Downloaded from https://www.everyspec.com FM 1-509 to. Generally, bursting or cracking of a tube is due to improper installation, damage caused by collision with an object, or excessive vibrations. When tubing fails, the cause should be determined. Replacements should be of the same size and material as the original, or an acceptable substitute listed in the applicable maintenance manual may be used. Repairs. A damaged line should be carefully removed so that it may be used as a template or pattern for the replacement item.
If the old piece of tubing cannot be used as a pattern, make a pattern key by placing one end of a piece of soft wire into one of the fittings where the tube is to be connected; then form the bends that are necessary to place the opposite end of the wire into the other connection. When the template satisfactorily spans the area between the fittings, it can be used as a pattern to bend the new tube. Select a path with the least amount of bend. This reduces flow loss and simplifies bending. If possible, use a path with all bends in the same plane. Never select a path that requires no bends; tube cannot be cut or flared accurately or installed satisfactorily without bends.
Bends absorb vibration and permit the tubing to expand or contract under temperature changes. If the tube is small (under 1/4 inch) and can be hand-formed, casual bends may be made. If the tube must be machine-formed, definite bends must be made to avoid a straight assembly. All bends must start a reasonable distance from the end fittings. This is because the sleeves and nuts must be slipped back along the tube during the fabrication of flares and during inspections. In all cases, the new tube assembly should be so formed before installation that pulling or deflecting the assembly into alignment by the coupling nuts is not necessary.
The objective in bending the tube is to obtain a smooth bend without flattening the tube. Usually a tube is bent with a tube bender; only in extreme emergencies would a tube be bent without using a hand-held or mechanical bending tool. A hand-held tube bender has a hand-clip handle, radius block, and slide-bar handle. The two handles act as levers to provide the mechanical advantage necessary to bend the tubing. A mechanical tube bender is issued as a kit. The kit contains the necessary equipment and instructions to bend tubing from 1/4 to 3/4 inch in diameter. This tube bender is used with metal tubing such as aircraft high-strength stainless steel.
Rigid tubing is repaired by replacing fittings and splicing sections of tubing using the permaswage repair procedure. Repairs may be done on or off the helicopter. The basic repair method is to mechanically swage the permaswage fitting onto the tube with a hydraulically operated tool. Fittings are permanent unions, elbows, tees, and crosses; flared, flareless, and separable sleeves; and combinations of permanent and threaded fittings. The portable hydraulic power supply provides pressure required to operate the swaging tool. MIL-H-5606 fluid is fed to the tool through a l/4-inch quick-disconnect, high-pressure hose.
A swaging pressure of 5,500 psi may be applied to all tubing sizes and materials by manually operating the hand pump or using air-to-hydraulic fluid pressure from a 60- to 2-2