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Aircraft Systems > Basic Hydraulics > Flashcards

Basic Hydraulics Flashcards

1
Q

science relating to the behavior of liquids under various conditions and in aircraft

A

hydraulics

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2
Q

provides a means of operating large and remote components that it would not be possible to operate satisfactorily by other means

A

hydraulic system

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3
Q

provide a means of power transmission through the medium of hydraulics through an incompressible fluid via pipelines and actuators

A

aircraft systems

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4
Q

provide the power for the operation of components

A

hydraulic systems

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5
Q

stated that if a force is applied to a liquid in a confined space, then this force will be felt equally in all directions

A

Blaise Pascal

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6
Q

17th century mathematician concerned with Pascal’s Law

A

Blaise Pascal

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7
Q

Principle where all hydraulic systems operate

A

Pascal’s Law

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8
Q

force employed when a hydraulic system is operated

A

pressure

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9
Q

created only when an attempt is made to compress fluids

A

hydraulic pressure

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10
Q

Without some form of _____, there can be no pressure

A

restriction

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11
Q

required to deliver a flow of fluid into the system

A

pump

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12
Q

In hydraulic systems, this restriction is provided by movable pistons which travel backwards and forwards in cylinders.

A

hydraulic jacks or actuators

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13
Q

invented a hydraulic press called the Bramah Press

A

Joseph Bramah

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14
Q

The _____ the area under load, the greater the pressure generated. The _____ the area under pressure, the greater will be the load available.

A

smaller, larger

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15
Q

Name at least 3 hydraulic fluid properties

A
  • Incompressible
  • Good Lubricating Properties
  • Good Viscosity
  • High Boiling Point/Low Freezing Point
  • High Flash Point/Non-Flammable
  • Chemically Inert/Non-Corrosive
  • Resistant to Evaporation
  • Free from Sludging and Foaming
  • Reasonably Priced
  • Readily Available
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16
Q

DEF STAN 91-48 is also known as

A

H515 NATO, OM15, MIL-H-5606F

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17
Q

Clean mineral hydraulic fluid

A

DEF STAN 91-48

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18
Q

hydraulic fluid colored red

A

DEF STAN 91-48

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19
Q

Used with synthetic neoprene rubber seals

A

DEF STAN 91-48

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20
Q

Recommended for all hydraulic systems under high pressures and low or very low temperatures

A

DEF STAN 91-48

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21
Q

temperature for DEF STAN 91-48

A

-54 deg cel to 90 deg cel

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22
Q

Phosphate ester based synthetic hydraulic fluid

A

Skydrol

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23
Q

hydraulic fluid purple in color

A

Skydrol

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24
Q

Used with Synthetic Butyl Rubber Seals

A

Skydrol

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25
Q

Prolonged exposure will damage skin and eyes

A

Skydrol

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26
Q

Very high flashpoint

A

Skydrol

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27
Q

flashpoint of Skydrol

A

170 deg cel

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28
Q

less prone to cavitation

A

Skydrol

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29
Q

Force is expended in overcoming static resistance (friction) which are:

A
  • Friction in cylinders caused by moving parts
  • Piston rods rubbing against bearings and seals
  • Fluid rubbing against the pipe walls
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30
Q

Large bore pipes and frictionless pistons would allow ______ of the force to be utilized but would incur large weight and cost penalties.

A

nearly 100%

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31
Q

Friction between pistons and cylinders and piston rods and bearings cannot be completely eliminated, it can only be lessened by _______.

A

good design and workmanship

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32
Q

The friction between the walls of the pipes and the fluid depends upon:

A
  • velocity of the fluid in the pipes
  • Length, bore, and the internal finish of the pipes
  • number of bends
  • viscosity of the oil
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33
Q

prevents leakage of fluid in hydraulic systems

A

seals

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34
Q

prevent fluid leaks by being squeezed between two non-moving surfaces

A

static seals, gaskets, packing

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35
Q

these seals are effective in one direction only

A

U and V ring seals

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36
Q

these seals are often used where pressure is applied in either direction

A

O ring seal, square section seal

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37
Q

it is usually fitted with O-ring, where high pressures are used

A

stiff backing ring

38
Q

retains the shape of the seal and prevents it from being squeezed between the two moving surfaces

A

stiff backing ring

39
Q

these seals require lubrication to remain effective

A

dynamic seals

40
Q

_____ of the bearing surface or a slight seepage from the seals is normally acceptable.

A

wetting

41
Q

often installed on actuators to prevent any grit that may be deposited on the piston rod from contaminating the seals

A

wiper ring

42
Q

Components of a Basic Hydraulic System

A

Reservoir, Pump, Filter, Relief Valve, Selector Valve, Actuator

43
Q

delivers oil to the pump and receives oil from the actuators

A

reservoir of oil

44
Q

either hand, engine, or electrically driven

A

pump

45
Q

enables the operator to select the direction of the flow of fluid to the required service and providing a return path for the oil to the reservoir

A

selector valve or control valve

46
Q

actuate the component

A

jack or set of jacks or actuators

47
Q

keep the fluid clean

A

filter

48
Q

as a safety device to relieve excess pressure

A

relief valve

49
Q

Apart from light aircraft breaks, it has little practical use

A

Passive Hydraulic System

50
Q

in such a system, the pump supplies the pressure

A

Active Hydraulic System

51
Q

Two Types of Active Hydraulic System

A

Open Center System, Closed System

52
Q

main advantage of this system is that it is simple, the main disadvantage is that only one service can be operated at a time

A

Open Center System

53
Q

Fluid is passed directly to the reservoir when no services are being operated

A

offloaded condition

54
Q

When the actuator reaches the end of its travel, selector is ________ in order to offload the pump and allow other services to be selected.

