Centered Internal Gear Pump
Another design of internal gear pump is
illustrated in figures 4-5 and 4-6. This pump
consists of a pair of gear-shaped elements, one
within the other, located in the pump chamber.
The inner gear is connected to the drive shaft of
the power source.
The operation of this type of internal gear
pump is illustrated in figure 4-6. To simplify the
explanation, 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. The tooth form of each
gear is related to that of the other in such a way
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 X. In view A,
tooth 1 of the inner gear is meshed with space 1
of the outer gear. As the gears continue to rotate
in a clockwise direction and the teeth approach
point X, tooth 6 of the inner gear will mesh with
space 7 of the outer gear, tooth 5 with space 6,
and so on. During this revolution, tooth 1 will
mesh with space 2; and during the following
revolution, tooth 1 will mesh with space 3. As a
result, the outer gear will rotate at just six-sevenths
the speed of the inner gear.
At one side of the point of mesh, pockets of
increasing size are formed as the gears rotate,
while on the other side the pockets decrease in size.
In figure 4-6, the pockets on the right-hand side
of the drawings are increasing in size toward the
bottom of the illustration, while those on the
left-hand side are decreasing in size toward the
top of the illustration. The intake side of
the pump would therefore be on the right and the
discharge side on the left. In figure 4-5, since the
right-hand side of the drawing was turned over
to show the ports, the intake and discharge appear
Figure 4-5.Centered internal gear pump.
Figure 4-6.Principles of operation of the internal gear
reversed. Actually, A in one drawing covers A in
pump uses the same principle of
the external gear pump described