Fluid Lines and Fittings

Question 1

What two general types of fluid lines are commonly used in aircraft plumbing?

Answer 1

Metal tubing (rigid lines) and flexible hose

Question 2

How is metal tubing classified in size?

Answer 2

Metal tubing is sized by outside diameter in 1/16 increments, and wall thickness.

Question 3

What are the parts of a military standard flareless-tube fitting?

Answer 3

A body, sleeve, and a nut.

Question 3

What caution must be observed when deburring the end of tubing after cutting?

Answer 3

Extreme care that the wall thickness is not fractured or reduced in size.

Question 4

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

Answer 4

The single flare and the double flare.

Question 4

What are the identification markings usually found on flexible rubber hose?

Answer 4

Hose size, manufacturer, date of maintenance, pressure and temperature limits.

Question 5

What is the principle advantage of flexible Teflon hose?

Answer 5

High operating strength at elevated temperature.

Question 5

When fabricating a flexible hose, what percent of the total length must be allowed for freedom of movement under pressure?

Answer 5

From 5 to 8 % of its total length

Question 6

How can you tell that a flexible hose has been installed in a twisted position?

Answer 6

By the identification stripe running along the hose length.

Question 7

What happens to a flareless tube fitting when it is overtightened?

Answer 7

The nut drives the cutting edge of the sleeve deeply into the tube, causing the tube to be weakened.

Question 8

What type of fittings (material) should be used with stainless steel tubing?

Answer 8

Stainless steel fittings.

Question 8

In addition to being securely clamped in place, how should metal, fuel, oil, and hydraulic lines be installed in an aircraft?

Answer 8

They should be electrically connected(grounded to the aircraft structure)

Question 9

When inspecting fittings, how may a flareless fitting be distinguished from a flared tube type?

Answer 9

There is no flare cone and no space between the threads and the end of the fitting.

Question 10

What is the purpose of a sleeve on a flared-tube connection?

Answer 10

The nut fits over the sleeve and when tightened, draws the sleeve and tubing flare tightly against the male fitting to form the seal.

Question 11

What percentage of flattening is allowed when bending metal tubing?

Answer 11

Do not exceed 75% of the original diameter

Question 11

Scratches and nicks may be repaired if they are less than what percent of the wall thickness?

Answer 11

10 percent

Question 11

How is flared tubing affected by overtightening of the fitting?

Answer 11

The tube flare is likely to be damaged, forming a weak point which may fail when under pressure.

Question 12

Flexible hoses should be clamped at least every how many inches?

Answer 12

24 inches

Question 13

When selecting a flexible hose for use in a phosphate ester based hydraulic fluid (Skydrol) system, the hose should be made of which synthetic rubber compound?

Answer 13

Butyl

Question 14

What is the difference between flare angles for aviation and automotive flares?

Answer 14

Aviation is 37 degrees, Automotive is 45.

Question 15

Name at least two types of synthetic materials commonly used in the manufacture of flexible hoses.

Answer 15

Buna-N, Neoprene, Butyl, Ethylene propylene Diene Rubber (EPDM), and Teflon.

Question 16

Name at least two considerations when installing flexible hose assemblies.

Answer 16

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

Question 16

What is the maximum interval for repeating the required markings on a flexible hose?

Answer 16

Not more than nine inches along the length of the hose.