Pneumatic System Components

A B C D E F PUSH PULL PUSH PULL PUSH Backup rings O-ring Backup rings Extractor tool Cylinder Extractor tool Backup rings Cylinder mouthCylinder O-ring Removal tool Cylinder mouth Removal tool Removal tool (hook type) Extractor tool (pull type) Removal tool (hook type) Extractor tool (push type) Internal O-ring removal (using pull-type Internal O-ring removal (using push-type extractor and hook-type removal tools) extractor and hook-type removal tools) Backup ring O-ringO-ring Backup ring O-ring extractor tool Backup ringBackup ring Removal tool PUSH Extractor tool O-ring removal tool Removal tool (hook type) Extractor tool (push type) Removal tool (hook type) Extractor tool (hook type) Dual internal O-ring removal (using push-type Internal O-ring removal (using wedge-type extractor and hook-type removal tools) extractor and hook-type removal tools) Removal tool Removal spoon External O-ring removal (using spoon-type extractor removal tools) Extractor tool Removal tool (hook type) Extractor tool (wedge type) External O-ring removal (using wedge-type extractor and hook-type removal tools) through a pressurization module. The standby reservoir is connected to the system B reservoir for pressurization and servicing. The positive pressure in the reservoir ensures a positive flow of fluid to the pumps. The reservoirs have a standpipe that prevents the loss of all hydraulic fluid if a leak develops in the engine-driven pump or its related lines.

The engine-driven pump draws fluid through a standpipe in the reservoir and the AC motor pump draws fluid from the bottom of the reservoir. [Figure 12-63] 12-38 Cylinder mouth O-ring receiving groove Sharp edges corners and threads Soft thin-wall metallic sleeve Installation tool Sharp edges and corners O-ring receiving grooves Threads area O-ring receiving grooves Paper cover Paper entering sleeve Sharp edges and threads O-ring receiving grooves Installation tool push type Internal O-Ring Installation (using metallic sleeve to avoid O-ring damage from sharp edges or threads and push-type installation tool) Internal O-Ring Installation (using paper entering sleeve to avoid O-ring damage from sharp edges or threads and push-type installation tool) External O-Ring Installation (using paper cover to avoid O-ring damage from sharp edges or threads) A C B Pumps Refer to Figure 12-64 for the following description. Both A and B hydraulic systems have an engine-driven pump (EDP) and an ACMP. The system A engine-driven pump is installed on the number 1 engine and the system B engine-driven pump is installed on the number 2 engine. The AC pumps are controlled by a switch on the flight deck. The hydraulic case drain fluid that lubricates and cools the pumps return to the reservoir through a heat exchanger. [Figure 12-65] The heat exchanger for the A system is installed in the main fuel tank No. 1, and the heat exchanger for the B system is installed in the main fuel tank No. 2. Minimum fuel for ground operation of electric motor-driven pumps is 1,675 pounds in the related main tank. Pressure switches, located in the EDP and ACMP pump output lines, send signals to illuminate the related LOW PRESSURE light if pump output pressure is low. The related system pressure transmitter sends the combined pressure of the EDP and ACMP to the related hydraulic system pressure indicator.

Filter Units Filter modules are installed in the pressure, case drain, and return lines to clean the hydraulic fluid. Filters have a differential pressure indicator that pops out when the filter is dirty and needs to be replaced. Power Transfer Unit (PTU) The purpose of the PTU is to supply the additional volume of hydraulic fluid needed to operate the autoslats and leading- edge flaps and slats at the normal rate when system B EDP malfunctions. The PTU unit consists of a hydraulic motor and hydraulic pump that are connected through a shaft. The 12-39 FWD Stabilizer Trim Motor Stabilizer trim actuation on the aircraft is provided by two 3,000- psi, constant-displacement, nine-piston, bent-axis hydraulic motors. Each motor produces 77.3 in-lb torque at 2,250 psid with a rated speed of 2,700 rpm and an intermittent speed of 4,050 rpm. Displacement is 0.216 in2/rev; weight is 3.9 lb.

Emergency Passenger Door Actuator Plays a critical role in safety; extends to open door when actuated by nitrogen gas pressure. Assembly reaches full extension in 2.75 to 4.16 seconds with output force of 2,507 to 2,830 lb. Hydraulic Motor- Driven Generator The hydraulic motor-driven generator (HMDG) is a servo- controlled, variable displacement, inline axis-piston hydraulic motor integrated with a three-stage, brushless generator. The HMDG is designed to maintain a steady state generator output frequency of 400 ±2V (at the point of regulation) over a rated electrical output range of 10kVA. Trailing Edge Flap Drive Motor Trailing edge flap actuation is provided by one 3,000-psi, constant-displacement, nine- piston, bent-axis hydraulic motor. The motor produces 21.4 in-lb torque at 2,250 psid with a rated speed of 3,750 rpm and an inter- mittent speed of 5,660 rpm. Displacement is 0.596 in2/rev; weight is 6.5 lb.

