Mod : 4584
ATR 42 Model : 400/500
PNEUMATIC SYSTEM
AIR
P 2
NOV 99
100
1.03
.
20
CROSSFEED
The crossfeed valve installed on the crossfeed duct is designed to connect LH and RH
air lbeed systems.
- On the ground, it is always open except when both engines are running and
propeller brake is disengaged.
- In flight, the crossfeed valve is normally closed. This is a spring loaded closed,
solenoid controlled, pneumatic shut off valve. The valve is closed with solenoid
deenergized.
LEAK DETECTION SYSTEM
A continuous monitoring system is installed in order to detect overheat due to duct
leakage and to protect the structure and components in the vicinity of hot air ducts :
- Wing leading edge and wing to fuselage fairing,
- Upper and lower fuselage floor,
- Air conditioning pack area.
In order to ensure rapid leak sensing, a Kevlar envelope is installed around the major
part of the high temperature ducts to collect and direct leaking air to the sensing
elements.
The sensing system includes two single loop detection assemblies, one for the RH
and one for the LH air duct systems.
The sensing elements comprise a control lead (nickel wire) embedded in an insulating
material and are integrated in an inconel tube connected to aircraft ground.
Each sensing element is permanently subjected to the temperature of the
compartment it protects. For any temperature higher than a preset value : 153
°
C
(307
°
F) applied to a part of the sensing element, the resistance of the eutectic mixture
rapidly decreases and the central lead is grounded. This results in an alert signal
processed in a control unit which triggers illumination of LEAK It. After one second
time delay, the associated pack valve, HP valve and BLEED valve (and GRD X FEED
valve if the left loop is affected) are automatically latched closed.
Note : In case of LEAK, the crew must consider the associated bleed system as
inoperative for the rest of the flight.
OVERHEAT CONTROL SYSTEM
This system includes switches (thermal resistances) which are installed on the
engines, near the HP compressors exit.
These switches, which are duplicated for safety, ensure that the bleed valve and the
bleed air shut-off valve are closed whenever any abnormal over temperature
conditions occur. They operate at 274
°
C (525
°
F) and are controlled by the MFC.
Note : In case of OVHT, the associated bleed system may be recovered after a
cooling time.
AA
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