MECHANICAL (CENTRIFUGAL) GOVER-
fuel control valve for the desired fuel flow. Oil from the
NOR SECTION. The mechanical governor section is
SSPU lube oil system is supplied to the governor oil
shown in the left side of figure 7-12. The main
pump gears through check and relief valves. The
components in the mechanical governor section are the
resulting oil pressure forces the loading piston up. As
governor power piston, governor pilot valve, speeder
the loading piston moves up, the governor terminal
spring, flyweights, buffer piston, compensation land,
shaft, through linkage, positions the fuel control valve
and needle valve assemblies. As we discuss each of
to decrease the rate of fuel flow. A decrease in oil
these components and their functions, notice how the
pressure causes the loading piston to move downward,
principles of operation are similar to those of the
causing the governor terminal shaft to position the fuel
components in the electric governor section.
control valve to increase the rate of fuel flow.
Governor Pilot Valve. The role of the governor
Actuator Power Piston, Pilot Valve, and
pilot valve is to control the oil flow to and from the
Restoring Spring. Along with the actuator pilot valve
governor power piston. The description in the following
and the restoring spring, the actuator power piston plays
paragraph of how the governor pilot valve and governor
an important role in the relationship between the SSPU
power piston work should give you abetter idea of how
speed and the speed control signal. (See fig. 7-12.)
the governor actuator unit, through linkage, controls the
When the SSPU speed increases, the speed control
required fuel flow.
signal decreases. The restoring spring raises the actuator
Governor Power Piston, Flyweights, Speeder
pilot valve, causing the oil under the actuator power
Spring, and Buffer Piston. Two opposing forces move
piston to drain back to the SSPU oil sump. The resulting
the governor pilot valve: (1) the speeder spring force
change in oil pressure causes the loading piston and the
tends to push the valve down; (2) the centrifugal force
actuator power piston to move downward. As both
of the rotating flyweights tends to force it up.
pistons move downward, the terminal shaft rotates and
During steady-state speed, the governor pilot valve
positions the fuel control valve to decrease the fuel flow.
will tend to remain centered. No oil will flow, of course,
While both pistons are moving down, the load on the
when the pilot valve is centered. However, when the
restoring spring begins to increase. (The load is created
speeder spring setting is slightly higher than that of the
by the force of the first restoring lever pushing down on
actuator, the valve will not center and the resulting oil
the second restoring lever.) The actuator power piston
pressure will hold the power piston against its stop.
continues to move downward until the restoring spring
force offsets the speed control signal. When the actuator
At steady-state speed, the actuator pilot valve is
pilot valve is centered, movement of both the actuator
centered. When a load is applied, the SSPU speed and
power piston and the terminal shaft will stop. These
governor speed decrease. The speeder spring force is
now greater than the force of the flyweights, so the pilot
events work in reverse when the SSPU speed decreases
valve is now pushed down by the speeder spring. When
and the speed control signal increases.
pressure oil flows to the buffer piston, it moves towards
Actuator Pilot Valve, Armature Magnet and
the power piston. The oil displaced by the buffer piston
Solenoid Coil. Locate the actuator pilot valve,
forces the power piston up, the loading piston rises, and
armature magnet, and solenoid coil in the electric
the terminal shaft rotates to increase fuel to meet the new
governor section of figure 7-12. The main function of
load demand. When the fuel requirement is met, the
the actuator pilot valve is to control oil flow to the
terminal shaft and power piston movement stop. Then,
actuator power piston. An armature magnet is connected
the pilot valve centers and the SSPU speed increases to
to the actuator pilot valve. This magnet is suspended in
normal speed, thereby decreasing the force of the
a field flux created by the solenoid coil. The solenoid
flyweights.
coil receives electrical signals from the SSPU speed
Compensation Land and Needle Valve
control unit.
Assemblies. Centering of the pilot valve is aided by
During steady-state speed, the speed control signals
differential pressure created across the compensation
will tend to center the actuator pilot valve. When the
land by the action of the needle valve. As the power
actuator pilot valve is centered, no oil will flow to the
piston moves upward, the needle valve orifice starts to
actuator power piston and movement of both the
displace the oil pressure created by the movement of the
actuator power piston and the governor terminal shaft
buffer piston, and soon equalizes the oil pressure above
will stop.
and below the compensation land. his oil displacement
7-17
