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737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
36-11-00-211
PNEUMATIC - ENGINE BLEED AIR - BAR AND PRSOV
PNEUMATIC - ENGINE BLEED AIR - BAR AND PRSOV
EFFECTIVITY
GUN ALL 36-11-00
Page 15
D633A101-GUN Jun 10/2003
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
36-11-00-211
Purpose
The 450F (232C) thermostat bleeds off pressure that operates
the pressure regulator and shutoff valve (PRSOV). This occurs
when engine bleed air temperature is more than 450F (232C).
The 450F (232C) thermostat supplies the PRSOV a temperature
control function.
Physical Description
The 450F (232C) thermostat has these parts:
* Ball valve assembly with a sense line connection
* Mounting flange with index pin
* Shielded sensor.
Location
The 450F (232C) thermostat is in the engine bleed air duct.
Access is through a strut access panel.
Functional Description
The 450F (232C) thermostat operates by thermal expansion of a
fluid. The thermostat sensor is in the bleed air duct downstream
of the precooler. This portion of the thermostat has oil filled
coils. As the oil expands, it pushes the ball valve open. The
higher the duct temperature, the more the oil expansion, and
the more the ball valve opens. The 450F (232C) thermostat
starts to open at 450F (232C) and is full open by 490F (254C).
When the ball valve is open, control pressure is bled from the
PRSOV. The reduction in control pressure causes the PRSOV to
move toward closed and reduces the flow of bleed air. The
lower flow of bleed air has these effects:
* Decreases the thermal load on the precooler
* Delays a 490F (254C) overtemperature bleed trip off
condition
* Decreases duct pressure.
The precooler system normally controls engine bleed air
temperature to 390-440F (199-227C). The 450F (232C) thermostat
supplies a temperature limit function to the PRSOV.
Training Information Point
Nonstop operation of the 450F (232C) thermostat (and the
resultant low duct pressures) can result from a dirty or clogged
precooler. Nonstop operation can also be caused by a defective
precooler control system.
PNEUMATIC - ENGINE BLEED AIR - 450F THERMOSTAT
EFFECTIVITY
GUN ALL 36-11-00
Page 16
D633A101-GUN Jun 10/2003
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
36-11-00-214
PNEUMATIC - ENGINE BLEED AIR - 450F THERMOSTAT
PNEUMATIC - ENGINE BLEED AIR - 450F THERMOSTAT
EFFECTIVITY
GUN ALL 36-11-00
Page 17
D633A101-GUN Jun 10/2003
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
36-11-00-214
Purpose
The BAR, PRSOV, and 450F thermostat regulate bleed air
pressure and temperature.
Functional Description
The BAR gets unregulated air from the interstage manifold. The
unregulated air goes to the overpressure switch and to the
reference pressure regulator.
The reference pressure regulator decreases the pressure to a
constant control pressure. The control pressure then goes to a
relief valve and a latching solenoid.
The relief valve prevents damage to the PRSOV if the reference
pressure regulator fails.
The latching solenoid controls the flow of air to chamber A of
the PRSOV actuator and the 450F thermostat. The PRSOV
actuator opens the valve against spring force and pressure in
chamber B. The combination of forces on the actuator cause the
valve to regulate the downstream pressure to 42 psi (nominal).
The 450F thermostat monitors the temperature of the engine
bleed air. If the temperature increases to 450F (232C), the 450F
thermostat opens and bleeds off control pressure to the PRSOV.
The decrease in control pressure causes the PRSOV to move
towards closed and decreases the flow of bleed air.
GUN 018
The overpressure switch is a safety device. If supply air to the
BAR gets to 180 psi, the switch closes and causes a bleed trip
off condition.
GUN 001-017, 019-099, 101-118, 201-999
The overpressure switch is a safety device. If supply air to the
BAR gets to 220 psi, the switch closes and causes a bleed trip
off condition.
GUN ALL
PNEUMATIC - ENGINE BLEED AIR - BAR, 450F THERMOSTAT, AND PRSOV - FUNCTIONAL DESCRIPTION
EFFECTIVITY
GUN ALL 36-11-00
Page 18
D633A101-GUN Oct 10/2006
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
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