Text-only reference. Published from the recorded official FAA General Chapter 9 PDF. Diagrams, photographs, and figure artwork are not reproduced here; use the official FAA PDF for those materials.
9-6 37° A. Single-flared end B. Double-flared end flared (B) tube ends. 1, 2, and 3) illustrates the presetting operation, which is performed as follows: 1. Cut the tube to the correct length, with the ends perfectly square. Deburr the inside and outside of the tube. Slip the nut, then the sleeve, over the tube (step 1), lubricate the threads of the fitting and nut with hydraulic fluid. 2. Place the fitting in a vise (step 2), and hold the tubing firmly and squarely on the seat in the fitting. (The tube must bottom firmly in the fitting.) Tighten the nut until the cutting edge of the sleeve grips the tube.
To determine this point, slowly turn the tube back and forth while tightening the nut. When the tube no longer turns, the nut is ready for tightening. 3. Final tightening depends upon the tubing (step 3). For aluminum alloy tubing up to and including 1⁄2" outside diameter, tighten the nut from 1 to 11⁄6 turns. For steel tubing and aluminum alloy tubing over 1⁄2" outside diameter, tighten from 11⁄6 to 11⁄2 turns. After presetting the sleeve, disconnect the tubing from the fitting and check the following points: The tube should extend 3⁄32" to 1⁄8" beyond the sleeve pilot; otherwise, blowoff may occur. The sleeve pilot should contact the tube or have a maximum clearance of 0.005" for aluminum alloy tubing or 0.015" for steel tubing. A slight collapse of the tube at the sleeve cut is permissible. No movement of the sleeve pilot, except rotation, is permissible.
9-7 Beading Tubing may be beaded with a hand beading tool, with machine beading rolls, or with grip dies. The method to be used depends on the diameter and wall thickness of the tube and the material from which it was made. The hand beading tool is used with tubing having 1⁄4" to 1" outside diameter. [Figure 9-15] The bead is formed by using the beader frame with the proper rollers attached. The inside and outside of the tube is lubricated with light oil to reduce the friction between the rollers during beading. The sizes, marked in sixteenths of an inch on the rollers, are for the outside diameter of the tubing that can be beaded with the rollers.
Separate rollers are required for the inside of each tubing size, and care must be taken to use the correct parts when beading. The hand beading tool works somewhat like the tube cutter in that the roller is screwed down intermittently while rotating the beading tool around the tubing. In addition, a small vise (tube holder) is furnished with the kit. Other methods and types of beading tools and machines are available, but the hand beading tool is used most often. As a rule, beading machines are limited to use with large diameter tubing, over 115⁄16", unless special rollers are supplied. The grip-die method of beading is confined to small tubing.
Fluid Line Identification Fluid lines in aircraft are often identified by markers made up of color codes, words, and geometric symbols. These markers identify each line’s function, content, and primary hazard. Figure 9-16 illustrates the various color codes and symbols used to designate the type of system and its contents. Fluid lines are marked, in most instances, with 1" tape or decals. [Figure 9-17A] On lines 4" in diameter (or larger), lines in oily environment, hot lines, and on some cold lines, steel tags may be used in place of tape or decals. [Figure 9-17B] Paint is used on lines in engine compartments where there is the possibility of tapes, decals, or tags being drawn into the engine induction system.
In addition to the above-mentioned markings, certain lines may be further identified regarding specific function within a system (e.g., drain, vent, pressure, or return). Lines conveying fuel may be marked FLAM [Figure 9-17]; lines containing toxic materials are marked TOXIC in place of FLAM. Lines containing physically dangerous materials, such as oxygen, nitrogen, or FreonTM, may be marked PHDAN. Aircraft and engine manufacturers are responsible for the original installation of identification markers, but the aviation mechanic is responsible for the replacement when it becomes necessary. Tapes and decals are generally placed on both ends of a line and at least once in each compartment through which lines run. In addition, identification markers are placed immediately adjacent to each valve, regulator, filter, or other accessories within a line. Where paint or tags are used, location requirements are the same as for tapes and decals.
Fluid Line End Fittings Depending on the type and use, fittings have either pipe threads or machine threads. Pipe threads are similar to those used in ordinary plumbing and are tapered, both internal and external. External threads are referred to as male threads and internal threads are female threads. When two fittings are joined, a male into a female, the thread taper forms a seal. Some form of pipe thread lubricant approved for particular fluid application should be used when joining pipe threads to prevent seizing and high-pressure leakage. Use care when applying thread lubricant so that the lubricant does not enter and contaminate the system. Do not use lubricants on oxygen lines. Oxygen reacts with petroleum products and can ignite (special lubricants are available or oxygen systems).
