Fluid lines and fittings

Question 1

What are the 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 fitting 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 most significant differences between AN AC fittings?

Answer 7

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

Question 8

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

Answer 8

The nut and the ferrule or sleeve

Question 9

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

Answer 9

Flareless fittings do not 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 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 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 is properly installed. A twisted lay line indicates an incorrectly installed 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 flare-less fitting is over-tightened?

Answer 19

the tube is weakened when the nut drives the cutting edge 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.