Figure 5-28. Ether Injection System.
Section VIII. FUEL FILTERS
a. Primary Filters (Fig. 5-29). Metal filters are
Thorough and careful filtration is
used as primary filters because the fine particles that will
necessary especially to keep diesel engines efficient.
pass through them are not injurious to the supply pump.
Diesel fuels are more viscous than gasoline and contain
The filter element is usually of the metal disk type, as
more gums and abrasive particles that may cause
described in paragraph 4-2. Solids larger than 0.005 in.
premature wear of Injection equipment. The abrasives
(0.127 mm) remain outside the metal disks, while the
may consist of material that is difficult to eliminate during
larger foreign matter and the majority of the water settles
refining, or they even may enter the tank during careless
to the bottom of the bowl. From here, the foreign matter
Whatever the source, it is imperative that
can be removed through a drain plug. A ball relief valve
means be provided to protect the system from abrasives.
in the filter cover enables the oil to bypass the filter
element if the disks become clogged.
Most diesel engine designs
Include at least two filters in the fuel supply systems to
b. Secondary Filters (Fig. 5-30). Fabric filters,
protect the closely fitted parts in the pumps and nozzles.
because of their greater filtering qualities, are used
The primary filter usually is located between the fuel tank
principally as main filters for protecting the fuel injection
and the fuel supply pump. The primary filter contains a
Many of the filters In use are similar to the
coarse filter medium that removes the larger foreign
lubricating oil filters described in paragraph 8-13. The
matter. The secondary filter usually is located between
bag-type filter also is used. The filtering medium is a
the fuel supply pump and the fuel injection pump. The
large bag of close, evenly woven, lintless, acid-resisting
secondary filter contains a fine filter medium that
textile material. Maximum benefit is derived from the
removes even the most minute traces of foreign matter
bag's large area by keeping the sides of the
from the fuel. Additional filtering elements frequently are
installed between the Injection pump and the nozzle.
5-36. Types. Diesel fuel oil filters are referred to as
full-flow filters, because all the fuel must pass through
them before reaching the injection pumps. A diesel fuel
filter usually incorporates an air valve to release any air
that might accumulate in the filter during operation.