Page 1 D633W101-BEJ Sep 05/2002

AIR CONDITIONING -PACK FLOW CONTROL -INTRODUCTION

Engine Bleed System Bias
For some low flow conditions, the flow control system sends signals to the pneumatic system. These signals adjust the engine bleed air temperature or HPSOV set-point. Lower bleed air temperature lets the pack operate with less restriction to air flow. A higher HPSOV set point lets the pneumatic system supply more air at low engine power settings.
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AIR CONDITIONING -PACK FLOW CONTROL -INTRODUCTION

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AIR CONDITIONING -PACK FLOW CONTROL -GENERAL DESCRIPTION

General
The CTC and ASCPC have interfaces with the flow control components and with some of the pack temperature sensors. The CTC and ASCPC measure the pack air flow, control the flow control and shutoff valves, and monitor pack temperatures.
CTC Functions
If the APU is on, the CTC closes the lower valve and opens the upper valve. The APU controller controls air flow to the packs. If the APU is not on, the CTC adjusts the valves to control pack air flow.
The upper valve controls flow at low altitudes. The lower valve controls air flow at high altitudes. If the upper or lower valve fails, the other valve controls flow at all altitudes.
The CTC uses data from the pack flow sensor to measure the volume of air going into the pack. With data from the primary heat exchanger inlet temperature sensor, the CTC calculates the mass air flow to the pack. The CTC uses air flow data to control and monitor the operation of the valves.
The CTC closes the upper and lower valves if any of these conditions occur:
*
Pack switch OFF

*
Flow schedule 0

*
Compressor discharge overheat

*
Pack outlet overheat

*
Pack failure.

ASCPC Functions
The ASCPC closes the upper and lower valves if any of these conditions occur:
*
Pack switch OFF

*
Stall warning

*
Compressor discharge overheat.

For these conditions, the valve close signals are redundant with the CTC valve close signals.
If the CTC fails or looses power, the ASCPC gives backup flow control. The upper valve closes and the lower valve controls. For backup up flow control, it is necessary to have valid data from the pack outlet and compressor discharge temperature sensors inside the pack. An overheat condition at either temperature sensor closes the valves.
The ASCPC sends one of five flow schedules to the CTC. The CTC uses the flow schedule data to make decisions about the amount of air to send to the packs. A stall warning or ground engine start condition causes the ASCPC to send flow schedule
0. The CTC closes the flow control and shutoff valves for flow schedule 0.
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AIR CONDITIONING -PACK FLOW CONTROL -GENERAL DESCRIPTION

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AIR CONDITIONING -PACK FLOW CONTROL -COMPONENT LOCATIONS

Component Locations
Each pack has these flow control components in the ECS bay:
*
Primary heat exchanger inlet temperature sensor

*
Lower flow control and shutoff valve

*
Pack flow sensor

*
Upper flow control and shutoff valve.

The components are interchangeable between packs.
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AIR CONDITIONING -PACK FLOW CONTROL -COMPONENT LOCATIONS

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AIR CONDITIONING -PACK FLOW CONTROL -FLOW CONTROL AND SHUTOFF VALVES

Purpose
The flow control and shutoff valves control the air flow to the packs.
Physical Description
The upper and lower flow control and shutoff valves are interchangeable. These are the parts of the valve:
*
A proximity switch

*
A locking plug

*
A locking crank/position indicator

*
A pneumatic actuator

*
A disc

*
Two torque motors.

Functional Description
The flow control and shutoff valves operate by a pneumatic actuator which moves the disc in the valve. If there is no air pressure from the pneumatic system, a spring in the actuator closes the valve.
With no power to the torque motors, the connections to ambient air pressure close. Supply pressure pushes the valve open against the force of the spring in the actuator.
　
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