-
each L/G downlock
-
each L/G door uplock
-
each L/G door (open position).
The L/G control lever has two positions, UP to retract the L/G, and DOWN to extend the L/G. Signals are sent to the LGCIUs when a selection is made. The L/G control lever has a baulk device which stops movement of the lever to the UP position, when the aircraft is on the ground. One of the LGCIUS sends a signal to release the baulk device, to let the L/G control lever move (to the UP position). It is not necessary for the LGCIU to be in control when it sends the signal.
The L/G isolation safety valve, the L/G selector valve and the L/G door selector valve are solenoid operated valves in the hydraulic system. Signals from the LGCIUs control the operation of the selector valves. A signal from the Air Data/Inertial Reference System (ADIRS) (Ref. 34-10-00) and the L/G control lever, controls the operation of the safety valve.
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B. Hydraulic System
The hydraulic system has:
-actuators that move the mechanical L/G components
-electro-hydraulic valves to control the operation of the actuators
-
mechanically operated valves to let the doors to be opened on the ground
-
mechanically operated valves to operate the free fall extension system.
Each L/G has these actuators:
-
a L/G retraction-actuator
-
a L/G downlock actuator
-
a L/G uplock actuator
-
a door actuator
-
a door uplock actuator.
Pressurized hydraulic fluid is sent to the actuators through the electro-hydraulic valves to move the related mechanical components. The electro-hydraulic valves which follow are installed in the system:
-
a L/G isolation safety valve 49GA
-
a selector valve and manifold assembly 2524GM, which includes a L/G
door selector valve 41GA and a L/G selector valve 40GA.
The sequence of operations is controlled by the LGCIU.
The L/G isolation safety valve 49GA is a two-position valve that isolates the L/G hydraulic supply from the Green hydraulic system, (when its solenoid is de-energized). This stops extension of the L/G when the aircraft speed is more than 264 kt to prevent damage.
The selector valve and manifold assembly 2524GM controls the flow of hydraulic fluid to:
-
the door open lines
-
the door close lines
-
the L/G extend lines
-
the L/G retract lines.
The L/G door selector valve 41GA and the L/G selector valve 40GA operate independently from each other.
To open the L/G doors (for access on the ground) each L/G bay has a mechanically-operated door-bypass valves. These valves isolate the door actuator from the doors-close pressure-line and hydraulically connect the two sides of the actuator together. This prevents movement of the doors if the system is pressurized, and makes the system safe during maintenance. The doors will only move, if the ground-opening-handle is moved to the closed position.
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To let the L/G extend (by gravity) the Free Fall Extension System (Ref. 32-33-00) has mechanically operated cut-out and vent valves to prevent a hydraulic fluid lock in the actuators.
The system also has safety valves and restrictor valves.
The safety valves keep hydraulic fluid upstream of the safety valve if a leak occurs downstream.
The restrictor valves are installed in the selector valve and manifold assembly to control the rate of fluid flow through the L/G extend lines.
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