At high speeds the charging accumulator
adds its volume of fuel to the volume of
transfer pump supplied fuel insuring com-
plete pumping plunger charging.
The hydraulic head also contains a pas-
sage, which connects transfer pump pres-
sure to the interior of the housing. Located
in this passage is a vent wire assembly
which permits a small flow of fuel to be
vented into the housing as well as purging
any air entrained in the fuel. From the hous-
ing the air can be vented from the pump
via the return line connector/housing pres-
sure regulator and returned to the fuel tank.
This flow of return oil to the fuel tank also
serves to carry the heat from the pump dur-
ing operation.
Fuel not used for injection and not inter-
nally leaked into the housing flows
through a return passage in the hydraulic
head. This fuel is also ported to a high-pres-
sure spill accumulator that absorbs pres-
sure spikes created by the spilling of in-
jection pressure into transfer pump pres-
sure at the end of each discharge pump-
ing sequence. Another head locking screw
connects this passage through the hydraulic
head with a passage on the side of the
housing, which is plumbed, to the back-
side of the transfer pump pressure regu-
lator piston. When this pressure becomes
high enough to move the regulating pis-
ton against the force exerted by the trans-
fer pump regulating spring, the piston’s
movement uncovers a regulator slot al-
lowing this fuel to be bled back to the in-
let side of the transfer pump.
D. Transfer Pump (Figures 1.6a, b, c)
The positive displacement vane type fuel
transfer pump consists of a stationary liner
and four spring-loaded blades that are car-
ried in slots in a drive shaft driven blade
retainer. Since the inside diameter of the
liner is eccentric to the drive shaft axis, ro-
tation of the shaft, blade retainer and
blades results in the blades moving up and
down in their slots. This rotation and blade
movement results in changes in volume
between each adjacent pair of blades.
Figures 1.6a through 1.6c illustrate the
pumping principle. Radial movement
causes a volume increase in the quadrant
between blades 1 and 2 (Figure 1.6a). In
this position the increasing quadrant is in
registry with a kidney shaped inlet slot in
the porting plate. The increasing volume
causes fuel to be drawn in from the kidney
slot area. After blade 2 passes out of reg-
4
Fig. 1.6a Liner
Blade 2
Blade 1
Then, as blade 1 passes the edge of the
outlet kidney slot, located 180°from the in-
let slot, (Figure 1.6c) the charge of fuel be-
gins to be pressurized and flows into the
outlet slot. As the drive shaft rotates, the
istry with the kidney slot and the volume be-
tween blades 1 and 2 no longer increases,
the fuel between the blades is carried
around to the top of the liner (Figure 1.6b).
Inlet Port
