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bleed air manifold, upstream of the precooler. Functioning as a
bleed-off anticipator, it responds to the rate of temperature change,
not the temperature change itself. Rapid heating of the sensor
causes an internal ball to become unseated which, in turn, bleeds off
a portion of the pneumatic signal that modulates the HP bleed air
pressure regulator and shutoff valve. This action prevents excessive
overshoots of the HP bleed air pressure regulator and shutoff valve
and bleed air temperature sensor combination which may cause
unstable control.
(3) Precooler Outlet Temperature Sensor:
The precooler outlet temperature sensor is installed in the bleed air
manifold, downstream of the precooler. As part of the engine fan air
control system, it works in conjunction with the precooler
temperature control anticipator sensor, the precooler outlet
temperature controller and the precooler fan air modulating valve’s
servo air pressure regulator and torque motor to maintain engine fan
airflow through the precooler at the desired amount. As the bleed air
manifold temperature changes, the sensor reacts accordingly by
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-36-00
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October 11/02
Revision 8
changing resistance. This change in resistance is transmitted to the
precooler outlet temperature controller, which in turn will change the
output voltage to the servo air pressure regulator and torque motor.
The servo air pressure regulator and torque motor then changes the
electrical signal to a pneumatic signal to position the precooler fan
air modulating valve accordingly. The temperature sensors (as well
as the temperature controllers and servo air pressure regulator and
torque motors) receive power from the Essential 28V DC bus
through the L BLEED AIR and R BLEED AIR circuit breakers,
respectively.
(4) Precooler Temperature Control Anticipator Sensor:
The precooler temperature control anticipator sensor is also
installed in the bleed air manifold, downstream of the precooler. Like
the bleed air temperature anticipator sensor, it responds to the rate
of temperature change, not the temperature change itself. This
prevents excessive overshoots of the fan air modulating valve and
precooler outlet temperature sensor combination which may cause
unstable control. The anticipator’s outputs, combined with the
precooler outlet temperature sensor outputs, are used by the
precooler outlet temperature controller to create an electrical signal
for the precooler valve servo air pressure regulator and torque motor
which, in turn, controls the precooler fan air modulating valve. The
temperature anticipator sensors receive power from the Essential
28V DC bus through the L BLEED AIR and R BLEED AIR circuit
breakers, respectively.
(5) Bleed Air Overpressure Switch:
A bleed air overpressure switch is installed in the bleed air manifold
duct to provide input signals when manifold pressures reach 75±5
psi. When this threshold is reached, an amber L-R BLEED PRESS
HI caution message is displayed on CAS. The switches receive
power from the warning lights power system.
(6) Bleed Air Pressure Transmitter:
A bleed air pressure transmitter (transducer) is installed in the bleed
air manifold duct to provide input signals to the bleed air pressure
indicator’s digital readout of the bleed air system pressure. The
transmitter also provides input signals used to present the L/R
BLEED AIR PRESS readings on the APU/BLEED and ENGINE
START system pages. The transmitters and the indicators receive
power from the Essential 28V DC bus through the L BLEED AIR IND
and R BLEED AIR IND circuit breakers, respectively.
(7) Bleed Air Overtemperature Switch (550°F):
A bleed air overtemperature switch is installed to alert the crew
when manifold bleed discharge temperatures reach 550°F (288° C).
When this threshold is reached, an amber L-R BLEED AIR HOT
caution message is displayed on CAS. The switches receive power
from the equipment overheat protection system.
F. Bleed Air Isolation Valve:
Located in the tail compartment, the bleed air isolation valve is installed in
the crossover duct between the left and right bleed air manifolds. It
OPERATING MANUAL
2A-36-00 PRODUCTION AIRCRAFT SYSTEMS
Page 6
October 11/02
Revision 8
provides a means to isolate the left and right side pneumatic systems when
closed (its normal position). Conversely, when open, it joins the left and
right side pneumatic systems, allowing the use of APU bleed air for both
ECS packs during two pack air conditioning operations. In addition, it
　
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