The most probable cause of a FUEL PRESS
LOW light is failure of the affected wing jet
pump. It is normal for the FUEL PRESS LOW
annunciator to illuminate if the engine fails or
is shutdown. However, if the thrust lever is
placed in CUTOFF, the FUEL PRESS LOW
warning along with other engine related mes-
sages, is replaced with a single advisory mes-
sage “L or R ENGINE SHUTDOWN.”
The low-pressure switches are DC powered
through the L R FUEL PRESS LOW circuit
breakers, respectively, in the ENGINE group
of circuit breakers on the left and right circuit
breaker panels.
RAM-AIR VENT SYSTEM
GENERAL
The ram-air vent system provides pressurization
and ventilation for the wing and fuselage fuel
tanks inflight. A single ram-air inlet, a NACA
vent scoop, is located slightly forward of and
below the leading edge of the left engine pylon
(Figures 5-10 and 5-11). Ram-air entering the
scoop passes through a tube to a surge tank ar-
rangement located in the top, aft part of the
fuselage tank. An open tube extends from the
surge tank to the forward, top part of the fuse-
lage tank to ventilate that part of the tank. There
is a small drain line which drains the NACA vent
scoop to an exit point in the lower fuselage.
A combination vacuum relief and/or pressure
relief valve (opens at 2 to 3 psi differential)
is also installed within the fuselage tank to
allow for fuel tank venting as a back up to the
ram-air vent system.
EXPANSION LINES
Two, 3/4 inch, open-ended expansion lines
connect the high points at the outboard ends
of the wing tanks with the high point in the
fuselage tank (Figure 5-11). These lines allow
pressure to equalize between all three fuel
tanks. This concept allows all venting to occur
through the fuselage tank and eliminates the
need for any exterior wing vent hardware.
Fuel can also flow through these lines from the
wing tanks to the fuselage tank if, during sin-
gle point refueling, the wing tanks become
full before refueling is terminated.
LEARJET 45 PILOT TRAINING MANUAL
5-16
FOR TRAINING PURPOSES ONLY
FlightSafety
international
Figure 5-10. Ram–Air Vent Scoop
To Next Page
Loading...