B. Prior to starting actual fueling, the fueling-valve-open light bulbs should be tested by pressing each light cover. If the fueling quantity indicators are being used they should be tested for operation by actuating the fueling indicator test switch. If the indicators are working, operation of the switch will cause the pointer to move towards zero. After completing the check of the instruments, the cap can be removed from the fueling receptacle and the fueling hose connected. Opening the appropriate fueling valves makes the airplane ready to receive fuel. Starting the pumping operation pressurizes the fueling lines, allowing fuel to flow into the tanks (Fig. 2).
C. If external power is connected, the fueling quantity indicators will record the fuel quantity in the tanks. If a partial fuel load is required, the fueling shutoff valves are closed when the indicators show the required amount of fuel is in the tanks. If the fueling shutoff valves are not closed, fuel will continue to flow into the tanks until they are full. When a tank reaches the full condition, the fueling float switch cuts off electrical power to the pressure fueling system shutoff valve solenoid to close the valve. When the flow meter on the fueling truck no longer indicates fuel flow, all the tanks are full. After turning off the fueling truck pump the fueling hose can be disconnected and the receptacle cap replaced.
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28-21-0 Page 8 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Aug 01/96
PRESSURE FUELING SYSTEM - TROUBLE SHOOTING
1. General
A. The following trouble shooting procedures are based on the performance of the pressure fueling system during a routine fuel servicing (refueling) operation and are presented in tree-type format. The fueling steps (heavy-line boxes) are connected by shaded arrows to show the OK condition path. When all steps in the OK condition path check out, the system is operable.
B. When a fueling step does not produce normal results, follow the NOT OK line to the box containing the trouble symptom. Turn to the procedure indicated and continue to follow a single line by analyzing the results of each fueling step until the required corrective action is determined. Perform the specified corrective action; then repeat the step at which the failure was encountered.
C. All trouble shooting procedures are based on the assumption that wiring is OK and that electrical power is available. If the corrective action in the procedure does not correct the problem, check wiring continuity per applicable diagram in the Wiring Diagram Manual (WDM).
D. Malfunctions of the fueling shutoff valves can be due to either mechanical or electrical trouble within valve, or within DC float switch which senses shutoff level in fuel tank. If shutoff of fueling flow does not occur at normal full tank capacity but will stop by placing fueling shutoff valve switch in CLOSE position, the source of the trouble is probably in the float switch. Fuel shutoff calibration is usually unnecessary since shutoff level is set by the float switch which is installed on a non-adjustable mounting bracket. If consistent high or low shutoff levels are experienced, look for bent, damaged, or incorrect float switch mounting bracket.
2. Prepare for Trouble Shooting
A. For more accurate determination of fueling shutoff fuel quantities and comparison with previous measured fuel quantities, it is recommended that airplane be placed in normal attitude (0 degree roll and 1 degree nose down).
B. Check that fuel tank(s) for trouble shooting are empty (Ref 28-23-0, Maintenance Practices) or have a known quantity of fuel, less than 88% full.
C. Provide pressure fueling source (Ref 12-11-0, Fuel Servicing – Pressure Fueling) but do not connect to fueling receptacle. Fueling truck or hydrant system should have an accurate flowmeter for measuring fuel input.
D. Provide external electric power (Ref Chapter 24, Electrical Power).
E. Check that GROUND EP REFUELING and FUEL QUAN circuit breakers on P6 circuit breaker panel are closed.
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Feb 15/79 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 28-21-0 Page 101
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