when fuel pressure drops below 0.25 psi. The
light extinguishes when pressure increases
above 1.0 psi. Illumination of a FUEL PRES
annunciator light is an indication of loss of fuel
pressure to the engine. The probable cause is
failure of the affected wing jet pump in air-
planes equipped with jet pumps.
NOTE
The engine-driven pump is capable
of suction-feeding enough fuel to sus-
tain engine operation without either
the wing standby pump or jet pump.
However, 25,000 feet is the highest al-
titude at which continuous operation
should be attempted in this event; the
limiting factor is that possible dam-
age to the engine-driven pump may
occur due to reduced fuel flow.
PRESSURE-RELIEF VALVES
A 75-psi relief valve is installed in each main fuel
line on the engine side of the main shutoff valve.
The valves relieve pressure buildup caused by
thermal expansion of trapped fuel when the en-
gines are shut down by venting fuel overboard.
FUEL DRAIN VALVES
D r a i n v a l v e s a r e l o c a t e d a t l o w p o i n t s
throughout the fuel system for draining con-
densation or sediment. A small amount of
fuel should be drained from each valve dur-
ing exterior preflight inspection. The valves,
spring-loaded to the closed position, are lo-
cated as follows: two on each tip tank, one for
the crossflow valve, one for each wing, one
for each line to the engines, one for each fuel
filter, and one for the fuselage tank (Figure
5A-8). On model 23, filter drains are inside
the tail compartment.
A drain is located at each fuel vent sump. These
valves must be completely drained during the
exterior preflight inspection to prevent possi-
ble blockage of the fuselage ram-air vent line.
5A-11
FOR TRAINING PURPOSES ONLY
LEARJET 20 SERIES PILOT TRAINING MANUAL
FlightSafety
international
FLUSH SUMP
DRAINS
ENGINE LINE
DRAIN
FORWARD
FUEL VENT SUMP DRAIN
FUEL FILTER
DRAINS
FLUSH SUMP
DRAINS
ENGINE LINE
DRAIN
FUSELAGE
TANK DRAIN
REAR FUEL VENT SUMP
DRAIN
WING SUMP
DRAINS
CROSSFLOW
DRAIN
Figure 5A-8. Fuel Drain Locations
