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Module 11 > 11.11 Hydraulic Power (ATA 29) > Flashcards

11.11 Hydraulic Power (ATA 29) Flashcards

1
Q

What is the purpose of a hydraulic reservoir?

A

It compensates for variations in the need for hydraulic fluid caused by the operation of components

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2
Q

When the gear is up, would the fluid in the reservoir show more or less hydraulic fluid?

A

It would show less hydraulic fluid in the reservoir

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3
Q

What are hydraulic systems on aircraft used for?

A
  • brakes
  • Flight controls
  • cargo doors
  • landing gear
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4
Q

What is 1 bar in psi?

A

1 bar = 14.5psi

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5
Q

What is 3000psi in bar?

A

207bar

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6
Q

What is 5080psi in bar?

A

350bar

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7
Q

What are the two types of hydraulic pressure?

A
  • hydrostatic pressure

- hydrodynamic Pressure

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8
Q

What colour is mineral oil?

A

Red

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9
Q

What colour is synthetic oil?

A

Violet/purple

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10
Q

What are the two names used for synthetic oils?

A

Skydrol and Hyjet

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11
Q

What is it called when a fluid has the tendency to absorb water?

A

Hygroscopic

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12
Q

What is the disadvantage of using synthetic oil?

A

They are hygroscopic and this changes the freezing and lubrication characteristics

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13
Q

What are the oil characteristics required?

A
  • low flammability
  • good lubrication
  • resistance to freezing
  • non evaporating
  • non foaming
  • chemical stability
  • hygroscopic quality
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14
Q

What are packings?

A

Also called seals - prevent leaks from component housings and provide a seal between different fluid pressures
(O-ring)

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15
Q

In areas where there is a high differential pressure, what additional packing can also be added if the seal alone cannot withstand it?

A

A backup ring made from Teflon

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16
Q

What material are packing seals made from?

A

Rubber

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17
Q

When are dynamic seals used?

A

Where stroking or rotational movement occur

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18
Q

When selecting seals to use, what should be considered?

A
  • the working temperatures

- the forces acting upon them

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19
Q

How are airbus hydraulic systems identified?

A

Colours - green, yellow and blue

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20
Q

How are Boeing hydraulic systems identified?

A

Numbers - 1,2,3,4

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21
Q

In hydraulic systems, what is meant by each system being independent?

A

Fluid exchange does NOT take place

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22
Q

What is the pressure distribution section of a hydraulic system called?

A

A manifold

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23
Q

What is the purpose of the cylindrical shape of the hydraulic reservoir?

A

The shape resists changes in differential pressure caused by changes in altitude or temperature

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24
Q

What is mounted inside the reservoir to prevent the sudden movement of hydraulic fluid if the aircraft suddenly loses altitude?

A

A sheet metal baffled mounted horizontally

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25
Q

What is mounted on the inside of the hydraulic reservoir to indicate the levels of fluid to the crew in the cockpit?

A

A quantity transmitter - mounted on the side

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26
Q

Where is the drain valve located on a hydraulic reservoir?

A

At the bottom

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27
Q

What is the purpose of the quantity gauge on the side of the reservoir?

A

It provides a visual indication of the fluid level

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28
Q

Why is the hydraulic reservoir pressurised?

A

To ensure a positive supply of hydraulic fluid always reaches the pumps.
It also prevents foaming, cavitation and evaporation

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29
Q

What are the two methods of pressurising the hydraulic reservoir?

A

Hydraulic = using a piston to create pressure

Air pressure = via one of the engines (or pneumatic system if engines failed)

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30
Q

What is a reservoir pressurisation manifold also known as on some aircraft?

A

A reservoir pressurisation module

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31
Q

What is the purpose of a hydraulic restrictor?

A

It reduces the amount of airflow through the pipe. This means it prevents total loss if there is an air leak from the engine to the manifold.

32
Q

Why is the air from the engine required to be regulated before it enters the reservoir?

A

It is at a much higher pressure than needed

33
Q

What component regulates the air from the engine for the hydraulic reservoir?

A

The pressure reducing valve

34
Q

Why do aircraft that only use pneumatic systems to pressurise the hydraulic reservoir not need to regulate the air?

A

The air is already regulated

35
Q

What is the purpose of the fluid separator in a hydraulic system?

A

It removes any water contained in the air.

36
Q

Where is the water collected from the fluid separator stored?

A

Into a container and is drained via the drain valve

37
Q

If pressurising the hydraulic reservoirs on the ground, what is used?

A

Nitrogen bottles

38
Q

What is the purpose of a check valve in a hydraulic system?

A

To maintain the air pressure in the reservoir

39
Q

How can a hydraulic reservoir be depressurised for maintenance?

A

Via the depressurising valve located on each of the reservoirs

40
Q

What is a hydraulic accumulator?

A

A device which potential energy is stored to exert a force on an incompressible fluid

41
Q

What are the 4 types of hydraulic accumulators?

A
  • weight loaded
  • spring type
  • piston type
  • bladder type
42
Q

Which types of hydraulic accumulators aren’t widely used today?

