Fluid Lines and Fittings

Question 1

Of what material are most low-pressure rigid fluid lines made?

Answer 1

1100-1/2 hard or 3003-1/2 hard aluminum alloy tubing.

Question 2

What is the difference between the flare angle for aircraft and automotive fittings?

Answer 2

Aircraft fittings have a 37° flare angle and automotive fittings use 45°

Question 3

Is the size of a rigid fluid line determined by its inside or its outside diameter?

Answer 3

By its outside diameter.

Question 4

Where are quick-disconnect fluid line couplings normally used in an aircraft hydraulic system?

Answer 4

In the lines that connect the engine-driven pump into the hydraulic system.

Question 5

Is the size of a flexible hose determined by its inside or its outside diameter?

Answer 5

by its inside diameter.

Question 6

Of what material should rigid fluid lines be made that carry high-pressure (3,000 psi or greater) hydraulic fluid?

Answer 6

Annealed or 1/4-hard corrosion-resistant steel.

Question 7

What is the principal advantage of Teflon hose for use in an aircraft hydraulic system?

AM.I.D.K2

Answer 7

Teflon hose retains its high strength under conditions of high temperature.

Question 8

How tight should an MS flareless fitting be tightened?

AM.I.D.K3

Answer 8

Tighten the fitting by hand until it is snug, and then turn it with a wrench for 1/6-turn to 1/3-turn. Never turn it more than 1/3-turn with a wrench.

Question 9

What damage can be caused by overtightening an MS flareless fitting?

AM.I.D.K3

Answer 9

Overtightening drives the cutting edge of the sleeve deep into the tube and weakens it.

Question 10

What kind of rigid tubing can be flared with a double flare?

Answer 10

5052-O and 606-T aluminum alloy tubing in sizes from 1/8-inch to 3/8-inch OD.

Question 11

What should be done to the end of a tube that is to be flared?

Answer 11

The cut end should be polished to remove any sharp edges that could cause the tubing to crack.

Question 12

What is the minimum amount of slack that must be left when a flexible hose is installed in an aircraft hydraulic system?

Answer 12

The hose should be at least 5% longer than the distance between the fittings. This extra length provides the needed slack.

Question 13

How much pressure is used to proof-test a flexible hose assembly?

Answer 13

This varies with the hose, but it is generally about two times the recommended operating pressure for the hose.

Question 14

Why is it important to use a torque wrench when securing fluid hose and line fittings?

Answer 14

If the connection is too loose, it may leak. If the connection is too tight, it can cause the fitting to become damaged and fail.

Question 15

What is the purpose of using torque seal on a critical fitting after installation?

Answer 15

If a visual inspection reveals that the torque seal has broken, it is an indication that the fitting may have loosened.

Question 16

Why is it important to understand system configurations during aircraft maintenance?

Answer 16

A lack of understanding of a system could lead to fluid lines being reversed or incorrectly installed, leading to a potentially hazardous situation.

Question 17

What safety equipment should be considered when working on fluid lines?

Answer 17

Depending on the types of fluid, safety equipment may include gloves and clothing protection, eye protection, spill containment materials, respirator, and fire extinguisher.

Question 18

How can an aviation mechanic determine what fluids are contained in the hoses and fluid lines that are encountered when working on an aircraft?

Answer 18

Fluid lines and hoses are labeled at regular intervals to identify the type of fluid. Additionally, the aircraft maintenance manual provides information on each aircraft system.

Question 19

What risk mitigation action should occur prior to working on any pressurized fluid system?

Answer 19

The system must be depressurized prior to beginning any work on the system.

Question 20

What is the function of the lay line (the identification stripe) that runs the length of a flexible hose?

Answer 20

To show the mechanic whether or not the line was twisted when it was installed. The line should be straight, not spiraled. A twisted hose may move from its intended position and chafe or interfere with outer systems.

Question 21

What is the danger of a loosened fitting or a hose that has moved out of position?

Answer 21

A loosened fitting may leak or allow a hose to move out of position. A hose that has moved out of position may chafe on adjacent structures and begin to leak, or it may cause interference and damage to other systems.

Question 22

What precaution must be used when applying torque to a fluid line?

Answer 22

The fitting that the line is being torqued to must be held in position with a second wrench to prevent twisting or damage to the secondary fitting or line.