TM 5-4240-501-14&P
THEORIES OF OPERATION
Governing
GOVERNING
While some people think that a governor on an engine is
to prevent overspeeding, the real purpose in the small
engine field is to maintain a desired speed regardless of
load. With a fixed throttle position, the engine could
speed up if the load was lightened; if the load is
increased the engine would slow down or even stop.
A governor on the other hand will close the throttle if the
load is lightened or open the throttle to obtain more
power if the load is increased.
Basically, governors consist of two types the pneumatic
or air vane type, Fig. 34, and the mechanical or flyball
weight type, Fig. 35.
The pneumatic governor as illustrated in Fig. 34 is
operated by the force of the air from the flywheel fins.
When the engine is running the air from the fins pushes
against the air vane. The air vane is connected to the
carburetor throttle by means of a link. The force and
movement of these parts tends, to close the carburetor
and thus slow down the engine speed.
Opposed to this is the governor spring which tends to
pull the opposite way, opening the throttle. This spring is
usually connected to an adjustable control of some kind
so that the tension on the spring can be changed at the
will of the operator. Increasing the tension of the spring
will increase the engine speed. Decreasing the tension
will lower the engine speed. The point at which the pull
of the spring equals the force of the air vane is called the
"governed speed"
ENGINE NOT RUNNING
ENGINE RUNNING
Figure 34.
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