Meticulously inspect all hydraulic hose and fittings at normal intervals to make sure airworthiness. Investigate any proof of fluid loss or leaks. Verify metal tubes for leaks, loose anchorage, scratches, kinks, or other harm. Inspect fittings and connections for leakage, looseness, cracks, burrs, or other harm. Replace or repair defective components. Make certain the hoses do not chafe against one particular a further and are appropriately secured and clamped.
a. Replacement of Metal tube. When inspection shows hydraulic hose to be broken or defective replace the complete line or, if the broken section is localized, a repair section might be inserted. In replacing aircraft hose, generally use tubing of the very same size and material as the original line. Use the old tubing as a template when bending the new tube, unless it is also drastically broken, in which case a template can be created from soft iron wire. Soft aluminum tubing (1100, 3003, or 5052) beneath half-inch outdoors diameter might be bent by hand. For all other tubing use an acceptable hand or energy tube-bending tool. Bend tubing very carefully to steer clear of excessive flattening, kinking, or wrinkling. A compact quantity of flattening in bends is acceptable, but do not exceed 75 % of the original outdoors diameter. Excessive flattening will bring about fatigue failure of the hydraulic tube. When installing the replacement tubing line it up appropriately with the mating aspect so that it is not forced into alignment by tightening of the coupling nuts.
b. Hose couplings and Tube Connections. Several tube connections are created utilizing flared tube ends with normal connection fittings: AN-818 (MS 20818) nut and AN-819 (MS 20819) sleeve. In forming flares, reduce the tube ends square, file smooth, eliminate all burrs and sharp edges, and completely clean. The tubing is then flared utilizing the right 37-degree aviation flare forming tool for the size of tubing and kind of fitting. A double flare is utilized on soft aluminum tubing three/eight-inch outdoors diameter and beneath, and a single flare on all other tubing. In generating the connections, use hydraulic fluid as a lubricant and then tighten. Overtightening will harm the tube or fitting, which might bring about a failure. Beneath-tightening might bring about leakage which could outcome in a technique failure.
CAUTION: Mistaken use of 45-degree automotive flare forming tools might outcome in improper tubing flare shape and angle causing misfit, anxiety and strain, and probable technique failure.
c. Repair of aircraft hydraulic Metal Tube Lines. Minor dents and scratches in tubing might be repaired. Scratches or nicks not deeper than 10 % of the wall thickness in aluminum alloy tubing, that are not in the heel of a bend, might be repaired by burnishing with hand tools. Replace lines with serious die marks, seams, or splits in the tube. Any crack or deformity in a flare is unacceptable and bring about for rejection. A dent significantly less than 20 % of the tube diameter is not objectionable unless it is in the heel of a bend. A severely-broken line really should be replaced nonetheless, it might be repaired by cutting out the broken section and inserting a tube section of the very same size and material. Flare each ends of the undamaged and replacement tube sections and make the connection by utilizing normal unions, sleeves, and tube nuts.If the broken portion is quick adequate, omit the insert tube and repair by utilizing one particular union and two sets of connection hose fittings.
d.Replacement of Versatile Hose. When replacement of versatile hose is important, use the very same kind, size, aspect quantity, and length of hose as the line to be replaced. Verify TSO needs. If the replacement of a hose with a swaged-finish kind fitting is important, acquire new hydraulic hose assemblies of the right size and composition. Particular synthetic oils demand a specially compounded synthetic rubber hose, which is compatible. Refer to the aircraft manufacturer's service info for the right aspect quantity for the replacement hose. If the fittings on each and every finish are of the right kind or sleeve kind, a replacement might be fabricated. Just before cutting new versatile wire braided hose to the right size, tape the hose tightly with masking tape and reduce in the center of the masking tape to protect against fraying. The use of a mandrel will protect against cutting the inside of the hose when inserting the fittings. Set up hose assemblies without having twisting. A hose really should not be stretched tight involving two fittings as this will outcome in overstressing and eventual failure. The length of hose really should be enough to supply about five to eight % slack. Steer clear of tight bends in flex lines as they might outcome in failure. Under no circumstances exceed the minimum bend radii.
(1) Teflon hose is utilized in a lot of aircraft systems due to the fact it has superior qualities for specific applications. Teflon is compounded from tetrafluoroethylene resin which is unaffected by fluids commonly utilized in aircraft. It has an operating variety of -65°F to 450 °F. For these motives, Teflon hose is utilized in hydraulic and engine lubricating systems exactly where temperatures and pressures preclude the use of rubber hose. While Teflon hose has superb efficiency qualities, it also has peculiar qualities that demand further care in handling. It tends to assume a permanent set when exposed to higher stress or temperature. Do not try to straighten a hose that has been in service. Any excessive bending or twisting might bring about kinking or weakening of the tubing wall. Replace any hose that shows indicators of leakage, abrasion, or kinking. Any hose suspected of kinking might be checked with a steel ball of right size.The ball will not pass by way of if the hose is distorted beyond limits.
(2) If the hose fittings are of the reusable kind, a replacement hose might be fabricated. When a hose assembly is removed, the ends really should be tied, so that the preformed shape will be maintained.
(3) All versatile hose installations really should be supported at least each 24 inches. Closer supports are preferred. They really should be very carefully routed and securely clamped to steer clear of abrasion, kinking, or excessive flexing. Excessive flexing might bring about weakening of the hose or loosening at the fittings.