(2)  
Main gearbox drain port

 (3)  
Oil tank drain port (master MCD)

 B.  
The magnetic chip detectors, which includes a housing with an integral check valve and a magnetic probe, serve to catch and remove ferrous metal particles from the oil system.

 10. Fuel/Oil Cooler Bypass Valve and Solenoid (Fig.1)
_________________________________________
 A.  The bypass valve for the fuel/oil cooler includes a solenoid, a slide assembly, and a cartridge valve and housing. It is made to control the flow of engine oil to the fuel/oil cooler when oil cooling is necessary.
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B.  The bypass valve is installed on the bottom of the fuel/oil cooler and includes electromagneticly controlled, three way spool valves, which, when energized, will bypass engine oil around the fuel/oil cooler. The bypass valve is operated by a single dual-coil solenoid, which uses engine oil as servo pressure. Each channel of the electronic engine control (EEC) controls one coil of the solenoids. The solenoid valve is supplied 28 volts dc electrical power by solid state switching in the EEC. A pressure (regulator) relief valve is installed in the engine oil system to bypass the oil in cold start conditions.
 C.  With no electrical signal, the normally closed solenoid operated pilot valve bleeds return pressure for the engine oil to the pilot cavity on the right side of the slide valve for the engine oil system. Because the left side of the slide valve is always bled to engine oil return, the slide valve is pressure balanced during the condition. Oil pressure for the integrated drive generator (IDG) applied on the actuation rod helps the spring which drives the slide valve to the right, which lets normal flow through the engine oil and IDG oil system heat exchangers.
 D.  When the dual-coil solenoid-operated pilot valve is energized, engine oil pressure is bled to the pilot cavity on the right side of the slide valve. Since the left side of the slide valve is bled to return, there is a differential pressure which drives the slide valve and actuation rod against the spring and into the bypass position.
 E.  If the differential pressure between the inlet and outlet of the fuel/oil cooler is more than 50 psid (345 kPad), the force on the relief valve poppet will cause the relief valve spring to collapse, which lets the poppet open and pass the necessary flow from the engine oil inlet to the outlet of the fuel/oil cooler.
 F.  When energy is removed from the two solenoid coils, the spring returns the engine oil system to the non-bypass mode.
 11. Operation
_________
 A.  Functional Description
 (1)  
Engine oil flows from the oil tank to the pressure stage inlet of the lubrication and scavenge oil pump. The pressurized oil then flows to the main oil filter where a pressure relief (bypass) valve opens at 60 psid to keep continuous oil if there is a clogged main oil filter. A differential pressure switch (Ref 79-35-00) supplies flight deck indication of an impending/current filter element bypass condition.

 (2)  
From the main oil filter, the oil flows through a pressure (regulator) relief valve for the oil system which opens at a maximum oil system pressure of 520 psi (3585 kPa).

 (3)  
The oil then goes to the air/oil heat exchanger. The air/oil heat exchanger valve, controlled by the EEC, lets fan discharge air or

 2.5 bleed air go through it for engine oil cooling. The valve stays closed at the fuel temperature of the fuel pump outlet which are less than 118°C, and starts to open (modulates) to hold a constant 119°C fuel temperature. The valve is fully open at fuel temperature more than 119°C for maximum cooling. An internal bypass valve in the air/oil heat exchanger opens at 50 psid (345 kPad) to bypass the exchanger core during cold engine starts.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / PW4000 SERIES /747-400 / ENGINES/MAINTENANCE MANUAL ////////////////////////
　
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