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ASA General and Airframe Oral > Hydraulic and Pneumatic Systems > Flashcards

Hydraulic and Pneumatic Systems Flashcards

1
Q

What kind of filter is a micronic filter?

A

A filter with a special paper element.

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2
Q

What is a double-action pump?

A

A pump that delivers fluid with the movement of the pump handle in both directions.

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3
Q

Why do most engine-driven hydraulic pumps have a shear section in their drive couplings?

A

if the pump should seize, the shear section will break, disconnecting the pump from the engine and preventing further damage.

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4
Q

What are the two basic types of hydraulic fluid used in modern aircraft?

A

Mineral base fluid and phosphate ester base fluid.

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5
Q

Does the main hydraulic pump take its fluid from the bottom of the reservoir, or from a standpipe?

A

The main pump normally takes its fluid from a standpipe, while the emergency pump takes its fluid from the bottom of the reservoir. If a break in the system should allow the main pump to pump all of its fluid overboard, there will still be enough fluid in the reservoir to allow the emergency system to extend the landing gear and actuate the brakes.

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6
Q

Why are some hydraulic reservoirs pressurized?

A

Pressurization ensures that fluid will be supplied to the inlet of the pumps at a high altitude where there is not enough atmospheric pressure to do this.

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7
Q

What are two ways aircraft hydraulic reservoirs may be pressurized?

A

By an aspirator in the fluid return line or by bleed air from one of the engine compressors.

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8
Q

What is used to flush a hydraulic system that uses Skydrol hydraulic fluid?

A

Trichlorethylene or the solvent recommended by the aircraft manufacturer.

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9
Q

What is used to flush a hydraulic system that uses mineral base hydraulic fluid?

A

Naphtha
Varsol
Stoddard solvent

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10
Q

Where can you find the type of hydraulic fluid required for a particular aircraft?

A

In the maintenance manual for the aircraft. This information is also on a placard on the system reservoir.

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11
Q

What type of pump is a gear pump considered?

A

A gear pump is a constant displacement, high pressure pump.

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12
Q

What type of pump is a piston pump with a variable cam plate considered?

A

Fuel pumps may be divided into two distinct system categories: (1) constant displacement and (2) variable displacement. A piston pump with a variable cam changes the effective (not actual) length of each piston stroke. This makes this type of pump a variable displacement with constant pressure.

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13
Q

What is the purpose of an accumulator in an aircraft hydraulic system?

A

The accumulator holds pressure on the hydraulic fluid in the system. The pressure is held by compressed air or nitrogen acting on the fluid through a bladder, a diaphragm, or a piston.

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14
Q

What is a single-action hydraulic actuating cylinder?

A

A linear actuating cylinder that uses hydraulic fluid under pressure to move the piston in only one direction. The piston is returned by a spring.

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15
Q

What is the difference between a single-acting and double-acting hand pump?

A

Single-action pumps move fluid on only one direction of handle operation. Double-acting hand pumps move fluid on both directions of handle movement.

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16
Q

If a system requires a lower pressure than system pressure, what type of valve is used?

A

A pressure reducer valve.

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17
Q

What is used to remove phosphate-ester base hydraulic fluid from aircraft tires?

A

Soap and water.

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18
Q

How can you be sure that a replacement seal in a hydraulic component is compatible with the fluid used in the system?

A

Use only the seal identified by part number that is specified in the component maintenance manual.

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19
Q

What must be done to the lines that are disconnected when replacing an aircraft hydraulic system component?

A

They must be capped with the correct fluid line cap or plug. Masking tape or other types of adhesive tape should never be used.

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20
Q

What must be done before a pressurized reservoir is serviced?

A

All of the pressure must be bled off.

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21
Q

What system fault could cause an accumulator pre-charge pressure to increase?

A

A leaking seal in the accumulator that allows fluid to pass into the air side of the accumulator.

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22
Q

What is the first step when checking hydraulic reservoir fluid level?

A

Verify that the hydraulic systems are set to the configuration specified in the maintenance manual. For example: landing gear down, gear doors retracted, parking brake off, thrust reversers retracted, and pressure accumulators set to the correct pressures.

23
Q

What is the most likely cause of hydraulic fluid flowing through a filter bypass valve?

A

The filter has become clogged.

24
Q

What are two basic differences between a hydraulic and a pneumatic system?

A

The fluid in a pneumatic system is compressible and that used in a hydraulic system is incompressible. A pneumatic system has no return system.

25
Q

What type of pump is used in a low-pressure pneumatic system?

A

A vane-type pump.

26
Q

What are two functions of a low-pressure pneumatic system in an aircraft?

A

to operate the gyros in flight instruments, and to inflate pneumatic deicer boots.

