S-M56-MM-0369-(1)-01-B
Variable Bleed Valve (VBV) System SchematicFigure 8
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CFM56 ENGINES
737-300/400/500/ /MAINTENANCE MANUAL ////////////////////////
E.  The fuel gear motor, actuated by the VBV control valve in the MEC, drives the system to the commanded (open, closed or modulated) position with the required power. The VBV feedback mechanism relays the bleed valve position to the MEC as the system approaches the commanded position. The VBV control valve is moved towards the null position (or minimum opening needed to neutralize the bleed valve loads) as the bleed valve approaches the end of its stroke. This reduces motor speed and allows the motor to engage the end-of-stroke stops at low impact force.
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CFM56 ENGINES
737-300/400/500/ /MAINTENANCE MANUAL ////////////////////////
VARIABLE BLEED VALVE SYSTEM - MAINTENANCE PRACTICES
___________________________________________________
 1.  General
_______
 A.  This page block gives the procedure to operate the variable bleed valve (VBV) system. The procedure can be used:
 -
to put the bleed valve doors in the open or closed position

 -
to do a check of the system operation after a component replacement - or to go along with the trouble-shooting procedure.

 B.  The VBV system can be operated by:
 -an external pressure source (Task 2)
 -a manual movement (Task 3)
 -motoring the engine (Task 4).
 An external pressure source is recommended.

 TASK 75-32-00-862-001-C00
 2.  VBV System Actuation Procedure - External Pressure Source
_________________________________________________________
 A.  Equipment
 (1)  
856 A1084, Cart - Hydraulic, CFM International, P.O. Box 15514, Cincinnati, OH 45215

 (2)
Container - 1 gallon (4 liter) capacity, for fuel

 B.  Consumable Materials
 (1) D00124 Oil - Lubricating, MIL-L-6081, Grade 1010 (CP2369)
 NOTE: Filtered (10 micron) fuel can be used as an alternative.
____
 C.  References
 (1)
AMM 71-00-00/501, Power Plant

 (2)
AMM 71-11-02/201, Fan Cowl Panels

 D.  Access
 (1)  
Location Zones
 506 Engine No. 1 - Fan Frame
 606 Engine No. 2 - Fan Frame

 (2)  
Access Panels
 5746L Engine No. 1 - Left Fan Cowl Panel
 5846R Engine No. 2 - Left Fan Cowl Panel

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CFM56 ENGINES
737-300/400/500/ /MAINTENANCE MANUAL ////////////////////////
E. Operate the VBV System (Fig. 201)
 S 012-002-C00
 (1)  
Open the left fan cowl panel (AMM 71-11-02/201).

 S 492-003-C00

 (2)  
Put a container below the VBV open and closed end tube connections at the main engine control (MEC).

 S 032-004-C00

 (3)  
Disconnect the flexible hoses from the VBV OPEN and CLOSE fittings on the MEC.

 (a)  Put caps on the open MEC fittings.
 S 492-005-C00
 (4)  Connect the supply and return hoses from the hydraulic cart to the VBV open and close flexible hoses.
 S 862-006-C00
 CAUTION:_______DO NOT USE MORE THAN 300 PSI (2100 KPA). DAMAGE TO THE VBV SYSTEM CAN BE CAUSED FROM TOO MUCH PRESSURE.
　
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