AP GN Fluid Lines and Fittings

Which coupling nut should be selected for use with 1/2 inch aluminum oil lines which are to be assembled using flared tube ends and standard AN nuts, sleeves, and fittings?

AN-818-5
AN-818-16
AN-818-8

Metal tubing fluid lines are sized by wall thickness and

outside diameter in 1/16 inch increments.
inside diameter in 1/16 inch increments.
outside diameter in 1/32 inch increments.

Rolling-type flaring tools are used to flare _____________________, ________________, and _________________ tubing.

Stainless steel, hard copper, mild steel.
Titanium, soft copper, corrosion resistant steel.
Soft copper, aluminum, brass.

From the following sequences of steps, indicate the proper order you would use to make a single flare on a piece of tubing:

Place the tube in the proper size hole in the flaring block.
Project the end of the tube slightly from the top of the flaring tool, about the thickness of a dime.
Slip the fitting rod and sleeve on the tube.
Strike the plunger several light blows with a lightweight hammer or make and turn the plunger one-half turn after each blow.
Tighten the clamp bar securely to prevent slippage.
Center the plunger or flaring pin over the tube.

1, 3, 5, 2, 4, and 6.
3, 1, 6, 2, 5, and 4.
3, 1, 2, 6, 5, and 4.

Hydraulic tubing, which is damaged in a localized area to such an extent that repair is necessary, may be repaired

by cutting out the damaged area and utilizing a swaged tube fitting to join the tube ends.
only by replacing the tubing section run (connection to connection) using the same size and material as the original.
by cutting out the damaged section and soldering in a replacement section of tubing.

What is the advantage of a double flare on aluminum tubing?

Ease of construction.
More resistant to damage when the joint is tightened.
Can be applied to any size and wall-thickness of tubing.

A certain amount of slack must be left in a flexible hose during installation because, when under pressure, it

expands in length and diameter.
expands in length and contracts in diameter.
contracts in length and expands in diameter.

The term “cold flow” is generally associated with

the effects of low temperature gases or liquids flowing in hose or tubing.
Impressions left in natural or synthetic rubber hose material.
flexibility characteristics of various hose materials at low ambient temperatures.

What is the color of an AN steel flared-tube fitting?

Black.
Blue.
Red.

Which of the following statements is/are correct in reference to flare fittings?

1. All things have an identifying shoulder between the end of the threads and the flare cone.

2. AC and AN fittings are considered identical except for material composition and identifying colors.

3. AN fittings are generally interchangeable with AC fittings of compatible material composition.

1
1 and 3.
1, 2, and 3.

Flexible lines must be installed with:

a slack of 5 to 8 percent of the length.
a slack of at least 10 to 12 percent of the length.
enough slack to allow maximum flexing during operation.

The maximum distance between end fittings to which a straight hose assembly is to be connected is 50 inches. The minimum hose length to make such a connection should be

54-1/2 inches.
51-1/2 inches.
52-1/2 inches.

Excessive stress on fluid or pneumatic metal tubing caused by expansion and contraction due to temperature changes can be best avoided by

using short, straight sections of tubing between fixed parts of the aircraft.
using tubing of the same material as the majority of the adjoining structure.
providing bends in the tubing.

The material specifications for a certain aircraft require that a replacement oil line be fabricated from 3/4-inch 0.072 5052-0 aluminum alloy tubing. What is the inside dimension of this tubing?

0.606 inch
0.688 inch
0.750 inch

In most aircraft hydraulic systems, two-piece tube connections consisting of a sleeve and a nut area are used when a tubing flare is required. The use of this type connector eliminates

the flaring operation prior to assembly.
the possibility of reducing the flare thickness by wiping or ironing during the tightening process.
wrench damage to the tubing during the tightening process.

During installation, MS flareless fittings

are normally tightened by turning the nut a specified amount, unless the manufacturer has torque values.
should be assembled by applying an anti-seize compound to both surfaces of the fitting and flare.
are normally tightened by applying torque in small increments to prevent over-heating the tube mating surfaces.

When flaring aluminum tubing for use with AN fittings, the flare angle must be

37 degrees.
39 degrees.
45 degrees.

Scratches or nicks on the straight portion of aluminum alloy tubing may be repaired if they are no deeper than

20 percent of the wall thickness.
1/32 inch or 20 percent of wall thickness, whichever is less.
10 percent of the wall thickness.

