11.11 Flashcards
What psi do large aircraft hydraulics work up to
5000 pai
What psi do large aircraft hydraulics work up to
5000 psi
What advantages are there of hydraulics
They are easy to control and give accurate results.
It is easy to check if there is any leakage in the system.
It has automatic lubrication systems and protects from corrosion.
The hydraulic system does not cause sparks and is safe on flights.
It is easy to repair and maintain.
What disadvantages is hydraulics
Using inappropriate fluids damages the components of the hydraulic system.
Leakage of fluids can cause ignition of fire hazards.
Contamination in the system or fluids affects the performance and even damages the system.
What’s 1 bar in psi
14.5
What psi do civil aircraft hydraulic systems work with
3000 psi
What’s hydrostatic and hydrodynamic pressure what ones used in ac
Hydro static - pressure produced by static or nearly static fluids (this is the type used in ac)
Dynamic- pressure caused by movin liquids
What’s hydrostatic and hydrodynamic pressure what ones used in ac
Hydro static - pressure produced by static or nearly static fluids (this is the type used in ac)
Dynamic- pressure caused by movin liquids
What’s in place for hydraulic redundancy
3 systems
What’s on open centre hydraulic system
One that had fluid flow but no pressure in the system when the actuating members are idle
What’s the difference between the selector valve in the open centre hydraulics system ans the closed centre system
Always connected in a series in open centre systems
What does every hydraulic system need
A mechanical or electric system
What’s the fluid doing in the closed centre hydraulic system
Fluids under pressure whenever pumps operating
What’s the fluid doing in the closed centre hydraulic system
Fluids under pressure whenever pumps operating
What controls the pressure of a closed centre system with a variable displacement pump
Pumps integral pressure mechanism compensator
What regulates the pressure and what acts as a back up device in a closed centre hydraulic system with a constant delivery pump
Pressure regulator
Relief valve
What’s an advantage of the open centre hydraulic system over the closed centre hydraulic system
The continuous pressurisation of the system is eliminated
What does the gradual build up of pressure of the open centre system provide
Smooth actuation of surface but this means it takes a lot longer to move that then the closed system
Are closed or open centre systems more commonly used
Closed due to speed of actuation
What’s a benifit of power boost systems
Reduce weight by eliminating hydraulic lines and quantities of the fluid
What type of characteristics do ac oils need to have
Low flammability
Corrosion resistance
Good lubricating quality
Resistance to freezing
Non-evaporating
Non-foaming
Chemical stability (the ability of the oil to resist oxidation and deterioration for prolonged periods, this reduces the need for frequent oil changes)
Hygroscopic quality
What happens to viscosity as temp decreases
Increases
What’s chemical stability
Liquids resistance to oxidation and deterioration over long periods
What’s a flash point
The point in which a liquid gives off another vapour in sufficient quantity to ignite momentarily or flash when a flames applies
What a fire point
The temp in which a substance gives off a Vapour in a sufficient quantity to ignite and continue to burn when exposed to a spark or flame
What colour is mineral based oil and where’s it used
Red
Used in systems wheee the fire hazards low
What characteristics does polyalphaolefin based hydraulic fluids have
Fire resistant
High viscosity at low temps (DISADVANTAGE)
What are properties of phosphate ester based fluids (skydrol)
Most common used
Extremely fire resistant but not fire proof so can burn
What’s the difference between type 1 ans two phosphate ester based fluids
1 is low density
2 is average density
What advantages do class 1 phosphate ester hydraulic fluids over 2
Weight saving
What advantages do class 1 phosphate ester hydraulic fluids over 2
Weight saving
Why are type v fluids being developed instead of type iv
To get a more thermally stable fluid at high temps
Why are type v fluids being developed instead of type iv
To get a more thermally stable fluid at high temps
Should hydraulic fluids be mixed
No
What paints are skydrol resistant
Epoxies and polyurethanes
What are the two types of hydraulic fluid contaminants
Abrasive - sand chips and rust
Non abrasive - oil oxidation’s, seals and soft particles
What’s in place at the hydraulic fill connector in pressurised filling
It has a restrictor
Where’s the hydraulic sampling located and why’s hydraulic fluid sampled
In the HP manifold of each hydraulic system
To check for water and reduction in fluid performance
How often should hydraulic fluid be sampled
Every year or 3000 flights
When malfunctions it should be checked too
If suspected to be contaminated should be drained and replaced
What do reservoirs also do as well as store the fluid
Acts as an overflow for excess fluid forced out of the system by thermal expansion
And to compensate for varying in demands of hydraulic fluid
What’s in place to prevent The fluid in the hydraulic from having random movement
Baffle plates
What’s in place to prevent The fluid in the hydraulic from having random movement
Baffle plates
What’s incorporated in the filler neck of hydraulic reservoir
