11.11 Hydraulic Fluids

• System Layout

Purpose and Working Principle

• Hydraulic systems enable the operation of aircraft components.
• Early aircraft used hydraulic brakes, evolving to power heavier components in larger aircraft.
• Necessary for activating landing gear, cargo doors, flaps, slats, flight control surfaces, and brakes.

Complexity and Components

• Varies from simple manual brake systems to complex systems powering flight controls and more.
• Consists of subsystems with pumps, reservoirs, accumulators, heat exchangers, and filters.
• Operating pressures range from hundreds to 5000 PSI.

Advantages

• Light weight, easy installation and inspection, minimal maintenance
• Nearly 100% efficient due to minimal fluid friction.

Application

• Powers flight controls, landing gear, brakes, steering, slats, flaps, thrust reversers, cargo doors, and windshield wipers.
• Easy to control, accurate, leak detection, automatic lubrication, corrosion protection, spark-free.

Disadvantages

• Inappropriate fluids can damage the system.
• Fluid leaks pose fire hazards.
• Contamination affects performance and can damage the system.

Pressure Basics

• Represented by 'P' (force 'F' acting on area 'A'), measured in Newtons.
• Pressure is force divided by area, measured in Pascals (1 N/m²).
• Hydraulic pressure typically measured in bar (100 kPa) or psi (1 bar ≈ 14.5 psi).
• Civil aircraft usually operate at 207 bar (3000 psi).
• Boeing 787 uses approximately 30 gpm at 5,000 psi electric-motor-driven hydraulic pumps to save space and weight.

Pressure Types

• Hydrostatic pressure: Pressure from static or nearly static fluids, used in aircraft hydraulic systems.
• Hydrodynamic pressure: Pressure from moving liquids with minimal internal friction.

Basic Components for System Layout

• Reservoir: Stores hydraulic fluid.
• Motor-driven pump: Increases fluid pressure and flow.
• Hand pump: Mechanical backup for increasing fluid pressure and flow.
• One-way check valve(s): Allow fluid movement in one direction only.
• Pressure relief valve: Prevents over-pressurisation.
• Directional/selector valve: Directs fluid to extend or retract the actuator.
• Actuator: Provides movement, is attached to the control surfaces.
• Filter: Prevents contamination and foreign object damage.

Redundancy

• Several independent systems for safe flight, identified by names or numbers.
• Airbus: blue (center), green (left), and yellow (right).
• Boeing: left (red), center (blue), and right (green).
• Multiple systems require independent mechanical or electrical backups.
• Systems operate independently with storage, pressurisation, and user divisions.
• Pressure distribution sections are called manifolds (Airbus) or modules (Boeing).
• Main components are stored in compartments, often in the main gear bay.

Open-centre Hydraulic Systems

• Fluid flows, but no pressure when mechanisms are idle.
• Pump circulates fluid through selector valves back to the reservoir.
• Selector valves connected in series; fluid flows freely until a valve operates a mechanism.
• Activating a valve directs fluid to the actuator, blocks flow to the reservoir, and builds pressure.
• Pressure rises until the relief valve unseats and allows fluid to flow back to the reservoir.
• Operation depends on the selector valve type, either manually engaged/disengaged or pressure disengaged.

Closed-centre Hydraulic Systems

• Fluid is always under pressure when the pump operates.
• Actuators arranged in parallel, selector valves not in series.
• Pressure controlled by regulator if using a constant delivery pump; relief valve as backup.
• If using a Variable Displacement Pump (VDP), the pressure is controlled by the pump's compensator.
• Compensator reduces pump flow as pressure increases, bypasses fluid for cooling and lubrication.

Comparison

• Open-centre systems eliminate continuous pressurisation and have less pressure surge, providing smoother operation
• Open-centre systems are slower than closed-centre systems.
• Closed-center systems are more widely used because they have instantaneous operation.

Evolution of Hydraulic Systems

• Early aircraft used manual flight controls with hydraulic brakes.
• Hydraulic power boost systems introduced as aircraft became larger and faster, assisting the flight crew.
• Small power packs reduce weight by removing hydraulic lines and large fluid quantities.

Hydraulic Power Pack System

• Compact unit with electric pump, reservoir, valves, filters, and pressure relief valve.
• Eliminates the need for centralised power supply, reducing weight and leakage.
• Driven by engine gearbox or electric motor, some with integrated actuators.

