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Avionics > HYDRAULIC AND PNEUMATIC SYSTEMS > Flashcards

HYDRAULIC AND PNEUMATIC SYSTEMS Flashcards

1
Q

To protect packing rings or seals from damage when it is necessary to install them over or inside threaded sections, the

A

Threaded section should be covered with a suitable sleeve

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2
Q

To prevent external and internal leakage in aircraft hydraulic units, the most commonly used type of seal is the

A

O – ring seal

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3
Q

Which allows free fluid flow in one direction and no fluid flow in the other direction?

A

Check valve

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4
Q

Select the valve used in a hydraulic system that directs pressurized fluid to one end of an actuating cylinder and simultaneously directs return fluid to the reservoir from the other end.

A

Selector

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5
Q

What function does the absolute pressure regulator perform in the pneumatic power system?

A

Regulates the compressor inlet air to provide a stabilized source of air for the compressor

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6
Q

(1) Relief valves are used in pneumatic systems as damage-preventing units.
(2) Check valves are used in both hydraulic and pneumatic systems.
Regarding the above statements,

A

Both no. 1 and 2 are true

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7
Q

One of the distinguishing characteristics of an open-center selector valve used in a hydraulic system is that

A

Fluids flow through the valve in the off position

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8
Q

What type of packings should be used in hydraulic components to be installed in a system containing Skydrol?

A

Packing materials made for easter based fluid

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9
Q

Relief valves are used in pneumatic systems

A

As damage preventing units

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10
Q

An aircraft pneumatic system, which incorporates an engine-driven multistage reciprocating compressor, also requires

A

A moisture separator

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11
Q

The removal of air from an aircraft hydraulic system is generally accomplished

A

By operating the various hydraulic components through several cycles

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12
Q

Pneumatic systems utilize

A

Relief valve

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13
Q

The component in the hydraulic system that is used to direct the flow of fluid is the

A

Selector valve

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14
Q

What type of selector valve is one of the most commonly used in hydraulic systems to provide for simultaneous flow of fluid into and out of a connected actuating unit?

A

Four port , closed center valve

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15
Q

What is the purpose of using backup rings with O-rings in hydraulic systems above 1,500 PSI?

A

Prevent high pressure from extruding the seal between the moving and stationary part

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16
Q

The purpose of the pressure regulator in a hydraulic system is to

A

Maintain system operating pressure within a predetermined range and to unload the pump

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17
Q

A flexible sealing element subject to motion is a

A

Packing

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18
Q

Which characteristics apply to aircraft hydraulic systems?
1. Minimum maintenance requirements.
2. Lightweight.
3. About 80 percent operating efficiency (20 percent loss due to fluid friction).
4. Simple to inspect.

A

1,2,4

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19
Q

If a rigid tube is too short for the flare to reach its seat before tightening, pulling it into place by tightening

A

May distort the flare

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20
Q

The installation of a new metal hydraulic line should be made with

A

Enough bends to allow the tube to expand and contract with temperature changes and to absorb vibration

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21
Q

Extrusion of an O-ring seal is prevented in a high-pressure system by the use of a

A

Back up ring on the side of the O – ring away from the pressure

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22
Q

What is one advantage of piston-type hydraulic motors over electric motors?

A

There is no fire hazard if the motor is installed

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23
Q

Generally, the first step in removing an accumulator from an aircraft is to

A

Relieve system pressure

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24
Q

If a hydraulic brake system uses neoprene rubber packing materials, the correct hydraulic fluid to service the system is

A

Mineral based oil

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25
Q

The internal resistance of a fluid which tends to prevent it from flowing is called

A

Viscosity

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26
Q

What is the viscosity of hydraulic fluid?

A

The internal resistance of fluid which tends to prevent it from flowing

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27
Q

Which is a characteristic of petroleum base hydraulic fluid?

A

Flammable under normal condition

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28
Q

(1) When servicing aircraft hydraulic systems, use the type fluid specified in the aircraft manufacturer’s
maintenance manual or on the instruction plate affixed to the reservoir or unit.
(2) Hydraulic fluids for aircraft are dyed a specific color for each type of fluid.
Regarding the above statements,

A

Both no. 1 and 2 are true

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29
Q

Petroleum base hydraulic fluid is which color?

