Fluid Lines and Fittings

Question 1

8192. 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?
      A— AN-818-5.
      B— AN-818-16.
      C— AN-818-8.

Answer 1

C— AN-818-8.

An AN-818-5 nut will fit a 5/16-inch tube. (The last dash number is the tube diameter in 1/16-inch increments.) An AN-818-16 nut will fit a 1-inch tube. An AN-818-8 nut will fit a 1/2-inch tube.

Question 2

8193. Metal tubing fluid lines are sized by wall thickness and
      A— outside diameter in 1/16 inch increments.
      B— inside diameter in 1/16 inch increments.
      C— outside diameter in 1/32 inch increments.

Answer 2

A— outside diameter in 1/16 inch increments.

Metal tubing used in aircraft fluid power installations is sized by its outside diameter, which is measured fractionally in sixteenths of an inch.

Question 3

8193-1.
Rolling-type flaring tools are used to flare __________, __________, and ___________ tubing.
A— Stainless steel, hard copper, mild steel.
B— Titanium, soft copper, corrosion resistant steel.
C—Soft copper, aluminum, brass.

Answer 3

C—Soft copper, aluminum, brass.

Use rolling-type flaring tools only to flare soft copper, aluminum, and brass tubing. Do not use with corrosion resistant steel or titanium.

Question 4

8194. From the following sequences of steps, indicate the proper order you would use to make a single flare on a piece of tubing:
      1) Place the tube in the proper size hole in the flaring block.
      2) Project the end of the tube slightly from the top of the flaring tool, about the thickness of a dime.
      3) Slip the fitting nut and sleeve on the tube.
      4) Strike the plunger several light blows with a lightweight hammer or mallet and turn the plunger one-half turn after each blow.
      5) Tighten the clamp bar securely to prevent slippage.
      6) Center the plunger or flaring pin over the tube.

A— 1, 3, 5, 2, 4, and 6.
B— 3, 1, 6, 2, 5, and 4.
C— 3, 1, 2, 6, 5, and 4.

Answer 4

B— 3, 1, 6, 2, 5, and 4.

The correct sequence for making a single flare on a piece of tubing is:
(3) Slip the fitting nut and sleeve on the tube.
(1) Place the tube in the proper size hole in the flaring block.
(6) Center the plunger or flaring pin over the tube.
(2) Project the end of the tube slightly from the tip of the f laring tool, about the thickness of a dime.
(5) Tighten the clamp bar securely to prevent slippage. (4) Strike the plunger several light blows with a lightweight hammer or mallet. Turn the plunger one-half turn after each blow.

Question 5

8195. Hydraulic tubing, which is damaged in a localized area to such an extent that repair is necessary, may be repaired
      A— by cutting out the damaged area and utilizing a swaged tube fitting to join the tube ends.
      B— only by replacing the tubing section run (connection to connection) using the same size and material as the original.
      C— by cutting out the damaged section and soldering in a replacement section of tubing.

Answer 5

A— by cutting out the damaged area and utilizing a swaged tube fitting to join the tube ends.

If a piece of high-pressure hydraulic tubing is damaged in a localized area, the damage can be cut out and a new piece of tubing cut to replace the damaged section. Swage-type splice fittings are slipped over each end of the tubing, and the fittings are swaged to the tube ends.

Question 6

8196. What is an advantage of a double flare on aluminum tubing?
      A— Ease of construction.
      B— More resistant to damage when the joint is tightened.
      C— Can be applied to any size and wall-thickness of tubing.

Answer 6

B— More resistant to damage when the joint is tightened.

Tubing made of 5052-O and 6061-T aluminum alloy in sizes from 1/8- to 3/8-inch OD should be flared with a double flare. Double flares are smoother than single flares and are more concentric. Also, the extra metal makes the flare more resistant to the shearing effect when the f ittings are torqued.

