If it is too cold, the oil will resist movement
between the parts and flow too slowly for proper
that is insoluble in water is required. In other
lubrication. If the oil pressure is too low, it will
cases, the grease must be resistant only to weather-
not supply enough oil to the bearing for proper
ing or during washing.
cooling. If the pressure is too high, it may cause
4. Satisfactory performance in use. The grease
high-speed antifriction bearings to skid and not
must perform satisfactorily in the equipment and
under the conditions it was intended.
It would be impossible to cover all the
different parts of every type of engine oil system
Properties of greases vary with the type of
in use today. Therefore, this text presents a
soap used in manufacturing. Military specifica-
representative sample of various parts common
tions specify the operating conditions or applica-
to different types of oil systems.
tions. Table 5-2 contains information on some of
the most frequently used greases.
TYPES OF LUBRICATION SYSTEMS
Engines use a wet-sump, dry-sump, or a
combination of both as lubricating systems. Wet-
sump engines store the lubricating oil in the engine
Oil systems used in jet engines are relatively
or gearbox. Dry-sump engines use an external
simple in design and operation, but their
tank mounted on the engine or somewhere in the
function is important. The principal purposes of
aircraft structure near the engine. Under the dry-
the oil system are the same as those covered under
sump lubrication system is another type called the
lubricating oils--to provide an adequate supply
hot tank system. You should know the similarity
and operation of these systems.
pressure and temperature, to remove heat from
system and deposit them in the filters.
The ability of the oil to lubricate correctly
Engines needing a limited supply of oil and
depends upon its temperature and pressure. If the
cooling can use a wet-sump type (fig. 5-1). The
oil is too hot, it will not have enough viscosity.
Figure 5-1.-Wet-sump lubrication system.