space 1 of the outer gear. As the gears continue to rotate
in 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 forth. During this
revolution, tooth I will mesh with space 3. As a result,
the outer gear rotates at 1,400 rpm, and the outer gear
will rotate at 1,200 rpm.
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. The pockets
on the right-hand side of the drawings are increasing in
size as one moves down the illustration, while those on
the left-hand side are decreasing in size. The intake side
of the pump would therefore be to the right and the
discharge to the left. Since the right-hand side of the
drawing in figure 10-5 was turned over to show the
ports, the intake and discharge appear reversed.
Actually, A in one drawing covers A in the other.
VANE PUMP. Figure 10-7 illustrates a vane pump
of the unbalanced design. The rotor is attached to the
drive shaft and is rotated by an outside power source,
such as an electric motor or gasoline engine. The rotor
is slotted, and each slot is fitted with a rectangular vane.
These vanes, to some extent, are free to move outward
in their respective slots. The rotor and vanes are
enclosed in a housing, the inner surface of which is
offset with the drive axis.
As the rotor turns, centrifugal force keeps the vanes
snug against the wall of the housing. The vanes divide
the area between the rotor and housing into a series of
chambers. The chambers vary in size according to their
respective positions around the shaft. The inlet port is
located in that part of the pump where the chambers are
expanding in size so that the partial vacuum
(low-pressure area) formed by this expansion allows
liquid to flow into the pump. The liquid is trapped
between the vanes and carried to the outlet side of the
pump. The chambers contract in size on the outlet side,
and this action forces the liquid through the outlet port
and into the system.
The pump is referred to as unbalanced because all
of the pumping action takes place on one side of the shaft
and rotor. This causes a side load on the shaft and rotor.
Some vane pumps are constructed with an
elliptical-shaped housing that forms two separate
pumping areas on opposite sides of the rotor. This
cancels out the side loads; therefore, such pumps are
used quite extensively in power steering units in CESE
to provide the flow.
Figure 10-7.-Typical vane type of hydraulic pump.