Flexible hose used in aircraft systems is classified in size according to the

outside diameter.
wall thickness.
inside diameter.

When a Teflon hose has been in service for a time, what condition may have occurred and/or what precaution should be taken when it is temporarily removed from the aircraft?

The hose interior must be kept wet with the fluid carried to prevent embrittlement/deterioration.
The hose may become stiff and brittle if not flexed or moved regularly.
The hose may have developed a set, or have been manufactured with a pre-set shape, and must be supported to maintain its shape.

A scratch or nick in aluminum tubing can be repaired provided it does not

appear in the heel of a bend.
appear on the inside of a bend.
exceed 10 percent of the tube OD on a straight section.

Which of the following hose materials are compatible with phosphate-ester base hydraulic fluids?

Butyl and Teflon.
Neoprene and Teflon.
Teflon and Buna-N.

Which tubings have the characteristics (high strength, abrasion resistance) necessary for use in a high-pressure (3,000 PSI) hydraulic system for operation of landing gear and flaps?

2024-T or 5052-0 aluminum alloy.
Corrosion-resistant steel annealed or 1/4H.
1100-1/2H or 3003-1/2H aluminum alloy.

When installing bounded clamps to support metal tubing

paint removal from tube is not recommended as it will inhibit corrosion.
paint clamp and tube after clamp installation to prevent corrosion.
remove paint or anodizing from tube at clamp location.

In a metal tubing installation,

rigid straight line runs are preferable.
tension is undesirable because pressurization will cause it to expand and shift.
a tube may be pulled in line if the nut will start on the threated coupling.

Which of the following tools is best to use when cutting soft aluminum tubing?

Hand-operated wheel-type tubing cutter.
Angle grinder with cut-off wheel.
Circular saw equipped with an abrasive cutting wheel.

The primary purpose of providing suitable bends in fluid and pneumatic metal tubing runs is to

clear obstacles and make turns in aircraft structures.
provide for access within aircraft structures.
prevent excessive stress on the tubing.

Which of the following statements is true regarding minimum allowable bend radii for 1.5 inches OD or less aluminum alloy and steel tubing of the same size?

The minimum radius for steel is greater than for aluminum.
The minimum radius for steel is less than for aluminum.
The minimum radius is the same for both steel and aluminum.

A gas or fluid line marked with the letters PHDAN is

a dual-purpose pneumatic and/or hydraulic line for normal and emergency system use.
used to carry a hazardous substance.
a pneumatic or hydraulic system drain or discharge line.

Which statement is true regarding the variety of symbols utilized on the identifying color-coded bands that are currently used on aircraft plumbing lines?

Symbols are composed of various single colors according to line content.
Symbols are always black against a white background regardless of line content.
Symbols are composed of one to three contrasting colors according to line content.

If a flared tube coupling nut is overtightened, where is the tube most likely to be weakened/damaged?

Along the entire length of the sleeve and tube interface.
At the edge of the sleeve and straight portion of the tube.
At the sleeve, fitting nut, or tube flare.

When installing a castle nut, and the nut castellation does not align with the cotter pin hole in the bolt within the torque range, the acceptable practice is to

back the nut off and align it to the nearest hole.
continue tightening the nut to the next hole.
change the nut or washer and try again.

Which statement concerning Bernoull’s principle is true?

The pressure of a fluid increases at points where the velocity of the fluid increases.
The pressure of a fluid decreases at points where the velocity of the fluid increases.
It applies only to gases and vaporized liquids.

(1) Bonded clamps are used for support when installing metal tubing.

(2) Unbonded clamps are used for support when installing wiring.

Regarding the above statements,

Only 1 is true.
Both 1 and 2 are true.
Neither 1 nor 2 is true.

Which statement is true regarding flattening of tubing in bends?

The small diameter of the flattened portion must not be less than 65 percent of the original outside diameter.
The small diameter of the flattened portion must not be less than 75 percent of the original outside diameter.
The small diameter portion in the bend cannot exceed more than 75 percent of the diameter of straight tubing.

A 3/8 inch aircraft high pressure flexible hose as compared to 3/8 inch metal tubing used in the same system will

have higher flow capabilities.
have equivalent flow characteristics.
usually have interchangeable applications.

AP GN Fluid Lines and Fittings

Jon K

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