Engine Tune-Up
LIMITING SPEED MECHANICAL GOVERNOR
(Fast Idle Cylinder)
The limiting speed governor equipped with a fast idle
air cylinder is used on certain engines where the
engine powers both a vehicle and auxiliary equipment.
The fast idle system consists of a fast idle air cylinder
installed in place of the buffer screw and a throttle
locking air cylinder mounted on a bracket fastened to
the governor cover (Fig. 1). An engine shutdown. air
cylinder, if used, is also mounted on the governor
cover.
The fast idle air cylinder and the throttle locking air
Fig. 2 - Fast Idle Air Cylinder
cylinder are actuated at the same time by air from a
nected to a yield link so the operator cannot overcome
common air line. The engine shutdown air cylinder is
the force of the air cylinder holding the speed control
connected to a separate air line.
lever in the idle position while the engine is operating
at the single fixed high idle speed.
The air supply for the fast idle air cylinder is usually
controlled by an air valve actuated by an electric
Operation
solenoid. The fast idle system should be installed so
that it will function only when the parking brake
During normal operation, the governor functions as a
system is in operation to make it tamper proof.
limiting speed governor.
The accelerators to governor throttle linkage is con-
For operation of auxiliary equipment, the vehicle is
stopped and the parking brake set. Then, with the
engine running, the low-speed switch is placed in the
O N position. When the fast idle air cylinder is
actuated, the force of the dual idle spring (Fig. 2) is
added to the force of the governor low speed spring,
thus increasing the engine idle speed.
The governor now functions as a constant speed
governor at the high idle speed setting, maintaining a
near constant engine speed regardless of the load
within the capacity of the engine. The fast idle system
Fig. 3 - Throttle Locking Air Cylinder
Fig. 1 - Governor with Fast Idle Cylinder
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