A

Red

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30
Q

Which of the following is adversely affected by atmospheric humidity if left unprotected?
1. MIL-H-5606 hydraulic fluid.
2. Skydrol hydraulic fluid.
3. None of the above.

A

2

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31
Q

Which is a characteristic of synthetic base hydraulic fluid?

A

High flash point

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32
Q

Which statement about fluids is correct?

A

All fluids readily transmit pressure

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33
Q

Two types of hydraulic fluids currently being used in civil aircraft are

A

Mineral base and phosphate ester base

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34
Q

Which of the following lists only desirable properties of a good hydraulic fluid?

A

Low viscosity, chemical stability, high flashpoint, high fire point

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35
Q

Characteristics of MIL-H-8446 (Skydrol 500 A & B) hydraulic fluid are

A

Light purple color, phosphate ester base, fire resistant, butyl rubber seals

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36
Q

Where can information be obtained about the compatibility of fire-resistant hydraulic fluid with aircraft materials?

A

Manufacturer technical bulletin

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37
Q

Characteristics of MIL-H-5606 hydraulic fluid are

A

Red color, petroleum base, will burn, uses synthetic rubber seals

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38
Q

Characteristics of MIL-H-7644 hydraulic fluid are

A

Blue color, vegetable base, will burn, natural rubber seals

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39
Q

If an aircraft hydraulic system requires mineral base hydraulic fluid, but phosphate ester base hydraulic fluid is used, what will be the effect on the system?

A

System will be contaminated , fluids will not blend, and the seals will fail

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40
Q

What is used to flush a system normally serviced with MIL-H-5606 hydraulic fluid?

A

Naptha or varsol

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41
Q

Components containing phosphate ester-base hydraulic fluid may be cleaned with

A

Stoddard solvent

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42
Q

How can the proper hydraulic fluid to be used in an airplane be determined?

A

Consult the aircraft manufacturers manual

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43
Q

Phosphate ester base hydraulic fluid is very susceptible to contamination from

A

Water in the atmosphere

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44
Q

(1) Materials which are Skydrol compatible or resistant include most common aircraft metals and
polyurethane and epoxy paints.
(2) Skydrol hydraulic fluid is compatible with nylon and natural fibers.
Regarding the above statements,

A

Both no.1 and 2 are true

45
Q

The hydraulic component that automatically directs fluid from either the normal source or an emergency source to an actuating cylinder is called a

A

Shuttle valve

46
Q

The primary purpose of a hydraulic actuating unit is to transform

A

Fluid pressure into useful work

47
Q

The primary function of the flap overload valve is to

A

prevent flaps from being lowered at airspeeds which would impose excessive structural loads

48
Q

A unit which transforms hydraulic pressure into linear motion is called

A

Actuating cylinder

49
Q

If it is necessary to adjust several pressure regulating valves in a hydraulic system, what particular sequence, if any, should be followed?

A

Units with highest pressure settings are adjusted first

50
Q

If an aircraft’s constant-pressure hydraulic system cycles more frequently than usual and no fluid leakage can be detected, the most probable cause is

A

Low accumulator air preload

51
Q

Unloading valves are used with many engine-driven hydraulic pumps to

A

Relief the pump pressure

52
Q

What safety device is usually located between the driving unit and hydraulic pump drive shaft?

A

Pump drive coupling shear section

53
Q

Which valve installed in a hydraulic system will have the highest pressure setting?

A

Thermal relief valve

54
Q

Excluding lines, which components are required to make up a simple hydraulic system?

