*
Tank quantity reaches the volumetric top-off (VTO) value

*
System test switch is in (test position).

You set the load select value at the IRP. The refueling operation section describes this.
The FQPU memory has the VTO values for each tank. When a tank quantity equals the VTO value, the tank is full. The FQPU removes the refuel-valve-open commands for that tank.
Refuel Valve Indication
The refuel valve position switch closes when the valve opens. This sends a signal to the EEU. The EEU sends an ARINC 629 signal to the FQPU. The FQPU sends an ARINC 429 signal to the IRP. The IRP turns on the valve open light (not shown).
Overfill Protection
If fuel flows into a surge tank, the related surge tank float switch closes. This supplies a ground to energize the overfill control relay. The relay removes power from all the refuel valves. Immediately, all the refuel valves close at the same time.
The overfill control relay has a latching ground. After the fuel in the surge tank drains out, the relay stays energized. You must operate the overfill reset switch to remove the latching ground.
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PRESSURE REFUEL -FUNCTIONAL DESCRIPTION -CONTROL

The overfill reset switch disables the overfill protection. When the overfill reset switch is in the reset position, the surge tank float switches and the overfill test switch can not energize the overfill control relay.
Overfill Test
You use the overfill test switch to do a test of the overfill protection. The switch supplies a ground, similar to a closed surge tank float switch, to energize the overfill control relay. Immediately, all the refuel valves close at the same time.
Overfill Indication
The overfill indication light on the IRP comes on for these conditions:
*
A surge tank float switch is closed

*
The overfill control relay is energized

*
The overfill test switch is in (test position).

Training Information Point
When you set the total fuel load, the FQPU calculates the fuel load quantities for each tank two times. It calculates when you set the total fuel load, and when the main tanks are almost full. When the main tanks are almost full, the FQPU usually opens the center tank refuel valves again.
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PRESSURE REFUEL -FUNCTIONAL DESCRIPTION -CONTROL

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PRESSURE REFUEL -OPERATION

General
The refuel station gets power when the refuel station door opens. The quantity indications take 60 seconds to show after the door opens. The station has bonding points and an interphone jack. There is a placard on the refuel station door with the refuel procedure.
The refuel procedure is also in the maintenance manual. It includes warnings and cautions. The procedure has these tasks:
*
Pressure refueling with a set fuel quantity

*
Pressure refueling with a no set fuel quantity

*
Pressure refueling with inoperative fuel valves

*
Pressure refueling with inoperative fuel quantity display.

Normal Refuel Procedure
This is a brief summary of the refuel procedure when you do the set or no set fuel quantity tasks:
*
Make sure you use approved electrical grounding or bonding

*
Connect the refuel nozzles

*
Do the indicator test

*
Set the fuel load as necessary

*
Put the refuel valve control switches in the OPEN position

*
Start the fueling source

*
Put the refuel valve control switches in the CLOSED position after automatic shutoff, or when the required fuel load is in the tanks

*
Stop the fueling source

*
Remove the fuel nozzles

*
Make sure all refuel valves and switches are in the CLOSE position.

When you use the total load select set switch to set the fuel load, do not operate the refuel valve switches until all of the refuel valves close automatically. The FQPU makes corrections to the fuel distribution when refueling is 95 percent complete. If you operate refuel valve switches before refueling is complete, the fuel distribution may be incorrect.
When you do not set a quantity, valves close when the tanks are full. You can also put a refuel valve control switch to the close position to stop fuel flow into a tank at a specific quantity that shows on the fuel quantity display.
Refuel Procedure With Inoperative Fuel Valves
When the valve control is set to the open position and a valve light does not come on, it shows that the valve is not open. This is a brief summary of the refuel procedure you can use:
　
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