TM 55-1520-240-23-8
10-1
FUEL SYSTEM
(Continued)
10-1
If either fuel supply system becomes inoperative, both
engines can be supplied by the other system by opening
the engine crossfeed valves. The valves operate on 28
vdc from the No. 1 dc bus and are controlled from the
overhead fuel control panel.
NO BREAK - WORK HARDER
Pressure from each forward main fuel pump is also
used to operate a respective jet pump. Pressure to
each jet pump is provided by a line tapped into the feed
line between its main fuel pump, and feed line check
valve. A suction line from each jet pump is connected
to the pressure refueling lines, such that when either
of the forward main pumps are operated, pressure
through its jet pump causes fuel to be drawn from the
pressure refueling lines. On aircraft with 68 , a vacuum
relief check valve is installed to prevent a vacuum from
forming in the pressure refueling lines. The valve is
drawn open as fuel is pulled from the lines, allowing air
to displace the fuel.
NO BREAK - WORK HARDER
Each of the engine fuel gate valves and the two
crossfeed valves has indicating lights next to it that come
on during the time the valve is opening or closing. The
lights will also come on and remain on if the valve stops
at any position other than fully open or closed.
NO BREAK - WORK HARDER
Power to operate the indicator lights comes from the 28
vdc buses.
10-16
