2 to tank 3. Reverse flow from tank 3 is prevented
1 and 4 keep fuel from entering the refuel line and
by a flapper check valve on tank 3 interconnect
the feed tanks.
valve.
As fuel from the hot fuel recirculation system
If the right engine is shut down and/or right
increases wing fuel, the wing motive flow pilot
motive flow boost pressure is lost, the tank 3
valve and motive flow shutoff valve open,
pressure-operated interconnect valve opens. Tank
allowing wing transfer. A flapper check valve at
each wing ejector inlet prevents transfer from one
4 interconnect line is always open. Fuel gravity
wing to the other.
feeds from tanks 3 and 4 to tank 2. Reverse flow is
prevented by the flapper check valve on tank 2
Transfer motive flow pressure to each wing
interconnect valve and tank 3 flapper check valve.
ejector is controlled by the normally open wing
damage shutoff valve in tank 4. If wing damage
On some series aircraft, motive flow pressure
occurs, the pilot sets the INTR WING switch to
to the tank 1 fuel low-level shutoff and pressure-
operated interconnect valve controls gravity feed
INHIBIT on the cockpit EXT LT control panel.
to tank 2. The fuel low-level shutoff valve
This closes the wing damage shutoff valve,
energizes closed when fuel in tank 2 is below 700
preventing loss of fuel through a wing transfer
motive flow line and stopping wing transfer.
to 900 pounds. The closed fuel low-level shutoff
valve stops motive flow fuel to the pressure-
If normal wing transfer does not occur, all
wing fuel can be gravity transferred to tank 4 with
operated interconnect valve, allowing the flapper
to swing open. Once the flapper is open, fuel in
5 degrees of roll. A check valve in each gravity
tank 1 can gravity feed to tank 2. The positions of
transfer line prevents reverse flow.
the tank 2 and tank 3 pressure-operated intercon-
FUSELAGE TRANSFER
nect valves are tested using the fuel check panel.
CENTER OF GRAVITY (CG)
Fuselage transfer (transfer from tanks 1 and
CONTROL SYSTEM
4 to tanks 2 and 3) starts when the fuel level
sensors open the transfer shutoff valves in tanks
2 and 3.
The fuel quantity gauging intermediate device
Fuel flow (transfer) from tanks 1 and 4
continuously compares the ratio of fuel between
tanks 1 and 4. When tank 1 transfers fuel at a
transfer jet ejectors enters a fuselage transfer
faster rate than tank 4, the transfer control valve
manifold that supplies fuel to a transfer shutoff
valve in feed tanks 2 and 3 and to the dump valve.
in tank 1 is energized closed, stopping transfer
Transfer from the tank 1 or 4 ejector alone is
from tank 1. Tank 1 will not resume transfer until
tank 4 transfers (depletes) fuel to within the
enough to keep both the feed tanks full at
parameters defined by the intermediate devices.
maximum engine demand.
If fuel distribution in tanks 1 and 4 has caused
When a transfer tank is empty, the transfer
the aircraft CG to be further aft than desired, a
pilot valve and transfer shutoff valve close,
preventing transfer motive flow pressure from
CG caution will display on the left digital display
indicator.
entering the transfer line. Fuel transfer between
fuselage transfer tanks is prevented by check
Once tank 1 depletes below 150 pounds of
fuel, the intermediate device will stop monitoring
valves in the inlets of each transfer jet ejector.
tanks 1 and 4 fuel ratios. Tank 1 will then transfer
Fuel levels in the feed tanks are maintained
fuel until the transfer pilot valve closes the shutoff
by a fuel level sensor and transfer shutoff valve
valve.
within each feed tank.
If transfer from tanks 1 and 4 to the feed tanks
fails, fuel gravity transfers through an always
open interconnecting line in the bottom of tank
4 and through an orifice in the interconnect valve
REVIEW SUBSET NUMBER 7
in tank 1. If motive flow pressure to either engine
fuel boost jet ejector or engine fuel turbine boost
Q1. In the F-18 fuel transfer system, what fuel
tanks feed the engines?
pump is interrupted, tanks 2 and 3 fuel gravity
feed through the ejector to the engine.
If the left engine shuts down and/or left
motive flow boost pressure is lost, the tank 1 and
tank 2 pressure-operated interconnect valves open.
Q2. When does fuel transfer from the wing
This allows fuel to gravity feed from tanks 1 and
start?
