Hydraulic System - Center System Show Schematic only

Center Hydraulic System

Left System Leak from Center System Right System Shutdown Left Engine Shutdown Right Engine Power Transfer Unit (operates if Left engine failed or Left EDP pressure low) Reserve brakes Ram Air Turbine (automatically operates when both engines have failed) Ram Air Turbine Manual Deployment Switch Alternate Brakes Left Thrust Reverser Rudder Ratio Landing Gear - Normal System Operation Spoilers Yaw Dampers Ailerons ETOPS equiped aircraft only Flaps and Slats - Normal System Operation Nosewheel Steering Elevators Spoilers Rudder Elevator Feel Stabilizer Ailerons Normal Brakes Right Thrust Reverser Power Transfer Unit Spoilers

General

The center system powers only the flight controls.

The system consists of a reservoir, two electric motor-driven pump and a Ram Air Turbine (RAT) pump.

Fluid Supply

Hydraulic fluid is supplied to each hydraulic pump from an independent reservoir. The reservoir is pressurized by the Bleed Air system to ensure positive fluid flow. A quantity measuring system provides information to the EICAS status display. RF displays when a reservoir requires refilling prior to dispatch (quantity < 0.75).

Sys Press Rsvr. The RSVR light illuminates and the EICAS advisory message C HYD QTY displays when the reservoir quantity is low (quantity < 0.5). The RSVR also illuminates and the EICAS advisory message C HYD RSVR PRESS displays when the reservoir air pressure is low.

The reservoir has a stand pipe to maintain reserve hydraulic fluid for use by the Ram Air Turbine in the event of a center system hydraulic Leak. With fluid level at the top of the standpipe, quantity is approximately 0.15.

Electric Pumps

The two center electric motor-driven pumps are similar to the left system pump. The C2 pump is load shed automatically to reduce electrical loads if only one electrical generator is operating and both Electric Pump Switches are ON.

The pump PRESS light illuminates and the EICAS advisory message C HYD ELEC 1 or C HYD ELEC 2 displays when the pump output pressure is low. The pump OVHT light illuminates and the EICAS advisory message C HYD 1 OVHT or C HYD 2 OVHT displays when the pump temperature is high.

System Pressure Indications

The SYS PRESS light illuminates and the EICAS caution message C HYD SYS PRESS displays when the hydraulic system pressure is low.

Hydraulic system pressure displays on the EICAS status page. When both electric motor-driven pumps are inoperative, the EICAS status page displays the Ram Air Turbine output pressure.

Ram Air Turbine

Right System