A strainer to prevent debris gettin in it during servicing
What ac are non pressurised hydraulics used for
ac designed for violent manoeuvres, ac that don’t fly at high manoeuvres
How are hydraulic reservoirs slightly pressurised
Due to thermal expansions and return of fluid to the reservoir from main system
What does a hydraulic reservoir temperature transducer do
Provides hydraulic fluid temp information for the flight deck
How many filters are in a reservoir pressurisation module
2
How many check valves are in the reservoir pressurisation module
What’s used on the bleed valve of the reservoir pressurisation module when being used
A rag
Before servicing the reservoir what needs to be ensured
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
What’s a hydraulic accumulator
Where potential energy is stored in the form of compressed gas or spring
Acts as a pulsation absorber/smoothener
How’s a spherical accumulator work
Divided into two chambers with the upper chamber that contains hydraulic fluid ans the bottoms contains nitrogen with a rubber diaphragm
How’s a spherical accumulator work
Divided into two chambers with the upper chamber that contains hydraulic fluid ans the bottoms contains nitrogen with a rubber diaphragm
The nitrogen forces the fluid out when rewuired
Are cylindrical or rectangular reservoirs used in high pressure systems
Cylindrical
What’s the accumulator preload
When the compressed nitrogen chamber is charged to a predetermined pressure lower than the systems operating pressure
Where are mechanical hydraulic pumps mounted
Accessory gearbox of main engine
Where’s the electric pump mounted
Away from engine in wheel well or hydraulics bay
What are the two types of hydraulic pumps and what type is most commonly used in hydraulic systems
Displacement and positive displacement
Positive
What do constant displacement pumps do
Provide a constant volume of fluid regardless of the pressure demands
What type of pump is a gear type power pump
Positive displacement pump
What type of pump is a gerotor pump
Positive displacement
What’s the main type of main system pump
Piston pumps
What’s the main type of main system pump
Piston pumps
Are piston pumps constant or variable displacement pumps
Both
What do the pump drive couplings in a piston pump act as
Safety devices
What does the displacement of hydraulic fluid depend on in incline piston pumps
The size and number of pistons as well as there stroke length
What does the displacement of hydraulic fluid depend on in incline piston pumps
The size and number of pistons as well as there stroke length
What oils can be mixed
Mineral oils NOT SYNTHETIC
Are variable displacement pumps or displacement pumps more energy efficient
Variable
When are electric pumps or alerternat8fn current motors used
Primary pumps and used in emergencies or on ground when engines aren’t available
What type of pump is air driven pump
How are they used
Vdp
As demand pumps (usually driven used ram air or RAT)
What does ACMP stand for
Alrernating current motor pump
What are hand driven pumps made for
Emergencies and testing
What’s the benifit of a single refilling port on a hand pump
Reduces chances of fluid contamination
What are the three types of hand pumps and which one is the least effective
Single action (least effective)
Double action
Rotary
What are 3 uses for emergency and back up pressurisation
To help maintain pressurisation if there’s a high user demand
To replace main pressurisation if a fault occurs
For maintenance purposes on the ground when engines aren’t running
What are 3 uses for emergency and back up pressurisation
To help maintain pressurisation if there’s a high user demand
To replace main pressurisation if a fault occurs
For maintenance purposes on the ground when engines aren’t running
What does the rat provide
Hydraulic and electrical
How’s the rat retracted
Hydraulically
What can be done to prevent rat operation
Safety locking pins
Cbs pulled
How does the PTU supply back up for hydraulics
By converting energy using a drive shaft
DOESNT TRANSFER THE HYDRAULIC LIQUID
How does the PTU supply back up for hydraulics
By converting energy using a drive shaft
DOESNT TRANSFER THE HYDRAULIC LIQUID
What build up are Electrically driven hydraulic pumps
Nine piston variable displacement hydraulic pumps
How are electrically driven hydraulic pumps made up
Nine piston variable displacement pump
What causes 85% of hydraulic system failure
Contamination
What are wire mesh filters usually used for
Surface cleaning
What are micro glass filters designed to provide
Best FILTRATION
What size particles does the micro glass filter prevent the passage off
Bigger than 10 microns
What size particles does the micro glass filter prevent the passage off
Bigger than 10 microns
What are cellulose paper filters made of
Resin impregnated Cellulose which is pleated
What’s the filter head
To the ac structure and connecting lines
What does the filter bypass valve do
Opens if the filter clogs
What does the filter bypass valve do
Opens if the filter clogs
What happens upstream of a clogged filter
Increased pressure
What happens upstream of a clogged filter
Increased pressure
What are the most common types of filters
Ball type
Sleeve type
Poppet type
What can pressure relief valves be used as
A system relief valve
Thermal relief valve
What’s one purpose of pressure regulators
