Hydraulic System Show Schematic only

Hydraulic System

Leak from Left System Leak from Center System Leak from 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

Introduction

The airplane has three independent hydraulic systems:

The hydraulic systems power the:

 

Flight control system components are distributed so that any one hydraulic system can provide adequate airplane controllability.

The Left and Right systems are each powered by one engine pump and one electric pump. The Center hydraulic system is powered by two electric pumps. If required, a Ram Air Turbine (RAT) can provide power to the flight controls portion of the center hydraulic system.

Hydraulic fluid is supplied to each hydraulic pump from the associated system reservoir. The reservoirs are pressurized by the Bleed Air System.

Heat Exchanger

AMM A heat exchanger in each system cools pump case drain fluid as the fluid returns to the reservoir. The three identical heat exchangers are in the wing fuel tanks and use fuel as a coolant. The left and right system heat exchangers are at the inboard end of the left and right main fuel tanks, respectively. The center system heat exchanger is adjacent to the left system exchanger. A minimum of 1827 kilograms (600 gallons/4020 pounds) of fuel is required in each main tank to provide hydraulic fluid cooling.

Hydraulic Driven Generator

A Hydraulic Driven Generator is installed on some airplanes. It can be powered by either the Left Hydraulic System or the Right Hydraulic System through the Power Transfer Unit (PTU). When signalled to operate, the PTU can supply hydraulic power to the Flaps and Slats, Landing Gear, Nose Wheel Steering, and the Hydraulic Driven Generator (As installed). If required, a Ram Air Turbine can power the center hydraulic system.

Note : "Partial ETOPS Provisioned" refers to 757 airplanes that are equipped with most of the parts required for ETOPS operations, including an HMG Control Valve and associated plumbing, but NOT the HMG itself. For these aircraft, the Control Valve is wirelocked in an INOP position. Later 757 airplanes with partial ETOPS provisions also omit the HMG control valve.

Left System