Airframe Systems & Components: Hydraulic & Pneumatic Systems 🔊

Question 1

What are the three principal categories of hydraulic fluids?

Answer 1

Mineral (5606), polyalphaolefin (83282), and phosphate ester (skydrol)

Question 2

What is the color of mineral based hydraulic fluid?

Answer 2

red

Question 3

How do you determine which type of hydraulic fluid to use in a specific system?

Answer 3

It is specified in the Aircraft Maintenance Manual or on the instruction plate attached to the reservoir on the unit being serviced

Question 4

What will happen to the seals in a vegetable base hydraulic system if it is serviced with mineral based or phosphate ester based fluids?

Answer 4

Seals will swell, break down, and block the system

Question 5

When installing a chevron seal what must be considered?

Answer 5

It is directional and must be installed with pressure going toward the open side of the seal

Question 6

When hydraulic lines have been disconnected, what precautions should be taken to prevent contamination of the system?

Answer 6

They should be capped or plugged immediately after disconnecting

Question 7

What happens to the hydraulic fluid flow if the filter element becomes clogged with foreign matter?

Answer 7

There is a bypass valve which routes the hydraulic fluid directly from the inlet port to the outlet port

Question 8

What is a micronic filter?

Answer 8

A paper element filter

Question 9

Name the filters used in aircraft pneumatic systems.

Answer 9

Paper pleated and screen type

Question 10

Why are some hydraulic reservoirs pressurized?

Answer 10

To ensure a positive flow of fluid to the engine driven pump at high altitudes

Question 11

What methods are used to pressurize hydraulic reservoirs?

Answer 11

Some systems use a variable displacement hydraulic pump, engine bleed air, or hydraulic system pressure acting on a small piston inside of a reservoir. Another method is an aspirator or Venturi.

Question 12

What are two types of accumulator housings?

Answer 12

Spherical or cylindrical

Question 13

Name three types of hydraulic accumulators.

Answer 13

Diaphragm type, bladder type, and piston type

Question 14

What is the purpose of a pressure relief valve in a hydraulic system?

Answer 14

It is to limit the amount of pressure in the system

Question 15

What is the purpose of an unloading valve in a closed hydraulic system?

Answer 15

It is designed to provide a low-pressure path for the fluid to flow from the pump back to the reservoir when the system has no flow requirements

Question 16

What is the function of a wing flap overload valve?

Answer 16

It prevents possible structural damage to the flaps or the flap system that might result from the flaps being lowered at excessive speeds

Question 17

What is the purpose of the shear-able section in a hydraulic pump?

Answer 17

If the pump were to seize, the shear section will disconnect the pump from the engine, allowing the engine to continue to operate

Question 18

What are two different types of hydraulic pumps?

Answer 18

Hand pumps or power pumps, also classified as positive displacement or non positive displacement

Question 19

What pump is most suitable for low pressure pneumatic systems?

Answer 19

A vane type pump

Question 20

What protects a direct pressure type hydraulic pressure gauge from pressure surges?

Answer 20

A dampening device in the form of a very small restrictor is installed in the line leading to the gauge or at the inlet to the gauge itself

Question 21

What are pneumatic systems used for in aircraft?

Answer 21

To operate brakes, open and close doors, starting, pump driving, and operating emergency devices

Question 22

What happens to the air after a pneumatic system is operated?

Answer 22

The air is dumped overboard

Question 23

Why should a pneumatic system be purged periodically?

Answer 23

To remove contamination, moisture, or oil from components and lines

Question 24

What is the purpose of the relief valve in a pneumatic system?

Answer 24

It protects the system against over pressurization (thermal expansion) by venting excess pressure to the atmosphere

Question 25

What is the purpose of an accumulator?

Answer 25

They are used to prevent hydraulic system shock when under high load demand conditions

Question 26

What would cause a hydraulic filer to go into full bypass mode allowing unfiltered fluid into the system?

Answer 26

A clogged filter