outlet and the HP element inlet. Relief valves are
sensor. It meters the required fuel for all engine
incorporated in the filter head to bypass the fuel
operating conditions.
if the filter becomes clogged. The LP filter inlet
The LFV is directly controlled by the governor
and outlet pressures are shown on the engine
actuator. During start and running of the engine,
gauge panel.
the LFV is positioned by the governor to limit the
amount of fuel to the fuel nozzles. The governor
High-Pressure Filter
control circuit receives inputs of engine speed,
The HP filter assembly is mounted on the
CIT, fuel valve position, and TIT. The CDP
bottom of the fuel pump. It has a filter, bypass
pressure is provided to the LFV directly. The
valve, two check valves, and a solenoid-operated
control circuit sets the LFV through the governor
paralleling valve. The filter is a 33-micron disk
actuator. This provides the proper amount of fuel
type. It is removable for servicing. The bypass
to the engine for all engine power and acceleration
valve opens to permit continuous flow if the filter
settings.
becomes clogged. If one HP gear element fails,
The fuel valve position sensor is an LVDT.
the check valves permit engine operation from the
It is mechanically linked to the LFV metering
other element.
sleeve and senses fuel valve position. The linkage
moves the sleeve to the actuator. As it does this,
Pressure Relief Valve
the amount of excitation voltage at the LVDT
output is changed. The output of the LVDT is
The pressure relief valve is closed during
normal engine operation. If the pump discharge
proportional to the position of the fuel metering
pressure reaches 500 10 psig above the bypass
sleeve. A comparator compares inputs from the
line pressure, the relief valve opens. This permits
electronic control unit (ECU) and the LVDT. This
excess fuel to return to the pump inlet.
is done to correctly position the fuel valve.
Excess fuel from the pump is returned to the
Model 104 Liquid Fuel Valve
secondary pump suction by the bypass valve. Like
The LFV is mounted on the left, lower side
the model 104 LFV, this is done to maintain
of the engine. It is mechanically and hydraulically
constant pressure at the metering valve.
connected to the EG actuator. The hydraulic
Electrohydraulic Governor Actuator
connection is through the CIT/CDP sensor and
the start temperature limit control valve. The LFV
The EG actuator is engine driven. It is
has a metering valve, an acceleration limiter, and
mounted on the left side of the AGB. Its output
a bypass valve. It meters the required fuel for all
shaft is mechanically linked to the LFV. It receives
engine operating conditions. The EG actuator
signals from the EG control box and positions the
LFV. The LFV, in turn, meters fuel to the engine.
linkage and the acceleration limiter (internal part
of the fuel valve) control the metering valve
The governor actuator incorporates normal
position. This, in turn, allows control of the fuel
control by the EG system and backup control by
flow.
a centrifugal governor. Each is independently able
The acceleration limiter schedules fuel flow
to position the output shaft to maintain engine
during start as a function of CIT and CDP.
speed.
During start and rapid acceleration, the limiter
An integral oil pump provides servo oil
overrides the governor input. This prevents
pressure for governor operation as well as other
compressor surge (stall) and excessive TIT. The
functions. Engine lube oil pressure from the AGB
limiter linkage (internal) is actuated by servo oil
is supplied to the actuator pump through an
pressure from the EG actuator. This is regulated
external line. During normal operation, an output
by the CIT/CDP sensor.
signal from the EG control box produces a force
To accurately meter fuel flow, you have to
on an armature magnet. The magnet is attached
to a pilot valve plunger and moves the plunger
maintain a constant pressure drop across the
metering valve. This is done when the bypass valve
up or down. The pilot valve plunger directs servo
opens and returns excess fuel from the pump
oil pressure to change the position of the output
shaft. If the electrical signal to the governor
outlet to the pump inlet.
actuator is interrupted, it may attempt to
Model 139 Liquid Fuel Valve
overspeed the engine. If this happens, the pilot
Like the model 104, the model 139 LFV is
valve plunger and terminal shaft will be positioned
toward the maximum fuel flow position. When
mounted on the left side of the engine. It is
mechanically connected to the EG actuator. It has
the engine speed exceeds a preset limit (about
a fuel metering valve and a fuel valve position
14,300 rpm), the centrifugal governor will assume
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