(c)
The 12 variable bleed valves assemblies are made up of 11 secondary bleed valve and ballscrew actuator units, and one master bleed valve and ballscrew actuator units. Each unit has a speed reduction gearbox and a ballscrew actuator linked to a bleed valve door.
(d)
A bleed valve main flexible shaft installed between the bleed valve and master ballscrew actuator and the fuel gear motor.
(e)
The 12 variable bleed valves have 11 bleed valve flexible shafts installed between the bleed valve and ballscrew actuators.
(3)
A flexible feedback cable to transmit to the MEC the position of the bleed valve system.
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CFM56 ENGINES
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SEE A
FEEDBACK ROD
FEEDBACK LEVER
FEEDBACK
BLEED VALVE CABLE AND MASTER BALLSCREW ACTUATOR
FEEDBACK
REVERSER
BLEED VALVE ARM
AND BALLSCREW
ACTUATOR
(11 UNITS)
BLEED VALVE BLEED VALVE
STOP MECHANISM FUEL GEAR MOTOR
FLEXIBLE SHAFTS FWD(11 UNITS)
A
S-M56-MM-0924-(1)-00-B
Variable Bleed Valve (VBV) System Component Location
Figure 1
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CFM56 ENGINES
737-300/400/500/ /MAINTENANCE MANUAL ////////////////////////
FAN OUTLET FAN OGV
SPLITTER
GUIDE VANES INNER
FAIRING S-M56-MM-0925-(1)-00-B
Variable Bleed Valve (VBV) System Airflow Diagram Figure 2
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CFM56 ENGINES
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D. The VBV actuation system provides an angular output through the fuel gear motor, master ballscrew actuator and 11 ballscrew actuators. The system is connected by the 11 flexible shafts. There are 11 ferrules installed in the fan frame struts to provide support for the flexible shafts. The system is designed to open, close or modulate the 12 VBV's to an intermediate position in response to an input command signal. The VBV's remain fully synchronized throughout their complete stroke by the continuous mechanical flexible shaft arrangement. The MEC supplies high pressure fuel to hydraulically operate the VBV actuation system. The master ballscrew actuator and the corresponding bleed valve are connected to the MEC by a push-pull feedback cable. The feedback cable provides VBV position bias to the MEC.
2. Bleed Valve Fuel Gear Motor (Fig. 3)
___________________________
A. The bleed valve fuel gear motor consists of a positive displacement gear motor and end-of-stroke stop mechanism. The motor, which is driven by high pressure fuel (PF), controls the position of the bleed valves. It consists of two spur gears guided during rotation by needle bearings. The motor converts pressurized fuel into rotary shaft power which is driven through the bleed valve stop mechanism to the gear reduction stage of the bleed valve and master ballscrew actuator.
B. Sealing at the drive gear shaft is provided by carbon seals. A secondary lip seal is mounted on the output shaft for further sealing. Fuel, which could leak past the different sealing provisions, is drained overboard through the starter air discharge duct fitting.
3. Bleed Valve Stop Mechanism (Fig. 4)
__________________________
A. The bleed valve stop mechanism is installed inside the fan frame mid box structure between the bleed valve fuel gear motor and the bleed valve and master ballscrew actuator at the 9:30 o'clock position.
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