Fluid Lines and Fitttings

Question 1

What are two types of fluid lines commonly found 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 is sized according to wall thickness and outside diameter. Outside diameter is measured in 1/16th inch increments.

Question 3

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

Answer 3

Stainless steel fittings.

Question 4

What is the function of the sleeve on a flared-tube fitting?

Answer 4

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

Question 5

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

Answer 5

The single flare and the double flare.

Question 6

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

Answer 6

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

Question 7

What are the significant differences between AN and AC fittings?

Answer 7

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

Question 8

What are the names of the parts of a flareless tube fitting?

Answer 8

The nut and sleeve.

Question 9

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

Answer 9

Flareless fittings don’t have a flare cone and there is no space between the threads and the end of the fitting.

Question 10

What is the effect of over-tightening a flare type fitting?

Answer 10

The sealing surface may be damaged or the flare cut off.

Question 11

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

Answer 11

The lines must be electrically bonded to the structure.

Question 12

What are some of the important advantages of Teflon tubing?

Answer 12

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

Question 13

Describe the identification markings commonly found on flexible hoses.

Answer 13

A lay line, identification such as a Mil Spec number, the manufacturer’s name or symbol, the hose size and a date code.

Question 14

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

Answer 14

The lay line will be straight if the hose if properly installed. A twisted lay line indicates an incorrect installation.

Question 15

How are flexible hose sizes designated?

Answer 15

By the inside diameter, measured in 1/16th inch increments.

Question 16

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

Answer 16

The wall thickness must not be reduced in size or fractured.

Question 17

Describe the operation of quick disconnect couplings.

Answer 17

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

Question 18

If you fabricate a replacement for a flexible hose, what percentage of the total length must be added to allow for movement under pressure?

Answer 18

5 to 8 percent.

Question 19

What happens to the tube when a flareless fitting is overtightened?

Answer 19

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

Question 20

Why are quick disconnect fittings used?

Answer 20

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

Question 21

Name the parts of a Military Standard flareless-tube fitting?

Answer 21

A body, sleeve, and nut.

Question 22

What are the identification markings that are usually found on flexible rubber hose?

Answer 22

Hose size, manufacturer, date of manufacture, pressure, and temperature limits.

Question 23

Name at least two synthetic materials commonly used in the manufacture of flexible hose.

Answer 23

Buna-N, Neoprene, Butyl, Ethylene, Propylene-Diene rubber, Teflon.

Question 24

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

Answer 24

Butyl.

Question 25

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

Answer 25

Not more than nine inches along the length of the hose.

Question 26

What percentage of flattening is allowed when bending metal tubing?

Answer 26

Do not exceed 75% of original diameter.

Question 27

How can you tell that flexible hose has been installed in a twisted position?

Answer 27

By the identification stripe running along the hose length.

Question 28

Name at least two considerations when installing flexible hose assemblies.

Answer 28

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

Question 29

Flexible hose should be clamped at least every how many inches?

Answer 29

24 inches.

Question 30

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

Answer 30

10%.

Question 31

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

Answer 31

Aviation is 37 degrees, automotive is 45 degrees.