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M11 > 11.11 Hydraulics > Flashcards

11.11 Hydraulics Flashcards

1
Q

What pressure do hydraulic systems normal work under?

A

3000psi

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2
Q

What two types of hydraulic pressure is there?

A
  • Hydrostatic pressure

- hydrodynamic pressure

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3
Q

What type of pressure is produced by static or nearly static fluids?

A

Hydrostatic

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4
Q

What type of pressure is produced by moving liquids?

A

Hydrodynamic

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5
Q

What’s the advantage of using fluids rather than gases to transmit force?

A

Pressurise quicker and transmit force more efficiently

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6
Q

What are the colours of hydraulic fluid? [2]

A
  • Mineral oil = red

- Synthetic oil = violet

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7
Q

What 2 types of hydraulic fluid are there?

A
  • mineral oil

- synthetic oil

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8
Q

Can mineral oil and synthetic oil mixed?

A

No

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9
Q

What’s a typical name for synthetic hydraulic fluid? [2]

A
  • Skydrol

- hyjet

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10
Q

What characteristics are required for hydraulic fluid? (7)

A
  • low flammability
  • good lubrication quality
  • resistance to freezing
  • non-evaporating
  • non-foaming
  • chemical stability (resist oxidation and deterioration)
  • hygroscopic quality
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11
Q

If a fluid is hygroscopic, what does it have a tendency to do?

A

Absorb water

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12
Q

What is another name for packing?

A

Seals

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13
Q

What is the function of packing? [2]

A
  • Prevent leaks from the components housing

- provide a seal between two different fluid pressures

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14
Q

What are seals usually made out of?

A

Rubber materials and back up rings from Teflon

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15
Q

What do manufacturers of packings have to consider? [2]

A
  • Materials used depending on the job they do

- whether it’s for a mineral or synthetic oil

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16
Q

What must be considered when choosing seals? [2]

A
  • Working temperature

- strength of the forces that act upon them

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17
Q

What are static seals used to seal against?

A

Steady and pulsating pressure

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18
Q

What are dynamic seals used to seal against?

A

Stroking or rotational movements

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19
Q

What can the pressure distribution section often called?

A

The manifold

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20
Q

What 1 main component does each hydraulic system have?

A

Reservoir completely independent from other reservoirs

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21
Q

What does the cylindrical shape of a reservoir resist?

A

Changes in differential pressure caused by different altitudes and temperatures

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22
Q

What is the purpose of the pressurisation of the reservoir?

A

To ensure a positive supply of fluid to the pumps

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23
Q

Where are the supply pipe to pressurisation pump and return pipe located on the reservoir?

A

At the bottom of the reservoir

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24
Q

What can you find in the reservoir to prevent hydraulic fluid from moving upwards if there was a sudden loss of altitude?

A

A sheet metal baffle

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25
Q

What components can you find on the reservoir? (5 components)

A
  • Quantity gauge
  • quantity transmitter
  • low level switch
  • drain valve
  • reservoir pressurisation/air manifold
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26
Q

What does the pressurisation of the reservoir prevent? [3]

A
  • Foaming
  • evaporation
  • cavitation of the fluid
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27
Q

What 2 types of methods are there for pressurising the reservoir?

A
  • Hydraulic pressure

- air pressure

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28
Q

With air pressurisation in the reservoir, what is the main source of this air?

A
  • One of the engines

- Pneumatic system will provide back up pressurisation

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29
Q

What pressure are reservoirs usually kept at?

A

50psi

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30
Q

What is attached to the reservoir pressurisation manifold? [4]

A
  • check valves
  • filters with a differential pressure indicator
  • pressure reducing valve
  • fluid separator (fitted with a drain valve and a ground connector)
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31
Q

When might you need to depressurise the hydraulic reservoir?

A

For maintenance of system components

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32
Q

What type of assembly is the depressurising valve?

A

Spring and piston assembly

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33
Q

What is a hydraulic accumulator?

A

A device that stores potential energy store

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34
Q

When are accumulators used?

A

To accumulate energy and to smooth out pulsations

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35
Q

How is the energy stored in an accumulator?

A

Available for instantaneous use, released at a great force that what can be supplied by the pump alone

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36
Q

What can accumulator also act as?

A

Surge or pulsation absorbers

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37
Q

What 4 types of accumulators principals are there?

A
  • Weight loaded piston type
  • diaphragm (bladder) type
  • spring type
  • hydropneumatic piston type
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38
Q

What are the functions of accumulators? (5 functions)

A
  • stores energy
  • absorbs pulsations
  • cushions operating shock
  • supplement pump delivery
  • maintains pressure
39
Q

What are the two types of hydraulic piston pumps?

A
  • variable displacement

- fixed displacement

40
Q

What is the mechanism called where movement is created? (VDP)

A

Wobble plate/yoke/swash plate

41
Q

Does the wobble plate move with the pistons? (VDP)

A

No, it is a fixed component and doesn’t rotate with engine rotation

42
Q

What happens to the fluid output when the wobble plate reduces the piston stroke?

A

Reduction in flow output

43
Q

What is the boost pump called in the VDP?

A

Impeller

44
Q

What does the impeller do in a VDP?

A

Precharges the fluid from the reservoir as it enters the pump, preventing cavitation

45
Q

What does the pump compensator valve do?

A

Alters the angle of the wobble plate according the pressure of the system via the actuator piston

46
Q

What can stop the VDP output?

