Learjet 60 - Hydraulic System

Learjet 60

Pilot's Manual
HYDRAULIC SYSTEM
ocoaom 9#9
HYDRAULICS &
LANDING
GEAR
The aircraft hydraulic system
supplies hydraulic pressure
for opera-
tion of the aircraft landing gear, brake,
flap, spoiler and thrust rever-
ser systems . Hydraulic
fluid is supplied from the
hydraulic reservoir
through
shutoff valves to the engine-driven hydraulic
pumps for dis-
tribution to the required
systems upon demand . The
engine-driven,
variable-volume hydraulic
pumps will normally maintain
system
pressure
between 1400 and 1550 psi . A
pressure relief valve installed
between the high-pressure
and return lines will open to
relieve pres-
sure in excess
of 1750 psi . Reservoir pressure
is maintained at
approx-
imately 20 psi by bleed air
supplied through a
pressure regulator .
Reservoir
pressure in excess of 20
psi is relieved overboard
by a pres-
sure relief
valve and a vacuum relief valve
prevents negative
pressure
in the reservoir . Two
precharged (850 psi)
hydraulic accumulators
are
installed
to dampen and absorb
pressure surges . Both
accumulator in-
dicators
are located under the right engine
behind a transparent
sight
panel . The right-hand accumulator
is plumbed for
the brakes, landing
gear
and flaps ; the left-hand
accumulator is plumbed
primarily to
power thrust
reverser operations but assists
the main system
accumu-
lator for landing gear, flap
and brake operation .
Two high-pressure
filters
and one return filter prevent
hydraulic fluid
contamination .
The return
filter incorporates a bypass
valve which will open
in the
event it becomes clogged
. Both the high-pressure
and return filter in-
corporate an overpressure bypass
button . An
auxiliary hydraulic
pump is
installed to provide system
pressure in the
event of a mal-
function or during
engine-off ground operations
.
The thrust reverser
hydraulic system
incorporates a
mechanically
controlled
isolation valve that
will shut off
hydraulic fluid to the
thrust
reverser system if it senses
that hydraulic pressure
in the main
hydraulic system has
dropped below
approximately 150 psi .
This pre-
vents thrust reverser activation
in the unlikely
event of engine driven
pump failure
. A one-way check valve
downstream of the
thrust rever-
ser system ensures that
fluid does not back-up from
the main system .
Two motor-driven
firewall shutoff valves
can stop hydraulic fluid
flow to the engine-driven
hydraulic pumps in the
event of an emer-
gency or engine fire .
Each shutoff valve is
operated by the corre-
sponding ENG FIRE PULL T-handle
on the glareshield .
(Refer to EN-
PM-123
Change 2