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CFM56 ENGINES (CFM56-7) 737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
75-32-00-031
ENGINE AIR - VBV SYSTEM - DOORS
ENGINE AIR - VBV SYSTEM - DOORS
EFFECTIVITY
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D633A101-GUN Feb 10/2003
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
CFM56 ENGINES (CFM56-7) 737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
75-32-00-031
General
The EEC uses these data to schedule the variable bleed valves
(VBVs) position:
* P0
* PT
* TAT
* T25
* VSV position
* N1 speed
* N2 speed
* Thrust lever resolver angle (TRA).
Control
The VBV system operates automatically. The EEC normally gets
P0, PT and TAT from the ADIRUs through the DEUs. The EEC
gets N1, N2, T25 and VSV position from engine sensors and TRA
from the thrust lever resolver. The EEC uses this data to
schedule an angular position for the VBV doors. The EEC sends
a command signal to the HMU. The HMU sends servo fuel
pressure to move the pistons in the two VBV actuators. The
actuators connect with the twelve VBV doors through an
actuation ring. The VBVs control the amount of LPC discharge
air that goes to the secondary airflow.
Each actuator has a LVDT. The EEC uses the LVDTs to monitor
the position of the actuators. One LVDT sends an electrical
signal to channel A of the EEC. The other LVDT sends an
electrical signal to channel B.
Operation
In general, during steady state operation, the VBVs go more
closed as N1 speed increases. The VBVs are closed above
about 80 percent N1 speed.
The EEC commands the VBV doors to be more open during
these conditions:
* Rapid engine deceleration
* Thrust reverser operation
* Potential icing conditions.
Training Information Point
You can see VBV door position in the engine maintenance
pages of the control display unit (CDU).
See the engine indicating section for more information on the
engine maintenance pages in the CDU. (SECTION 73-21)
ENGINE AIR - VBV SYSTEM - FUNCTIONAL DESCRIPTION
EFFECTIVITY
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Page 10
D633A101-GUN Jun 10/2003
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
CFM56 ENGINES (CFM56-7) 737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
75-32-00-040
ENGINE AIR - VBV SYSTEM - FUNCTIONAL DESCRIPTION
ENGINE AIR - VBV SYSTEM - FUNCTIONAL DESCRIPTION
EFFECTIVITY
GUN ALL 75-32-00
Page 11
D633A101-GUN Feb 10/2003
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
CFM56 ENGINES (CFM56-7) 737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
75-32-00-040

　
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