EGB-2P governor/actuators are available with the
The proportional actuator requires a continuous
terminal shaft extending from either or both sides of the
electric input signal. This is in contrast to the nominally
case. They can be furnished with the speed-adjusting
zero input signal under steady-state conditions for
shaft (for the ballhead governor section) extending on
integrating-type actuators. Woodward 2301 electric
either side. However, most units use a speed-adjusting
controls are used to furnish the control input signal for
screw in the top cover. They omit the speed-adjusting
the proportional actuator. The exact 2301 control used
shaft entirely.
depends upon the operating scheme of the installation.
Control assemblies are available to sense speed,
OPERATION
frequency, load, and other combinations.
The schematic arrangement of the EGB-2P is shown
The following are the essential elements of the
in figure 9-13. The parts are in their relative positions
actuator section of the EG-B2P;
during normal operation. Oil enters the unit through
Electrohydraulic transducer, which directs
either of the two inlet holes in the side of the base. The
pressure oil to and from the power piston to actuate the
oil passes from the suction to the pressure side of the
fuel or steam control mechanism. It consists of a
pump. After filling the oil passages, the pump builds up
solenoid attached to the pilot valve plunger.
the oil pressure. When the pressure is high enough to
overcome the relief valve spring force, it pushes the
Pilot valve plunger, which controls oil flow to
relief valve plunger back to uncover the bypass hole. Oil
and from the power piston by positioning the control
then recirculates through the pump.
land to add or drain oil to the actuator power piston.
Rotation of the pump in the opposite direction from
Solenoid coil, which responds to the given output
that shown in figure 9-13 closes the open check valves
of the electric control. This moves the pilot valve
and opens the closed check valves.
plunger down, directing oil to the power piston.
The loading piston positions the terminal shaft.
Power piston, which moves the terminal shaft of
Constant oil pressure is applied to the upper side of the
loading piston. This tends to move it in the decrease fuel
the actuator.
direction. Either the governor power piston or the
Actuator terminal shaft, which is the attachment
actuator power piston can move the loading piston in the
point for the engine or turbine fuel linkage.
increase fuel direction. This is because the effective
area on which the control oil pressure acts is greater on
Strict linearity of terminal shaft travel versus load
the power piston than on the loading piston.
is not required. However, the linkage should be
arranged to give the same degree of linearity given
In the event of an electrical failure, the unit goes to
conventional speed-sensing governors.
minimum fuel. If the actuator goes to minimum fuel,
apply a 9-volt dc supply to the transducer. This takes
The centrifugal governor section has three
the actuator toward maximum fuel. This allows the
operating adjustments. Once set, these adjustments do
governor to take control. Adjust the speed-adjustment
not usually require further adjustment. These settings
screw to give the desired steady-state speed. If the unit
are listed below.
has a manual override knob on the cover, push it down
and turn it to the right. This locks out the actuator
1. Speed setting. An external adjustment used to
control.
set the speed at which the ballhead governor will
control.
Actuator Control
2. Speed droop. An internal adjustment used to
permit parallel operation of units controlled by the
The actuator's pilot valve plunger controls the flow
ballhead governor.
of oil to and from its power piston. The pilot valve
plunger is connected to an armature magnet. This
3. Needle valve. An external adjustment used to
magnet is spring-suspended in the field of a two-coil
stabilize the ballhead governor.
polarized solenoid. The output signal from the electric
The actuator section of the EGB-2P has no external
control is applied to the polarized coil. This produces a
operating adjustments. The actuator uses oil from the
force, proportional to the current in the coil. This tends
engine lubricating system or from a separate sump. It
to force the armature magnet and pilot valve plunger
down. The restoring spring force tends always to raise
does not have a self-contained sump.
9-16
