The hydraulic system of the B777 is dived into three independent hydraulics systems, these are: left, right and center. These three hydraulic systems provide power to the:
Each hydraulic pump receives hydraulic fluid from the associated system reservoir, which will be pressurized by a bleed air system. Only the right (1.3.1.a) and center (1.3.2.b) hydraulic system will be discribed due to the fact that the the left hydraulic system only provides power to the left reverser and the flight controls, which will not be relevant for this analyse. However, the right and left hydraulic systems are identical. The only difference between them are the components they power.
The right hydraulic system (appendix x) will power the normal brakes, flight controls and the right trust reverser. The right hydraulic system contains an engine driven (primary) pump and an electric driven (demand) pump. The demand pump is driven by an electric motor and provide supplementary hydraulic power for periods of high system demand. Beside providing hydraulic power, it will also provide a backup hydraulic power source for the engine-driven primary pump. If the R ENG driven (primary) pump fails, the right hydraulic demand pump will take over. The right demand pump is controlled by the demand Right pump selector. The "ON" position means that the right demand pump runs continuously. When the "AUTO" position is selected, the right demand pump will only operate during take-off, landing and when the primary pump pressure is low.
1.3.1.b Center Hydraulic system
The center hydraulic system (appendix x) will power the:
Nose gear stearing
Reserve brakes
Main gear stearing
Trailing edge flaps
Landing gear actuation
Leading edge slats
Alternate brakes
Main gear stearing
The center hydraulic system consist of two electric motor-driven (primary) pumps. These primary pumps are also known as primary C1 and C2 pumps. During normal conditions in flight the C2 pump in the "ON" position will be load shed. This means that the pump is not running when:
The generator capacity is exceeded
All other electric pumps are running
There is a single source of electrical power
In case the primary pumps are inoperative (INOP) the center hydraulic system will activate two air-driven demand pumps. These center demand pumps will provide supplementary hydraulic power for periods of high system demand. Beside providing hydraulic power, the center demand pumps will also provide a backup hydraulic power source for the center system primary pumps (driven by an electric motor).
The center hydraulic demand pumps can serve the center hydraulic system by selecting the C1 and C2 demand pump selectors to "ON". When the selector is in the "ON" position the demand pump will run continuously. However if both C1 and C2 demand pumps are selected to the "ON" position, only the C1 demand pump will operate (it is not possible to operate both center demand pumps simultaneously in the "ON" position). In the "AUTO" position, a demand pump operates when logic anticipates a large demand or when a primary pump pressure is low and/or center hydraulic system pressure is low. The Air Driven Pump (ADP) receives pressurized air from the airplane pneumatic system.
Appendix X Right hydraulic system
The figure below shows a schematic overview of the right hydraulic system (circled in red)
1. Right primary engine selector pump
2. Right demand electric selector pump
3. Right engine pump
4. Right electric pump
5. Shutoff valve
6. Fire handle
Explanation:
a) If the right engine selector pump is switched to "ON", it will activate the right engine-driven pump. This right primary engine-driven pump will provide hydraulic power to the normal brakes, right reverser and flight controls.
b) Before engine start, the right demand electric-driven pump selector knob will be set to "AUTO". In case the right primary pump is INOP, the right demand pump will switch automatically on. This results in providing power to the normal brakes, right reverser and the flight controls.
c) In case the fire handle is pulled, the shutoff valve and the right primary pump will automatically shutdown.
Appendix X Center hydraulic system
The figure bellow shows a schematic overview of the center hydraulic system (circled in red)
1. Primary C 1/2 electric selector
pump.
2. Demand C1/2 air selector pump
3. C1 electric pump
4. C2 electric pump
5. C1 air pump
6. C2 air pump
Explanation:
a) If the center electric selector pump is switched to "ON", it will activate the center electric-driven pump. This center primary electric-driven pump will provide hydraulic power to nose gear & steering, alternate/reserve brakes, main gear & steering, flaps and flight controls.
b) Before engine start, the center C1/2 demand air-driven pump selectors knob will be set to "AUTO". In case the center primary pumps are INOP, the center demand pump will switch automatically on. This results in providing power to the nose gear & steering, alternate/reserve brakes, main gear & steering, flaps and flight controls.
