C. In the static position (engine not running) bleed valves may be either open or closed, depending upon gravity and/or drag caused by contact of the valves with the cylinder walls. During periods of engine operation, compressor discharge air pressure exerted on the valve faces acts to force valves into the open position.
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Bleed System Schematic -Closed 500
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500 Bleed System Schematic -Closed
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Bleed System Schematic -Open 500
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500 Bleed System Schematic -Open Oct 20/83 (Incorporating P&WA SB 5425) 75-31-0 Figure 2 (Sheet 2) Page 5 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
Bleed Control Start Valve
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P&WA 75-30, Page 7/8, Sep 01/83
D. Pressure Ratio Bleed Control: When Ps3 pressure on one side of the diaphragm in the pressure ratio bleed control increases to the point where it overcomes combined Pt2 and spring pressure forces, the poppet valves in the control reverse position, the muscle valve transfers, and Ps4 actuating air is directed to the back side of bleed valves. This Ps4 air acting on the larger area of the back side of the valves is sufficient to overcome compressor discharge air acting on the valve faces and the valves close. When the Ps3/Pt2 differential pressure decreases, the procedure is reversed. Ps4 actuating pressure on the back side of the valves is reduced to ambient, and internal engine pressure forces bleed valves open.
E. Start Bleed Control Valve: With engine shut down or starting up, spring pressure forces a poppet valve closed. As Ps4 pressure increases during starting cycle, valve closing pressure is overcome and Ps4 air proceeds into the engine, closing the 13th stage bleed valve.
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COMPRESSOR BLEED SYSTEM - INSPECTION/CHECK
1. Periodic Inspection
A. General
(1)
These inspection procedures are a normal function of operating organizations. They consist of required inspections and minor adjustments necessary on the JT8D engine. The nature and conditions of engine operation determine the time interval between required inspections. For this reason, the intervals described in the Periodic Inspection Chart in this section are labeled Routine, Minor, and Major.
(2)
Engine compartment cleanliness is important because the extensive mass air flow tends to draw foreign objects into the engine. Thoroughly clean the entire engine compartment with a vacuum cleaner after completion of any work. Keep the compartment free of dirt, oil, and grease, and remove all unused parts, such as nuts, washers, and pieces of lockwire. Immediately cover all apertures resulting from disconnection of tubing or parts. Use external caps on all tube openings, not internal plugs.
(3)
Carefully inspect the compressor bleed system without dismantling to ensure that all connections are tight and free from leaks and that lines, tubing, and controls are secure.
B. Periodic Inspection Chart
COMPRESSOR BLEED SYSTEM
Component Nature of Inspection Inspection Time Remarks
Routine Minor Major
Pressure Ratio Bleed Control Pressure Ratio Bleed Control Ps3 Pressure Air Supply Strainer, P/N 44056, (Located in Fitting on Front of High Pressure Bleed Pad at 11 o'clock Position) a. Security of Mounting. b. Security of Accessible lines and fittings. a. Foreign matter; strainer damaged X X X X X Replace strainer, or if serviceable, clean with a standard solvent then dry with compressed air.
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COMPRESSOR BLEED SYSTEM - INSPECTION/CHECK
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