TM 1-1520-240-BD 7-9. 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 applicable. 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. CAUTION When   positioning   hose   damps   or tightening screws, take care to 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 primarily used where flexibility is essential and 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 when applicable. 7-13.  INSTALLATION .      When      installing      flareless fittings, use the following procedure to tighten nuts. a. Tightening   Fittings.      Use   a   torque   wrench   to tighten flareless fitting nuts as follows:  1/4-inch tubing: 135 to 145 inch-pounds  3/8-inch tubing: 215 to 245 inch-pounds  1/2inch tubing: 470 to 510 inch-pounds b. Leaks.  If the connection leaks during a pressure check, tighten the nut an additional 1/6 of a turn. c. 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 edges.     Remove burrs or sharp edges as required.     Slip seal over tube end to position shown in Figure 7-4.     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. 7-5