When the pilot valve plunger is pushed back to its
the magnet and pilot valve plunger. When the unit is
running under steady-state conditions, these opposing
centered position, movement of the power piston,
loading piston, and terminal shaft stop.
forces are equal. The pilot valve plunger is then
centered This means the control land of the plunger
Position of the actuator shaft is proportional to the
exactly covers the control port in the pilot valve bushing.
electric input signal to the actuator. An increase in the
With the pilot valve plunger centered, no oil flows to or
electric input signal caused by a decrease in engine or
from the power piston.
turbine speed or an increase in unit speed setting creates
An increase in engine or turbine speed or a decrease
similar movements in the opposite directions.
in unit speed setting will cause the following actions to
This recenters the pilot valve plunger and stops
movement of the terminal shaft.
The governor pilot valve plunger controls the flow
of oil to its power piston. If the plunger is centered, no
oil flows through the pilot valve. The power piston is
then stationary. The greater of two opposing forces, the
As the actuator power piston moves down, the
upward force of the flyweights and the downward force
following actions occur:
of the speeder spring, moves the pilot valve plunger.
With the pilot valve centered, there is one speed at which
the centrifuged force of the flyweights is equal and
opposite to the speeder spring force.
With the speed setting of the governor set slightly
higher than the actuator, the centrifugal force of the
rotating flyweights is not sufficient to lift the pilot valve
plunger to its centered position. With the actuator
controlling, pressure oil is continually directed to the
underside of the governor power piston. This holds it
up against its stop. This is why the power piston of the
governor is against its stop when the actuator is
With the unit running on speed with the governor
controlling, the pilot valve plunger is centered. If a load
is added to the engine, the following actions occur: