Rigid Tubing Installation, Inspection, and Repair

9-10 Tubing AN819 sleeve AN818 nut ELECTRICAL CONDUIT ELECTRICAL CONDUIT ELECTRICAL CONDUIT ELECTRICAL CONDUIT ELECTRICAL CONDUIT WATER FUEL LUBRICATION PNEUMATIC XXXXXXXXXXXX HYDRAULIC COOLANT AIR CONDITION AIR CONDITION AIR CONDITION AIR CONDITION COMPRESSED GAS COMPRESSED GAS COMPRESSED GAS COMPRESSED GAS COMPRESSED GAS INSTRUMENT AIR INSTRUMENT AIR INSTRUMENT AIR INSTRUMENT AIR INSTRUMENT AIR BREATHING OXYGEN BREATHING OXYGEN BREATHING OXYGEN BREATHING OXYGEN BREATHING OXYGEN FIRE PROTECTION FIRE PROTECTION FIRE PROTECTION FIRE PROTECTION FIRE PROTECTION DE-ICING VACUUM INERTING FLUID INERTING FLUID INERTING FLUID INERTING FLUID INERTING FLUID WARNING SYMBOL A B FUEL FLAM FUEL FLAM and metal tags (B).

Rigid Tubing Installation and Inspection

Before installing a line assembly in an aircraft, inspect the line carefully. Remove dents and scratches, and be sure all nuts and sleeves are snugly mated and securely fitted by proper flaring of the tubing. The line assembly should be clean and free of all foreign matter. Connection & Torque Never apply compound to the faces of the fitting or the flare, as it destroys the metal-to-metal contact between the fitting and flare, a contact which is necessary to produce the seal. Be sure that the line assembly is properly aligned before tightening the fittings. Do not pull the installation into place with torque on the nut. Correct and incorrect methods of installing flared tube assemblies are illustrated in Remember that these torque values are for flared-type fittings only. Always tighten fittings to the correct torque value when installing a tube assembly. Overtightening a fitting may badly The sleeve is manufactured 3 percent smaller, frozen in liquid nitrogen, and expanded to 5 percent larger than the line. During installation, the fitting is removed from the liquid nitrogen and inserted onto the tube. During a 10 to 15 second warming up period, the fitting contracts to its original size (3 percent smaller), biting down on the tube, forming a permanent seal. Cryofit fittings can only be removed by cutting the tube at the sleeve, though this leaves enough room to replace it with a swaged fitting without replacing the hydraulic line. It is frequently used with titanium tubing.

The shape memory technology is also used for end fittings, flared fittings, and flareless fittings. [Figure 9-27] 9-11 ELBOW AN821 ELBOW AN823 TEE AN825 ELBOW AN822 TEE AN824 TEE AN826 CROSS AN827 UNION AN832 ELBOW AN833 TEE AN834 ELBOW AN837 ELBOW AN838 ELBOW AN839 TEE AN804 PLUG AN814 PLUG AN806 UNION AN815 NUT AN817 NUT AN818 SLEEVE AN819 CAP AN820NIPPLE AN816ADAPTOR AN807 BOLT AN774 BOLT AN775 ELBOW AN776 ELBOW AN777 ELBOW AN778 TEE AN779 AN744 to AN932 Material: Aluminum alloy........................................................................................................................................... (code D) Steel ........................................................................................................................................................... (code, absence of letter) Brass .......................................................................................................................................................... (code B) Aluminum bronze ....................................................................................................................................... (code Z–for AN819 sleeve) Size: The dash number following the AN number indicates the size of the tubing (or hose) for which the fitting is made in 16ths of an inch.

This size measures the outer diameter of tubing and the inner diameter of hose. Fittings that have pipe threads are coded by a dash number, indicating the pipe size in 8ths of an inch. The material code letter, as noted above, follows the dash number. 9-12 1¹⁄8 ³⁄16 ¹⁄4 ⁵⁄16 ³⁄8 ¹⁄2 ⁵⁄8 ³⁄4 ⁷⁄8 1 1¹⁄4 1¹⁄2 1³⁄4 2 ²¹⁄32 ⁷⁄8 1¹⁄8 1⁵⁄16 1³⁄4 2³⁄16 2⁵⁄8 3¹⁄2 4³⁄8 5¹⁄4 6¹⁄8 7 ³⁄8 ⁷⁄16 ⁹⁄16 ³⁄4 ¹⁵⁄16 1¹⁄4 1¹⁄2 1³⁄4 3 3³⁄4 5 7 8 120 250 420 480 850 1,150 70 100 210 300 500 700 90–100 135–150 180–200 270–300 450–500 650–700 900–1,000 1,000–1,100 1,200–1,400 1,500–1,800 20–30 30–40 40–65 60–85 75–125 150–250 200–350 300–500 500–600 500–700 600–900 850–1,050 950–1,150 –2 –3 –4 –5 –6 –8 –10 –12 –14 –16 –20 –24 –28 –32 Tubing Outer Diameter (inches) Fitting Bolt or Nut Size Aluminum Alloy Tubing, Bolt, Fitting, or Nut Torque (in–lb) Steel Tubing, Bolt Fitting, or Nut Torque (in–lb) Hose End Fittings and Hose Assemblies MS28740 or Equivalent End Fitting Minimum Bend Radii (inches) Steel Minimum Maximum Alum. Alloy 1100-H14 5052-0 damage or completely cut off the tube flare, or it may ruin the sleeve or fitting nut. Failure to tighten sufficiently also may be serious, as this condition may allow the line to blow out of the assembly or to leak under system pressure. The use of torque wrenches and the prescribed torque values prevents overtightening or undertightening. If a tube fitting assembly is tightened properly, it may be removed and retightened many times before reflaring is necessary.