A
  • weighted type

- mechanical spring type

43
Q

What are the main functions of hydraulic accumulators?

A
  • stores energy
  • absorbs pulsations (from pumps)
  • cushions operating shock
  • supplements pump delivery (smaller pump can be used)
  • maintains pressure
44
Q

What is important to remember about reading the pressure gauge on a hydraulic accumulator?

A

The gauges aren’t usually calibrated and should be used for quick reference only.
Manufacturer pressure/temperature charts should be referred to before taking readings

45
Q

What should be done before charging a hydraulic accumulator with nitrogen?

A

Purge the hose

NEVER USE OXYGEN OR AIR

46
Q

What are hydraulic reservoirs pressurised to?

A

50psi

47
Q

What are the two types of hydraulic pump?

A
  • fixed displacement

- variable displacement

48
Q

What is the process called where fluid is forced out of the cylinders by the pistons in a hydraulic pump called?

A

Fluid displacement

49
Q

How does a hydraulic pump work?

A

A wobble plate, yoke or swash plate (depending on manufacturer) is displaced causing movement of the pistons to displace hydraulic fluid

50
Q

What is the boost pump of a VDP also known as?

A

An impeller

51
Q

What is the purpose of a boost pump in a VDP?

A

It prevents cavitation and increases the pressure of the fluid (known as pre-charging)

52
Q

What is cavitation of hydraulic fluid?

A

The formation of bubbles in a liquid

Can cause damage to pumps etc

53
Q

Where is the pump compensator valve calibrated to activate at 3000psi?

A

It is set in the workshop

54
Q

What is the purpose of the filter inside the case drain of a hydraulic pump?

A

It provides the mechanic with indication of how much wear is occurring inside the pump

55
Q

What is a fixed displacement pump (FDP)?

A

A hydraulic pump that has a fixed angle of displacement of the pistons. Found usually on cargo doors etc.
The mechanic varies the input to the pump by manual operation

56
Q

What is an engine driven pump (EDP)?

A

It is a type of VDP that is permanently connected to the engine

57
Q

If an engine fire occurs, how does the pilot turn off the EDP?

A

An electric motor operates a shut off valve located between the EDP and the reservoir, activated by the fire handles in the cockpit

58
Q

What are electric pumps also known as?

A

Demand pumps

59
Q

What is the purpose of electric hydraulic pumps?

A

They assist with maintaining the pressurisation when the EDP’s cannot do this

60
Q

What is the problem with using electric pumps?

A

They get very hot and cannot be used for too long

61
Q

What is an ADP?

A

An air driven pump

  • a type of VDP
  • another form of demand pump when the EDP cannot maintain the main pressure
62
Q

How does an air driven pump work?

A

It uses high pressure air from the pneumatic system to drive a turbine (which in turn drives the pump)

63
Q

How is the speed of the turbine of an air driven pump altered?

A

By the speed control valve (opening and closing) which changes the airflow

64
Q

What is the purpose of Auxiliary pressurisation of hydraulic systems?

A
  • to maintain pressurisation at high user demand
  • replace main pressurisation when the system has a fault (RAT)
  • for maintenance when engines aren’t running
65
Q

How is the RAT deployed?

A

By a push button in the cockpit

66
Q

How long does the RAT take to deploy when the pilots have pressed the push button?

A

Less than 1 second

67
Q

What type of pump is the Ram Air Turbine (RAT)?

A

A VDP

68
Q

What is a power transfer unit (PTU)?

A

It transfers hydraulic power between two systems via pump-motor combinations.
No transfer of fluid occurs

Pistons arranged like a VDP - can reverse direction (motor/pump)

69
Q

If there is a serious fault with one of the hydraulic systems and the PTU automatically powers on, what can be done to prevent further damage to the failed system?

A

A cockpit switch de-energises the PTU

70
Q

What is a ground-cart used for?

A

During maintenance - to pressurise hydraulic systems

71
Q

What are the four components of a filter?

A
  • filter bowl
  • filter head
  • filter element
  • filter bypass
72
Q

What is another name for a differential pressure indicator on a filter?

A

A pop-out indicator

73
Q

What is the most important part of a filter, and what is it made up of?

A

The filter element

  • metal
  • plastic
  • paper material
74
Q

What is a high pressure manifold?

A

It moves the pressurised fluid from the hydraulic pumps to the hydraulic users

75
Q

What is he purpose of a priority valve on a hydraulic manifold?

A

Its purpose is to close the valve when there is high demand in the system. It closes off to the less-vital users.
- it does not destroy pressure like the pressure relief valve, instead it adjusts the distribution to high/low priority

76
Q

The high pressure filter (Airbus) cleans the fluid entering the manifold. What do Boeing aircraft call this filter?

A

The pressure filter

77
Q

What are the two types of sensors found on a high pressure manifold?

A
  • two pressure switches which detect low system pressure caused by pump malfunctions or system leaks
  • pressure transmitter monitors system pressure at all times

Module 11 (4 decks)

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