Manage the outputs of the pump to maintain the system operating pressure to a certain range
What are pressure reducers used for
Used in systems that need to be provided with a steady pressure into the system that operates at a lower pressure
How are v rings installed
With the open end of the v facing towards the pressure
2 part seal with a male and female seal that sit together
How are v rings installed
With the open end of the v facing towards the pressure
2 part seal with a male and female seal that sit together
Where are U-cup seals or U-rings used
In brake units
What pressures do U cup seals get exposed to
Less than 1000 psi in ONE DIRECTION
What pressures do U cup seals get exposed to
Less than 1000 psi in ONE DIRECTION
What are red o rings compatible with
What are blue o rings compatible with
Red- feul
Blue- hydraulic
What are red o rings compatible with
What are blue o rings compatible with
Red- feul
Blue- hydraulic
What’s used in systems where there’s a high differential pressure to strong for a single o ring
Back up rings
What are back up rings made from
Teflon
Where should back up rings be installed in relation to the o ring
Dowstream
What should be checked when checking back up rings with the coils
They aren’t separated more than 1/4 inch
What’s the difference between the application of the static and dynamic doors
Static- used to seal against steady or pulsating pressure
Dynamic- used Wheres stroking or rotational move,emits occur
What’s the difference between the application of the static and dynamic doors
Static- used to seal against steady or pulsating pressure
Dynamic- used Wheres stroking or rotational move,emits occur
What materials are used for gaskets
Asbestos
Copper
Cork
Rubber
Where’s asbestos gaskets used
Places where heat resistance is needed
Where’s asbestos gaskets used
Places where heat resistance is needed
Where are solid copper gaskets used
Spark plugs
Where it needs to be non compressible but yet semi soft
Where are cork gaskets used
For an oil seal
Where’s rubber gaskets used
Where there’s a need for a compressible gasket
Where’s rubber gaskets used
Where there’s a need for a compressible gasket
What’s a selector valve
Used to control the direction of movement of a hydraulic actuating cylinder
What’s the difference between an open and closed CENTRE selector valve
An open centre allows a continuous flow of system hydraulic fluid regardless if the selector is even able to actuate a unit
A closed centre valve blocks the flow f fluid through valve when it’s in neutral or off
What’s the difference between an open and closed selector valve
An open centre allows a continuous flow of system hydraulic fluid regardless if the selector is even able to actuate a unit
A closed centre valve blocks the flow f fluid through valve when it’s in neutral or off
What’s the most common selector valve
Closed centre selector valves with 4 ports
What are sequence valves
Sequence valves control the sequence of operation between two branches in a circuit; they enable one unit to automatically set another unit into motion
How’s the opening pressure of the pressure controlled sequence valve obtained
By adjusting the tension of the spring they normally holds the piston in the closed position
What do priority valves do
Gives priority to critical hydraulic subsystems over non critical systems
What are quick disconnect valves used for
To prevent loss of fluid when units are removed
What do non return valves do
Allows a liquid or gas’s to flow through itself in only one direction
What do non return valves do
Allows a liquid or gas’s to flow through itself in only one direction
What’s the purpose of shuttle valve
To isolate to normal system from the alternate or emergency system
What’s a hydraulic fuse do
It senses a sudden increase in flow and then shuts off the fluid flow to preserve hydraulic fluid for the rest of the system
What’s a hydraulic fuse do
It senses a sudden increase in flow and then shuts off the fluid flow to preserve hydraulic fluid for the rest of the system
What’s special about the movement of a rotary actuator
They’re not limited to the 90 degrees pivot arc of typical cylinders and can go 180,360,720
What’s special about the movement of a rotary actuator
They’re not limited to the 90 degrees pivot arc of typical cylinders and can go 180,360,720
Where are rotary actuators usually used
On nose wheel steering
Why are heat exchangers used in hydraulic systems
It extends the life of the fluid nd pump
What a non disconnecting pipe fittings used for
To repair broken pipes
What’s the difference between the pressure switch and the pressure transducer
The switch is more likely to be used on pressure systems of a hugger importance of safety
What’s the difference between the pressure switch and the pressure transducer
The switch is more likely to be used on pressure systems of a hugger importance of safety
What do bourdon tubes do
Liquid and pneumatic pressure measurement
What’s the usual differential pressure measurement of a bourdon tube
100,000 psi
What’s a HMDG what’s it do
Hydraulic motor driven generating an can provide electrics in the event of a electrical failure
What’s the disadvantages of fly by wire systems
If a actuator fails then the whole system has to be stopped
What’s better fly by wire or power by wire (pbw)
Power by wire is more efficient and reliable
What are baffles for
To prevent any feul surging due to changes in ATTITUDE