Modern High-performance Systems

• Use power supply systems with fly-by-wire controls, eliminating cables or push rods.
• Flight crew input is electronically sent to servos that use hydraulic pressure.
• Some aim to reduce hydraulic usage in favor of electrical systems.

Boeing 787

• Boeing 787 is designed with more electrical systems than hydraulic systems.
• Large aircraft have complex, closed-centre systems with triple redundancy.
• Hydraulic Fluids

Ideal Hydraulic Fluid Properties

• Low flammability
• Corrosion resistance
• Good lubricating quality
• Resistance to freezing
• Non-evaporating
• Non-foaming
• Chemical stability
• Hygroscopic quality

Performance

• Modern aircraft need high-performance oils.
• Fluids are used to transmit forces as they are nearly incompressible.
• Pascal's Law: pressure applied to a confined liquid is transmitted equally.
• Manufacturers specify the best liquid based on working conditions, service, temperature, and pressure.

Gas vs Fluid

• Gases are easily compressed.
• Fluids pressurize quickly and efficiently transmit force.

Viscosity

• Internal resistance to flow.
• High viscosity gives a good seal but too much leads to power loss.
• Low viscosity leads to rapid wear.
• Measured using viscometers or viscosimeters.

Chemical Stability

• Ability to resist oxidation and deterioration.
• High temperatures reduce lifespan.
• Localised hot spots can degrade the liquid.
• High-viscosity liquids resist heat better.

Flash and Fire Point

• Flash point: temperature at which vapour ignites momentarily.
• Fire point: temperature at which vapour ignites and continues to burn.
• High flash and fire points are desirable for hydraulic liquids.

Types of Hydraulic Fluids

• Use the correct fluid to avoid damage.
• Do not assume hydraulic fluids are compatible.
• Do not mix fluid types.
• Refer to manufacturer manuals for replacement fluid.

Principal Categories

• Minerals
• Polyalphaolefins
• Phosphate esters

Mineral-based Fluids

• MIL‑H‑5606 is oldest.
• Simply a rust-inhibited version of MIL‑H‑5606 is MIL‑H‑6083.
• Red in color

Polyalphaolefin-based Fluids

• MIL‑H‑83282 is fire-resistant, however it has high viscosity at low temperatures.

Phosphate Ester-based Fluid (Skydrol®)

• Extremely fire-resistant and used in most commercial transport aircraft.
• Use types IV and V fluids.

Type IV Classes

• Class I: low density.
• Class II: standard density.
• Type V fluids being developed for higher thermal stability.

Compatibility with Aircraft Materials-

• Skydrol does not affect common aircraft metals if kept free of contamination.
• Thermoplastic resins may be softened by Skydrol.
• Epoxies and polyurethanes are Skydrol® resistant.
• Use special accessories compatible with the fluid.

Hydraulic Fluid Contamination

• Inevitable trouble results from contamination.

Contaminants

• Abrasives: core sand, weld spatter, machining chips, rust.
• Non-abrasives: oil oxidation products, soft particles from seals.

Contamination Check

• Check if contamination is suspected or the system has been operated at high temperatures.
• Visually clean liquid may still be unfit for use.
• Large impurity particles indicate excessive wear, and systematic troubleshooting is required.

Fluid Sampling

• Fluid samples should be taken from the reservoir, and other locations.
• Samples must be taken in accordance with the applicable manufacturer's instructions.

Contamination Control

• Filters provide adequate control.
• Minimize contamination during all operations.
• Clean or replace the filter element if the system becomes contaminated.

Hydraulic System Flushing

• Necessary when fluid is contaminated.
• Should be done according to the manufacturer's instructions.
• Check the flush cart for contamination before flushing.

Hydraulic Servicing

• Reservoir filling
• Fluid sampling
• Required to maintain system efficiency.
• Can be filled manually or with pressurised ground equipment.

Pressurised Filling

• Occurs at the service panel.
• Fluid passes through a restrictor and ground service filter.
• Filling selector used to select the reservoir.

Manual Filling

• Uses a hand pump instead of ground equipment.
• Fluid passes through the fill valve and then the system.

