CAUTION:  DO NOT ALLOW ADAPTER ASSEMBLY TO FALL, DAMAGE TO WING SKIN OR FUEL TANK SEALING MAY RESULT.

(4)  
Slide port adapter assembly from between fuel line flanges and lift clear.

D.  Install Defueling Valve Port Adapter Assembly (Fig. 401)
(1)  
Clean O-ring grooves and machined surfaces of port adapter, fuel line flanges, and front spar with naphtha and wipe dry with lint-free cloth.

(2)  
Install new O-rings, lightly lubricated with fuel into grooves on port adapter assembly.

(3)  
Carefully slide port adapter assembly into position between fuel line flanges.

CAUTION:  DO NOT DISLODGE OR PINCH O-RING WHEN INSERTING PORT ADAPTER ASSEMBLY.

(4)  
Install bolts attaching fuel line flanges to adapter assembly.

(5)  
From outside fuel tank, install port adapter assembly mounting bolts and washers and torque 100 to 140 pound-inches.

(6)  
Perform steps 3.D.(1) thru 3.D.(4) to install gate assembly.

E.  Restore Airplane to Normal Configuration
(1)  
Install fuel tank access panel (Ref 28-11-11 R/I).

(2)  
Close defueling valve access panel.

500 
28-23-11 Page 404  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Nov 15/67 

FUEL QUANTITY INDICATING SYSTEM - DESCRIPTION AND OPERATION
EFFECTIVITY
Airplanes with Non-Precalibrated Indicators
1. General
A.  The fuel quantity indicating system measures the weight of usable fuel in the fuel tanks. Three fuel quantity indicators on the pilots' center instrument panel (P2) and three indicators at the fueling station provide visual indication of the fuel weight in each of the three tanks. In addition, a fuel summation unit located on the first officer's auxiliary panel P23 provides continuous three-tank summation signal input to an on-board computer where it is converted to an on-demand display of combined tank total remaining fuel or is used by the computer in various performance parameters. In each of fuel tanks No. 1 and 2, five fuel measuring sticks are provided to determine fuel quantity of the respective tank by mechanical means.
B.  System components are located in the control cabin, in the fuel tanks, and at the fueling station (Fig. 1). Control cabin components consist of three fuel quantity indicators, one fuel summation unit, and a fuel quantity indicators press-to-test switch. Fuel tank components consist of tank units, compensator units and fuel measuring sticks. Three fueling quantity indicators and a fueling quantity indicators test switch are located at the fueling station. The fueling quantity indicators are interchangeable with the corresponding fuel quantity indicators located on pilots' center instrument panel (P2) provided they are recalibrated to their new location.
C.  The overall system is composed of three subsystems, one for each tank. Each subsystem consists of a fuel quantity indicator, a fueling indicator, a compensator unit and a number of tank units. The tank units in each tank are connected in parallel and positioned so that only usable fuel is measured. Fuel is the variable dielectric. Capacitance values of the tank units in each tank are added to give a single capacitance value, which is transmitted to each fuel quantity indicator. The fuel quantity indicator shows continuously the weight of fuel remaining in the tank. The fueling quantity indicators on the fueling control panel repeat the fuel quantity shown by the fuel quantity indicators in the control cabin. The fueling quantity indicators operate only when fueling station door is open.
5C8
Feb 20/89 28-41-0 Page 1
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

K84817
Fuel Quantity Indicating System Component Location  5A7 
28-41-0  Figure 1 (Sheet 1)  Sep 20/81 
Page 2 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

581  Fuel Quantity Indicating System Component Location 
May 15/79  Figure 1 (Sheet 2)  28-41-0 
Page 2A/2B 
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G43290
580  Fuel Quantity Indicating System Component Location 
Oct 20/92  Figure 1 (Sheet 3)  28-41-0 
Page 3 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

2.  Tank Units
A.  The tank units are cylindrical capacitors mounted throughout each fuel tank to sense fuel level variations and, as a result of capacitance change, transmit electrical signals to the fuel quantity indicators (Fig. 1). The tank units consist of two coaxial cylinders rigidly spaced at intervals throughout their length by insulating centering spacers. The inner electrode is a variable diameter tube of electroformed nickel alloy and is connected to the amplifier input. The outer electrode is an aluminum alloy tube of constant diameter and is connected to the 400 -Hz excitation voltage lead. The diameter of the inner electrode is profiled to provide an output signal linear with respect to the volume of fuel in the tank. Openings at the ends of tank units allow fuel to assume the same level between the two cylinders as that in the fuel tank. Tank units are located in the fuel tanks so that errors due to airplane attitude are kept to a minimum.
　
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