10 Fluid Lines And Fittings

Question 1

1. What are the 2 types of fluid lines commonly found in aircraft?

Answer 1

Rigid metal lines and flexible hoses.

Question 2

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

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

Answer 3

Stainless steel fittings.

Question 4

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

5. Describe the 2 types of flares commonly used on aircraft tubing.

Answer 5

Single and double flare.

Question 6

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 don’t.

Question 7

7. What are the most 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

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

Answer 8

The nut and the ferrule or sleeve.

Question 9

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

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

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

Answer 11

The lines must be electrically bonded to the structure.

Question 12

12. What are some of the important advantages of Teflon tubing?

Answer 12

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

Question 13

13. Describe the identification markings commonly found on flexible hoses.

Answer 13

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

Question 14

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

15. How are flexible hose sizes designated?

Answer 15

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

Question 16

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

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

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

5-8%

Question 19

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

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.