elements for both supply and scavenging must be
to shut off the oil supply to the engine in
of larger capacity or more of them.
emergency conditions.
Some oil tanks include an oil temperature bulb
It is common to use small individual scavenge
pumps in the remote sections of an engine. This
in the outlet line. These bulbs send the tem-
assures proper scavenging of the lubricating oil.
perature of the oil to indicators in the instrument
In all types of pumps, the scavenge elements have
panel. Oil quantity units or sight gauges are also
a greater pumping capacity than the pressure
located on the oil tank. A sight gauge gives a
visual indication of oil level. A quantity indicator
element. This is to prevent oil from collecting in
the bearing sumps.
connects electrically to a gauge in the instrument
The pumps may be one of several types, each
panel. A quantity indicator uses a float-type unit
located in the tank and an electrical transmitter
type having certain advantages and limitations.
The three most common oil pumps are gear,
on the outside of the tank.
gerotor, and piston types. The first being the most
used and the last the least used. Each of these
Oil Pumps
pump types have several different designs. This
The oil pump supplies oil under pressure to
makes it impractical to try to completely cover
each type. However, a pump representative of
engine points that require lubrication. Most
lubrication pumps have both a pressure supply
each of the three types is discussed.
element and a scavenge element. However, some
GEAR-TYPE OIL PUMP.-- The gear-type oil
oil pumps serve a single function; they either
pump shown in figure 5-6 has only two elements
supply or scavenge the oil. The number of
(one for pressure oil and one for scavenge).
pumping elements, both pressure and scavenge,
However, this type of pump could have several
depends largely on the type and model of the
elements.
engine. For instance, the axial-flow engines have
Notice in figure 5-6 a relief valve in the
a long rotor shaft and use more bearings than a
discharge side of the pump. This valve limits the
centrifugal-flow engine. Therefore, the oil pump
Figure 5-6.-Cutaway view of gear-type oil pump.
5-10