Engine-Driven Pump Hydraulic power for the left and right systems is supplied by two 48-gpm variable-displacement, 3,000-psi pressure compensated in-line pumps. Displacements 3.0 in2/rev; weight is 40.1 lb. AC Motor Pump Auxiliary power is provided by a 3,110-psi, 12-gpm, 8,000-rpm fluid-cooled motor pump. Some AC motor pumps feature a ceramic feed-through design. This protects the electrical wiring from being exposed to the caustic hydrauic fluid environment. Ram Air Turbine Pump A 3,025 psi in-line piston pump provides 20 gpm at 3,920 rpm, delivering hydraulic power for the priority flight control surfaces in the event both engines are lost or a total electrical power failure occurs. Displacement is 1.25 in2/rev; weight is 15 lb.

Leading Edge Slat Drive Motor Leading edge slat actuation on the aircraft provided by one constant- displacement, nine-piston, bent-axis hydraulic motor. The motor produces 544.3 in-lb torque at 2,250 psid with a rated speed of 3,170 rpm and an intermittent speed of 4,755 rpm. Displacement is 1.52 in2/rev; weight is 13.21 lb. Power Transfer Unit The transfer of hydraulic power (but not fluid) between the left and right independent hydraulic system is accomplished with a nonreversible power transfer unit (PTU) that provides an alternate power source for the leading and trailing edge flaps and the landing gear, including nose gear steering, which are normally driven by the left hydraulic system. The PTU consists of a bent-axis hydraulic motor driving a fixed displacement, in-line pump. Rated speed is 3,900 rpm. Displacement of the pump is 1.39 in2/rev and displacement of the motor is 1.52 in2/rev. The unit weight is 35 lb.

Nose Wheel Steering System Consists of a digital electronic controller, hydro- mecharical power unit, mounting collar, tiller, and rudder pedal positon sensors. The hydro- mecharical power unit (an integrated assembly) includes all the hydraulic valving, power amplification, actuation, and damping components. PTU uses system A pressure to drive a hydraulic motor. TheSystem A reservoir hydraulic motor of the PTU unit is connected through a shaft Forward bulkhead with a hydraulic pump that can draw fluid from the system B reservoir. The PTU can only transfer power and cannot transfer fluid. The PTU operates automatically when all of Standby reservoir the following conditions are met: • System B EDP pressure drops below limits.

• Aircraft airborne. • Flaps are less than 15° but not up. Keel beam System B reservoir 12-40 System B System A Alternate brakes Ground spoilers Autopilot A Flight spoilers Nose wheel steering Landing gear Alternate nose wheel steering Normal brakes Trailing edge flapsAutopilot B Flight spoilers No. 2 thrust reverser Yaw damper No. 1 thrust reverser Rudder Ailerons Leading edge flaps & slats Auto slats Elevator + elevator feel Standby system Landing gear transfer unit M M M EDP ACMP ACMP ACMP Landing Gear Transfer Unit The purpose of the landing gear transfer unit is to supply the volume of hydraulic fluid needed to raise the landing gear at the normal rate when system A EDP is lost. The system B EDP supplies the volume of hydraulic fluid needed to operate the landing gear transfer unit when all of the following conditions are met: • Aircraft airborne.

• No. 1 engine rpm drops below a limit value. • Landing gear lever is up. • Either or both main landing gear not up and locked. Standby Hydraulic System The standby hydraulic system is provided as a backup if system A and/or B pressure is lost. The standby system can be activated manually or automatically and uses a single electric ACMP to power: • Thrust reversers. • Rudder. • Leading edge flaps and slats (extend only). • Standby yaw damper. Indications A master caution light illuminates if an overheat or low pressure is detected in the hydraulic system. An overheat light on the flight deck illuminates if an overheat is detected in either system A or B and a low-pressure light illuminates if a low pressure is detected in system A and B.