Hydraulic Fluid Sampling

• Sampling valve located on the High‑pressure (HP) manifold.
• Analysis checks for water and performance.
• The sampling valve is a needle-type valve with a fluid inlet aperture.

Hydraulic Sampling Schedule

• Routine sampling: at least once a year or every 3000 flight hours.
• Unscheduled maintenance: when malfunctions may have a fluid-related cause.
• Suspicion of contamination: when contamination is suspected, before and after fluids are replaced.

Hydraulic System Leak Test

• Tests for leakage which occurs in main user components such as the flight controls.
• Does not test pressurisation or distribution leaks.
• Internal leaks are not easily seen.

Test Manifold

• Some aircraft have a leak measurement manifold which is linked to HP manifold and outlets.
• Manual selector valves isolate hydraulic flow to specific parts.

Note

• Other aircraft use hydraulic power switches for measurement.

Health and Handling

• Always use gloves and eye protection.
• Fluid on skin or eyes, should be washed off immediately.
• Spilled synthetic oil should be cleaned up for safety.
• Use a respirator to remove organic vapours and mists.

Handling Synthetic Oil

• Synthetic oil is toxic to humans.
• Avoid ingestion of any hydraulic fluid.
• Synthetic-oil based fluids are phosphate ester-based and are good solvents.
• Repeated or prolonged exposure may cause drying of the skin.
• Hydraulic Reservoirs and Accumulators

Hydraulic Reservoirs

• Stores fluid
• Replenishes leaks
• Overflow basin for thermal expansion
• Compensates for variations in fluid need
• Furnishes a place for purging air bubbles
• Separates matter from fluid

Reservoirs

• Pressurised
• Non-pressurised
• Each reservoir has supply and return pipes at the bottom.
• Baffle plates/fins prevent vortexing and surging.
• Strainers prevent entry of foreign matter during servicing.
• Reservoirs could have an internal trap.
• Most aircraft have emergency hydraulic systems

Disclaimer

• Maintaining hydraulic reservoirs can be dangerous.
• Always adhere to the safety instructions.

Non-pressurised Reservoirs

• Used in aircrafts with no violent maneuvers, moderate height, or in pressurised area.
• Cylindrical shape.
• Filter elements filter return fluid.
• Generally, use visual gauges to indicate fluid quantity.
• Slightly pressurised due to thermal expansion and return fluid.
• Vent directly to atmosphere or cabin with check valve/filter.

Non-pressurised Reservoir Components

• Pressure and vacuum relief valve.
• Manual air bleed valve.
• The manual air bleed valve is actuated before servicing or replacing components.

Pressurised Reservoirs

• Designed for high altitude flight and required when reservoirs are in non-pressurized area of an aircraft.

Components of a Pressurised Reservoir

• Reservoir pressure relief valve: Prevents over-pressurisation.
• Sight glasses: Visual indication for flight crew and maintenance.
• Reservoir sample/drain valve: Used to draw a sample.
• Reservoir temperature transducer: Provides temperature information (not shown)
• Reservoir quantity transmitter: Transmits fluid quantity to flight deck.

Module

• Reservoir pressurisation module supplies bleed air, includes filters, check valves, test port, manual bleed valve, gauge port.
• Maintenance: Remove pressure with bleed valve before maintenance, use rag to catch spray.

Fluid-pressurised Reservoirs

• Pressurised by hydraulic system pressure.
• Small piston pushes a larger one against reservoir fluid.
• The Piston Amount that is exposed outside the reservoir indicates fluid quantity indicator.

Reservoir Ports

• Pump suction
• Return
• Pressurising
• Overboard drain
• Bleed port
• Fluid level indicated by markings on the pressurising cylinder.

Cover Markings

• Full at zero system pressure (FULL ZERO PRESS)
• Full when the system is pressurised (FULL SYS PRESS)
• REFILL

Reservoir Servicing

• Non-pressurized: Pour fluid through filler strainer or use quick disconnect.
• Pressurized: Central filling station in the ground service bay.
• Built-in hand pump or pressure fill port.

Before Servicing Ensure

• Spoilers are retracted
• Landing gear is down
• Landing gear doors are closed
• Thrust reversers are retracted
• Parking brake accumulator pressure reads at least 2500 psi (172 bar)

Hydraulic System Components

• Hydraulic ground service station provides fluid servicing: all three reservoirs are serviced from the same location.