9-8 Fitting TubeSleeve pilot Sleeve cutting edge Sleeve Tube nut STEP 1 STEP 2 Slight deformation permissible .005" maximum aluminum alloy tubing .015" maximum corrosion-resistant steel tubing STEP 3 Machine threads have no sealing capability and are similar to those used on common nuts and bolts. This type of fitting is used only to draw connections together or for attachment through bulkheads. A flared tube connection, a crush washer, or a synthetic seal is used to make the connection fluid tight. Machine threads have no taper and do not form a fluid-tight seal. The size of these fittings is given in dash numbers, which equal the nominal outside diameter in sixteenths of an inch.
Universal Bulkhead Fittings When a fluid line passes through a bulkhead, and it is desired to secure the line to the bulkhead, a bulkhead fitting should be used. The end of the fitting that passes through the bulkhead is longer than the other end(s), which allows a locknut to be installed, securing the fitting to the bulkhead. Fittings attach one piece of tubing to another or to system units. There are four types: (1) bead and clamp, (2) flared fittings, (3) flareless fittings, and (4) permanent fittings (Permaswage™, Permalite™, and Cyrofit™). The amount of pressure that the system carries and the material used are usually the deciding factors in selecting a connector.
The beaded type of fitting, which requires a bead and a section of hose and hose clamps, is used only in low- or medium- pressure systems, such as vacuum and coolant systems. The flared, flareless, or permanent-type fittings may be used as connectors in all systems, regardless of the pressure. AN Flared Fittings A flared tube fitting consists of a sleeve and a nut. [Figure 9-18] The nut fits over the sleeve and, when tightened, draws the sleeve and tubing flare tightly against a male fitting to form a seal. Tubing used with this type of fitting must be flared before installation. The male fitting has a cone-shaped surface with the same angle as the inside of the flare. The sleeve supports the tube so that vibration does not concentrate at the edge of the flare and distributes the shearing action over a wider area for added strength.
Fitting combinations composed of different alloys should be avoided to prevent dissimilar metal corrosion. As with all fitting combinations, ease of assembly, alignment, and proper lubrication should be assured when tightening fittings during installation. Standard AN fittings are identified by their black or blue color. All AN steel fittings are colored black, all AN aluminum fittings are colored blue, and aluminum bronze fittings are cadmium plated and natural in appearance. A sampling of AN fittings is shown in Figure 9-19. Figure 9-20 contains 3/32" to 1/8" 9-9 handle (4). connection that is virtually maintenance free. Swaged fittings are used to join hydraulic lines in areas where routine disconnections are not required and are often used with titanium and corrosion-resistant steel tubing. The fittings are installed with portable hydraulically-powered tooling, which is compact enough to be used in tight spaces. [Figure 9-24] If the fittings need to be disconnected, cut the tubing with a tube cutter. Special installation tooling is available in portable kits. Always use the manufacturer’s instructions to install swaged fittings. Typical Permaswage™ fittings are shown in Figure 9-25.
One of the latest developments is the Permalite™ fitting. Permalite™ is a tube fitting that is mechanically attached to the tube by axial swaging. Permalite™ works by deforming the fitting into the tube being joined by moving a ring, a component of the Permalite™ fitting, axially along the fitting length using a Permaswage™ Axial swage tool. Typical Permalite™ fittings are shown in Figure 9-26. Cryofit Fittings Many transport category aircraft use Cryofit fittings to join hydraulic lines in areas where routine disconnections are not required. Cryofit fittings are standard fittings with a cryogenic sleeve. The sleeve is made of a shape memory alloy, Tinel™.
additional information on sizes, torques, and bend radii. AN flared fittings are different from MS flareless fittings and they are not interchangeable. AN flared fittings are easily recognized, because they have a cone at the end of the fitting while the MS flareless fitting has a straight end. [Figure 9-21] MS Flareless Fittings MS flareless fittings are designed primarily for high-pressure (3,000 psi) hydraulic systems that may be subjected to severe vibration or fluctuating pressure. [Figure 9-22] Using this type of fitting eliminates all tube flaring, yet provides a safe and strong, dependable tube connection. The fitting consists of three parts: a body, a sleeve, and a nut. [Figure 9-23] The internal design of the body causes the sleeve to cut into the outside of the tube when the body and nut are joined. The counterbore shoulder within the body is designed with a reverse angle of 15° for steel connectors and 45° for aluminum fittings. This reverse angle prevents inward collapse of the tubing when tightened and provides a partial sealing force to be exerted against the periphery of the body counterbore.
Swaged Fittings A popular repair system for connecting and repairing hydraulic lines on transport category aircraft is the use of Permaswage™ fittings. Swaged fittings create a permanent