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ENGINE FUEL AND CONTROL - DISTRIBUTION - FUEL NOZZLE FILTER
EFFECTIVITY
GUN ALL 73-11-00
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BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
CFM56 ENGINES (CFM56-7) 737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
73-11-00-008
Purpose
There are ten unstaged and ten staged fuel nozzles in the
combustion chamber. The burner staging valve (BSV) controls
fuel flow to the ten staged fuel nozzles. The BSV has two
positions, open and closed. The EEC sends a signal to the HMU
to close the BSV.
General Description
When closed, the BSV prevents fuel flow to the staged nozzles.
Fuel flows only to the unstaged nozzles.
When the staged nozzles are closed, all metered fuel goes
through the ten unstaged nozzles only. This gives a stronger
spray pattern during low fuel/air ratio operation. A stronger
spray pattern helps prevent engine flame out in rain and snow
conditions. Low fuel/air ratio operation normally occurs when
engine thrust command is reduced during descent.
At higher fuel/air ratios, the BSV opens and lets fuel flow to the
staged nozzles. Fuel now flows through both the unstaged and
staged fuel nozzles.
The BSV has four switches. These switches give BSV position to
channel A and channel B of the EEC. Each EEC channel gets a
signal from two switches. You get the BSV switch position
information from EEC BITE on the CDU.
Location
The BSV is at the 6:00 position of the engine core section.
ENGINE FUEL AND CONTROL - DISTRIBUTION - BURNER STAGING VALVE
EFFECTIVITY
GUN ALL PRE SB CFM56-7B 73-44 73-11-00
Page 22
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BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.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
73-11-00-009
ENGINE FUEL AND CONTROL - DISTRIBUTION - BURNER STAGING VALVE
ENGINE FUEL AND CONTROL - DISTRIBUTION - BURNER STAGING VALVE
EFFECTIVITY
GUN ALL PRE SB CFM56-7B 73-44 73-11-00
Page 23
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BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.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
73-11-00-009
Functional Description
The burner staging valve (BSV) opens to send fuel to the ten
staged fuel nozzles. The EEC software logic schedules BSV
operation. The EEC controls the hydromechanical unit (HMU) to
operate the BSV. Switches in the BSV send position signals to
both EEC channels.
The EEC uses these inputs to find fuel/air ratio in the combustor:
* T3 (high pressure compressor discharge temperature)
* PS3 (high pressure compressor discharge pressure)
* FMV position (fuel flow)
* N2 speed
* Air/ground signal from DEU.
The EEC controls the BSV based on fuel air ratio. At low fuel/air
ratios, the EEC energizes the BSV solenoid in the HMU. The
HMU then sends servo fuel pressure to close the BSV. The
closed BSV stops metered fuel flow to the staged fuel nozzles.
Metered fuel goes only to the unstaged nozzles in the
combustion chamber. In this condition, each of the 10
unstaged fuel nozzles supply more fuel to the combustor. The
higher flow of fuel in each nozzle causes a stronger spray
pattern. The stronger spray pattern helps prevent engine flame
out in rain, snow, and ice conditions.
At higher fuel/air ratios, the EEC deenergizes the BSV solenoid
in the HMU. The HMU removes servo fuel pressure from the
BSV. The BSV opens and metered fuel goes to the staged fuel
nozzles. Metered fuel now flows to all 20 nozzles in the
combustion chamber.
The BSV has an override function. An override valve causes the
BSV to open at higher fuel flows when the BSV is commanded
closed by the HMU. The high fuel pressure associated with high
fuel flow causes the override valve to block the return flow of
BSV control fuel. The fuel pressures on each side of the BSV
shuttle valve become equal. This lets the spring move the
shuttle valve to the open position. The override valve makes
sure the engine provides the commanded thrust if the BSV is
incorrectly commanded closed.
The EEC always commands the BSV open for these conditions
(unstaged):
* N2 speed less than 55%
* N2 speed greater than 80%
* Engine at steady state on the ground
* EEC cannot read the BSV position.
The EEC finds a no dispatch condition and sends a signal to the
DEU when one of these failures occur:
* BSV failed in the closed position
* Control current to the BSV solenoid out of range and EEC in
single channel operation.
　
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