A

returned to neutral

55
Q

The relief valve will relieve excess pressure if the selector is ______ to its neutral position.

A

not returned

56
Q

Its great advantage is that multiple services can be operated at the same time. However, its use is only limited by the volume flow capacity of the pump.

A

Closed System

57
Q

With this type of system, operating pressure is maintained in that part of the system which leads to the selector valves, and some method is used to prevent over-loading the pump.

A

Closed System

58
Q

fitted in systems that employ a fixed volume pump (constant delivery) to divert pump output to the reservoir when pressure has built up to normal operating pressure

A

automatic cut-out valve

59
Q

Difference of a Closed System and an Open Center System

A
  • two or more services can be operated at the same time
  • not important to return the selector valve to neutral once operation is complete
60
Q

Why is it not important to return the selector valve to neutral once operation is complete in a closed system?

A

A closed system is designed to deal with the consequent pressure increase.

61
Q

Extra fluid is stored in the reservoir due to the following reasons:

A
  • No system is leak free.
  • Fluid expands and contracts as heated or cooled.
  • Actuator need more fluid when they are extended than contracted.
  • Cavitation
62
Q

monitor the system in a reservoir

A

quantity transmitter unit

63
Q

prevents debris in entering the reservoir

A

filling inlet (normally sealed with filler cap)

64
Q

fitted in both suction and pressure lines that is at both sides of the pump

A

filters

65
Q

protects the pump

A

suction filter

66
Q

ensures the cleanliness of fluid during use

A

pressure filter

67
Q

filter in the fluid return line to the reservoir to remove particles picked up during operation

A

return filter

68
Q

allows unfiltered fluid to pass to the system when the element becomes clogged

A

relief or bypass valve

69
Q

This type of filter element must be changed at regular intervals before clogging occurs

A

relief or bypass valve

70
Q

draws oil from the reservoir and deliver a supply of fluid to the system

A

pumps

71
Q

used to provide alternate supply as part of the redundancy provision for the safe operation of the aircraft

A

air pump, ram air turbine, power transfer unit (PTU)

72
Q

may be the only source of power in a small, light aircraft hydraulic system; may also be used on larger aircraft in some cases

A

hand pumps

73
Q

allows ground servicing to take place without the need for engine running; so that the lines and joints can be pressure tested; so that cargo doors can be operated without power

A

hand pumps

74
Q

Classification of Pumps

A
  • Constant Delivery (Fixed Volume) Pump
  • Constant Pressure (Variable Volume) Pump
75
Q

Supplies fluid at constant rate irrespective of demand and therefore needs an automatic cut out or relief valve to return the fluid to the reservoir

A

Constant Delivery (Fixed Volume) Pump

76
Q

fitted to a system employing a constant delivery (fixed volume) pump, to control system pressure and to return fluid to the reservoir

A

Automatic Cut-Out Valve

77
Q

This pump supplies fluid at a variable volume and controls its own pressure

A

Constant Pressure (Variable Volume) Pump

78
Q

Constant Pressure (Variable Volume) Pump is typically fitted in modern aircraft whose systems operate at ________.

A

3,000 to 4,000 psi

79
Q

This is fitted:
a) To store hydraulic fluid under pressure
b) To dampen pressure fluctuations
c) To allow for thermal expansion
d) To provide an emergency supply of fluid to the system in then event of pump failure
e) To prolong the period between cut out and cut in time of the ACOV and so reduce the wear on the pump
f) Provides the initial fluid when a selection is made, and the pump is cut out

A

hydraulic accumulator

80
Q

Used to convert fluid flow into linear or rotary motion

A

hydraulic jacks or actuators

81
Q

consist of an outer cylinder within which slides a piston and seal assembly

A

hydraulic jacks or actuators

82
Q

passes through a seal and wiper ring assembly fitted into the end of the cylinder

A

piston rod (or ram)

83
Q

Hydraulically operated in one direction only; normally used as a locking device; has more fluid in the cylinder when the rod is extended

A

Single Acting Actuator

84
Q

actuator used in most aircraft systems

A

double acting unbalanced actuator

85
Q

equal force can be applied to both sides of the piston on this actuator; often used in applications such as nose wheel steering; Either one or both sides of the piston rod may be connected to a mechanism

A

double acting balanced actuator

86
Q

formed when fluid is trapped between the piston of the actuator and a non-return valve or a selector valve at its neutral position

A

hydraulic lock

87
Q

used to maintain or limit fluid pressures in various parts of a hydraulic system

A

relief valves, pressure maintaining valves, pressure reducing valves

88
Q

components used to control the flow of fluid to the various services operated by the hydraulic system

A

flow control components

89
Q

Give at least three flow control components

A
  • non-return valves
  • restrictor valves (or choke)
  • selectors
  • electrically operated selectors
  • shuttle valves
  • sequence valves
  • modulators
  • flow control valves
  • fuses
90
Q

disadvantage of pneumatics

A

air is extremely compressible

Aircraft Systems (9 decks)

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