REPAIR OF METAL TUBE LINES . Minor dents
and scratches in tubing may be repaired. Scratches or
nicks no deeper than 20% of the tubing wall thickness,
that are not in the heel of a bend, may be repaired by
burnishing with hand tools. This is not necessary in
itself, but under a "Quick-Fix" sortie concept it will aid
the technician in his damage evaluation. Repair lines
with severe die marks, seams, or splits. Any crack or
deformity in the flare is also unacceptable and cause for
rejection. A dent less than 20% of the tube diameter is
acceptable unless it is in the heel of the bend. Severely
damaged line should be replaced. However, line may
be repaired by cutting out the damaged section and
inserting a repair section. Use hydraulic repair kit when
7-10. REPAIR HIGH-PRESSURE TUBING . Cut out
and remove the damaged portion of tubing using the
tubing to union method. Square, dean, and deburr the
rough edges of the remaining tubing. If the damaged
section of tubing does not exceed the length of a union,
a new section is not needed. If flared AN fittings are to
be used, place nuts and sleeves on prepared original
tubing facing toward the end of the tubing. Then flare
the end of the tubing. Place unions in position and
torque. Measure the distance between the two installed
unions. Next, prepare a replacement section using the
same method as for the original line. Install the
replacement section, torque properly, and check for
pressure (Figure 7-3). MS flareless fittings may also be
used in this repair. Ridged tubing may be repaired by
using high pressure flex hose from hydraulic repair kit.
Clamp tubing as required.
When positioning hose damps or
prevent the screws from chafing or
damaging adjoining parts. Where
damage is possible, reposition the
clamps on the hose.
7-11. BD HOSE REPAIR. Aircraft hose assemblies are
vibrations are present. Therefore, battle damaged hose
normally will be replaced and not repaired. Use
hydraulic repair kit when applicable.
7-12. REPLACEMENT OF FLEX HOSES. When
replacement of flex hose becomes necessary, use the
same type, size, and length when possible. High
pressure hose can be used to replace medium pressure
hose. Install hose assemblies without twisting. Never
stretch hose tight between two fittings; this will result in
overstressing and eventual failure. The replacement
hose should be long enough to provide slack Avoid tight
bends in flex hose. Tight bends could result in hose
failure. Do not try to straighten a hose that is in use or
that will be reinstalled. Any excessive bending or
twisting may cause kinking or weakening of the tube
wall. All flex hoses should be supported at least every
24 inches. Closer supports are preferred. The hoses
should be carefully routed and securely damped to
avoid abrasion, kinking, or excessive flexing. Excessive
flexing may cause weakening of the hose or loosening
of the fittings. Partial hose replacement is also possible
if union fittings are available. Use hydraulic repair kit
7-13. INSTALLATION . When installing flareless
fittings, use the following procedure to tighten nuts.
Tightening Fittings. Use a torque wrench to
tighten flareless fitting nuts as follows:
135 to 145 inch-pounds
215 to 245 inch-pounds
470 to 510 inch-pounds
Leaks. If the connection leaks during a pressure
check, tighten the nut an additional 1/6 of a turn.
Persistent Leaks.. If leakage persists, loosen,
and completely disconnect nut. Inspect surfaces,
correct or dean, and retorque.
7-14. FLARELESS FITTING SEAL . To eliminate
leakage of flareless tube end fittings, use a Teflon ring
seal. It is used as a temporary repair method where
scratches or other sealing surface imperfections have
caused undesirable sealing effects (See Figure 7-4). To
install this seal:
Inspect the tube end for burrs or sharp
Remove burrs or sharp edges as required.
Slip seal over tube end to position shown in
Hand tighten the B-nut to the point of
sharply increasing torque.
Tighten B-nut one wrench flat beyond point
of initial torque increase.
Make pressure check.