Accumulators-

• Potential energy is stored as compressed gas, spring, or weight.
• Accumulates energy and smooths out pulsations.
• Allows smaller fluid pump and instantaneous use.
• Absorbs surges to cushion hydraulic hammers.

Accumulator Types

• Spherical
• Cylindrical
• Spherical accumulator: Steel sphere divided by diaphragm, fluid above, nitrogen/air below.
• Fluid enters the fluid port which can compress the bladder or diaphragm.

Cylindrical Hydraulic Accumulators

• Cylinder with threaded end caps and a piston assembly separating fluid from air/nitrogen.
• Cylindrical cylinder is designed for high-pressure applications.

Types

• Diaphragm
• Spring
• Hydro-pneumatic piston
• Hydro-pneumatic piston types use a gas (nitrogen) as a spring cushion.

Accumulator-compressed Nitrogen

• Compressed nitrogen is charged to the unit until it's designed preload is set.
• Hydraulic system pump must create a pressure within the system greater than 1300 psi (90 bar) before the hydraulic fluid can actuate the piston.
• Compressed nitrogen expands and this causes the piston to force fluid from the accumulator

Maintenance

• Consists of inspections, minor repairs, component replacement, and testing.
• Rapid, violent release of pressurised air/nitrogen.
• Released air/nitrogen can turn objects into lethal projectiles.
• Always refer to Aircraft Maintenance Manual (AMM).
• Ensure all preload air (nitrogen) pressure has been discharged prior to disassembly.
• Wear Personal Protective Equipment (PPE) that includes gloves and safety glasses.

Checks

• Hydraulic system unpressurised.
• Charging must be referred to the AMM.

Instructions

• With a suitably calibrated inflation adapter and gauge to the charging valve fit to the unit.
• Release the accumulator pressure to zero, observe fluid leakage.
• Purge the nitrogen charging cylinder hose, connect it to the inflation adapter.
• Slowly inflate the accumulator to the desired base pressure.
• Close charging valve for stabilisation.
• Stabilised, assess against pressure against calibrated gauge and adjust accordingly.
• Seal system with AMM instructions.

Warning

• Risk of explosion and fire.
• Never use oxygen or compressed air to pre-charge an accumulator.
• Always charge accumulators with dry nitrogen.
• Pressure Generation: Electric, Mechanical, and Pneumatic

Introduction

• All aircraft hydraulic systems have at least one power-driven pump and may include a hand pump as an additional unit when the power-driven pump is inoperative.
• The pump is the driver of fluid flow, generates pressure in the hydraulic system.

Drive

• Driven mechanically, electrically, or with pneumatic air.
• Mechanically-driven pumps are the primary source of pressure generation on most aircraft.
• Electrical motor-driven pumps fulfill the same role as mechanically-driven pumps, but the drive shaft is turned by an electrical motor.
• Pneumatically-driven pumps are used as on-demand pumps to supplement the primary pumps.

Combination

• Today's modern aircraft use a combination of engine-driven power pumps, electrically-driven power pumps, pneumatically-driven power pumps, Power Transfer Units (PTU), and aRAT-driven pump in a highly effective, fully redundant aircraft hydraulic system.

Pump Classification

• Positive displacement
• Non-positive displacement
• Most pumps used in hydraulic systems are positive displacement.

Non-positive Displacement

• A non-positive displacement pump produces a continuous flow.

Constant Displacement Pumps

• Constant displacement pumps pumps a fixed or unvarying quantity of fluid through the outlet port during each revolution of the pump.

Gear Type Power Pump

• Gear type power pump is an example of a positive displacement pump and delivers a constant (fixed) volume.

Gerotor Pump

• A Gerotor pump is a gerotor type power pump.
• Another positive displacement, fixed volume example.

Piston Pumps

• Piston pumps are the most common type of main system (positive displacement) pump and can be constant-displacement or variable-displacement pumps.
• Have drive shaft and drive coupling that is considered a safety device.

Axial Inline Piston Pump

A typical constant-displacement axial type pump has an angular housing of the pump causing a corresponding angle to exist between the cylinder block and the drive shaft plate to which the pistons are attached.

Bent Axis Piston Pump

• One of the pump configurations that causes the pistons stroke when the pump shaft is turned.

