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757 MAINTENANCE MANUAL
 WING THERMAL ANTI-ICING - DESCRIPTION AND OPERATION
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 1.  General_______
 A.  Engine bleed air provides inflight thermal anti-icing to three outboard slats on each wing. System components include: wing thermal anti-ice (TAI) valves, telescoping ducts, spray tubes, wing and engine anti-ice control panel, and a test panel.
 B.  System electrical power comes from a DC bus, through a circuit breaker on overhead circuit breaker panel P11.
 2.  Component Details (Fig. 1)_________________
 A.  Wing Thermal Anti-Ice (TAI) Valve
 (1)  
The wing TAI valve controls the flow of engine bleed air into the leading edge anti-ice ducts. One valve is located above the strut position in each wing. The valve is set to keep duct air pressure between 20-28 psi.

 (2)  
An indicator on the valve shows when it is CLOSED or NOT CLOSED. The valve can be manually set to the full open or full closed position by rotating a hex head bolt on the valve housing. The valve can only be locked in the closed position.

 (3)  
Energizing the TAI valve solenoid opens an upstream air passage to the actuator diaphragm. Upstream air pressure overcomes the forces of the return spring and the closing diaphragm. The actuator diaphragm opens the valve vane.

 (4)  
De-energizing the TAI valve solenoid closes the upstream air passage to the actuator diaphragm. The actuator diaphragm is vented to ambient air. Upstream air pressure on the closing diaphragm and the return spring close the valve vane. Upstream air pressure keeps the valve vane in closed position.

 (5)  
Downstream (regulated) pressure is sensed by the pilot pressure regulator. If downstream pressure exceeds the adjustment setting of the pilot regulator, a valve bleeds off actuator diaphragm pressure. The closing diaphragm and return spring partially close the valve vane, lowering downstream pressure.

 B.  Telescoping Duct
 (1)  Each wing has a telescoping duct connecting the wing supply manifold to the leading edge distribution duct. Bleed air can be fed to the leading edge slats regardless of slat position.
 C.  Flexible Coupling
 (1)  Flexible couplings join the leading edge ducts where the slats are separated. The couplings allow for alignment errors during slat movements. There are 2 couplings per wing, between the leading edge slats.
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 30-11-00
 ALL  ú ú 02 Page 1 ú Jun 20/95

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