Boeing 777 Hydraulic System The Boeing 777 is equipped with three hydraulic systems. The left, center, and right systems deliver hydraulic fluid at a rated pressure of 3,000 psi (207 bar) to operate flight controls, flap systems, actuators, landing gear, and brakes. Primary hydraulic power for the left and right systems is provided by two EDPs and supplemented by two on-demand ACMPs. Primary hydraulic power for the center system is provided by two electric motor pumps (ACMP) and supplemented by two on-demand air turbine-driven pumps. The center system provides hydraulic power for the engine thrust reversers, 12-41 FWD INBD Outlet Inlet INBD FWD To No. 1 hydraulic pump No. 1 pump pressure From case drain filter Hydraulic system A heat exchanger Hydraulic supply (fire) shutoff valve No. 1 Engine pump supply No. 1 Pump pressure Case drain return line Rear sparHydraulic line connectors Bonding jumper Mounting clamp (3 places) Tubing coil Wing structure primary flight controls, landing gear, and flaps/slats. Under Left & Right System Description emergency conditions, hydraulic power is generated by the The left and right hydraulic systems are functionally the same.

ram air turbine (RAT), which is deployed automatically The left hydraulic system supplies pressurized hydraulic and drives a variable displacement inline pump. The RAT fluid to operate the left thrust reverser and the flight control pump provides flow to the center system flight controls. systems. The right hydraulic system supplies pressurized [Figure 12-66] 12-42 Bleed air Supply

Pressure

Return EDP = Engine driven pump ACMP = AC motor pump ADP = Air driven pump L ACMP C1 ACMP C2 ACMP L ACMP L EDP R EDP CenterLeft Right LDG GR ALTN Extend DC HYD pump ISLN C1 ADP C2 ADP ISLN SOV

Heat

exchanger (left main tank)

Heat

exchanger (right main tank)

Heat

exchanger (right main tank) SOV returnreturn return Main landing gear actuation LE slats primary drive Main gear steering Nose landing gear actuation Nose wheel steering Tail flight controls Wing flight controls Thrust reverser Tail flight controls Wing flight controls Thrust reverserTE flaps primary drive Tail flight controls Wing flight controls RAT Reservoir fill selector valve Altn/Res brakes Normal brakes hydraulic fluid to operate the right thrust reverser, flight control systems, and the normal brake system. [Figure 12-67] Reservoir The hydraulic system reservoirs of the left and right system contain the hydraulic fluid supply for the hydraulic pumps.

The reservoir is pressurized by bleed air through a reservoir pressurization module. The EDP draws fluid through a standpipe. The ACMP draws fluid from the bottom of the reservoir. If the fluid level in the reservoir gets below the standpipe, the EDP cannot draw any fluid any longer, and the ACMP is the only source of hydraulic power. The reservoir can be serviced through a center servicing point in the fuselage of the aircraft. The reservoir has a sample valve for contamination testing purposes, a temperature transmitter for temperature indication on the flight deck, a pressure transducer for reservoir pressure, and a drain valve for reservoir draining.

Pumps The EDPs are the primary pumps for the left and right hydraulic systems. The EDPs get reservoir fluid through the EDP supply shutoff valves. The EDPs operates whenever the engines operate. A solenoid valve in each EDP controls the pressurization and depressurization of the pump. The pumps are variable displacement inline piston pumps consisting of a first stage impeller pump and a second stage piston pump. The impeller pump delivers fluid under pressure to the piston pump. The ACMPs are the demand pumps for the left and right hydraulic systems. The ACMPs normally operate only when there is high hydraulic system demand.

Filter Module Pressure and case drain filter modules clean the pressure flows and the case drain flows of the hydraulic pumps. A return filter module cleans the return flow of hydraulic fluid from the user systems. The module can be bypassed if the filter clogs, and a visible indicator pops to indicate a clogged filter. The heat exchanger, which is installed in the wing fuel tanks, cools the hydraulic fluid from ACMP and EDP case drain lines before the fluid goes back to the reservoir. Indication The hydraulic system sensors send pressure, temperature, and quantity signals to the flight deck. A reservoir quantity transmitter and temperature transducer are installed on each of the reservoirs, and a hydraulic reservoir pressure switch is located on the pneumatic line between the reservoir 12-43 PFCSBrakes (R SYS)T/R S Sample valve From RSVR servicing Heat exchanger ACMP filter module GND SVC RTN disc SYS pressurized XDCR Temp XDCR ACMP EDP Pressurized XDCR GND SVC pressurized disc RLF valve RSVR pressurized SW Return filter module RSVR pressurized module EDP filter module EDP supply shutoff valve RSVR pressurized shutoff valve Drain valve RSVR pressurized relief valve RSVR temperature XDCR Pressurized air Supply

Pressure

Return Depress solenoid valve Temperature XDCR Pressurized XDCR pressurization module and the reservoir. The ACMP and EDP filter modules each have a pressure transducer to measure pump output pressure. A temperature transducer is installed in the case drain line of each filter module and measures pump case drain fluid temperature. A system pressure transducer measures hydraulic system pressure. A pressure relief valve on the EDP filter module protects the system against overpressurization. [Figure 12-67] Center Hydraulic System The center hydraulic system supplies pressurized hydraulic fluid to operate these systems. [Figure 12-68] • Nose landing gear actuation.