Question 7

8197. A certain amount of slack must be left in a flexible hose during installation because, when under pressure, it
      A— expands in length and diameter.
      B— expands in length and contracts in diameter.
      C— contracts in length and expands in diameter.

Answer 7

C— contracts in length and expands in diameter.

When flexible hose is installed in an aircraft, it must be given a certain amount of slack because when pressure is applied to the hose, it contracts in length and expands in diameter.

Question 8

8198. The term “cold flow” is generally associated with
      A— the effects of low temperature gasses or liquids f lowing in hose or tubing.
      B— impressions left in natural or synthetic rubber hose material.
      C— flexibility characteristics of various hose materials at low ambient temperatures.

Answer 8

B— impressions left in natural or synthetic rubber hose material.

Cold flow describes the deep, permanent impression left in a natural or synthetic rubber hose by the pressure of hose clamps or supports.

Question 9

8199. What is the color of an AN steel flared-tube fitting?
      A— Black.
      B— Blue.
      C— Red.

Answer 9

A— Black.

Steel AN flared tube fittings are colored black. Aluminum alloy AN fittings are colored blue.

Question 10

8200. Which of the following statements is/are correct in reference to flare fittings?
      1) AN fittings 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
      A— 1.
      B— 1 and 3.
      C— 1, 2, and 3.

Answer 10

A— 1.

AN flare fittings have a shoulder between the end of the threads and the flare cone. In AC fittings the threads go all the way to the cone. AN fittings are dyed blue or black and AC fittings are gray or yellow. The threads on an AN fitting are coarser than those on an AC fitting. AN and AC fittings are not interchangeable.

Question 11

8201. Flexible lines must be installed with
      A— a slack of 5 to 8 percent of the length.
      B— a slack of at least 10 to 12 percent of the length.
      C— enough slack to allow maximum flexing during operation.

Answer 11

A— a slack of 5 to 8 percent of the length.

When flexible lines are installed in a fluid power system, they should be between 5 percent and 8 percent longer than the space between the fittings.
This extra length (this slack) makes allowance for expansion in the system due to heat and for the fact that a hose contracts in its length when it is pressurized.

Question 12

8202. 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
      A— 54-1/2 inches.
      B— 51-1/2 inches.
      C— 52-1/2 inches.

Answer 12

C— 52-1/2 inches.

When a flexible line is installed in a fluid power system, it should be between 5 percent and 8 percent longer than the space between the fittings.
If the distance between the fittings is 50 inches, the hose should be at least 5 percent longer than this, or 52- 1/2 inches long.

Question 13

8203. Excessive stress on fluid or pneumatic metal tubing caused by expansion and contraction due to temperature changes can best be avoided by
      A— using short, straight sections of tubing between fixed parts of the aircraft.
      B— using tubing of the same material as the majority of the adjoining structure.
      C— providing bends in the tubing.

Answer 13

C— providing bends in the tubing.

Never select a path for a rigid fluid line that does not require bends in the tubing. Bends are necessary to permit the tubing to expand and contract under temperature changes and to absorb vibration.

Question 14

8204. 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?
      A— 0.606 inch.
      B— 0.688 inch.
      C— 0.750 inch.

Answer 14

A— 0.606 inch.

Find the inside diameter of a tube by subtracting two times the wall thickness from its outside diameter.
0.750 – 2(0.072) = 0.606 inch
The inside diameter is 0.606 inch.

Question 15

8205. In most aircraft hydraulic systems, two-piece tube connectors consisting of a sleeve and a nut are used when a tubing flare is required. The use of this type connector eliminates
      A— the flaring operation prior to assembly.
      B— the possibility of reducing the flare thickness by wiping or ironing during the tightening process.
      C— wrench damage to the tubing during the tightening process.

Answer 15

B— the possibility of reducing the flare thickness by wiping or ironing during the tightening process.

