engines use both mechanical and hydraulic governors on the engines of the following type:
limiting speed governor
mechanical speed governor
low-speed limiting speed mechanical governor
constant speed governor (earlier engines)
limiting speed mechanical governor
SG hydraulic governor
PSG hydraulic governor
diesel engines the type of governor used is dependent on the particular engine
application; therefore, setup can vary slightly between engines. All Detroit diesel
mechanical governors are easily identifiable by a nameplate attached to the governor
housing. The following letters are typical examples.
double-weight limiting speed (mobile equipment)
single-weight limiting speed (mobile equipment)
single-weight variable speed (industrial and marine)
variable low-speed limiting speed (highway vehicles)
double-weight dual range governor (highway vehicles)
SG, PSG, SGX,
of all these governors, whether mechanical or hydraulic, are to control engine speed and
correct for any change in load applied or removed from the engine. They all work on the
basic principle of weights against spring pressure; therefore, all governors are of the
action of all these governors is the same,the two most common types found on a Detroit
diesel enginethe limiting and variable speed governors.
speed type governor is found in both single- and double-weight version and can also be
found on both in-line and V-type engines. Riveted on the side of the governor housing is
an identification plate, which shows the following:
such as DWLS, meaning double-weight limiting speed
whether the limiting speed governor is of the single- or double-weight variety, the action
of the governor is the same. The purpose of the limiting speed governor is as follows:
engine idle speed
the maximum speed of the engine
application of the engine determines whether a single- or double-weight governor will be
used. The most prominent application for the limiting speed governor is highway truck
engines, since the governor has no control in the intermediate engine speed range.
the operator to have complete control of the injector rack movement through throttle
action alone. his permits fast throttle response for engine acceleration or deceleration.
speed mechanical governor is found extensively on industrial and marine applications,
since it is designed for the following functions:
the engine idle speed
the maximum engine speed hydraulic-type governors (industrial and generator sets)
the engine speed at any position between idle and maximum as desired and set by the
and reaction of the variable speed mechanical governor is similar to that of the limiting
speed type with just a few exceptions. Since the variable speed mechanical governor
controls speed through-out the total rpm range, there is no intermediate range as with the
limiting speed governor. The variable speed governor uses only one set of weights and one
In a variable
speed mechanical governor, any given but with a difference only in purpose, we will
discuss throttle setting or load from idle to maximum speed, a state of balance can exist.
If, however, the load is increased or decreased, a corrective action will be initiated.
The bell crank lever and pivoting differential lever will be moved by the action of the
governor spring or weights to reestablish a state of balance.
governor can only react and change to the rpm of the engine.
speed mechanical governor is readily identifiable from the limiting speed governor by the
fact that it has only one lever on the top of the governor cover, which is the stop/run
lever. The speed control lever is located vertically on the end of the governor spring
housing. A large booster spring is attached between the speed control lever and a bracket
on the cylinder head, used to assist the operator in overcoming governor resistance during
throttle movement. The letters SWVS (single-weight variable speed) are stamped on
the governor identification plate.
Before performing any adjustments or
repairs to the governor, it is recommended that you consult the manufacturers