• Nose landing gear steering. • Alternate brakes. • Main landing gear actuation. • Main landing gear steering. • Trailing edge flaps. • Leading edge slat. • Flight controls. Reservoir The hydraulic system reservoir of the center system contains the hydraulic fluid supply for the hydraulic pumps. The reservoir is pressurized by bleed air through a reservoir pressurization module. The reservoir supplies fluid to the ADPs, the RAT, and one of the ACMPs through a standpipe. The other ACMP gets fluid from the bottom of the reservoir. The reservoir also supplies hydraulic fluid to the landing gear alternate extension system.

The ACMPs are the primary pumps in the center hydraulic system and are normally turned on. The ADPs are the demand pumps in the center system. They normally operate only when the center system needs more hydraulic flow capacity. The RAT system supplies an emergency source of hydraulic power to the center hydraulic system flight controls. A reservoir quantity transmitter and temperature transducer are installed on the reservoir. A hydraulic reservoir pressure switch is installed on the pneumatic line between the reservoir and the reservoir pressurization module. Filter Filter modules clean the pressure and case drain output of the hydraulic pumps. A return filter module cleans the return flow of hydraulic fluid from the user systems. The module 12-44 MLG actuation ALTN brakes NLG steering LG ALTN ext system ACMP C1 Filter MOD Filter MOD Filter MOD Filter MOD RAT check out module ACMP C2 ADP C1 ADP C2 RAT NLG Actuation MLG steering Trailing edge flaps PFCSLeading edge slats Sample valve GND SVC disc RTN Return filter MOD Drain valve RSV ISLN valveNG ISLN valve GND SVC disc pressSYS pressurized XDCR RSVR pressurized switch From RSVR servicing station Center SYS RTN Pressurized air Supply

Pressure

Return can be bypassed. The heat exchanger cools the hydraulic fluid from the ACMP case drains before the fluid goes back to the reservoir. ADP case drain fluid does not go through the heat exchangers. The ACMP and ADP filter modules each have a pressure transducer to measure pump output pressure. A temperature transducer in each filter module measures the pump case drain temperature. A system pressure transducer measures hydraulic system pressure. Pressure relief valves in each ADP filter module prevent system overpressurization. A pressure relief valve near ACMP C1 supplies overpressure protection for the center hydraulic isolation system (CHIS).

Center Hydraulic Isolation System (CHIS) The CHIS supplies engine burst protection and a reserve brakes and steering function. CHIS operation is fully automatic. Relays control the electric motors in the reserve and nose gear isolation valves. When the CHIS system is operational, it prevents hydraulic operation of the leading- edge slats. ACMP C1 gets hydraulic fluid from the bottom of the center system reservoir. All other hydraulic pumps in the center system get fluid through a standpipe in the reservoir. This gives ACMP C1 a 1.2-gallon (4.5 liter) reserve supply of hydraulic fluid. The reserve and nose gear isolation valves are normally open. Both valves close if the quantity in the center system reservoir is low (less than 0.40) and the airspeed is more than 60 knots for more than one second. When CHIS is active, this divides the center hydraulic system into different parts.

The NLG actuation and steering and the leading-edge slat hydraulic lines are isolated from center system pressure. The output of ACMP C1 goes only to the alternate brake system. The output of the other center hydraulic system pumps goes to the trailing edge flaps, the MLG actuation and steering, and the flight controls. If there is a leak in the NLG actuation and steering or LE slat lines, there is no further loss of hydraulic fluid. The alternate brakes, the trailing edge flaps, the MLG actuation and steering, and the PFCS continue to operate normally. If there is a leak in the trailing edge flaps, the MLG actuation and steering, or the flight control lines, the reservoir loses fluid down to the standpipe level (0.00 indication). This causes a loss of these systems, but the alternate brake system continues to get hydraulic power from ACMP C1. If there is a leak in the lines between ACMP C1 and the alternate brake system, all center hydraulic system fluid is lost.

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