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 TM 9-8000
the volume of fuel injected to the cylinders to be varied
in the delivery line combined with spring pressure causes
by changing the effective length of the pump stroke (the
the delivery valve to close. When the delivery valve
length of the pump stroke that occurs before the spill port
closes, It prevents fuel from the line from draining back
is uncovered by the bypass helix). The rack extends
Into the pump, which could cause the system to lose its
down the whole row of Injection pumps so that they are
prime. As the delivery valve seats, It also serves to
all operated simultaneously. The end result is that the
reduce pressure In the delivery line. The delivery valve
Injection pumps can be moved from full to no-fuel
has an accurately lapped displacement piston
delivery by moving the rack back and forth. The
Incorporated Into It to accomplish pressure relief. The
movement of the rack is controlled by the governor
pressure is relieved in the line by the Increase In volume
(para5-24).
as the delivery valve seats.
c. Fuel Injectors (Fig. 5-8). For proper engine
(5) When the plunger begins Its pump stroke It
covers both ports. When this happens, the pressure
performance, the fuel must be Injected Into the
exerted on the fuel causes the spring-loaded delivery
combustion space In a definite spray pattern. This is
valve to lift off of Its seat, thereby permitting fuel to
accomplished by the fuel Injector.
discharge Into the tubing that leads to the spray nozzle.
At the Instant that the bypass helix uncovers the spill
(1) The fuel enters the nozzle holder body
port, the fuel begins to bypass. This causes the
through the high-pressure Inlet. It then passes
pressure In the pump cavity to drop. The high pressure
Figure 5-8. Multiple Unit Injector.
5-11
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