Figure 1-24. Fuel intake flow diagram.

TM 9-2910-226-34

1-22. Fuel Flow. Fuel flows from the vehicle fuel tank

to the fuel supply pump inlet. The fuel supply pump

delivers fuel through the fuel filters to a tee installed

in the fuel density compensator inlet port. From the

tee, fuel flows to the density compensator and to the

inlet of the hydraulic head. Fuel flows through the

hydraulic head and the head outlets to the engine

cylinders. Excess fuel from the hydraulic head

passes through the overflow valve, which maintains

a constant fuel pressure in the hydraulic head. The

constant flow of fuel through the hydraulic head not

only supplies fuel for injection but also serves as a

coolant for the hydraulic head. A pressure regulator

valve (JJ, fig. 1-16) in the density compensator

maintains pressure at 20 to 21 psi. Excess fuel from

the density compensator and hydraulic head flows

back to the vehicle fuel tank.

1-23. Fuel Pumping and Distribution. a. The fuel

injection pump camshaft is driven at engine crank-

shaft speed. As the camshaft rotates, the tappet

moves the fuel plunger (U, fig. 1-16) up and

down. The quill shaft, driven off the camshaft,

drives the plunger drive gear which rotates the fuel

plunger. When the camshaft has rotated twice, the

fuel plunger has rotated 360 and completed six fuel

injection strokes.

b. At the intake phase (fig. 1-24), the fuel plunger

is on the base circle of the camshaft, the fuel plunger

is down, and fuel enters and fills the pressure

chamber. As the camshaft rotates, the fuel plunger

Figure 1-24. Fuel intake flow diagram.

closes off the inlet and outlet ports and is at the

beginning of delivery phase (fig. 1-25). The fuel in

the pressure chamber is pressurized and starts to

open the fuel delivery valve. At the delivery phase

(fig. 1-26) the fuel is under sufficient pressure to

fully open the fuel delivery valve. This highly

pressurized fuel then flows around the fuel plunger

annulus, through the distributing slot, which is now

alined with one of the six outlet passages, and out

the outlet passage to the injector nozzle. At the end

of delivery phase (fig. 1-27), after sufficient upward

movement of the fuel plunger, the spill passages

passes over the edge of the plunger sleeve. The fuel

pressure then escapes down the plunger vertical fuel

passage into the fuel sump which is at supply

pressure. The reduction of pressure causes the fuel

delivery valve to close.

Figure 1-25. Beginning of fuel delivery flow diagram.

1-27