Figure 10-4.-Lobe type of pump.
The inlet port is connected to the fluid supply line,
and the outlet port is connected to the pressure line.
Referring to the figure, the drive gear is rotating in a
counterclockwise direction, and the driven gear (idler
gear) is rotating in a clockwise direction. As the teeth
pass the inlet port, fluid is trapped between the teeth and
the housing; this liquid is carried around the housing to
the outlet port. As the teeth mesh again, the liquid
between the teeth is displaced into the outlet port. This
action produces a positive flow of liquid into the system.
A shear pin or shear section is incorporated in the drive
shaft to protect the power source or reduction gears if
the pump fails because of excessive load or binding of
A variation of the spur tooth pump is the lobe pump
(fig. 10-4), which is also used on many diesel-powered
equipments for an intake blower as well as in a variety
of hydraulic systems. The principle of operation of this
pump is exactly the same as the spur tooth. The lobes
are so constructed that there is a continuous seal (vane)
at the point of juncture at the center of the pump and also
on the housing.
Another popular style of gear pump is the internal
gear (fig. 10-5). This pump consists of a pair of
gear-shaped elements (one within the other) located in
Figure 10-5.-Internal gear type of pump.
Figure 10-6.-Principles of operation of the internal gear type
the pump chamber. The inner gear is connected to the
drive shaft of the source of power.
For an explanation of the operation of this type of
pump, refer to figure 10-6. The teeth of the inner gear
and the spaces between the teeth of the outer gear are
numbered. Note that the inner gear has one less tooth
than the outer gear has spaces. The tooth force of each
gear is related to that of the other in such away that each
tooth of the inner gear is always in sliding contact with
the surface of the outer gear. Each tooth of the inner gear
meshes with the outer gear at just one point during each
revolution. In the illustration, this point is at the top (X).
In view A, tooth 1 of the inner gear is in mesh with