Each engine hydraulic pump operates inde-
pendently to maintain the overall system pres-
sure at 2,210 to 3,600 psi.
Auxiliary Pump
The electrical motor-driven auxiliary pump is
a piston-type variable-volume pump similar
to the engine driven pumps. When the aux
pump is operating, a mechanical regulator au-
tomatically varies the output based on down-
stream demand and will limit output pressure
to 2,610-3,600 psi. The aux pump has a max-
imum capacity of 1.0 gallons per minute
(GPM). A large demand will cause the auxil-
iary pump pressure to drop. If the auxiliary
pump is operating and output pressure is less
than 1,900 psi an amber “AUX HYD PUMP
LO” message will be displayed on the CAS.
If the aux pump is on for 20 minutes, it auto-
matically shifts to a reduced capacity mode.
The volume is reduced to .75 gal. per minute
and the maximum output pressure is reduced
to 2,850 psi. Normal operation can be re-ini-
tiated by cycling the AUX HYD switch off
and back on.
The auxiliary hydraulic pump is located in the
tailcone, forward of the tailcone baggage com-
partment on the left side. It receives 28 VDC
power from the left essential bus, and is pro-
tected by two circuit breakers labeled AUX
HYD PUMP, PWR (power) and CTRL (con-
trol). These circuit breakers are located on the
pilot circuit breaker panel in the GEAR/HY-
DRAULICS group.
Auxiliary pump operation can be manually
initiated by depressing the “AUX HYD” mo-
mentary action pushbutton switch on the
gear/hydraulic control panel (Figure 13-2).
The caption within the switch/indicator an-
nunciates “ON” when the auxiliary pump is
operating, manually or automatically, and
blanks when it is off. The pump can be man-
ually controlled at any time on the ground or
inflight.
Automatic operation occurs according to the
following design philosophy:
• Pump OFF when aircraft is powered up.
• Automatically OFF when gear handle is
selected UP.
• Automatically ON when gear handle is
selected DN.
• Automatically OFF when aircraft is
powered down.
LEARJET 45 PILOT TRAINING MANUAL
13-4
FOR TRAINING PURPOSES ONLY
FlightSafety
international
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