PUMPS
SUB-SECTION 4B
the tip loads within reasonable limits. In the intra-vane, car-
PRINCIPLES OF OPERATION
tridge, full system pressure is continuously applied for out-
Fluid enters the pumping cartridge through the inlet port
ward, vane thrust only over the area between the vane and
and is discharged through the pressure plates to the outlet
insert. This area is small and thrust is correspondingly light.
ports. The action of the pumping cartridge is illustrated in
During vane travel through pressure areas, full system pres-
Figure 4B-24.
sure is also applied against the bottom of the vane. The
valving of pressure to and from the bottom area of the vane
The rotor is driven within the cam ring by the driveshaft,
is through holes drilled in the rotor, as shown in Figure
which is coupled to the pump drive. As the rotor turns,
4B-25. This selective application of pressure maintains the
centrifugal force on the vanes, aided by under-vane pressure
vane in constant radial hydraulic balance in all positions.
fed from the outlet port, causes them to follow the ellip-
tical inner surface of the cam ring.
The cam ring is shaped so that the two pumping chambers
Radial movement of the vanes and turning of the rotor
are formed 180 degrees apart (see Figure 4B-24). Thus,
cause the chamber volume between the vanes to increase as
opposing hydraulic forces which would impose side loads
the vanes pass the inlet section of the cam ring. This results
on the driveshaft cancel each other out.
in a low pressure condition which allows atmospheric pres-
sure to force fluid into the chambers.
The pressure plate seals the pump chamber as shown in
Figure 4B-26. System pressure is effective against the area
This fluid is trapped between the vanes and carried past a
at the back of the plate, which is larger than the area ex-
sealing land to the outlet section of the cam ring. As the
posed to the pumping cartridge. Thus, an unbalanced force
outlet section is approached, the chamber volume decreases
holds the plate against the cartridge, sealing the cartridge
and the fluid is forced out into the system.
and providing the proper running clearance for the rotor
and vanes. The pressure plate also contains passages for
The intra-vane design provides a means of controlling the
feeding pressure to the space between the vanes and inserts.
outward thrust of the vane against the cam ring to maintain
Figure 4B-24. Pump Cartridge Operation
4B-15
