Figure 20-3. Mechanical Advantage.
pressure is reached and allows the excess oil to be
Section II. 20-4. Gear Type oil pumps are shown in
delivered to the inlet side of the pump.
figure 20-4. In this type, a primary gear, driven by an
external member, drives a companion gear. Oil is forced
20-5. Rotary Type. The rotor oil pump (fig. 20-5)
into the pump cavity, around each gear, and out the other
side into the oil passages. The pressure is derived from
makes use of an inner rotor with lobes that match
the' action of the meshed gear teeth, which prevent oil
similarly shaped depressions in the outer rotor. Figure
from passing between the gears, and forces it around the
20-5 shows the manner in which the two rotors fit
outside of each gear instead. The oil pump Incorporates
together. The inner rotor is off center from the outer rotor.
a pressure relief valve, which is a spring- loaded ball that
The inner rotor is driven and, as it rotates, it carries the
rises when the desired
outer rotor around with it. The outer rotor floats freely in
the pump body.
Figure 20-4. Gear-Type Pumps.