A

Pump, reservoir, selector valve, and actuator

55
Q

Most variable displacement hydraulic pumps of current design

A

Contain a built in means of system pressure regulation

56
Q

In a gear-type hydraulic pump, a mechanical safety device incorporated to protect the pump from overload is the

A

Shear pin

57
Q

After installation of a rebuilt hydraulic hand pump, it is found that the handle cannot be moved in the pumping direction (pressure stroke). The most likely cause is an incorrectly installed

A

Hand pump out port check valve

58
Q

Pressure is a term used to indicate the force per unit area. Pressure is usually expressed in

A

Pounds per square inch

59
Q

If two actuating cylinders which have the same cross-sectional area but different lengths of stroke are connected to the same source of hydraulic pressure, they will exert

A

Equal amount of force and will move at the same rate of speed

60
Q

Using a hand pump, pressure of 100 PSI has been built up in a hydraulic system. The hand pump piston is 1 inch in diameter. A 1/2-inch line connects the hand pump to an actuating cylinder 2 inches in
diameter. What is the pressure in the line between the hand pump and the actuator?

A

100psi

61
Q

Heat exchanger cooling units are required in some aircraft hydraulic systems because of

A

High pressures and high rates of fluid flow

62
Q

Which is true regarding the ground check of a flap operating mechanism which has just been installed?

A

If the time required to operate the mechanism decreases with successive operations, it indicates the air is being worked out of the system

63
Q

A hydraulic system operational check during ground runup of an aircraft indicates that the wing flaps cannot be lowered using the main hydraulic system, but can be lowered by using the emergency hand
pump. Which is the most likely cause?

A

The fluid level in the reservoir is low

64
Q

Many hydraulic reservoirs contain a small quantity of fluid which is not available to the main system
pump. This fluid is retained to

A

Supply fluid to the auxiliary pump

65
Q

The unit which causes one hydraulic operation to follow another in a definite order is called a

A

Sequence valve

66
Q

The purpose of a hydraulic pressure regulator is to

A

Relieve the pump of its load when no actuating units are being operated

67
Q

Severe kickback of the emergency hydraulic hand pump handle during the normal intake stroke will indicate which of the following?

A

The hand pump port check valve is sticking open

68
Q

What type of valve in an aircraft hydraulic system permits fluid to flow freely in one direction, but restricts the rate at which fluid is allowed to flow in the other direction?

A

Orifice check valve

69
Q

The main system pressure relief valve in a simple hydraulic system equipped with a power control valve should be adjusted

A

With the power control valve held in the closed position

70
Q

A hydraulic accumulator is charged with an air preload of 1,000 PSI. When a hydraulic system pressure of 3,000 PSI is developed, the pressure on the air side of the accumulator will be

A

3000 psi

71
Q

How is the air in a hydraulic accumulator prevented from entering the fluid system?

A

By physically separating the air chamber from the oil chamber with a flexible or movable separator

72
Q

After a hydraulic accumulator has been installed and air chamber charged, the main system hydraulic pressure gauge will not show a hydraulic pressure reading until

A

The fluid side of the accumulator has been charged

73
Q

Which must be done before adjusting the relief valve of a main hydraulic system incorporating a pressure regulator?

A

Eliminate the action of the unloading valve

74
Q

Which seals are used with petroleum base hydraulic fluids?

A

Buna - n

75
Q

The air that is expended and no longer needed when an actuating unit is operated in a pneumatic system is

A

Exhausted or dump, usually overboard

76
Q

Some hydraulic systems incorporate a device which is designed to remain open to allow a normal fluid flow in the line, but closed if the fluid flow increases above an established rate. This device is generally
referred to as a

A

Hydraulic fuse

77
Q

When hydraulic system pressure control and relief units fail to function properly, how are most systems protected against overpressure?

A

A shear section of the main hydraulic pump drive shaft

78
Q

A worn hydraulic pump shaft seal can normally be detected by

A

Hydraulic fluid flowing from the pump drain line

79
Q

If an engine-driven hydraulic pump of the correct capacity fails to maintain normal system pressure during the operation of a cowl flap actuating unit, the probable cause is

A

Restriction in the pump outlet

80
Q

Before removing the filler cap of a pressurized hydraulic reservoir,

A

Relieve the air pressure

81
Q

What happens to the output of a constant-displacement hydraulic pump when the hydraulic system pressure regulator diverts the fluid from the system to the reservoir?

