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moves a ball valve that prevents air pressure from going to the
actuator to open the valve.
When the pack switch is in the AUTO or HIGH position, solenoid
C receives power to the open coils. The pressurized air flows to
the actuator. It pushes against spring force in the actuator to
open the butterfly plate (valve open). When the valve opens, air
flows to the static pressure sense port and the downstream
(total pressure) sense port.
The static and total pressure sense ports balance actuator
opening pressure for the auto and high flow servos. These ports
permit a measure of differential pressure in the venturi which
corresponds to the rate of airflow.
Solenoid B changes flow modes between the normal flow and
the high flow modes. It energizes when the pack switch is in the
AUTO position. This lets air flow to the auto flow servo (normal
flow mode). The auto flow servo controls flow rate as cabin air
pressure changes. The cabin pressure sense port provides a
cabin air pressure signal to the auto flow servo internal bellows.
This allows the flow control and shutoff valve to maintain the
desired flow rate as cabin pressure decreases. Normal flow
mode has an airflow rate of 75 pounds per minute (ppm).
When the pack switch is in the HIGH position, solenoid B deenergizes
(high flow mode). Actuator air flows to the APU/high
flow servo. The high flow servo has a strong bias to close. This
will let more air pressure go to the valve actuator. This
increases airflow. High flow mode is 105 ppm.
In cruise, if a pack shuts down from an overheat or if a (L or R)
pack switch is OFF, solenoid B de-energizes. This sets the
operating pack to high flow mode.
The APU high flow mode energizes solenoid A. The APU /high
flow servo has one more actuating piston than high flow. This
results in a higher spring-bias to close the servo. This lets more
pressure go to the valve actuator. APU/high flow mode has an
airflow rate of 131 ppm.
AIR CONDITIONING - COOLING - FLOW CONTROL AND SHUTOFF VALVE - MECHANICAL FUNCTIONAL DESCRIPTION
EFFECTIVITY
GUN 001-099, 201-999 21-50-00
Page 83
D633A101-GUN Oct 10/2005
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
21-50-00-807
Training Information Point
A manual control shaft on solenoid C lets you open the solenoid
manually.
The flow control and shutoff valve cabin pressure sense port is
connected by a sense line to an open port in the distribution
bay. This port must be clean for the flow control and shutoff
valve to properly control airflow.
AIR CONDITIONING - COOLING - FLOW CONTROL AND SHUTOFF VALVE - MECHANICAL FUNCTIONAL DESCRIPTION
EFFECTIVITY
GUN 001-099, 201-999 21-50-00
Page 84
D633A101-GUN Oct 10/2005
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
21-50-00-807
AIR CONDITIONING - COOLING - FLOW CONTROL AND SHUTOFF VALVE - MECHANICAL FUNCTIONAL DESCRIPTION
AIR CONDITIONING - COOLING - FLOW CONTROL AND SHUTOFF VALVE - MECHANICAL FUNCTIONAL DESCRIPTION
EFFECTIVITY
GUN 001-099, 201-999 21-50-00
Page 85
D633A101-GUN Oct 10/2005
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
21-50-00-807
Pack Switch OFF
When the pack switch is in the OFF position, 28v dc (battery bus)
energizes the close coil of solenoid C. When the close coil is
energized, the flow control and shutoff valve is closed.
Pack Switch AUTO
When the pack switch is in the AUTO position, 28v dc energizes
the open coil of solenoid C. When open coil of solenoid C is
energized, the FCSOV opens. This also moves a position switch
to open. The position switch gives a discrete signal to these
systems:
* Flight management computer system
* Common display system
* Pressurization system
* Temperature control system
* Recirculation system.
When either engine bleed switch is on, 28v dc energizes
solenoid B through the low flow mode relay (K18).
When solenoid B is energized, the FCSOV operates in the low
flow mode.
Solenoid B deenergizes when K18 energizes. K18 energizes
when both engine bleed switches are in the OFF position.
Also, solenoid B deenergizes when these things occur:
* Airplane in the air (the pack air/gnd relay (K10) goes to the
AIR position)
* Flaps up (the flap not up relay (K19) goes to the UP position).
When solenoid B deenergizes, the FCSOV operates in the high
flow mode.
Pack Switch HIGH
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