27
Q

Why do high-altitude aircraft that have pneumatic gyro instruments use pressure-actuated instruments rather than vacuum-actuated instruments?

A

At a high altitude there is not enough air mass to drive the gyros at their required speed.

28
Q

What effect would a dirty inline air filter have on the operation of pneumatic gyro instruments?

A

the instruments would not get enough air to spin up to their required speed.

29
Q

Of What material are the vanes in a dry type air pump made?

A

Carbon.

30
Q

What kind of device is used to control the speed of movement of the piston in a pneumatic actuator?

A

A variable orifice.

31
Q

What is the purpose of the moisture separator in a high-pressure pneumatic system?

A

The separator collects moisture from the air and holds it on a baffle until the system is shut down. When the inlet pressure to the moisture separator drops below 450 psi, a drain valve opens, and all of the accumulated moisture is discharged overboard. A moisture separator removes about 98% of the moisture in the air.

32
Q

What are two types of filters that are used in aircraft pneumatic systems?

A

Micronic (paper) type, and screen type.

33
Q

Where is the inlet air filter normally located for a pneumatic gyro instrument system powered by engine-driven air pumps?

A

Inside the cabin of the aircraft.

34
Q

Where is the inlet air filter normally located for a pneumatic gyro instrument system powered by engine-driven air pumps?

A

It is provided either by operating the aircraft engines, or from an external source of air through pressure-regulated test equipment.

35
Q

How is the air charge of an accumulator checked for proper servicing?

A

All hydraulic pressure must be bled from the system and the pressure is checked on the gauge.

36
Q

Is a chevron seal a one-way or two-way seal?

A

A one-way seal.

37
Q

To which side of a chevron seal should the pressure be applied?

A

The open side.

38
Q

Is an O-ring seal a one-way or a two-way seal?

A

A two-way seal.

39
Q

How can you be sure of getting an O-ring made of the correct material for a specific hydraulic component?

A

The O-ring must have the correct part number and it must have been obtained from a reputable source.

40
Q

On which side of an O-ring should the backup ring be placed?

A

On the side away from the source of pressure.

41
Q

What should be done to the sharp edges of threads and actuator pistons when installing O-rings?

A

The sharp edges should be covered with paper.

42
Q

Where are line-disconnect fittings normally located in an aircraft hydraulic system?

A

Normally in the lines that connect the engine-driven pump to the aircraft hydraulic system.

43
Q

What is the purpose of an orifice check valve in an aircraft hydraulic system?

A

An orifice check valve allows full flow of fluid in one direction through the valve, but restricts the flow in the opposite direction.

44
Q

What is the difference in function between a pressure regulator and a pressure relief valve?

A

Pressure regulators control overall system pressure. Pressure relief valves act as a back-up to the pressure regulator to prevent overpressure damage to the system and components.

45
Q

What does an unloading valve do in a hydraulic system?

A

The unloading valve, or pressure regulator, controls system pressure by shifting the pump outlet fluid from the pressurized system back into the reservoir when the system pressure is high enough. The fluid circulates with very little load on the pump until the system pressure drops to the regulator kick-in value. The pump then forces fluid into the system until the pressure builds back up to the regulator kick-out value.

46
Q

What is a sintered metal hydraulic fliter?

A

A surface filter whose element is made of powdered metal fused under heat and pressure.

47
Q

What is the purpose of the differential pressure indicator on a hydraulic filter?

A

It indicates when the filter is clogged and fluid is bypassing the filter element.

48
Q

What is a Cuno filter?

A

An edge filter made of a stack of thin metal discs separated by thin scraper blades. Contaminants collect on the edge of the disc and are periodically scraped out by rotating the discs. The contaminants collect in the bottom of the filter case for future removal.

49
Q

What is the danger of not relieving hydraulic system pressure before servicing or disassembly?

A

High-pressure fluid can be released, causing damage to aircraft systems or personnel.

50
Q

What precautions should be taken when working around high-pressure gases and fluids?

A

Wear the proper PPE and always depressurize the system in accordance with the aircraft maintenance manual prior to any disassembly.

51
Q

Where should hydraulic fluids be stored?

A

Many hydraulic fluids are flammable and should be stored in metal, flammable-resistant cabinets.

52
Q

What PPE should be considered when working with hydraulic fluids?

A

Always consult the SDS for the fluids. Eye protection and skin protection (gloves) are minimum PPE.

53
Q

What are the dangers of mixing hydraulic fluids?

A

the desired properties of the fluids will be compromised. Damage may occur to internal O-rings and seals, causing systems to fail.

54
Q

What is the risk of using the wrong seal or hydraulic fluid in a system?

A

Incompatible seals and hydraulic fluids will cause seals to deteriorate and fail, leading to a failure of the system.

ASA General and Airframe Oral (28 decks)

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