TEE AN826 TEE CROSS AN827 AN825 UNION AN832 TEE ELBOW AN833 AN834 ELBOW AN837 ELBOW AN839 ELBOW AN838 AN840 HOSE NIPPLE HOSE NIPPLE AN841 * HOSE ELBOW AN842 HOSE ELBOW AN843
HOSE ELBOW AN844 ELBOW AN847 · ELBOW AN848 * ELBOW AN845 *AN867 ELBOW AN846 *AN871 BUSHING CONNECTOR AN849 AN893 BUSHING AN894 * Inactive for new design.
FIGURE 5-8. AN plumbing fittings. Continued 106
AN COUPLING NIPPLE AN911 BUSHING AN912 PLUG AN913 ELBOW AN914 AN910 ELBOW AN915 ELBOW AN916 TEE AN917 REDUCER AN919 NUT AN924 CROSS AN918 TEE AN926 ELBOW AN927 Y AN ELBOW AN928 CROSS AN925 PLUG AN932 CAP AN92 FIGURE 5-8. AN plumbing fittings.-Continued sleeves, and tube flares are allowed to make up a complete fitting assembly. The use of dissimilar metals should be avoided since their contact will cause corrosion.
straight threads, but they have different pitch for the various types.
Flared-tube fittings are made of aluminum alloy, steel, or copper base alloys. For identifi- When combining AC and AN end connections, nuts, sleeves, or tube flares, if the nut will not move more than two threads by hand, stop and investigate for possible trouble.
The AN standard fitting is the most commonly used flared-tubing assembly for attaching the tubing to the various fittings required in aircraft plumbing systems. The AN standard fittings include the AN818 nut and AN819 sleeve. (See figure 5-8.) The AN819 sleeve is used with the AN818 coupling nut. All these fittings have cation purposes, all AN steel fittings are colored black, and all AN aluminum alloy fittings are colored blue. The AN 819 aluminum bronze sleeves are cadmium plated and are not colored The size of these fittings is given in dash numbers, which equal the nominal tube outside diameter (O.D.) in sixteenths of an inch.
Threaded flared-tube fittings have two types of ends, referred to as male and female. The male end of a fitting is externally threaded, whereas the female end of a fitting is internally threaded.
Cone angle Sleeve pilot Sleeve Tube shoulder. Bevel Tube Sleeve cutting edge Body • Nut FIGURE 5-9. Flareless-tube fitting.
The MS (Military Standard) flareless-tube fittings are finding wide application in aircraft plumbing systems. Using this type fitting eliminates all tube flaring, yet provides a safe, strong, dependable tube connection. The fitting consists of three parts: a body, a sleeve, and a nut. The body has a counterbored shoulder, against which the end of the tube rests. (See figure 5-9.) The angle of the counterbore causes the cutting edge of the sleeve to cut into the outside of the tube when the two are joined. Installation of flarelesstube fittings is discussed later in this chapter.
Quick-disconnect Couplings Quick-disconnect couplings of the self-sealing type are used at various points in many fluid systems. The couplings are installed at locations where frequent uncoupling of the lines is required for inspection and maintenance.
Quick-disconnect couplings provide a means of quickly disconnecting a line without loss of fluid or entrance of air into the system. Each coupling assembly consists of two halves, held together by a union nut. Each half contains a valve that is held open when the coupling is connected, allowing fluid to flow through the coupling in either direction. When the coupling is disconnected, a spring in each half closes the valve, preventing the loss of fluid and entrance of air.
The union nut has a quick-lead thread which permits connecting or disconnecting the coupling by turning the nut. The amount the nut must be turned varies with different style couplings. One style requires a quarter turn of the union nut to lock or unlock the coupling while another style requires a full turn.
Some couplings require wrench tightening;
others are connected and disconnected by hand The design of some couplings is such that they must be safetied with safety wire. Others do not require lock wiring, the positive locking being assured by the teeth on the locking spring, which engage ratchet teeth on the union nut when the coupling is fully engaged. The lock spring automatically disengages when the union nut is unscrewed. Because of individual differences, all quick disconnects should be installed according to instructions in the aircraft maintenance manual.
Flexible Connectors Flexible connectors may be equipped with either swaged fittings or detachable fittings, or they may be used with beads and hose clamps. Those equipped with swaged fittings are ordered by correct length from the manufacturer and ordinarily cannot be assembled by the mechanic.
They are swaged and tested at the factory and are equipped with standard fittings.
The fittings on detachable connectors can be detached and reused if they are not damaged;
otherwise new fittings must be used.
The bead and hose clamp connector is often used for connecting oil, coolant, and low-pressure fuel system tubing. The bead, a slightly raised ridge around the tubing or the fitting, gives a good gripping edge that aids in holding the clamp and hose in place. The bead may appear near the end of the metal tubing or on one end of a fitting.
TUBE FORMING PROCESSES Damaged tubing and fluid lines should be replaced with new parts whenever possible. Sometimes replacement is impractical and repair is necessary. Scratches, abrasions, and minor corrosion on the outside of fluid lines may be considered negligible and can be smoothed out with a burnishing tool or aluminum wool. Limitations on the amount of damage that can be repaired in this manner are discussed later in this chapter under "Repair of Metal Tube Lines." If a fluid line assembly is to be replaced, the fittings can often be salvaged; then the repair will involve only tube forming and replacement.
Tube forming consists of four processes: (1) Cutting, (2) bending, (3) flaring, and (4) beading.
If the tubing is small and of soft material, the assembly can be formed by hand bending during installation. If the tubing is ¼-inch diameter, or larger, hand bending without the aid of tools is impractical.