There are two types of flare fittings that can be used in aircraft hydraulic systems. One type is the single-piece AN817 nut, and the other is the two-piece MS20819 sleeve and an AN818 nut.
The AN818 nut and sleeve are preferred over the single-piece fitting because it eliminates the possibility of reducing the thickness of the flare by the wiping or ironing action when the nut is tightened.
With the two-piece fitting, there is no relative motion between the fitting and the flare when the nut is being tightened.

Question 16

During installation, MS flareless fittings

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

Answer 16

A— are normally tightened by turning the nut a specified amount, unless the manufacturer lists torque values.

MS flareless fittings are attached to the end of a metal tube by presetting the fitting on the tube.
Presetting consists of putting enough pressure on the f fitting to deform the ferrule and cause it to cut into the outside of the tube. Presetting is done by lubricating the threads of the presetting tool and the nut with hydraulic fluid, assembling the nut and ferrule on the tube, putting it in the presetting tool, and tightening the nut by hand until resistance is felt, then turning it with a wrench from 1 to 1- 1/4 turns.
When installing the fitting in an aircraft hydraulic system, tighten the nut by hand until resistance is felt and then turn it 1/6 to 1/3 of a turn (one hex to two hexes) with a wrench.

Question 17

8207. When flaring aluminum tubing for use with AN fittings, the flare angle must be
      A— 37°.
      B — 39°.
      C — 45°.

Answer 17

A— 37°.

The flare angle used with AN fittings is 37°.

Question 18

8208. Scratches or nicks on the straight portion of aluminum alloy tubing may be repaired if they are no deeper than
      A— 20 percent of the wall thickness.
      B— 1/32 inch or 20 percent of wall thickness, whichever is less.
      C— 10 percent of the wall thickness.

Answer 18

C— 10 percent of the wall thickness.

Scratches or nicks are allowed in a piece of aluminum alloy tubing provided it is no deeper than 10 percent of the wall thickness of the tube, and it is not in the heel of a bend.
Scratches and nicks should be burnished out of the tube, to prevent stress concentrations.

Question 19

8209.
Flexible hose used in aircraft systems is classified in size according to the
A— outside diameter.
B— wall thickness.
C— inside diameter.

Answer 19

C— inside diameter.

The size of flexible hose is determined by its inside diameter.
Sizes are in 1/16-inch increments and relate to corresponding sizes of rigid tubing with which it can be used.

Question 20

8209-1.
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?
A— The hose interior must be kept wet with the fluid carried to prevent embrittlement/deterioration.
B— The hose may become stiff and brittle if not flexed or moved regularly.
C— The hose may have developed a set, or have been manufactured with a pre-set shape, and must be supported to maintain its shape.

Answer 20

C— The hose may have developed a set, or have been manufactured with a pre-set shape, and must be supported to maintain its shape.

Teflon hoses develop a permanent set after having been in use for an extended period of time or may have been manufactured with a permanent set for the particular function, thus is should be supported to maintain its shape and prevent inadvertent straightening.

Question 21

8210. A scratch or nick in aluminum tubing can be repaired provided it does not
      A— appear in the heel of a bend.
      B— appear on the inside of a bend.
      C— exceed 10 percent of the tube OD on a straight section.

Answer 21

A— appear in the heel of a bend.

Scratches or nicks not deeper than 10 percent of the wall thickness in aluminum alloy tubing, that are not in the heel of a bend, may be repaired by burnishing (forcing the displaced metal back into the nick or scratch) with a polished steel burnishing hand tool.

Question 22

8211. Which of the following hose materials are compatible with phosphate-ester base hydraulic fluids?
      A— Butyl and Teflon.
      B— Neoprene and Teflon.
      C— Teflon and Buna-N.

Answer 22

A— Butyl and Teflon.

Butyl is not suitable for use with petroleum products, but is an excellent inner liner for phosphate-ester base hydraulic fluids.
Teflon hose is unaffected by any fuel, petroleum, or synthetic-base oils, alcohol, coolants, or solvents commonly used in aircraft.
Buna-N should not be used with phosphate-ester base hydraulic fluids.
Neoprene is not suitable for use with phosphate-ester base hydraulic fluids.

