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CAA Module 11 > Module 11.11 Hydraulic power > Flashcards

Module 11.11 Hydraulic power Flashcards

1
Q

What is the only loss of efficiency in hydraulic systems?

A

Fluid friction

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2
Q

What are the two types of hydraulic forces?

A
  • Hydrostatic
  • Hydrodynamic
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3
Q

How should pressurisation sources be installed?

A

In parallel

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4
Q

What are the pumps designed to supply?

A

The max demand pressure

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5
Q

How is the pressure reduced from the highest demand to the required pressure?

A

Pressure reduction valve

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6
Q

What is the purpose of the pressure relief valve?

A

To stop over pressurising of the system and relieves due to thermal expansion

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7
Q

What is an open centre system?

A

Is a system with fluid flow but no pressure in the system when the actuators are idle

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8
Q

What does the selector valve do?

A

Directs pressure to actuator and decides the pressure and return

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9
Q

What component is controlled to vary the outputs of the system?

A

Directional/selector valve

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10
Q

What will happen to the pressure when the selector valve moves?

A

It will drop

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11
Q

What is the reason for pressure surges?

A

Movement of the selector valve

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12
Q

Aircraft have multiple hydraulic systems are these interconnected?

A

No they are separate

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13
Q

When are power boost systems used?

A

To overcome high control forces, but flight crew still actuate via cable and push rod

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14
Q

What are the benefits to hydraulic power pack systems?

A
  • No need for a central system
  • Reduced weight as no need for long stretches of lines
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15
Q

What are the disadvantages of an open centre system?

A
  • One surface operated at a time
  • Slow actuation
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16
Q

How are the selector valves connected in an open centre system?

A

In series

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17
Q

What is the main advantage of a closed centre system?

A

Multiple user systems can be actuated at the same time

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18
Q

How are the selector valves connected in a closed centre system?

A

In parallel

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19
Q

What system is the most common on aircraft?

A

Closed centre system

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20
Q

What is the difference between flash and fire point?

A

Flash point, the vapour ignites momentarily

Fire point, the vapour ignites and continues to burn

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21
Q

What are the 3 categories of hydraulic fluids?

A
  • Mineral based
  • Polyoalphaolefin
  • Phosphate ester
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22
Q

Is Skydrol fireproof?

A

No

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23
Q

What are the two types of Phosphate -Ester fluids and their subclasses?

A

Type 4
- Class 1 Low density
- Class 2 Standard density
Type 5

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24
Q

Can different types of hydraulic fluid be mixed?

A

No

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25
Q

Where should contamination checks be taken from?

A

Reservoir and other locations

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26
Q

What are the two main servicing activities on hydraulic systems?

A
  • Reservoir filling
  • Fluid sampling
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27
Q

How is pressure refilling done?

A

Use of Ground Service Equipment

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28
Q

Where should the filling be done from and why?

A

Either in the suction or the return portion of the closed centre system, as between the pump and user there it is system pressure

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29
Q

Manual filling is done by what?

A

Hand pump

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30
Q

Refilling is never by done directly into what on large aircraft?

A

The reservoir

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31
Q

What should be done to the system before refilling?

A

Depressurised

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32
Q

How may a leak be found in a hydraulic system?

A
  • Visual inspection
  • Leak measurement valve
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33
Q

Where is the leak measurement valve located?

A

Between the user and the selector valve

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34
Q

During testing, pressure is directed through what?

A

The leak measurement valve

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35
Q

How are the specific parts isolated to test for leaks?

A

Manual selector valves

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36
Q

If there are 2 pumps connected too a reservoir how many suction and return lines are there?

A

Suction: 2
Return: 1

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37
Q

Where would non pressurised reservoirs be used?

A

Small aircraft with low flying altitudes

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38
Q

How is the fluid level checked in a non pressurised reservoir?

A

Visual gauge

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39
Q

Why is there a need for pressurised reservoirs?

A

To supply a positive fluid supply at high altitude

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40
Q

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

A

To allow fluid to travel one way but not the other

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41
Q

How may a hydraulic reservoir be pressurised?

A
  • Pneumatically
  • Hydraulically
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42
Q

How is a hydraulically pressurised reservoir pressurised?

A

Using system pressure

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43
Q

In a hydraulically pressurised reservoir how can the level be indicated?

A

The small piston extension

44
Q

Where would an accumulator be?

A

In between the pump and the user

45
Q

What is the purpose of an accumulator?

A
  • Smooth pulsations
  • Store energy
  • Recover pressure surges
46
Q

How are the chambers separated in a:
- Spherical accumulator?
-Cylindrical accumulator?

A

Spherical: A diaphragm
Cylindrical: A piston

47
Q

How is the piston sealed?

A

Double sealed to stop leaks

48
Q

What are the 3 principle methods of operation?

A
  • Diaphragm
  • Spring type
  • Hydro-pneumatic
49
Q

What can be said about the nitrogen pressure with respect to the system pressure?

A

The nitrogen pressure is less than the system pressure

50
Q

What must be done before checking the nitrogen base pressure?

A

Completely depressurise otherwise you will get a false reading

51
Q

How are the pumps classified?

A
  • Positive displacement
  • Non-positive displacement
52
Q

What types of delivery/volume does a positive displacement pump give out?

A
  • Constant
  • Variable
53
Q

Gear type power pump and Gerotor are examples of what?

A

Positive displacement fixed output

54
Q

What is the purpose of the shear sectioning the drive coupling?

A

To stop damage to the pump or drive shaft if a blockage or unusual conditions occur

55
Q

What dictates piston extension in a piston pump?

