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TRUCK GROUP SERVICE MANUAL
TM 5-4210-230-14&P-1
GENERAL
Two calibrated bypass jets in the vacuum passages
meter the vacuum from the venturi and the manifold to provide
the correct balance for proper operation of the governor. At
speeds below governing RPM this vacuum is weakened by air
bleeding through the governor valve in the governor spinner so
that no premature governing action will occur.
Filtered air from the carburetor air cleaner enters the
governor system through a passage in the main body and then
into the governor vent tube. The air flows through an air line to
the housing enclosing the governor rotor or spinner valve,
located in the distributor.
A combination of low pressure from the venturi and
manifold transmitted through the governor system passages
draws the air past the governor valve and through another air
line to the throttle actuating unit on the carburetor.
In the controlling unit centrifugal force acting on the rotor,
which has kept pace with engine speed, overcomes the tension
of the valve spring and tends to close the governor valve when
governing speed is reached. This greatly restricts the amount
of air bleeding through to the diaphragm on the carburetor, thus
allowing the combined venturi and manifold pressure differential
to operate the diaphragm. As the pressure differential across
the diaphragm increases, the diaphragm moves the governor
lever against the tension of the governor spring to close the
throttle plates.
The governed engine speed is held constant by
centrifugal force on the valve balanced against the tension of
the valve spring. Any slight change in engine speed due to load
variation will cause the governor valve to react immediately,
either increasing or decreasing the amount of air bleeding
through the governor valve orifice. A change in the amount of
air bleed will, in turn, cause an instant response from the
diaphragm to increase or decrease the throttle plate opening.
When the accelerator is released, control is taken from
the governor by the external throttle lever and the return spring
in the accelerator pedal linkage closes the throttle plates to
bring the engine to any desired lower speed.
A secondary control valve is used in conjunction with the
governor. The purpose of the secondary control valve (Figures
23 and 24) is to close the secondary throttle plates when
governed speed is reached, so that the engine cruises at
governed speed operating only the primary venturis. The
secondary control valve is operated by governor vacuum acting
upon the control valve diaphragm. Below governed speed air
flow through the governor ("spinner") valve weakens the
vacuum acting upon the control valve diaphragm. The
diaphragm spring holds the valve closed against its seat.
Primary venturi vacuum acting on the secondary diaphragm
controls position of the secondary throttle plates. When
governed speed is reached and the governor ("spinner") valve
closes (restricting the air flow), increased vacuum moves the
secondary control valve diaphragm compressing the valve
spring and opens the valve. This permits a flow of fresh air
through the valve into the secondary diaphragm chamber. The
flow of air weakens the vacuum acting on the secondary
diaphragm and allows the diaphragm spring to close the
secondary throttle plates.
CGES-125-T Page 13
PRINTED IN UNITED STATES OF AMERICA
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