Question 23

8212 .
Which tubings have the characteristics (high strength, abrasion resistance) necessary for use in a highpressure (3,000 PSI) hydraulic system for operation of landing gear and flaps?
A— 2024-T or 5052-0 aluminum alloy.
B— Corrosion-resistant steel annealed or 1/4H.
C— 1100-1/2H or 3003-1/2H aluminum alloy.

Answer 23

B— Corrosion-resistant steel annealed or 1/4H.

Rigid tubing made of corrosion-resistant steel, either annealed or 1/4 hard, is used in high-pressure hydraulic or pneumatic systems where high strength and abrasion resistance are important.

Question 24

8213. When installing bonded clamps to support metal tubing,
      A— paint removal from tube is not recommended as it will inhibit corrosion.
      B— paint clamp and tube after clamp installation to prevent corrosion.
      C— remove paint or anodizing from tube at clamp location.

Answer 24

C— remove paint or anodizing from tube at clamp location.

When a piece of metal tubing is installed in a bonded clamp, any paint or anodizing oxide film must be removed from the portion of the tube where the clamp is to fit. Both paint and the oxide film are electrical insulators

Question 25

8214. In a metal tubing installation,
      A— rigid straight line runs are preferable.
      B— tension is undesirable because pressurization will cause it to expand and shift.
      C— a tube may be pulled in line if the nut will start on the threaded coupling.

Answer 25

B— tension is undesirable because pressurization will cause it to expand and shift.

When making an installation of rigid metal tubing, each run of the tubing must have at least one bend in it to allow for the shifting of the line as it is pressurized.
There must be no tension on the line (the flare in both ends of the tube should rest squarely on the flare cones of the fittings and not have to be pulled into place with the nut).

Question 26

8214 -1.
Which of the following tools is best to use when cutting soft aluminum tubing?
A— Hand operated wheel-type tubing cutter.
B— Angle grinder with cut-off wheel.
C— Circular-saw equipped with an abrasive cutting wheel.

Answer 26

A— Hand operated wheel-type tubing cutter.

A hand operated wheel-type tubing cutter is the best tool to use when cutting aluminum tubing, or any tubing of moderately soft metal.

Question 27

8214-2.
The primary purpose of providing suitable bends in fluid and pneumatic metal tubing runs is to
A— clear obstacles and make turns in aircraft structures.
B— provide for access within aircraft structures.
C— prevent excessive stress on the tubing.

Answer 27

C— prevent excessive stress on the tubing.

When making an installation of rigid metal tubing, each run of the tubing must have at least one bend in it to allow for the shifting of the line as it is pressurized. This prevents excessive stress on the tubing.

Question 28

8214-3.
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?
A— The minimum radius for steel is greater than for aluminum.
B— The minimum radius for steel is less than for aluminum.
C— The minimum radius is the same for both steel and aluminum.

Answer 28

A— The minimum radius for steel is greater than for aluminum.

The minimum allowable bend radius for a 1.5 inch OD aluminum tubing is 5 inches. The minimum allowable bend radius for the same diameter steel tubing is 5.25 inches. Steel tubing in sizes smaller than 1.5 inch OD require a greater minimum bend radius than aluminum alloy tubing of the same size.

Question 29

8215. A gas or fluid line marked with the letters PHDAN is
      A— a dual-purpose pneumatic and/or hydraulic line for normal and emergency system use.
      B— used to carry a hazardous substance.
      C— a pneumatic or hydraulic system drain or discharge line.

Answer 29

B— used to carry a hazardous substance.

The marking PHDAN on a fluid line indicates that the fluid carried in the line is physically hazardous and dangerous to personnel.