A

The Swashplate

56
Q

In a bent axis pump what causes pistons to suck then pressurise the fluid?

A

Angular housing configuration

57
Q

Vane type is an example of what?

A
  • Constant
  • Positive
58
Q

How is the VDP different from a constant displacement pump?

A

The outlet pressure and flow rate can be altered

59
Q

How is the output varied in a VDP?

A

By changing the angle of the Swashplate

60
Q

What is an EDP?

A

Engine driven pump:
- Variable displacement
- Permanent engine connection

61
Q

What is the drive shaft turned by in an electric/Alternating Current Motor Pump (ACMP)?

A

An electric motor

62
Q

Why would an air driven pump be used?

A

To supplement the EDP if it can not maintain system pressure
- Can be auto or manually operated

63
Q

What are the types of hand pumps?

A
  • Rotating
  • Single acting
  • Double acting
64
Q

What is a pump system on airbus aircraft?

A

Power Transfer Unit

65
Q

What is the purpose of the Ram Air Turbine (RAT)?

A

Too provide electrical and hydraulic power if primary sources of power are lost

66
Q

What precaution should be taken before maintenance is carried out on systems that may deploy the RAT?

A

Pull CB’s or place inhibitors

67
Q

What is the main output of the RAT?

A

Hydraulic pressure

68
Q

When can the RAT be retracted?

A

Only on the ground

69
Q

What are the methods of pressurising the reservoir with air?

A
  • Engine/APU bleed air
  • GSE
70
Q

What are the different types of material used in filters?

A
  • Wire mesh
  • CRES
  • Microglass
  • Cellulose paper
71
Q

What are the main components of a filter assembly?

A
  • Filter head assembly
  • Filter bowl
  • Filter element
  • Filter bypass valve
72
Q

Where may a filter be located?

A

LP - after the user
HP - after the pump

73
Q

When would the filter bypass valve be opened?

A

When the filter is clogged and the pressure is building up.

Dirty fluid is preferred to no fluid

74
Q

If there is a differential pressure in a filter, what happens?

A

Filter bypass opens and the red indicator pops out

this also occurs for thermal lockout

75
Q

What are the valve types used in systems?

A
  • Ball type
  • Sleeve type
  • Poppet type
76
Q

Why may a pressure relief valve be used?

A

As a:
- System relief valve
- Thermal relief valve

77
Q

When would a relief valve be opened?

A

When the pressure in the line exceeds the max/system pressure

78
Q

What is the purpose of the pressure regulator?

A

Used to keep output pressure within a certain threshold and permit pump to turn without resistance

79
Q

Where would pressure relief and regulators be installed?

A

After the pump in the pressure subsystem

80
Q

Why would a pressure reducer valve be used?

A

To supply systems with a lower pressure than systems pressure

81
Q

What is the purpose of shutoff valve?

A

Two shutoff the system. Two positions on or off

82
Q

What is the purpose of each part in a 4 way valve?

A
  • Pressure
  • Return
  • 3rd and 4th connected to actuator
83
Q

Is there fluid flow in a closed centre system when valves are in neutral or off?

A

No fluid flow

84
Q

In fly-by-wire how are selector valves positioned?

A

Solenoid operated

85
Q

What is the purpose of a sequence valve?

A

Control the sequence of operation between two branches in a circuit

86
Q

What is given priority by a priority valve?

A

Critical systems over non critical when pressure is low

87
Q

How can a sequence valve be controlled?

A
  • Mechanically
  • Pneumatic
88
Q

What is a use of a sequence valve?

A

To ensure that the landing gear doors open first before the gear moves

89
Q

Where are quick disconnect valves used?

A

In suction and pressure lines either side of the pump

90
Q

How is the piston moved in the pressure controlled sequence valve?

A

When pressure builds up in the primary unit it lifts up the piston allowing the pressure to head to the secondary heavier unit

91
Q

What are non-return valves?

A

Valves that only permit flow in one direction

92
Q

What does a shuttle valve consist of?

A

2 inlets, 1 outlet

93
Q

What is a hydraulic fuse?

A

Safety device that shuts off supply when a fuse detects a sudden flow increase such as a burst in the pipe

94
Q

Where are hydraulic fuses found?

A
  • Brakes
  • Flaps and slats
  • Nose landing gear extension and retraction
  • Thrust reverser pressure and return
95
Q

In a single action actuator how is the actuator returned?

A

Via a spring

96
Q

How is a double acting actuator returned?

A

Hydraulically

97
Q

All seals can be classified into 3 groups what are they?

A
  • Gaskets
  • Packings
  • Wipers
98
Q

When would a gasket be used?

A

To seal two components that don’t move relative to each other

99
Q

When would a packing seal be used?

A

Seal internally on sliding components

100
Q

What should be done when installing/removing o-rings?

A
  • Avoid use of sharp tools
  • Use specialised tools
  • Inspect and clean parts that get new seals
  • Immerse o-ring in hydraulic fluid be fore installation
101
Q

What is the purpose of a back up ring?

A

To support the o-ring when it is subjected to differential loads

102
Q

Where should a pressure switch be installed?

A

After the pump

103
Q

When would the pressure circuit close the circuit to raise the alarm?

A

When the pressure is above or below a certain point

104
Q

What does a pressure transducer do?

A

Samples and records the pressure i.e. they display the actual pressure in the flight deck like 2900 psi

105
Q

What provides a pressure warning?

A

The pressure switch

106
Q

What does the power by wire system utilise?

A

Hydraulic packs local to the area

CAA Module 11 (22 decks)

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