Fluid Lines & Fittings

Question 0

How are rigid fluid lines sized, and what increments are used?

Answer 0

By outside diameter in 1/16inch increments, and by wall thickness in 1/1000inch increments.

Question 1

Name the two types of fluid lines used on aircraft.

Answer 1

Rigid and flexible lines.

Question 2

What markings are found on flexible hoses?

Answer 2

Size, manufacturing date, pressure range, and temperature limits.

Question 3

Identify the features of flared-tube fittings.

Answer 3

Flared-tube fittings consist of a sleeve and a B-nut, has a cone angle of 37 degrees, and are usually blue.

Question 4

What caution should be exercised when deburring?

Answer 4

Not to reduce wall thickness.

Question 5

Name the parts of a standard flare-less fitting.

Answer 5

The body, sleeve, and nut.

Question 6

Name two kinds of flares.

Answer 6

The single flare and the double flare.

Question 7

What is the advantage of flexible Teflon?

Answer 7

Extremely broad operating temperature range, compatible with nearly every liquid used, and has an almost limitless shelf and service life.

Question 8

How are flexible hoses sized?

Answer 8

By inside diameter at 1/16inch increments.

Question 9

How does a quick disconnect work?

Answer 9

Fluid coupling that incorporates a check valve (valve and spring) to prevent fluid loss when connecting or disconnecting.

Question 10

How do you determine if a line is twisted after installation?

Answer 10

By the lay line running the length of the hose, line should be straight not spiraled.

Question 11

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

Answer 11

Hose should be at least 5% longer than the distance between the fittings, extra length provides the needed slack.

Question 12

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

Answer 12

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

Question 13

What kind of fittings should be used on stainless steel lines?

Answer 13

Stainless steel.

Question 14

How should rigid, oil, fuel, and hydraulic lines be installed?

Answer 14

Routed through the aircraft for shortest practical length, and clamped and bonded to the structure with integrally bonded line support clamps.

Question 15

What is the purpose of a Quick Disconnect (QD)?

Answer 15

Faster installation or removal, prevents fluid loss, and no air or debris is allowed to enter the system.

Question 16

What is the difference between AN and AC flared tube fittings?

Answer 16

Cone angle, thread pitch, color, body length, and AN fittings have a shoulder between the end of the flare cone and the first thread while AC fittings do not.

Question 17

What is the purpose of a sleeve on a flared tube fitting?

Answer 17

The sleeve draws the tubing flare tightly against the male fitting to form a seal.

Question 18

What are some visual differences between a flare-less fitting and a flared fitting?

Answer 18

Flare-less fittings have no flare cone and no space between threads and the fitting.

Question 19

What are the effects of over torquing a flared fitting?

Answer 19

Damages the flare, causing a weak point in the tube.

Question 20

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

Answer 20

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

Question 21

When routing a fluid line parallel to an electrical wire bundle, which should be on top?

Answer 21

The electrical wire bundle should be on top.

Question 22

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

Answer 22

Where the engine-driven pump connects into the hydraulic system.

Question 23

How tight should an MS flareless fitting be tightened?

Answer 23

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 24

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

Answer 24

5052-O and 6061-T aluminum alloy tubing in sizes from 1/8-inch to 3/8-inch OD.

Question 25

What precautions should be taken when flaring a piece of aluminum alloy tubing?

Answer 25

The end of the tubing must be polished so it will not crack when it is stretched with the flaring tool.

Question 26

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

Answer 26

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

Question 27

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

Answer 27

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

Question 28

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

Answer 28

By its outside diameter.

Question 29

How can you distinguish an AN fluid line fitting from an AC fitting?

Answer 29

The AN fitting has a shoulder between the end of the flare cone and the first thread. The threads of an AC fitting extend all the way to the flare cone.

Question 30

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

Answer 30

Aircraft fittings have a 37 degree flare angle and automotive fittings use 45 degree.

Question 31

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

Answer 31

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

Question 32

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

Answer 32

To show the mechanic whether or not the line was twisted when it was installed. The line should be straight, not spiraled.

Question 33

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

Answer 33

By its inside diameter.

Question 34

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

Answer 34

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