Thoroughly inspect all hydraulic hose and fittings at normal intervals to assure airworthiness. Examine any evidence of fluid reduction or leaks. Examine metallic tubes for leaks, free anchorage, scratches, kinks, or other destruction. Examine fittings and connections for leakage, looseness, cracks, burrs, or other injury. Replace or fix defective aspects. Make absolutely sure the hoses do not chafe towards just one an additional and are correctly secured and clamped.
a. Alternative of Metal tube. When inspection shows hydraulic hose to be damaged or faulty swap the whole line or, if the ruined area is localized, a maintenance portion may perhaps be inserted. In replacing plane hose, always use tubing of the identical dimensions and substance as the initial line. Use the outdated tubing as a template when bending the new tube, unless of course it is also considerably ruined, in which scenario a template can be created from delicate iron wire. Comfortable aluminum tubing (1100, 3003, or 5052) underneath half-inch outside diameter could be bent by hand. For all other tubing use an acceptable hand or power tube-bending software. Bend tubing diligently to steer clear of too much flattening, kinking, or wrinkling. A compact total of flattening in bends is suitable, but do not exceed 75 per cent of the original outdoors diameter. Excessive flattening will bring about fatigue failure of the hydraulic tube. When putting in the substitution tubing line it up the right way with the mating aspect so that it is not forced into alignment by tightening of the coupling nuts.
b. Hose couplings and Tube Connections. A lot of tube connections are produced working with flared tube finishes with
common relationship fittings: AN-818 (MS 20818) nut and AN-819 (MS 20819) sleeve. In forming flares, minimize the tube ends sq., file sleek, take out all burrs and sharp edges, and comprehensively clear. The tubing is then flared utilizing the appropriate 37-degree aviation flare forming software for the size of tubing and variety of fitting. A double flare is utilized on tender aluminum tubing 3/8-inch outdoors diameter and beneath, and a single flare on all other tubing. In creating the connections, use hydraulic fluid as a lubricant and then tighten. Overtightening will harm the tube or fitting, which may well lead to a failure. Beneath-tightening may perhaps lead to leakage which could consequence in a program failure.
Warning: Mistaken use of 45-degree automotive flare forming instruments may perhaps outcome in poor tubing flare shape and angle causing misfit, worry and strain, and possible process failure.
c. Maintenance of aircraft hydraulic Metal Tube Traces. Insignificant dents and scratches in tubing may well be fixed. Scratches or nicks not further than 10 p.c of the wall thickness in aluminum alloy tubing, that are not in the heel of a bend, might be fixed by burnishing with hand applications. Swap strains with intense die marks, seams, or splits in the tube. Any crack or deformity in a flare is unacceptable and bring about for rejection. A dent fewer than 20 percent of the tube diameter is not objectionable until it is in the heel of a bend. A seriously-destroyed line must be replaced even so, it may possibly be repaired by cutting out the damaged portion and inserting a tube area of the very same sizing and product. Flare each ends of the undamaged and substitution tube sections and make the relationship by utilizing common unions, sleeves, and tube nuts.If the harmed portion is short sufficient, omit the insert tube and repair by applying 1 union and two sets of link hose fittings.
d.Substitute of Flexible Hose. When substitution of flexible hose is important, use the same kind, dimensions, element variety, and length of hose as the line to be changed. Check out TSO necessities. If the substitute of a hose with a swaged-end form fitting is essential, receive new hydraulic hose assemblies of the suitable size and composition. Certain synthetic oils require a specially compounded synthetic rubber hose, which is compatible. Refer to the aircraft manufacturer’s company details for the accurate component range for the substitute hose. If the fittings on each close are of the accurate variety or sleeve kind, a substitution may well be fabricated. Just before reducing new adaptable wire braided hose to the good dimension, tape the hose tightly with masking tape and slash in the center of the masking tape to avoid fraying. The use of a mandrel will avert slicing the inside of the hose when inserting the fittings. Set up hose assemblies with no twisting. A hose ought to not be stretched restricted between two fittings as this will result in overstressing and eventual failure. The duration of hose really should be adequate to provide about 5 to 8 % slack. Stay clear of restricted bends in flex lines as they may perhaps result in failure. Under no circumstances exceed the least bend radii.
(1) Teflon hose is utilized in quite a few plane units due to the fact it has outstanding attributes for certain apps. Teflon is compounded from tetrafluoroethylene resin which is unaffected by fluids usually made use of in plane. It has an operating range of -65°F to 450 °F. For these reasons, Teflon hose is utilized in hydraulic and engine lubricating devices where by temperatures and pressures preclude the use of rubber hose. Even though Teflon hose has excellent effectiveness features, it also has peculiar qualities that require added treatment in handling. It tends to suppose a lasting set when exposed to substantial stress or temperature. Do not endeavor to straighten a hose that has been in company. Any extreme bending or twisting may well result in kinking or weakening of the tubing wall. Switch any hose that demonstrates signals of leakage, abrasion, or kinking. Any hose suspected of kinking may be checked with a steel ball of appropriate measurement.The ball will not move by means of if the hose is distorted past boundaries.
(2) If the hose fittings are of the reusable sort, a substitute hose may be fabricated. When a hose assembly is eradicated, the finishes must be tied, so that the preformed form will be taken care of.
(3) All flexible hose installations should be supported at least just about every 24 inches. Closer supports are most popular. They ought to be thoroughly routed and securely clamped to prevent abrasion, kinking, or abnormal flexing. Extreme flexing could bring about weakening of the hose or loosening at the fittings.
