Aircraft system hydraulic system Flashcards
The ________in aircraft provide a means for the operation of aircraft components. The
operation of landing gear, flaps, flight control surfaces, and brakes is largely accomplished.
hydraulic system
Hydraulic system complexity varies from _____ aircraft that
require fluid only for manual operation of the wheel brakes to______ transport aircraft
where the systems are large and complex.
small;large
To achieve the necessary redundancy and
reliability, the system may consist of several subsystems. Each subsystem has a power
generating device (pump), reservoir, accumulator, heat exchanger, filtering system, etc.
hydraulic system
It states that pressure applied to any part of a confined liquid is
transmitted with undiminished intensity to every other part. Thus, if a
number of passages exist in a system, pressure can be distributed through all
of them by means of the liquid.
Pascal law
USERS OF HYDRAULICS IN A CESSNA AIRCRAFT
braking system,
USERS OF HYDRAULIC SYSTEM IN AIRBUS AIRCRAFT
flight controls, landing gear, brakes and nose wheel steering, cargo doors, thrust reverser, ram air turbine
ADVANTAGES OF USING HYDRAULICS
• Lightweight
• Ease of Installation
• Simplification of Inspection
• Minimum Maintenance Requirements
• Incompressible, and this fact enables movement to be transmitted through pipelines, over great
distances, without loss of time or motion.
• They provide good lubrication of components.
• Their viscosity is low enough to minimize friction in pipelines and to allow high-speed operation
of motors and pumps, but high enough to prevent leakage from components.
• They prevent internal corrosion in the system.
• They have a wide operating-temperature range.
used primarily to transmit and distribute forces
to various units to be actuated. Liquids are able to do this because they are
almost incompressible.
hydraulic fluid
IMPORTANT PROPERTIES OF A HYDRAULIC FLUID THAT IS USED IN AVIATION
viscosity, chemical stability, flash point, fire point
is the temperature at which a substance gives off vapor in sufficient
quantity to ignite and continue to burn when exposed to a spark or flame., a high ____ is required of desirable hydraulic liquids.
fire point
is the temperature at which a liquid gives off vapor in sufficient
quantity to ignite momentarily or flash when a flame is applied. It is desirable for hydraulic liquids because it indicates good resistance to combustion and a low degree of evaporation at normal temperatures.
flash point
It is another property that is exceedingly important in selecting a hydraulic
liquid. It is the liquid’s ability to resist oxidation and deterioration for long periods.
chemical stability
One of the most important properties of any hydraulic fluid. It is an internal resistance to flow. A liquid such as gasoline that has a low viscosity flows easily,
while a liquid such as tar that has a high viscosity flows slowly. Viscosity increases as
temperature decreases. A satisfactory liquid for a given hydraulic system must have enough body to give a good seal at pumps, valves, and pistons, but it must not be so thick that it offers resistance to flow, leading to power loss and higher operating temperatures. These factors add to the load and to excessive wear of parts. A fluid that is too thin also leads to rapid wear of moving parts or of parts that have heavy
viscosity
The instruments used to
measure the viscosity of a liquid is known as
viscometers or viscosimeters.
TYPES OF HYDRAULIC FLUIDS USED IN AVIATION
MINERAL-BASED FLUIDS, POLYALPHAOLEFIN-BASED FLUID, PHOSPHATE ESTER-BASED FLUID
is processed from petroleum. It has an odor
similar to penetrating oil and is dyed red.
mineral based fluids or MIL-H-5606
- good low temperature fluidity. (-65°F to 274°F)
- robust wear protection, oxidation and corrosion resistance
- high degree of flammability
mineral based fluids or MIL-H-5606
MIL-H-83282 is a fire-resistant hydrogenated _______ based fluid developed in the 1960s to overcome the flammability characteristics of MIL-H-5606.
polyalphaolefin or MIL-H- 83282
Fire Resistant
• Self-extinguishes when the flame/heat source is removed and has excellent flame propagation
inhibition properties.
• Corrosion Resistant
• Operating temperature limit is -40oF to 401oF
polyalphaolefin based fluid or MIL-H- 83282
These fluids are used in most commercial transport category aircraft and are extremely
fire-resistant. However, they are not fireproof and under certain conditions, they burn. In
addition, these fluids are very susceptible to contamination from water in the atmosphere.
Progressive development of these fluids occurred as a result of performance requirements
of newer aircraft designs. The airframe manufacturers dubbed these new generations of
hydraulic fluid, such as Skydrol® and Hyjet®, as types based on their performance.
PHOSPHATE ESTER-BASED FLUID
CHARACTERISTICS OF A PHOSPHATE ESTER BASED
HYDRAULIC FLUID LIKE MODERN SKYDROL
VERSION V AND HYJETVERSION V
- Improved flammability characteristics
- Low density
- Excellent corrosion protection
- Excellent low and high temperature viscosity balance
- Improved protection against electro-chemical corrosion
HYDRAULIC SYSTEM COMPONENTS
HYDRAULIC RESERVIOR HYDRAULIC PUMP HYDRAULIC FILTERS CHECK VALVE SHUTOFF VALVES PRESSURE RELIEF VALVE PRESSURE REGULATOR SELECTOR VALVE HYDRAULIC ACTUATOR ACCUMULATOR
is a steel sphere divided into two chambers by a synthetic
rubber diaphragm. The upper chamber contains fluid at system pressure, while
the lower chamber is charged with nitrogen or air.
accumulator
FUNCTIONS OF ACCUMULATOR
• Dampen pressure surges in the hydraulic system caused by actuation of a unit
and the effort of the pump to maintain pressure at a preset level.
