Fluid lines and fittings

Question 1

What are the two categories of fluid lines commonly used in aircraft?

Answer 1

Rigid, metal lines, and flexible hoses

Question 2

Describe the method of classifying metal tube according to size

Answer 2

Metal tubing a size accordingly to wall thickness and outside diameter outside diameter is measured and 1/16 inch increments

Question 3

Describe the method of classifying, flexible hose according to size 

Answer 3

Flexible hose sized according to inside diameter in 1/16 inch increments

Question 4

When installing stainless steel tubing, what type of fittings should be used

Answer 4

Stainless steel fittings

Question 5

What is the function of the sleeve on a flared tube feeding

Answer 5

The nut fits over the sleeve and draws the sleeve, and the tubing flared tightly against the male fitting to form the seal

Question 6

Describe the two types of flares, commonly used on aircraft tubing

Answer 6

The single flare, and the double flare

Question 7

What is the flare angle of aviation flares?

Answer 7

37°

Question 8

What is the difference between flare angles for aviation in automotive flares?

Answer 8

Aviation is 37° automotive is 45°

Question 9

How can you determine if a fitting is an AN type rather than an AC type

Answer 9

AN fittings have a shoulder between the flare cone, and the end of the threads AC fittings do not

Question 10

What are the most significant differences between AN and AC fittings

Answer 10

Sleeve length, thread pitch, in the shoulder between the threads, and the flare cone on AN fittings

Question 11

How do you tell a flare-less fitting from a flare type fitting?

Answer 11

Flare-less fittings don’t have a flare cone, and there is no space between the threads and the end of the fitting

Question 12

What is the effect of overtightening a flare type fitting?

Answer 12

The sealing surfaces may be damaged or the flare cut off

Question 13

In addition to being securely clamped, what is an additional requirement for installing metal fuel oil and hydraulic lines

Answer 13

The lines must be electrically bonded to the structure

Question 14

What are some of the important advantages of Teflon tubing?

Answer 14

It is compatible with nearly every liquid, has a broad operating temperature range low resistance to fluid flow and has a very long shelf life

Question 15

When selecting, flexible hose for use in a phosphate Ester based hydraulic fluid (skydrol) system the hose should be made of which synthetic rubber compound

Answer 15

Butyl

Question 16

Describe the identification markings, commonly found on flexible hoses

Answer 16

A Layline identification, such as a mil spec number, the manufactures name, or symbol the whole size, and a date code

Question 17

What is the maximum interval for repeating the required markings on a flexible hose?

Answer 17

Not more than 9 inches along the length of the hose

Question 18

How can you determine if a flexible hose has been correctly or incorrectly installed?

Answer 18

The lay line will be straight. If the hose is properly installed a twisted le line indicates an incorrect installation.

Question 19

When installing a flexible hose or rigid lines, next to electrical conduit or water bundles, what precautions should be

Answer 19

Route the hose or rigid line below the electrical conduit or wire bundles, and make certain that they are clamped and properly bonded

Question 20

When installing flexible hoses, what considerations should be made?

Answer 20

Slack, flexing, twisting, bending, clearance, and clamps

Question 21

How can a flexible hose be designated?

Answer 21

By the inside diameter measured and 1/16 inch increments

Question 22

What percentage of flattening is allowed when bending metal tubing?

Answer 22

Do not exceed 75% of original diameter

Question 23

Scratches and nicks may be repaired if they are less than what percent of the wall thickness

Answer 23

10%

Question 24

What precautions must be observed when deburring the end of a tube after it is cut

Answer 24

The wall thickness must not be reduced in size or fractured

Question 25

Describe the operation of quick disconnect couplings

Answer 25

Each half has a valve that is held open when coupled and is spring loaded closed when disconnected

Question 26

Why are quick disconnect fittings used?

Answer 26

To provide a quick means to connect or disconnect, a fluid line, without loss of fluid or entrance of air into the system

Question 27

If you fabricate a replacement for a flexible hose, what percentage of total length must be allowed for movement under pressure

Answer 27

5 to 8%

Question 28

What happens to the tube when a flare-less fitting is overtightened

Answer 28

The tube is weakened when the nut drives the cutting edge of the sleeve too deeply into the tube