A

A solenoid valve that can be activated in the flight deck

47
Q

What happens when the captain activate the depressurisation valve?

A

Piston moves up allowing pressurised fluid go to the compensator valve. Moving 2 pistons, allowing fluid to push the actuator piston changing the angle of the wobble plate. And also shuts the flow via a block valve

48
Q

What does a case drain do?

A

Drain line removing cooling fluid from the pump to the reservoir

49
Q

What does the seal drain do?

A

Drains fluid which comes through the driveshaft sealing

50
Q

How are the piston shoes lubricated and cooled?

A

Via very thin holes on the pistons

51
Q

Where are FDPs usually installed?

A

On ground service panels

52
Q

What are the main source of hydraulic power?

A

Engine driven pumps

53
Q

What is type of pump is the engine driven pump?

A

Variable displacement pump

54
Q

How is low pressure detected on the outside of all the system pumps?

A

Pressure switches

55
Q

If an engine fire was to occur, what is necessary to do?

A

Cut off the supply of hydraulic fluid

56
Q

When will the electric pump automatically start?

A

When the engine starts

57
Q

How can an electric pump be cooled? (2)

A
  • cooled by air or,

- hydraulic fluid that passes through

58
Q

What will the temperature switch in the electric pump do?

A

Alerts the flight deck when the pump gets too hot, so they can switch the pump off

59
Q

What is another name for electric pumps?

A

Demand pumps

60
Q

When will air driven pumps activate?

A

When electric pumps can’t maintain the system pressure

61
Q

What rotates the drive shaft of an air driven pump?

A

Air turbine driven by pneumatic system

62
Q

What does the gearbox do on an air driven pump?

A

Reduces the speed of air turbine to a suitable level for the Variable displacement pump

63
Q

What is the purpose of a shut-off and speed control valve in an air driven pump?

A
  • Shut off valve = solenoid valve energised by the flight deck, controlling the supply of pneumatic air. When shut, the turbine stops spinning
  • Speed control valve = controls the rotational speed of the air turbine
64
Q

What are the 3 uses of auxiliary pressurisation?

A
  • help main pressurisation if there is a high user demand
  • replace main pressurisation when a fault occurs
  • for maintenance purposes on the ground when the engines are not running
65
Q

What does RAT stand for?

A

Ram air turbine

66
Q

How is the RAT deployed?

A

Push button in the flight deck with spring tension to extend

67
Q

How does the RAT operate?

A

Air stream turns the propeller driving a variable displacement pump

68
Q

How is the RAT retracted?

A

Hydraulically

69
Q

How long does it take for the RAT to deploy?

A

Less than 1 second

70
Q

What is a PTU?

A

-Power transfer unit,

Transfer hydraulic power between 2 hydraulic systems with a motor/pump combination

71
Q

What doesn’t a PTU allow?

A

Fluid transfer

72
Q

What will you find in a PTU?

A

Fixed displacement pump/motor and variable displacement motor/pump

73
Q

Can the PTU transfer hydraulic power in either direction?

A

Yes, the pump/motor functions switch depending on the direction of power

FD motor and VDP
VD motor and FDP

74
Q

Why are filters important?

A

Prevent foreign particles from damaging important components

75
Q

What are the main components of a filter? (4)

A
  • filter head
  • filter bowl
  • filter element
  • filter bypass
76
Q

What is the purpose of the filter bypass?

A

To allow for unfiltered fluid to bypass the filter in the event of the filter becoming clogged and increasing pressure

77
Q

How is high pressure hydraulic distribution achieved?

A

Via lines, hoses, valves and manifolds

78
Q

What can the manifold include so that the main components are in one place? (3)

A
  • switches
  • filters
  • valves
  • transmitters
79
Q

What components does a manifold have that a pressure module doesn’t?(3)

A
  • Pressure transmitter,
  • Fluid sampling valve
  • Leak measurement solenoid valve
80
Q

What does the HP manifold have that prevent reverse flow back to the pumps?

A

Check valve

81
Q

What does the system pressure relief valve on the HP manifold do?

A

Prevent damage to the hydraulic system due to an over pressure

82
Q

What does the leak measurement solenoid do?

A

Test the internal leakage of the hydraulic components

83
Q

What is the purpose of a priority valve?

A

To close the hydraulic circuit to different users when there is a high demand in the system.
The valve closes the line that is less vital ensuring the more vital line gets enough pressure to operate

84
Q

What does an accumulator do?

A

Acts as a damper to smooth out pressure fluctuations

85
Q

What does the LP manifold combine?

A

All the return lines into a single line going back to the reservoir

86
Q

What does the LP filter have that the HP filter doesn’t?

A

Filter bypass

87
Q

Where can an indication of a pump malfunction be located?

A

LP manifold temperate sensor

88
Q

When the case drain fluid enters the module, what does it enter following this?

A

Heat exchanger to cool it before returning to the reservoir

89
Q

What are 2 types of lines used in hydraulics?

A
  • hoses

- pipes

90
Q

What are the 2 types of pipe fittings?

A

Disconnect able and non disconnect able

91
Q

What do hoses usually consist of?

A

Inner tube = Teflon and outer protective = steel wire

92
Q

What can you identify hydraulic lines?

A

With a sticker identification

Black circle, blue and yellow square

93
Q

What is the purpose of fluid sampling?

A

Analyses the fluid for water contamination and reduction in fluid performance

94
Q

What do aircraft have to have for a safe flight?

A

Enough redundancy systems similar in design

M11 (22 decks)

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