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 TM 5-685/NAVFAC MO-912
quency of cleaning and replacing filter elements.
(b) The fuel injection pump consists of a bar-
Adjust the frequency to meet unusual local operat-
rel and a reciprocating plunger. The reciprocating
ing conditions. Generally, all metal-edge and wire-
plunger takes a charge of fuel into the barrel and
mesh devices are called strainers, and all replace-
delivers it to the fuel-injecting device at the engine
able absorbent cartridge devices are called filters.
cylinder.
(4) Fuel injection nozzles for mechanical injec-
Fuel filters approved for military use consist of re-
placeable elements mounted in a suitable housing.
tion systems are usually of the spring-loaded,
Simplex and duplex type fuel filters are available.
needle-valve type. These nozzles can be adjusted to
Fuel strainers and filters must not contain pressure
open at the predetermined pressure. Consult the
relief or bypass valves. Such valves provide a means
manufacturer's specifications before adjusting fuel
injection valves. The nozzle components are as-
for the fuel to bypass the strainer or filter, thereby
permitting the fuel-injection equipment to be dam-
sembled carefully at the factory and must never be
aged by contaminated fuel. Filter capacity is gener-
intermixed. Most manufacturers use an individual
ally described in terms of pressure drop between the
pump for each cylinder (pump injection system) and
input and output sides of the filter. However, fuel oil
provide each cylinder with a spring-loaded spray
filters must be large enough to take the full flow of
valve. The spring keeps the needle from lifting until
the fuel oil pumps with a pressure drop across the
the pump has delivered oil at a pressure greater
filter not to exceed the engine manufacturer's speci-
than the spring loading. As soon as the pressure
fications. Fuel filter elements should be changed
lifts the needle, oil starts to spray into the engine
whenever the pressure drop across the filter nears
cylinder through an opening in the valve body.
(5) Diesel fu e suppliers try to provide clean
1
or reaches a specified value. Refer to manufactur-
er's instructions for information on the replacement
fuel. However, contaminants (water, sand, lint, dirt,
of filter elements. Filter capacity at a given pres-
etc.) are frequently found even in the best grades. If
sure drop is influenced by the viscosity of the fuel.
foreign material enters the fuel system, it will clog
The filter should have ample capacity to handle fuel
the nozzles and cause excessive wear of fuel pumps
and injection valves.
demand of the engine at full load. The larger the
(6) Sulphur, frequently found in fuel oil, is very
filter, the less frequently it will have to be cleaned
and the better the filtering performance will be.
undesirable. When sulfur is burned (during combus-
tion), sulfur dioxide and sulfur trioxide form. Both
3-5. Diesel cooling system.
substances will combine with water condensates to
Diesel engines are designed to be either air cooled
form sulfuric acid. The maximum amount of sulfur
acceptable in fuel oil must not exceed one percent.
or liquid cooled. Cooling is used to prevent the cyl-
inder walls, the head, the exhaust manifold, and the
The engine manufacturer's recommendation should
be used if acceptable sulfur in fuel oil requirements
lube oil from overheating.
a. An air-cooled system depends on an engine
are more restrictive. Strainers and filters capable of
removing fine particles are placed in the fuel line
driven fan to blow ambient air over the fluted or
finned surfaces of the cylinder head and through a
between supply tank and engine, or between engine
transfer pump and injection pump, or sometimes at
radiator type oil cooler, and over the exhaust mani-
fold. The exterior surfaces must be kept free of dirt
both places. The basic rule for placement of strain-
or corrosion. The oil must be kept free of sludge to
ers and filters is strainers before pumps, filters af-
ter pumps. A filter should be placed in the storage
secure adequate cooling. Air cooling is seldom used
on engines over 5 HP or on multicylinder engines.
tank fill line. This prevents accumulation of foreign
material in the storage tank. Strainers protect the
b. The liquid-cooled engine uses a treated coolant
transfer pumps. A strainer should also be placed
forced to circulate through passages in and around
the cylinder, head, exhaust manifold and a lube oil
ahead of each fuel flow meter. Always locate filters
heat exchanger. The hot coolant is passed through
and strainers where they are easily accessible for
the tubes of an air-cooled radiator, through the
cleaning or replacement. Duplex filters should be
tubes of an evaporative heat exchanger, or through
provided for engines that run continuously so that
a shell and tube heat exchanger. A typical liquid
filter elements can be cleaned while the engine is
running without interrupting its fuel supply. Pro-
system is shown in figure 3-7.
vide space under the edge of disk filters for a recep-
(1) Two basic types of liquid-cooling systems
tacle to receive material drained from the bottom of
are attached and remote.
the filter when it is cleaned. If the filter or strainer
(a) Attached. All components are mounted at
has an element that can be renewed or cleaned,
the engine. It is used with smaller and/or portable
engine generator sets and usually consists of an
space must be allowed to permit its easy removal.
engine-driven pump circulating treated coolant in a
Follow the manufacturer's recommendations on fre-
3-9
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