water and dirt separated from the fuel. From
to the injector nozzle maintains a constant pressure and
the filter the fuel passes to the fuel manifolds. The
returns the excess fuel to the supply tank.
The spray or injection nozzle extends from the top
into the injector.
of the cylinder head down into the combustion area. It
Figure 4-47.--Diagram of typical General Motors diesel fuel system.