Fluid Lines and Fittings practice questions

Answer: C) To keep the hose from slipping

• AIncorrect. Size is marked separately.
• BIncorrect. The bead is a retention feature.
• CCorrect. The bead helps hold the hose and clamp in place.
• DIncorrect. A bead is not a flare.

Answer: D) An AN818 nut and an AN819 sleeve

An AN flared tube connection uses an AN818 nut and an AN819 sleeve, slipped onto the tube before flaring. The sleeve backs the flare and the nut pulls it onto the fitting. MS21921/MS21922 parts belong to flareless fittings.

• AIncorrect. MS21921 nuts and MS21922 sleeves belong to the MS flareless fitting system. There the sleeve is preset onto an unflared tube.
• BIncorrect. An AN924 locknut secures a bulkhead fitting to a structure. Neither part backs up a tube flare.
• CIncorrect. The AN818 nut is correct, but the AN815 union is the fitting the flared tube end seats against. It is not slipped over the tube.
• DCorrect. The AN818 nut and AN819 sleeve go onto the tube before flaring. The sleeve supports the back of the flare, and the nut threads onto the fitting to draw the flare against the fitting cone.

Answer: B) It keeps the O-ring from extruding into the clearance gap

Backup rings are installed on the low-pressure side of an O-ring, or on both sides, to keep high pressure from extruding the O-ring into the clearance gap.

• AIncorrect. That is the job of a wiper (scraper) ring at the rod end. A backup ring sits in the seal groove beside the O-ring.
• BCorrect. Under high pressure an O-ring can be forced into the gap between the mating parts and be nibbled or cut. The backup ring blocks that gap and supports the O-ring.
• CIncorrect. Keeping the piston centered is the job of wear rings or bearing surfaces, not backup rings.
• DIncorrect. A backup ring is not designed to seal fluid by itself. The O-ring does the sealing, and the backup ring only supports it.

Answer: A) Kinking or flattening that restricts flow and shortens hose life

Each hose size has a minimum bend radius. Bending tighter than that can kink or flatten the hose, restrict flow, weaken the reinforcement and cause early failure.

• ACorrect. A bend tighter than the minimum radius can kink or collapse the hose, which restricts flow and strains the reinforcement. This lowers burst strength and causes early failure.
• BIncorrect. A tight bend adds restriction and turbulence. It does not help the system respond, and a kink can severely limit flow.
• CIncorrect. Overbending stresses the inner tube and reinforcement layers as well as the cover, so the hose's strength and service life go down.
• DIncorrect. Overbending weakens the hose's ability to contain pressure. It does not make the hose more resistant to surges.

Answer: B) 3/8 inch

• AIncorrect. The dash number is in sixteenths, not whole inches.
• BCorrect. Hose dash numbers are in sixteenths of an inch: 6/16 = 3/8 inch.
• CIncorrect. AN dash sizes are based on sixteenths of an inch.
• DIncorrect. 3/16 inch would be a dash 3 size.

Answer: B) The flare can be thinned, cracked, or cut off, so the joint may leak

Flared fittings must be torqued to the specified value. Overtightening can thin, crack, or cut off the flare or damage the sleeve and nut, causing leaks, while undertightening can let the joint leak or pull apart under pressure.

• AIncorrect. Torque beyond the specified value does not improve the seal. It deforms the flare and makes leaks more likely.
• BCorrect. Overtightening can severely damage or cut off the tube flare, or ruin the sleeve or nut, which can lead to leakage or failure.
• CIncorrect. Extra torque is not an approved locking method. Specified torque values, and safetying where required, must still be followed.
• DIncorrect. System pressure is set by the pump and regulating components, not by fitting torque. The real hazard is damage to the flare.

Answer: B) The system seals are attacked and the system is contaminated; it must be drained, flushed, and resealed

Mineral-based and phosphate ester hydraulic fluids, and the seals made for each, are incompatible. Servicing with the wrong fluid damages seals and contaminates the system, which then has to be drained, flushed and resealed.

• AIncorrect. The two fluid types are not compatible. The problem is seal damage and contamination, not a harmless color change.
• BCorrect. Skydrol systems use seals such as butyl rubber or ethylene-propylene, and mineral-based fluid is not compatible with them. The wrong fluid damages the seals and contaminates the system, so it must be drained, flushed and have its seals replaced per the manufacturer's instructions.
• CIncorrect. There is no allowable mixing percentage. Even a small amount of the wrong fluid can damage seals and contaminate the system.
• DIncorrect. One fluid does not neutralize the other. Changing the filter alone does not remove the contamination or fix damaged seals.

Answer: C) The line's contents and function, plus any hazard

Fluid line identification bands use color codes, words, and symbols to show what a line carries and which system it serves. They can also show hazards and flow direction.

• AIncorrect. Tubing material and size are identified from markings on the tubing stock or from the drawings and parts data, not from fluid line identification bands.
• BIncorrect. Fitting torque values come from torque tables or the maintenance manual. Identification bands do not carry torque data.
• CCorrect. Identification tapes use colors, words, and geometric symbols to identify the fluid and the system the line serves. They may also show hazards (such as flammable or toxic) and the direction of flow.
• DIncorrect. Test and inspection dates are recorded in maintenance records, not on fluid line identification bands.

Answer: B) The cure date, given as the quarter and year of manufacture

Synthetic rubber hose has a lay line and markings that include the cure date (quarter and year), size, manufacturer code and specification. The cure date helps the technician judge the hose's age.

• AIncorrect. The installation date goes in the maintenance records. It is not printed on the hose.
• BCorrect. The markings include the cure date (quarter and year), together with the hose size, manufacturer code and specification. The cure date is used to judge the hose's age and shelf life.
• CIncorrect. Hose condition and replacement are set by inspection and the manufacturer's data. A flight-hour life limit is not part of the markings.
• DIncorrect. Bulk hose is marked with generic identification data, not with information tied to a particular aircraft.

Answer: A) The taper wedges the threads tightly together as the fitting is tightened, forming a pressure-tight seal

Pipe threads are tapered so that tightening wedges the threads together into a pressure-tight seal, usually helped by thread sealant. Straight-thread fittings depend on O-rings or flares to seal instead.

• ACorrect. As a tapered pipe thread is tightened, the male and female threads wedge together and form the seal. Thread sealant or anti-seize compound is normally applied to the male threads, keeping it off the first thread.
• BIncorrect. That describes straight-thread (boss) fittings, which use parallel threads and seal with an O-ring. In a pipe-thread fitting, the threads themselves form the seal.
• CIncorrect. Once a tapered pipe fitting is tightened, it is locked by thread interference. Line alignment comes from swivel nuts or other adjustable fitting designs, not from the pipe thread.
• DIncorrect. In flared fittings, the flare and cone form the seal and the B-nut threads are straight. The taper on pipe threads has nothing to do with seating a flare.