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AGK - Systems > Hydraulic Systems > Flashcards

Hydraulic Systems Flashcards

1
Q

Hydraulic pumps and the 2 main types

A

Usually driven from the engine, RAT, PTU, hand driven

Or electrically driven for emergencies

2 main types = 
Constant delivery (fixed volume)
Constant pressure (variable volume)
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2
Q

Open centre system

A

Only one service can be operated at a time - only used on light a/c

Flaps/ undercarriage systems

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3
Q

Thermal relief valves

A

Relieve excess pressure caused by the expansion of trapped fluid as ambient temp increases

Sense pressure not temp

Usually operate at 3350psi

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4
Q

Sequence valves

A

Makes everything work in the correct sequence

Works hydraulically or mechanically

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5
Q

Hydraulic fuse

A

Once operated - services downstream will be isolated

Systems upstream will still work

Used in leak situations - lose service but keep the hydraulic fluid

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6
Q

Indications of a fast external leak in the hydraulic system

A

Contents - rapid loss
Pressure - nil
Temp - N/A

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7
Q

Shuttle valve

A

Provides a method of splitting 2 different supplies (normal and emergency) to a single service

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8
Q

Indications of an internal leak in the hydraulic system

A

Within in the system

Contents - no change
Pressure - no change
Temp - increase

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9
Q

Purpose of fin and barrels in the reservoir

A

Prevents the fluid moving around and creating foam

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10
Q

Modulator - hydraulic systems

A

Basically a flow control valve

Specific to the brake system

Speeds up the initial operation of the anti skid system

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11
Q

Linear (spool) valve selector

A

Uses pistons, controlled by pilot input to selected the desired direction of flow

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12
Q

Pressure reducing valve

A

Reduces main system pressure to a valve req for the operation of some services such as wheel brakes

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13
Q

Non return valve and how to check flow direction

A

Force pushes a spring open - low pressure forces the seal shut

Direction of the flow is indicated by the arrow on the casing

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14
Q

Mechanical overload protection system (blowback)

A

A form of pressure relief valve fitted in flap circuits an some spoiler circuits to prevent over pressure from aerodynamic forces causing damage to the a/c

Flaps moving to an intermediate/mid posn - once slowed moves to selected posn

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15
Q

Constant delivery

A

Fixed volume

Req ACOV and accumulators to stop excess pressure building

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16
Q

Indications of a slow external leak in the hydraulic system

A

Contents - slowly decrease
Pressure - no change
Temp - no change

17
Q

Variable volume (constant pressure) pump

A

Rotating with a series of pistons - driven by the engine - no ACOV/accumulator req

Swash plate is at an angle

As the pressure increases the control piston changes the angle of the swash plate and regulates the output volume as it senses the pressure downstream

18
Q

Shut off valves

A

Similar to fuses in that it can isolate services

Isn’t self regulating - has an external controller (on the f/d)

19
Q

Single acting actuator

A

Pressure to one side

Spring supplies the return force that returns the piston when pressure is released

Undercarriage door locks

20
Q

Electrical selector

A

Uses solenoids to electrically direct the flow

Has to have a manual redundancy

21
Q

Filters in the hydraulic system and 2 basic types

A

Removes fine particles from the fluid to prevent damage to seals and components

2 basic types
Paper element - replaceable
Metal element - cleanable

Before the pump = suction filter
After = pressure filter
Return line = return filter

22
Q

Accumulator charge

A

Pre charged with nitrogen at half the system value

23
Q

Why is the hydraulic reservoir pressurised

A

Prevents cavitation and allows for fluid expansion

Pressurised with bleed air

24
Q

Double acting balanced

A

Pressure to either side - force is the same either side due to equal surface areas

Nose wheel steering - req equal forces on both sides

25
Q

On start up the constant pressure pump q

A

The swash plate is at max deflection

Blocking valve off loads the pump

Pump is lubricated by hydraulic fluid

26
Q

Hydraulic lock

A

When fluid is trapped between the piston and the jack - fluid can’t get out - can’t flow and hydraulic lock is formed

27
Q

PTU

A

A back up power system

Uses a hydraulic motor connected to the remaining live system to drive the hydraulic pump in the failed system

Only transfers power not fluid

28
Q

Flight deck indications of hydraulic systems

A

Temp
Pressure
Contents

29
Q

ACOV

A

Automatic cut of valve

Directs the access fluid back to the reservoir in a hydraulic system using a constant volume pump

30
Q

Actuators and the 3 different types

A

Convert pressure energy into linear motion
Piston with a seal around it
Also called hydraulic jacks

3 types =
Single acting
Double acting balanced
Double acting unbalanced

31
Q

Double acting unbalanced actuator

A

Pressure either side - different surface areas = different forces in each direction

32
Q

Typical psi for a large a/c hydraulic system

A

3000 psi

33
Q

Quill drive

A

Pumps are driven by this

Has neck portion that will shatter/sear if the pump was to seize

34
Q

Tell tail button

A

Button pops when the bypass relief valve has been operated

Bypass relief - indicates the filter has been blocked so can no longer pass through it

Indicates the use of dirty oil

35
Q

Selectors

A

Purpose is to direct the hydraulic flow - dependant on the pilot selection

36
Q

Full flow relief valve

A

Protects the system from over pressurisation

Excess pressure acts against a spring causing ball to unseal

Makes excess flow go back to the reservoir

37
Q

Hydraulic fluid reservoir

A

Holds the fluid - will contain the correct fluid at the correct amount

Hold excess fluid to compensate for small leaks

38
Q

Accumulators and purpose

A

Contains pressurised gas and fluid in a cylinder separated by a piston or rubber diaphragm

Stores fluid under pressure 
Provides a small amount of pressurised fluid for an emerg 
Dampens pressure fluctuations 
Allows for thermal expansion 
Allows for small internal leaks
39
Q

Hydraulic motors

A

Operating screw jacks to drive flaps and slat mechanisms

Also known as an axel piston motor or bent axis motor

AGK - Systems (16 decks)

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