CFMI PROPRIETARY INFORMATION
CFM56-5B TRAINING MANUAL
EFG
VARIABLE BLEED VALVE
The purpose of the Variable Bleed Valve (VBV) system is to regulate the amount of air discharged from the booster into the inlet of the HPC.
To eliminate the risk of booster stall during low power conditions, the VBV system by-passes air from the primary airflow into the secondary.
It is located within the fan frame mid-box structure and consists of:
- A fuel gear motor.
-
A stop mechanism.

-
A master bleed valve.

-Eleven variable bleed valves.
-Flexible shafts.
-A feedback sensor (RVDT).
The ECU calculates the VBV position and the HMU provides the necessary fuel pressure to drive a fuel gear motor, through a dedicated servo valve.
EFFECTIVITY
75-31-00 Page 2
ALL CFM56-5B ENGINES FOR A319-A320-A321
ENGINE SYSTEMS Jan 03
CFMI PROPRIETARY INFORMATION

EFG
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CTC-201-143-01  VBV SYSTEM 
EFFECTIVITY ALL CFM56-5B ENGINES FOR A319-A320-A321 CFMI PROPRIETARY INFORMATION
 75-31-00 ENGINE SYSTEMS  Page 3 Jan 03 

CFM56-5B TRAINING MANUAL
EFG
VARIABLE BLEED VALVE
Fuel gear motor.
The fuel gear motor transforms high pressure fuel flow into rotary driving power to position the master bleed valve, through a screw in the stop mechanism.
The fuel gear motor is a positive displacement gear motor secured on the stop mechanism rear flange.
It has 2 internal spur gears, supported by needle bearings.
Sealing of the drive gear shaft is provided by carbon seals.
A secondary lip seal is installed on the output shaft and a drain collects any internal fuel leaks which could occur.
The fuel flow sent to the gear motor is constantly controlled by the ECU, via the fuel control valve of the HMU.

EFG

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CTC-201-145-01
EFFECTIVITY
75-31-00 Page 5
ALL CFM56-5B ENGINES FOR A319-A320-A321
ENGINE SYSTEMS Jan 03

CFMI PROPRIETARY INFORMATION
CFM56-5B TRAINING MANUAL
EFG
VARIABLE BLEED VALVE
Stop mechanism.
The stop mechanism limits the number of revolutions of the gear motor to the exact number required for a complete cycle (opening and closing) of the VBV doors.
This function supplies the reference closed position to install and adjust the VBV system.
The stop mechanism is located between the gear motor and the master ball screw actuator.
Its main components are:
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A flexible drive shaft, which connects the gear motor
to the master ballscrew actuator.

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A follower nut, which translates along a screw and
　
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