Hydraulic and Pneumatic power systems

Question 1

What are the three principle categories of hydraulic fluids?

Answer 1

1. Mineral (5606). 2. Polyalphaolefin (poly alpha olefin) (83282). 3. 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

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 base or phosphate ester base fluids?

Answer 4

The seals will swell, break down, and block the system.

Question 5

When installing a chevron seal what must be considered?

Answer 5

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

All lines and fittings 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 filter with a paper element.

Question 9

What methods are used to pressurize hydraulic reservoirs?

Answer 9

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

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 are the two types of accumulator housings?

Answer 11

Spherical, and cylindrical.

Question 12

Name three types of hydraulic accumulators.

Answer 12

The diaphragm type, bladder type, and piston type.

Question 13

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

Answer 13

It is to limit the amount of pressure in the system.

Question 14

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

Answer 14

The unloading valve 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. The unloading valve also acts as a
pressure regulator.

Question 15

What is the purpose of the shearable section in a hydraulic pump?

Answer 15

The shear section will disconnect the pump from the engine, allowing the engine to continue to operate.

Question 16

What is the function of a wing flap overload valve?

Answer 16

The purpose of the valve is to prevent possible structural damage to the flaps or the flap system that
might result from the flaps being lowered at excessive speeds.

Question 17

What are two different types of hydraulic pumps?

Answer 17

There are hand pumps and power pumps. Pumps can also be classified as positive displacement,
or nonpositive displacement.

Question 18

What pump is most suitable for low-pressure pneumatic systems?

Answer 18

A vane-type pump.

Question 19

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

Answer 19

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 20

For What purposes are pneumatic systems used in some aircraft?

Answer 20

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

Question 21

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

Answer 21

The air is dumped overboard.

Question 22

Why should a pneumatic system be purged periodically?

Answer 22

To remove contamination, moisture.

Question 23

What is the purpose of a pressure relief valve?

Answer 23

To limit the amount of pressure, thereby preventing failure of the system components.

Question 24

What is the purpose of an accumulator?

Answer 24

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

Question 25

What is an example of a phosphate ester base fluid?

Answer 25

Skydrol.

Question 26

What happens to plastic resins, vinyl compositions, lacquers, and oil base paints if exposed to a phosphate easter base hydraulic fluid such as skydrol?

Answer 26

The material will be damaged, softened and/or peeled.

Question 27

What precautions should be taken to minimize contamination during replacement of a hydraulic unit?

Answer 27

All lines should be plugged or capped after disconnecting.

Question 28

What are two types of engine-driven hydraulic pumps?

Answer 28

Constant-delivery and variable-delivery.

Question 29

What are sources of pneumatic power?

Answer 29

Storage bottles, vane-type pumps, and turbine engine compressors.

Question 30

What happens to the excessive pressure in a pneumatic system?

Answer 30

A relief valve will bleed it to the atmosphere.

Question 31

What must be accomplished with any accumulator prior to disassembling?

Answer 31

Make sure the air or preload has been discharged.

Question 32

What feature is built into a hydraulic pump-drive system to prevent engine damage in the event of pump seizure or overload?

Answer 32

A shear section in the pump-drive shaft.

Question 33

What would cause a hydraulic filter to go into open bypass, allowing unfiltered fluid into the system?

Answer 33

A clogged filter.

Question 34

What is the purpose of a pressure regulator?

Answer 34

To manage the output of the pump to maintain system pressure and allow the pump to turn without resistance.

Question 35

What is used in some hydraulic systems to supplement the power pump when several units are operated at the same time?

Answer 35

An accumulator.

Question 36

What is the purpose of restriction that are used in aircraft pneumatic system?

Answer 36

To control the rate of airflow.