Flareless Tube Installation Tighten the nut by hand until an increase in resistance to turning is encountered. Should it be impossible to run the nut down with the fingers, use a wrench, but be alert for the first signs of bottoming. It is important that the final tightening commence at the point where the nut just begins to bottom. Use a wrench and turn the nut one-sixth turn (one flat on a hex nut). Use a wrench on the connector to prevent it from turning while tightening the nut. After the tube assembly is installed, the system should be pressure tested. It is permissible to tighten the nut an additional one-sixth turn (making a total of one-third turn), should a connection leak.

If leakage still occurs after tightening the nut a total of one- third turn, remove the assembly and inspect the components for scores, cracks, presence of foreign material, or damage from overtightening. Several aircraft manufacturers include torque values in their maintenance manuals to tighten the flareless fittings. 9-13 TEE MS21909 TEE MS21910 TEE MS21911ELBOW MS21908 SLEEVE MS21922 NUT MS21917 BUSHING MS21915 PLUG MS21913 UNION MS21924 TEE MS21912 ADAPTER MS21923 NUT MS21921 REDUCER MS21916 CAP MS21914 ELBOW MS21925 ELBOW MS21926 TEE MS21905 SLEEVE MS20819 UNION MS21902 ELBOW MS21904 UNION MS21903 ADAPTER MS21900 ADAPTER MS21901 ELBOW MS21907 CROSS MS21906 Material: aluminum alloy Size of fitting in 16ths inch – 4⁄16 inch Design part number: adapter, flareless tube to AN flared tube Prefix: military specification MS 21900 –4 D 9-14 NutBody Sleeve Lower die/holder assembly Power unit Waged Fitting Hydraulic Tubing Disconnect Head assembly The following notes, cautions, and faults apply to the installation of rigid tubing.

Note: Overtightening a flareless tube nut drives the cutting edge of the sleeve deeply into the tube, causing the tube to be weakened to the point where normal in-flight vibration could cause the tube to shear. After inspection (if no discrepancies are found), reassemble the connections and repeat the pressure test procedures. Caution: Never tighten the nut beyond one-third turn (two flats on the hex nut); this is the maximum the fitting may be tightened without the possibility of permanently damaging the sleeve and nut. Common faults: Flare distorted into nut threads; sleeve cracked; flare cracked or split; flare out of round; inside of flare rough or scratched; and threads of nut or union dirty, damaged, or broken.

Rigid Tubing Inspection & Repair Minor dents and scratches in tubing may be repaired. Scratches or nicks not deeper than 10 percent of the wall thickness in aluminum alloy tubing, which are not in the heel of a bend, may be repaired by burnishing with hand tools. The damage limits for hard, thin-walled corrosion- resistant steel and titanium tubing are considerably less than for aluminum tubing and might depend on the aircraft manufacturer. Consult the aircraft maintenance manual for damage limits. Replace lines with severe die marks, seams, or splits in the tube. Any crack or deformity in a flare is unacceptable and is cause for rejection. A dent of less than 20 percent of the tube diameter is not objectionable, unless it is in the heel of a bend. To remove dents, draw a bullet of proper size through the tube by means of a length of cable, or push the bullet through a short straight tube by means of a dowel rod. In this case, a bullet is a ball bearing or slug 9-15 Incorrect—will damage flare or threads, or cause sleeve to crack under vibration if tightened Incorrect—may pull off or distort flare if tightened Correctly fitted and tightened .025 clearance between flare and shoulder before tightening Do not deflect into place.

Replace tube assembly. normally made of steel or some other hard metal. In the case of soft aluminum tubing, a hard wood slug or dowel may even be used as a bullet. [Figure 9-29] A severely damaged line should be replaced. However, the line may be repaired by cutting out the damaged section and inserting a tube section of the same size and material. Flare both ends of the undamaged and replacement tube sections and make the connection by using standard unions, sleeves, and tube nuts. Aluminum 6061-T6, corrosion-resistant steel 304-1/8h and Titanium 3AL-2.5V tubing can be repaired by swaged fittings. If the damaged portion is short enough, omit the insert tube and repair by using one repair union. [Figure 9-30] When repairing a damaged line, be very careful to remove all chips and burrs. Any open line that is to be left unattended for a period of time should be sealed, using metal, wood, rubber,