A

The output pressure reduces, but the volume remains the same

82
Q

Hydraulic system accumulators serve which of the following functions?
1. Dampen pressure surges.
2. Supplement the system pump when demand is beyond the pump’s capacity.
3. Store power for limited operation of components if the pump is not operating.
4. Ensure a continuous supply of fluid to the pump.

A

1,2,3

83
Q

Chattering of the hydraulic pump during operation is an indication

A

The air is entering the pump

84
Q

Quick-disconnect couplings in hydraulic systems provide a means of

A

Quickly connecting and disconnecting hydraulic lines without loss of fluid or entrance of air in the
system

85
Q

Which seal/material is used with phosphate ester base hydraulic fluids?

A

Butyl rubber

86
Q

A hydraulic pump is a constant-displacement type if it

A

Delivers a uniform rate of fluid flow

87
Q

A hydraulic motor converts fluid pressure to

A

Rotary motion

88
Q

A crossflow valve which is designed to bypass fluid from one side of an actuating cylinder to the other side, under certain conditions, may be found in some aircraft installed in the

A

Landing gear system

89
Q

Hydraulic fluid filtering elements constructed of porous paper are normally

A

Discarded at regular intervals and replaced with new filtering elements

90
Q

A pilot reports that when the hydraulic pump is running, the pressure is normal. However, when the pump is stopped, no hydraulic pressure is available. This is an indication of a

A

Leaking accumulator air valve

91
Q

If fluid is added to a reservoir in a constant pressure hydraulic system while the system is pressurized, what will result?

A

The fluid level will increase when the system pressure is reduced

92
Q

In a hydraulic system that has a reservoir pressurized with turbine-engine compressor bleed air, which unit reduces the air pressure between the engine and reservoir?

A

Air pressure regulator

93
Q

What is the main purpose of a pressurized reservoir in a hydraulic system?

A

Prevent hydraulic pump cavitation

94
Q

One of the main advantages of skydrol is its

A

Wide operating temperature

95
Q

Hydraulic fluid reservoirs are sometimes designed with a standpipe in one of the outlet ports in order to assure emergency supply of fluid. The outlet port with the standpipe in it furnishes fluid to the

A

Normal system power pump

96
Q

An emergency supply of fluid is often retained in the main hydraulic system reservoir by the use of a standpipe. The supply line is connected to the

A

inlet of the main system pump

97
Q

To check the air charge in a hydraulic accumulator,

A

Reduce all hydraulic pressure, then observe the reading on the accumulator air gauge

98
Q

How would the air pressure charge in the accumulator be determined if the engine is inoperative, but the system still has hydraulic pressure?

A

Operate a hydraulic unit slowly and note the pressure at which a rapid pressure drop begins as it goes toward zero

99
Q

How many of these seals are used with petroleum base hydraulic fluids?
1. Synthetic rubber.
2. Natural rubber.
3. Neoprene rubber.

A

1

100
Q

Hydraulic system thermal relief valves are set to open at a

A

Higher pressure than the system relief valve

101
Q

Chatter in a hydraulic system is caused by

A

Air in the system

102
Q

If hydraulic fluid is released when the air valve core of the accumulator is depressed, it is evidence of

A

A ruptured diaphragm and a leaking seals

103
Q

Although dents in the heel of a bend are not permissible, they are acceptable in the remainder of a hydraulic tube providing they are less than what percent of the tube diameter?

A

20

104
Q

If the hydraulic system pressure is normal while the engine-driven pump is running, but there is no pressure after the engine has been shut off, it indicates

A

No pressure in the accumulator

105
Q

The purpose of restrictors in hydraulic systems is to

A

Control the rate of movement of hydraulically operated mechanism

106
Q

A common cause of slow actuation of hydraulic components is

A

Internal leakage in the actuating unit

107
Q

A loud hammering noise in a hydraulic system having an accumulator usually indicates

A

Too low or no preload in the accumulator

108
Q

Teflon hose that has developed a permanent set from being exposed to high pressure or temperature should

A

Not be tightened or bent further

109
Q

In a typical high-pressure pneumatic system, if the moisture separator does not vent accumulated water when the compressor shuts down, a likely cause is a

A

Malfunctioning solenoid dump valve

Avionics (9 decks)

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