a shell and element design (fig. 5-8). However, most
filters used today are of the spin-on type, which allows
for faster change out since the complete filter is a
throwaway. Fuel filter elements or cartridges should be
replaced at the recommended interval designated by the
manufacturers service manual.
Should the engine run rough after a fuel
filter change, it is likely that air is trapped in the
system. Bleed all air from the filter by
loosening the bleed screw. In the absence of a
bleed screw, individually loosen the fuel lines
until all air has been vented.
The purpose of a fuel filter is mainly to remove
foreign particles as well as water. However, too much
water in a fuel filter will render it incapable of
protecting the system.
So to ensure this does not
happen, most diesel engine fuel systems are now
equipped with fuel filter/water separators for the main
Figure 5-8.Fuel filter assembly with replaceable element.
purpose of trapping and holding water that may be
mixed in with the fuel. Generally, when a fuel
filter/water separator is used on a diesel engine, it also
serves as the primary filter. There are a number of
manufacturers who produce fuel filter/water separators
with their concept of operation being common and only
design variations being the major difference. Basic
operation is as follows:
The first stage of the fuel filter/water separator
uses a pleated paper element to change water
particles into large enough droplets that will fall
by gravity to a water sump at the bottom of the
The second stage is made of silicone-treated
nylon that acts as a safety device to prevent small
particles of water that avoid the first stage from
passing into the engine.
Fuel injection pumps must be supplied with fuel
under pressure because they have insufficient suction
ability. All diesel injection systems require a supply
pump to transfer fuel from the supply tank through the
filters and lines to the injection pump. Supply pumps
can be either external or internal to the injection pump.
The two types of supply pumps used on diesel engines
today are the gear type and the vane type.
The remaining task to be accomplished by the fuel
system is to provide the proper quantity of fuel to the
cylinders of the engine. This is done differently by each
manufacturer and is referred to as FUEL INJECTION.
What grade of diesel fuel is used in warm and
What determines the lowest temperature at
which diesel fuel can be pumped through the
What is the most important characteristic of
What combustion chamber is designed
principally for the use in the multifuel engine?
What term is used to indicate the zero-droop
capability of a governor?
What type of governor uses a magnetic speed
pickup to monitor the rpm of the engine?
What component in a hydraulic governor
provides power to move the throttle of the