Inline Piston Pump

• The simplest type of axial piston pump is the swash plate design.
• Displacement is determined by size and number of pistons, is determined by a swash plate angle, and stroke stroke length.

Vane Pump

• The vane-type power pump is also a constant displacement pump.
• Rotar turns, sections passing its volume in a gradual motion whether minimum or maximum.

Variable Displacement Pumps (VDPs)

• Converts mechanical energy (rotation of a motor or engine) to hydraulic energy.
• Some variable piston pumps will perform opposite operations also and this includes a conversion from hydraulic energy to mechanical energy being the function of the hydraulic motor. The flow rate and outlet pressure of the variable displacement pump can be changed during its operation.
• Provides enhanced energy more efficiently than fixed displacement pumps.

Variable Displacement Pump (VDP) Operation

• Engine rotates the pump drive shaft, cylinder block, and pistons.
• Pumping action is due to piston shoes sliding on the shoe bearing plate.

Shaft Rotation

• Rotary motion is converted to piston reciprocating motion due to the yoke angle.

Leakage

• Internal leakage keeps the pump housing filled with fluid allowing lubrication of rotating parts for cooling.

Hydraulic Pressure Generation

• All aircraft hydraulic systems have at least one power-driven pump and may include a hand pump as an additional unit when the power-driven pump is inoperative.

Modern Transport Design

• A highly effective, fully redundant aircraft hydraulic system uses a combination of pumps:

Pump Types

• Engine-driven Pumps (EDPs)
• Electrically-driven power pumps (known as Alternating Current Motor Pumps (ACMPs))
• Pneumatically-driven power pumps (known as Air Driven Pumps (ADPs))
• Power Transfer Units (PTU)
• Ram Air Turbine (RAT) driven pump

Maintenance

• Modern-Driven Pumps are of variable delivery, compensator-controlled type and is the same for both pump types.

Engine-driven Pump (EDP)

• Main pressurisation to describe the generation of primary hydraulic power.
• Typically, the pump is mounted on the accessory gearbox of the main engine and is rotated by a shaft. The EDP is a variable displacement pump and is permanently connected to the engine.

Electric Pump or Alternating Current Motor Pump (ACMP)

• Often, the driveshaft is mechanically driven pumps, driven by an electrical motor. Electrically-driven pumps are installed as primary pumps and for use in emergencies or during ground operation when engines are not running.

Air-driven Pump (ADP)

• Pneumatically-driven pumps and these pumps are used as demand pumps to supplement the primary pumps. They are driven by air from the pneumatic system or by ram air; the ADP is a Variable Displacement Pump (VDP).

Hand Pumps

• Used in some older aircraft for the operation of hydraulic subsystems.
• Used as a backup unit.
• Used for testing purposes, as well as for use in emergencies.
• Hand pumps are also installed to service the reservoirs from a single refilling station.
• Station reduces the chances of the introduction of fluid contamination.

Types of hand pump

• Single-action
• Double-action
• Rotary

Action

• A single-action hand pump draws fluid into the pump on one stroke and pumps that fluid out on the next stroke.
• A rotary hand pump produces a continuous output while the handle is in motion.
• Emergency Pressure Generation

Pressurisation

• In emergencies varies and aircraft systems are designed to to ensure hydraulic pressure
• Maintained to critical components during loss of systems or engine failure.
• Alternating Current Motor Pumps (ACMPs) can be used, if Engine-driven Pumps (EDP) fail or at engine stall.
• For hydraulic, electric emergency power has a Ram Air Turbine (RAT).

Back-up

• To help the main pressurisation, to replace pressurisation defaults
• Is good for maintenance purposes when done on the ground and engines are not running.
• Emergency and backup pressurisation that is a Ram Air Turbine (RAT), Power Transfer Unit (PTU), Alternating Current Motor Pump (ACMP), and Ground Power Unit (GPU).

Ram Air Turbine (RAT)

• RAT is a VDP & is installed to provide electrical and hydraulic power in the event of failures. The RAT has to be manually activated or automatic.
• Hydraulically has to be used if retracted, has safety procedures with a lock during ground work.
• Can happen under testing and not having precaution, the test can automatically drop RAT.

