General: Fluid Lines & Fittings 🔊

Question 1

What are two commonly used fluid lines in aircraft plumbing?

Answer 1

Metal tubing or flexible hose and fittings

Question 2

How is metal tubing sized?

Answer 2

Outside diameter and wall thickness with outside diameter being measured fractionally in 16ths of an inch

Question 3

What material should be selected for high pressure rigid fuel lines?

Answer 3

Annealed or ¼hard corrosion resistant steel

Question 4

What type of material should fittings be made of when used with stainless steel tubing?

Answer 4

Stainless steel

Question 5

What percent of flattening is allowed when bending metal tubing?

Answer 5

25% max

Question 6

What precautions should be taken when routing fluid lines adjacent to electrical wiring?

Answer 6

Route the fluid lines below the electrical wiring and maintain a clearance of at least 6 inches whenever possible. In no case should fluid lines and electrical wiring be closer than ½ inch. Ensure both the wiring and the fluid lines are fastened to the aircraft structure by clamps or other methods which will maintain separation.

Question 7

What is the purpose of the identification stripe running along the length of a flexible tube?

Answer 7

The stripe is called a lay line and indicates if the hose has twisted during installation. There is no allowable twist

Question 8

What are some synthetic materials commonly used to manufacture flexible hoses?

Answer 8

Buna-N, butyl, ethylene propylene diene rubber, neoprene, and Teflon. BBENT

Question 9

How are standard AN type and AC type fluid line fittings indicated?

Answer 9

AN fluid lines are colored either blue or black, have coarser threads, and a small shoulder between the threads and the 37° flare cone. AC fluid lines are typically colored gray or yellow and are completely threaded all the way to the 35° flare cone.

Question 10

What is the purpose of using quick disconnect couplings in fluid systems?

Answer 10

They allow you to quickly disconnect a line without loss of fluid or air entering the system. Each half has a valve that’s open when coupled together and spring loaded to close when disconnected.

Question 11

How is flexible hose sized?

Answer 11

Inside diameter in 16th of an inch increments

Question 12

How much slack must be left in a flexible hose during installation?

Answer 12

5% to 8% of the total hose length to allow for freedom of movement under pressure

Question 13

How often should flexible hoses be clamped in place?

Answer 13

Every 24 inches

Question 14

What are some considerations when installing flexible hose assemblies?

Answer 14

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

Question 15

What pressure is used to proof test a flexible hose assembly?

Answer 15

Typically, 1.5x the recommended operating pressure of the hose

Question 16

What are the three parts of a military standard tube fitting?

Answer 16

Body, sleeve, and nut

Question 17

What will be the result of over tightening a flareless tube fitting?

Answer 17

The compression sleeves cutting edge will cut too deep into the tube and cause the tube to weaken. Flareless fittings are made up of the tube, compression sleeve, and a nut.

Question 18

What are the two kinds of flares used in aircraft plumbing systems?

Answer 18

A single flare and a double flare

Question 19

What is the difference between automotive and aviation flares?

Answer 19

Aviation flares should be 37° and automotive flares are 45°

Question 20

What is the advantage of flexible Teflon hose over rubber hose?

Answer 20

Teflon hoses have better resistance to chemicals and a higher strength property at higher temperatures

Question 21

What precaution should be taken when deburring and inspecting the flare end of a tube?

Answer 21

Care should be taken that the tube is not cracked and the wall thickness is not reduced by the deburring process

Question 22

What type of rubber is used in flexible lines that carry phosphate-ester hydraulic fluid?

Answer 22

Synthetic

Question 23

What type of information is on a hose lay line?

Answer 23

Type of hose and the quarter and year it was manufactured

Question 24

What are the identification marks usually found on flexible rubber hoses?

Answer 24

Lay line, hose size, manufacturer, date of manufacture, pressure, and temperature limits

Question 25

What is the distance between hose identification markings?

Answer 25

9 inches