(a)
Electrical: The wiring which drives the No. 3 reserve tank valves open, is opposite compared with the No. 2 reserve tank wiring.
(b)
Mechanical: Each adapter plate for the No. 3 reserve tank is rotated 90 degrees on the rear spar and the actuator is installed with the valve closed. Use the OPEN and CLOSED indication on the adapter plate when you use the manual override lever. Do not use the OPEN/CLOSED indication on the valve actuator.
3. Reserve Tank Transfer Check Valve (Fig. 1)
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A. The reserve tank transfer check valve prevents a reverse flow of fuel through the valve when the valves are open. The check valve consists of a valve body and a hinged flapper. The valve is installed on the outlet of the transfer line in the inboard main tank.
4. Reserve Tank Transfer Single Point Sensor
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A. The single point sensor provides a signal to the single point sensor (SPS) control card when the fuel quantity in the inboard main tank decreases below 40,200 lbs (18,200 kgs).
B. A single point sensor is located at the inboard end of each inboard main tank, installed on a mounting bracket with a cover bracket over it. A sensor consists of two concentric metallic cylinders, spaced to allow fuel between them; a mounting clamp; and wire leads (HI-Z, HI-Z SHIELD, and LO-Z) that extend from the sensor and connect to a terminal block on the mounting bracket.
C. The sensor is excited by the single point sensor (SPS) control card through the LO-Z lead. The resultant HI-Z capacitive current, which varies with fuel level between the sensor cylinders, is measured by the control card.
5. Reserve Tank Transfer Single Point Sensor Control Card
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A. The single point sensor (SPS) control card provides a low fuel signal to the fuel management system to initiate reserve tank fuel transfer.
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B. The SPS control card is a single-board printed circuit assembly installed in a slot in the fuel system card file. The card is retained in the card file by two captive screws that thread into holes in the card file. The card is easily replaced - no special tools are required. The card is located in the fuel system card file at file position A2 (equipment number Y5BA02).
C. The SPS control card operates two independent channels - one for the sensor in No. 2 main tank and the other for the sensor in No. 3 main tank. Each channel excites its sensor, measures sensor capacitance, and provides a discrete output to the fuel system management card. When the sensor capacitance indicates a fuel quantity greater than 6,000 gallons (22,712 liters), the output signal is absent (off). When the fuel quantity decreases to 6,000 gallons (22,712 liters), the output signal is activated (on).
D. The card contains two LEDs to indicate the status of the output signals from the channels. If the LED is illuminated, the sensor is not immersed in fuel and the output signal is on. If the LED is extinguished, the sensor is immersed in fuel and the output signal is off. A fail-safe circuit in the card ensures that the LEDs are extinguished (output signal is off) if the card fails, loses power, or loses the sensor signal.
E. Operation of the control card can be tested from the flight deck or at the fuel system card file. The flight deck test is accomplished by initiating the CMCS BITE for the control cards from any CDU. Both channels of the card are tested. An individual channel of the card can be tested locally using the two test switches on the front of the card. The BIT switch changes the state of the output signal to test the operation of the LED. The FAIL SAFE TEST switch provides a test of the fail-safe circuit in the card.
6. Main Tank Transfer Valve (Fig. 1)
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A. The main tank transfer valves are used to transfer fuel from No. 1 and No. 4 main tanks to No. 2 and No. 3 main tanks when dumping fuel through the jettison system. The valves are located in the outboard end of the inboard main tanks.
B. The valves consist of a valve body installed in the fuel tank, an electric motor-driven actuator installed on the aft side of the rear spar, and an adapter/shaft assembly connecting the actuator with the valve body.
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