Note

• When working on or around the RAT system all safety precautions as specified in the relevant Aircraft Maintenance Manual (AMM) must be observed at all times.

Power Transfer Units (PTUs)

• Used in PTUs and has different operations to it, depends on the configuration, can be only one direction or both directions being Fixed displacement or VDP
• Allows component operation
• Hydraulic, hydraulic pump units the same drive between with power.
• Pressurised hydraulic forces, moves unit and moves to next hydraulic.
• Power can automatic, manual selection the aircraft configuration

Electrically-driven Hydraulic Pumps

• Alternating Current Motor Pumps (ACMPs), use motor connects mechanically.
• 9 piston VDP.
• As a result from motor of the pump, heat increases.
• To prevent overheating, the motor is either cooled by air, the hydraulic fluid is circulated through the motor to cool it during operation.

Ground Pressurisation

• Ground equipment is used to pressurise the hydraulic system if there are no aircraft pressurisation systems available.
• Filters

Introduction

• The role to clean the dirt and contamination
• Prevents the failures for the system
• Modern designs use filter modules that contain filters and other components.

Location on Aircrafts

• Reservoir, on the pressure line, on other locations
• Remove particles during the use of selectors, pumps

Filters Types

• For any fluid powered system must have system well.
• Has to control for mechanical part and the outside weather.
• Fills in due the performance and the part.

Contamination for Contamination Type

• Has bad life to components.

Rating

• Micron smallest particle.
• Have multiple layers.

Materials

• Wire mesh
• Stainless steel
• Micro glass
• Cellulose paper

Types

• Surface and depth can be be applied.

Filter Qualities

• Wire Mesh Filters - Steel normally good surface.
• Stainless Steel Filters, has a higher quality than Wire Mesh Filters.
• Micro Glass - Better filtration quality and removes more than solids greater than 10 microns.
• Cellulose Paper Filters - resin-impregnated cellulose filter media.

Filter Components

• Has many styles for the positions on air craft
• Inline is most common type and assembly has a head bowl and element, with a bypass valve.

Sub-components Properties

• Head Assembly - Head that allows the connect.
• Bowl - Housing that contains the element
• Element - Most important part of the list
• Valve - To make module

Materials

• Some may include metal, paper ,plastic. Tiny holes help filter particles.
• equipped with a bypass relief valve.
• Preferred to have dirty than no flow.

Filter Differential Pressure Indicators

• Filter element because occluded.
• That the pressure increases and a switch activates.
• Pressure increases to activate warning
• Clogged causes bypass activation.

Maintenance

• Relatively easy.
• Has cleaning and replacing the material.

Instructions

• Filters using the micron-type
• Element replaced periodically.
• Reservoir filters cleaned or changed
• Cleaned
• Contact manufacturer

Pressure Control

• There are multiple types for this purposes, automatic.

Purpose

• Hydraulic is allowed to function, for that the pressure is set.
• Prevents errors and acts like safety feature.

Relief Valve

• Design has spring loaded to allow operation.
• Most common valve types Ball Sleeve Poppet

System Functions

• Safety device to other devices in area, to for protection in the hydraulic systems.
• Thermal relief to remove high pressure.

Pressure Regulators

• Manage the output, keep pressure in predetermined amount
• To the system when good operation.

Pressure Reducers

• Provide specific lower pressure when systems need than the provide pressures.

Functions

• Steady and is a system needs

Hydraulic Seals

• To stop fluid from moving certain point.
• Keep materials such as dust from entry. Increased due. Increased use is a part due the variance with temperature.
• No single seal will fill.

Purposes

• Metal finish from parts, motion if it's rotary
• Materials have to be fluid compatible.
• Divided types of seals Packing, gaskets, wipers
• Seal more than one type such as O and back up.
• Dynamic is on the inside.
• static in the fittings.

Packing Seals

• Types are V, U, O
• V-rings must be used with adapters and high ratings of pressure
• High ratings with assembly, has assembly specifications from manuafcturer.
• U-ring pressure only moves lip seals. Low with 100psi
• O-rings is made to be smaller than dimensions with good bi lateral rating.

O-ring Color Coding

• May indicate. Red is fuel, Blue is Hydraulic, seal identification provide what compound

Back-up Rings

• High differenital requires backup. MS made of Teflon don't age or affected during extreme temperatures or issues with high pressure systems. Sharp edges is needed to inspect. 1/4 seperation is the Teflon and must be used back O-rings.

