H31557
542  Gearbox to Oil Cooler Tube Installation 
Feb 01/76  Figure 401 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  79-21-71 Page 401 

OIL COOLER BYPASS VALVE - REMOVAL/INSTALLATION
1.  Remove Fuel/Oil Cooler Bypass Valve
A.  Remove locknuts and washers and remove bypass valve cover.
B.  Remove bypass valve assembly from valve cavity in oil cooler housing.
C.  Remove retaining ring and separate spring seat, spring, and valve from bypass valve seat.
2.  Install Fuel/Oil Cooler Bypass Valve
A.  Assemble valve, spring, and spring seat inside bypass valve seat and secure with retaining ring.
B.  Install new packing on bypass valve assembly and install valve assembly in oil cooler housing.
C.  Install cover, with new packing, on valve cavity and secure with washers and nuts.
500 
Aug 15/79  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  79-21-81 Page 401 

OIL COOLER BYPASS VALVE - INSPECTION/CHECK
1.  Inspection
A.  Check seating and sealing surfaces of bypass valve, valve seat, and spring seat which could impair function or sealing.
500 
Aug 15/79  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  79-21-81 Page 601 

OIL COOLER BYPASS VALVE - CLEANING/PAINTING
1.  Cleaning
A.  Clean all bypass valve parts in petroleum solvent (Varsol or equivalent) and dry with compressed air.
500 
Aug 15/79  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  79-21-81 Page 701 

OIL QUANTITY INDICATING SYSTEM - DESCRIPTION AND OPERATION
1.  General
A.  Engine oil quantity may be measured by use of a dipstick, attached to the engine oil tank manual filler cap, or by an electrically operated remote quantity indicating system.
B.  The remote oil quantity indicating system, for each engine, consists of a variable capacitance tank unit probe electrically connected to an indicator, on the center instrument panel, to form a self-balancing capacitance bridge circuit. (See figure 1.) A change in oil level alters the tank unit capacitance, creating an unbalanced condition in the bridge circuit. The resulting flow of current is amplified and used to actuate a servo motor which positions a potentiometer wiper in the indicator to rebalance the circuit. The indicator dial pointer is connected to the potentiometer wiper in the indicator to rebalance the circuit. The indicator dial pointer is connected to the potentiometer wiper and moves with the wiper to provide the oil quantity indication.
C.  A single PUSH-TO-TEST switch is used to check the operation of both remote quantity indicating systems simultaneously.
2.  Oil Quantity Tank Unit
A.  The oil quantity tank unit is an assembly that contains an electrical plug, a flange and probe. The probe is the capacitance part of the tank unit. It is also comprised of two separate capacitors. One is a quantity (depth) measuring capacitor, the other is a compensator unit which minimizes the effect of change in oil dielectric due to temperature or variations in composition.
B.  The upper section of the tank unit consists of two concentric electrodes insulated from each other by plastic centering spacers. The inner electrode is a plastic tube with two separate metallic areas printed on its surface. One area is active and is connected to the amplifier input of the quantity indicator. The other area borders against the active pattern and is grounded to prevent an electrostatic fringe forming around the active area. The outer electrode is an aluminum tube with an insulating finish on its outer surface.
C.  The lower, or compensator, section of the tank unit consists of two short tubular members separated by an air gap and insulated from each other. Since the compensator is at the lower end of the tank unit it will remain submerged to the lowest usable level of oil.
505 
May 01/03  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  79-31-0 Page 1 

H27804
Oil Quantity Indicating System  541 
79-31-0  Figure 1  May 01/03 
Page 2 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

D.  The lower end of the tank unit is open and permits oil to flow between the electrodes to the same level as that in the tank. The oil between the electrodes provides the variable dielectric which is the controlling factor of the system.
　
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