• Aid or supplement the power pump when several units are operating at once
by supplying extra power from its accumulated, or stored, power
• Store power for the limited operation of a hydraulic unit when the pump is
not operating.
• Supply fluid under pressure to compensate for small internal or external (not
desired) leaks that would cause the system to cycle continuously by action of
the pressure switches continually kicking in.
It converts hydraulic power to mechanical action. This is
connected to hydraulic system users and actuates the hydraulic
system users.
hydraulic actuator
This valve allows the changing of direction of the flow of
pressurized hydraulic fluid. This is done by rotation of the
integrated assembly of the valve.
selector valve
This is used in a Hydraulic System that is driven by engine driven pumps
(referring to the modern commercial airliners).
• One of its purpose is to manage the output of the pump
to maintain system operating.
• The other purpose is to permit the pump to turn without resistance (termed
unloading the pump) at times when pressure in the system is within normal
operating range.
pressure regulator
This is used in a Hydraulic System that is driven by engine driven pumps
(referring to the modern commercial airliners).
• One purpose of the pressure regulator is to manage the output of the pump
to maintain system operating.
• The other purpose is to permit the pump to turn without resistance (termed
unloading the pump) at times when pressure in the system is within normal
operating range.
pressure regulator
Pressure relief valves cannot be used as pressure regulators in large hydraulic
systems that depend on engine-driven pumps for the primary source of
pressure because the pump is constantly under load and the energy expended
in holding the pressure relief valve off its seat is changed into heat. This heat is
transferred to the fluid and, in turn, to the packing rings, causing them to
deteriorate rapidly.
NOTE
Hydraulic pressure must be regulated in order to use it to perform the desired
tasks. It is used to limit the amount of pressure being
exerted on a confined liquid. This is necessary to prevent failure of components
or rupture of hydraulic lines under excessive pressures.
PRESSURE RELIEF VALVE
are used to shut off the flow of fluid to a particular system or
component. In general, these types of valves are electrically powered. are also used to create a priority in a hydraulic system and are controlled
by pressure switches.
• In case of emergency (leaks, fire, pumps malfunction) these valves are used
to cutoff the flow of hydraulic fluid.
shut off valves
allows the flow of fluid in one direction only.
It prevents the backflow of hydraulic fluid.
check valve
designed to prevent the passage of solids greater than 10
microns (0.0003 94 inch) in size
micron element
is a screening or straining device used to clean the hydraulic fluid,
preventing foreign particles and contaminating substances from remaining in
the system.
• It may be located within the reservoir, in the pressure line, in the return
line, or in any other location the designer of the system decides that they are
needed to safeguard the hydraulic system against impurities.
hydraulic filter
This device is responsible in delivering hydraulic power into the
users of hydraulic system.
• Hydraulic power output 3000 psi.
hydraulic pump
is a tank in which supply of hydraulic fluid for the system is
stored.
• It furnishes a place for the fluid to purge itself of air bubbles
that may enter the system. Foreign matter picked up in the system may also
be separated from the fluid in the reservoir or as it flows through line filters.
HYDRAULIC RESERVIOR
Hydraulic Fluids like Phosphate esters are good solvents and
dissolve away some of the fatty materials of the skin. Repeated or
prolonged exposure may cause drying of the skin, which if
unattended, could result in complications, such as dermatitis or
even secondary infection from bacteria. Phosphate ester-based
fluids could cause itching of the skin but have not been known to
cause allergic-type skin rashes.
HEALTH AND HANDLING IN WORKING ON
HYDRAULICS
aircraft maintenance safety
COVERALLS, NITRILE GLOVES AND POLYMERIC GLOVES,SAFETY GOGGLES
ATA 29 - HYDRAULIC POWER
(AIRBUS)
The Aircraft has three independent hydraulic systems:
green, yellow, blue,
The three hydraulic system supply hydraulic power at
3000 psi to the users:
- Flight controls
- Landing gear
- Brakes
- Nose wheel steering
- Cargo doors
- Thrust reverser operation
Hydraulic fluid cannot be transferred from transferred from one system to another.
- A reservoir in each hydraulic system is pressurized with air to prevent cavitation.
- A power transfer unit enables the green system to be pressurized by the yellow
system and vice versa.
- Fire shutoff valves are located between the reservoirs and EDPs. They isolate the system
incase of fire.
Hydraulic fluid cannot be transferred from transferred from one system to another.
- A reservoir in each hydraulic system is pressurized with air to prevent cavitation.
- A power transfer unit enables the green system to be pressurized by the yellow
system and vice versa.
- Fire shutoff valves are located between the reservoirs and EDPs. They isolate the system
incase of fire.