Static and Dynamic Seals

• Static is for steady pulsation.
• Dynamic seals are use for stroke movement.

Seals

• Seal exposed potion from parts. Which can prevent dust.

Gaskets

• Static flats for seal

Gasket Materials

• Asbestos with heat. Copper is a spark plug with small compression
• For leak protection. Crod used for oil seal. Rubber to to apply compressable
• Caps and other system is used. O-rings shape is with many gaskets.

O-ring Installation

• Should tool properly never sharp. Need make sure no dust.
• Before use immerise and do twist or anything to keep parts as it come.
• Power Distribution

Introduction

• Hydraulic has many devices that makes functions occurs

Power-Distribution

• Through control of the speed of fluid flow, controling is done with Shut-off valves, selector valves, sequence valves, priority valves, quick disconnect valves, hydraulic fuses.

Shut-off Valves

• Shut-off fluid to component/system. They are electrically done and manually.

Selector Valves

• Direction components, and provides direction with in or out.
• Have open or closed control
• Open is done at all times during operation and the fluid at use has more usage.
• Closed stops pressure with off, or nuteral usage. Known more commonly with 4 ways

Description

• The closed-centred selector valves with four ports are the most used in aircraft hydraulic systems. These are known as four-way valves. All connects to return and pressure, or has a lever component for control. Selector may be poppet type rotary, spool or any type. Ports are for system components and requirements.

Selenoids

• Shown open and close valve

Valve positions

• Solenioid can unergized positions
• Energizes is can shift pressure

Sequence Valves

• Operation of order for branches, from auto, with landing gear to make landing smooth
• Has pressure for control ,or electric switches with multiple system controls with order.

Type of Control

• The opening to a set pressure to close
• If pressure increases enough with components. It has a piston that rises during openings components.

Mechanics

• The body is what contains, allows the check to through.
• Plunges stops to check for A's flow B.

Priority Valves

• To secondary or none systems to get use, when preesure is low.
• Ex. if has value of 2200, with go at that value. If below loses, and has control fluid.

Quick Disconnect Valves

• prevent from fluid waste to make it safely. Located after and before pump.

Non- return

• Can only moves in one function to make a safe transfer.

Different valves like it include

• Check valves
• Clack valves
• Reflux valves
• Retention valves
• One-way valves
• Most of the valves are not a system components or inline.
• Are automatic. They has direction if fluid.

Shuttle Valves

• The main to isolates the alternate
• Housings with parts has 3 for good use
• Normal system inlet, Outlet, Alternate or emergency system inlet
• When there is two or more in use creates multiple outputs

Hydraulic Fuses

• If high jump it flows turns off
• Brakes and edges, trust, and N's gear. Fuse and spring moves and keeps the pressure level to move fluid.

Hydraulic Actuators

• Tranforms, pressure to moving system
• Move system mechanically with movement and force. Made from a set piston and components like seals or cylinder.

Parts

• Consits of housing to allow movement, piston and one or port open.

• Double is the major difference.

• single action move only one way. Hydraulic Actuators

• In double has connection with 4 ways to valve, has on and off for components when set

Rotary Actuators

• The long that can move that normal do. From degree movement some components can be longer with more than what linear can provide Hydraulic Actuators

• A common type of rotary actuator used is the rack and pinion actuator. These are used in many Nose Wheel Steering (NWS) mechanisms.

Heat Exchangers

• Cool or maintain good, so last longer. Made of aliumium
• Made tanks to make operation and good.

Pipes and Hoses

• Make everything moves to make the pressure. Types are hoses or pipes.

Pipe Components

• Has removable or permenant. Fittings are connection devices where pipes meets

Detachable

• The connection links. Metal make the sleeves. Lock with nut. Detachable
• Has a bad joint is with where pipe.

Permanent

• Fix damages on areas with pressure to not get leaks. Called Swaging.

Hoses Classificaition

• Classified for the use pressures

Class

• Low mediums and high. Use always disconnecting.

Function

• Where supplies, to reservoirs, from them, from distributation, returns
• Help in making it to look at functions systems,
• Identification system to look operation or the colors, that help.

Indication and War...