Fluid Lines And Fittings

Question 1

What are the two types of fluid lines commonly found in aircraft?

Answer 1

Rigid metal lines.
Flexible hoses.

Question 2

Describe the method of classifying metal tube according to size.

Answer 2

It is sized according to wall thickness and outside diameter. Outside diameter is measured in 1/16 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 flare 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

Single flare.
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 and AC fittings?

Answer 7

Sleeve length.
Thread pitch.
Shoulder between the threads and the flare cone of AN fittings.

Question 8

What are the names of the parts of a flare-less tube fitting?

Answer 8

The nut.
The ferrule or sleeve.

Question 9

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

Answer 9

Flawless fittings don’t have a flare cone, and there’s no space between the threads and the end of the fitting.

Question 10

What is the effect of overtightening a flare type fitting?

Answer 10

The sealing surface may be damaged.
The flare may be 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

Compatible with nearly every liquid.
Has a broad operating temperature range.
Low resistance to fluid flow.
Very long shelf and service life.

Question 13

Describe the identification markings commonly found on flexible hoses.

Answer 13

A lay line.
Mil spec number.
Manufacturer’s name.
Hose size.
Data 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 incorrect installation.

Question 15

How are flexible hose sizes designated?

Answer 15

By the inside diameter.
Measured in 1/16 inch increments.

Question 16

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

Answer 16

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 then 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%

Question 19

What happens to the tube when a flareless fitting is over tightened?

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 disconnect or connect a fluid line without loss of fluid or entrance of air into the system.