Figure 5-24. Vacuum Operated Governor.

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Figure 5-23. Mechanical (Centrifugal) Governor.

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TM-9-8000 Principles of Automotive Vehicles Manual

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Figure 5-25. Timing Device.

TM 9-8000

Figure 5-24. Vacuum Operated Governor.

The amount of pressure reduction depends on the

corresponding increase in the pressure differential on

position of the governor valve and speed of the engine.

both sides of the diaphragm. The increase in pressure

It is this pressure differential that positions the diaphragm

differential causes the diaphragm and the control rod to

and, consequently, the control rod of the injection pump.

move against the pressure of the spring toward the no-

The governor valve is controlled by a lever that is

fuel position.

The control rod's position will stabilize

connected by suitable linkage to the foot throttle. There

when equilibrium is achieved in the diaphragm unit.

is no mechanical connection between the foot throttle

When the engine is operating at wide-open throttle, the

and the control rod of the injection pump.

pressure differential will be almost zero and spring force

will position the control rack in the full-fuel position.

c. If the engine is operating under load and the

d. For any position of the governor valve between

speed (rpm) is below governed speed, the velocity of air

passing through the venturi is comparatively low and only

idling and full load of the engine, the diaphragm finds its

a slight pressure differential is present. This will cause

relative position.

Because any movement of the

the spring to move the diaphragm and the injector pump

diaphragm also is transmitted to the control rod, the

control rack toward the full-fuel position. As the engine

amount of fuel delivery definitely is controlled at all

speed picks up, the pressure differential on both sides of

speeds. The diaphragm is moved in the direction of

the diaphragm and the spring will achieve equilibrium

less fuel delivery as the pressure drop between the

and the position of the control rod will stabilize. The

chambers is increased. The spring will move the control

same operating principles will apply in reverse to prevent

rod in the direction of greater fuel delivery as the

engine overspeed. As the engine speed increases, the

pressure drop is decreased.

velocity of air through the venturi increases, causing a

TA233460

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