Question 30

8215-1.
Which statement is true regarding the variety of symbols utilized on the identifying color-code bands that are currently used on aircraft plumbing lines?
A— Symbols are composed of various single colors according to line content.
B— Symbols are always black against a white background regardless of line content.
C— Symbols are composed of one to three contrasting colors according to line content.

Answer 30

B— Symbols are always black against a white background regardless of line content.

The fluid carried in fluid lines in an aircraft is identified by a series of color-coded bands around the line. These bands have from one to three contrasting colors. There is also a white band with black geometric symbols for the benefit of color-blind personnel.

Question 31

8215-2.
If a flared tube coupling nut is overtightened, where is the tube most likely to be weakened/damaged?
A— Along the entire length of the sleeve and tube interface.
B— At the edge of the sleeve and straight portion of the tube.
C— At the sleeve, fitting nut, or tube flare.

Answer 31

C— At the sleeve, fitting nut, or tube flare.

Overtightening a flared tube coupling nut will likely weaken or damage the tube and it is most likely to fail at the sleeve, f itting nut, or tube flare.

Question 32

8215-3.
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
A— back the nut off and align it to the nearest hole.
B— continue tightening the nut to the next hole.
C— change the nut or washer and try again.

Answer 32

C— change the nut or washer and try again.

When tightening castellated nuts on bolts, the cotter pin holes may not line up with the slots in the nuts for the range of recommended values. Except in cases of highly stressed engine parts, the nut may not be over-torqued. Remove hardware and realign the holes.

Question 33

8216. Which statement concerning Bernoulli’s principle is true?
      A— The pressure of a fluid increases at points where the velocity of the fluid increases.
      B— The pressure of a fluid decreases at points where the velocity of the fluid increases.
      C— It applies only to gases and vaporized liquids.

Answer 33

B— The pressure of a fluid decreases at points where the velocity of the fluid increases.

Bernoulli’s principle is one of the most useful principles we have to explain the behavior of fluid (either liquid or gas) in motion. Bernoulli’s principle tells us that if we neither add energy nor take any energy from fluid in motion, an increase in the velocity of the fluid (its kinetic energy) will result in a corresponding decrease in its pressure (its potential energy).

Question 34

8217. (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,
      A— only 1 is true.
      B— both 1 and 2 are true.
      C— neither 1 nor 2 is true.

Answer 34

B— both 1 and 2 are true.

Statement 1 is true. Bonded clamps (clamps in which the tube is contacted with a piece of bare metal) are used when installing metal tubing in an aircraft. Bonded clamps keep the tube at the same electrical potential as the aircraft structure.
Statement 2 is also true. Unbonded (cushion) clamps are used when securing wire bundles to the aircraft structure. The soft cushion in the clamp prevents abrasion wearing away the insulation on the wire.

Question 35

8217-1.
Which statement is true regarding flattening of tubing in bends?
A— The small diameter of the flattened portion must not be less than 65 percent of the original outside diameter.
B— The small diameter of the flattened portion must not be less than 75 percent of the original outside diameter.
C— The small diameter portion in the bend cannot exceed more than 75 percent of the diameter of straight tubing.

Answer 35

B— The small diameter of the flattened portion must not be less than 75 percent of the original outside diameter.

Tubing in the bend is often deformed, and the bend is not satisfactory if its small diameter is less than 75 percent of the outside diameter of the straight tubing.

Question 36

8218. A 3/8 inch aircraft high pressure flexible hose as compared to 3/8 inch metal tubing used in the same system will
      A— have higher flow capabilities.
      B— have equivalent flow characteristics.
      C— usually have interchangeable applications.

Answer 36

B— have equivalent flow characteristics.

Flexible hose may be used in any part of an aircraft fluid system where it has been proven by the aircraft manufacturer to be suitable. The hose must be able to carry the pressure, withstand the vibration, and pass the required fluid flow. The size of a flexible hose is approximately its inside diameter in 1/16-inch increments. This refers to the outside diameter of a rigid tube that has the equivalent flow characteristics.