Engine Gravel Protection Valve Installation 528
75-09-111 Figure 401 Nov 15/69
Page 402
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
ENGINE AND NOSE COWL ANTI-ICING - DESCRIPTION AND OPERATION
1. General
A. A thermal anti-icing system using engine bleed air is provided to prevent the formation of ice on the engine inlet nose cowl, nose dome, compressor inlet case and inlet guide vanes. There is a separate and independently controlled system for each engine.
B. The engine nose cowl leading edge is anti-iced by 13th-stage engine bleed air controlled by a thermostatic valve, a shutoff valve and tempered with ambient air by the use of an injector. The engine inlet nose dome, compressor inlet case and inlet guide vanes are anti-iced by 8th-stage engine bleed air controlled by fixed orifice plates and shutoff valves (Fig. 1). The three shutoff valves for each engine are controlled by a single switch so that the engine and the nose cowl anti-icing systems operate simultaneously. The switches and VALVE OPEN lights are located on the forward overhead panel.
2. Engine Anti-Icing Air Valve
A. An engine anti-icing air shutoff valve is provided in each of the two plumbing lines which supply 8th-stage engine bleed air to the inlet guide vanes and nose dome. The valves are located at the 11 o'clock, and 1 o'clock positions aft of the inlet guide vane case.
B. Each anti-icing air valve is motor -operated and when energized, drives to the fully open or closed position as determined by the control switch selection. The valve has an indicator which can be used during maintenance to determine valve position.
3. Nose Cowl Anti-Icing Air Valve
A. A nose cowl anti-icing air valve is provided in the plumbing line which supplies 13th-stage engine bleed air for anti-icing the nose cowl. The valve is located at approximately, the 4 o'clock position aft of the nose cowl.
B. The valve is motor-operated and when energized drives to the fully open or fully closed position as determined by the control switch selection. The valve has an override handle for manually positioning the valve and can be used also during maintenance to determine valve position.
4. Engine Anti-Icing Air Orifice
A. An orifice plate is located on the upstream side of each engine anti-icing air valve as a fixed part of the rear anti-icing tube assemblies. The orifice plates limit the volume of anti-icing air supplied to the inlet guide vane assembly. This keeps the guide vane assembly from becoming too hot preventing excessive temperature of the engine inlet air.
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May 15/72 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 75-11-0 Page 1
Engine and Nose Cowl Anti-Icing Component Location 511
75-11-0 Figure 1 Nov 01/74
Page 2
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
5. Nose Cowl Anti-Icing Thermostatic Valve
A. The nose cowl anti-icing thermostatic valve is located on the downstream side of the nose cowl anti-icing valve. The thermostatic valve limits the volume of anti-icing air supplied to the nose cowl. The valve opening is controlled by bi-metallic coils connected to a moving sleeve. The extent and direction of movement is in accord with the expansion or contraction of the coils caused by variation in temperature. The rotation of the sleeve covers or uncovers holes in the valve housing, thus forming a variable orifice controlling the flow of air.
6. Operation
A. The nose cowl and engine anti-icing systems use hot air bleed from the engine compressor section. The shutoff valves, for each engine, are operated by a single switch located on the forward overhead panel. (See figure 2.)
B. When the engine anti-icing air valves are opened hot air circulates around the engine inlet guide vane assembly. The air passes through each inlet guide vane and into the inner shroud which forms part of the engine front bearing hub. The air passes from the front hub into the engine nose dome and exhausts, through a slot, into the engine inlet air stream. The hot air passing through the valves is controlled by a fixed opening or orifice plate upstream of the valves.
C. When the nose cowl anti-icing air valve is opened hot air passes through the thermostatic valve and through the injector where it draws ambient air and then enters the nose cowl. At the injector, the hot air mixes with the lower temperature ambient air producing an air mixture warm enough to prevent icing of the nose cowl structure. The air mixture is directed against the interior surfaces of the nose cowl by means of a perforated distribution tube. The air is then exhausted through an opening at the bottom of the cowl.
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