Tube Cutting When cutting tubing, it is important to produce a square end, free of burrs. Tubing may be cut with a tube cutter or a hacksaw. The cutter can be used with any soft metal tubing, such as copper, aluminum, or aluminum alloy. Correct use of the tube cutter is shown in figure 5-10.
Cutting a tube open side of sues Tube Clean cut → FIGURE 5-10. Tube cutting.
A new piece of tubing should be cut approximately 10 percent longer than the tube to be replaced to provide for minor variations in bending.
Place the tubing in the cutting tool, with the cutting wheel at the point where the cut is to be made.
Rotate the cutter around the tubing, applying a light pressure to the cutting wheel by intermittently twisting the thumbscrew. Too much pressure on the cutting wheel at one time could deform the tubing or cause excessive burring. After cutting the tubing, carefully remove any burrs from inside and outside the tube. Use a knife or the burring edge attached to the tube cutter.
When performing the deburring operation use extreme care that the wall thickness of the end of the tubing is not reduced or fractured. Very slight damage of this type can lead to fractured flares or defective flares which will not seal properly.
fine tooth file can be used to file the end square and smooth.
If a tube cutter is not available, or if tubing of hard material is to be cut, use a fine-tooth hacksaw, preferably one having 32 teeth per inch. The use of a saw will decrease the amount of work hardening of the tubing during the cutting operation.
After sawing, file the end of the tube square and smooth, removing all burrs.
An easy way to hold small-diameter tubing, when cutting it, is to place the tube in a combination flaring tool and clamp the tool in a vise. Make the cut about one-half inch from the flaring tool. This procedure keeps sawing vibrations to a minimum and prevents damage to the tubing if it is accidentally hit with the hacksaw frame or file handle while cutting. Be sure all filings and cuttings are removed from the tube.
Tube Bending The objective in tube bending is to obtain a smooth bend without flattening the tube. Tubing under one-fourth inch in diameter usually can be bent without the use of a bending tool. For larger sizes, a hand tube bender similar to that shown in figure 5-11 is usually used.
To bend tubing with the hand tube bender, insert the tubing by raising the slide bar handle as far as it will go. Adjust the handle so that the full length of the groove in the slide bar is in contact with the tubing. The zero mark on the radius block and the mark on the slide bar must align. Make the bend by rotating the handle until the desired angle of bend is obtained, as indicated on the radius block.
Bend the tubing carefully to avoid excessive flattening, kinking, or wrinkling. A small amount of flattening in bends is acceptable, but the small diameter of the flattened portion must not be less than 75 percent of the original outside diameter. Tubing with flattened, wrinkled, or irregular bends should not be installed. Wrinkled bends usually result from trying to bend thin-wall tubing without using a tube bender. Examples of correct and incorrect tubing bends are shown in figure 5-12.
Tube bending machines for all types of tubing are generally used in repair stations and large maintenance shops. With such equipment, proper bends can be made on large diameter tubing and on tubing made from hard material. The production tube bender is an example of this type of machine.
The ordinary production tube bender will accommodate tubing ranging from /2-inch to 12- inch outside diameter. Benders for larger sizes are available, and the principle of their operation is similar to that of the hand tube bender. The radius blocks are so constructed that the radius of bend will vary with the tubing diameter. The radius of bend is usually stamped on the block.
When hand or production tube benders are not available or are not suitable for a particular bending operation, a filler of metallic composition or of dry sand may be used to facilitate bending.
When using this method, cut the tube slightly longer than is required. The extra length is for inserting a plug (which may be wooden) in each end.
After plugging one end, fill and pack the tube with fine, dry sand and plug tightly. Both plugs must be tight so they will not be forced out when the bend is made. The tube can also be closed by flattening the ends or by soldering metal disks in them. After the ends are closed, bend the tubing 109
Note: This bender can be slipped over partially connected tubes as it is Raise slide bar upward applied at direct point of bend.
Hight hand
2. Place tube Left hand
3. Drop clip over tube Note: Zero mark coincides with mark on block Left hand With right hand continue to bend tube to desired angle by pressing handle as shown below.
90° mark To remove bent tube. lift slide bar handle to original position and raise clip Right hand Left hand FIGURE 5-11. Tube bending.
over a forming block shaped to the specified radius.
In a modified version of the filler method, a fusible alloy is used instead of sand. In this method, the tube is filled under hot water with a fusible alloy that melts at 160° F. The alloy-filled tubing is then removed from the water, allowed to cool, and bent slowly by hand around a forming block or with a tube bender. After the bend is made, the alloy is again melted under hot water and removed from the tubing.
When using either filler method, make certain that all particles of the filler are removed so that none will be carried into the system in which the tubing is installed. Store the fusible alloy filler where it will be free from dust or dirt. It can be 110
Grip die Flaring tool " shown in vise Yake Perfect bend Flattened bend Wrinkled bend Kinked bend FIGURE 5-12. Correct and incorrect tubing bends.
re-melted and re-used as often as desired. Never heat this filler in any other than the prescribed method, as the alloy will stick to the inside of the tubing, making them both unusable.
Tube Flaring Two kinds of flares are generally used in aircraft plumbing systems, the single flare and the double fare. Flares are frequently subiected to extremely high pressures; therefore, the flare on the tubing must be properly shaped or the connection will leak or fail.
A flare made too small produces a weak joint, which may leak or pull apart; if made too large it interferes with the proper engagement of the screw thread on the fitting and will cause leakage.
crooked flare is the result of the tubing not being cut squarely. If a flare is not made properly, flaws cannot be corrected by applying additional torque when tightening the fitting. The flare and tubing must be free from cracks, dents, nicks, scratches, or any cther defects.
The Haring tool used for aircraft tubing has male and female dies ground to produce a flare of 35° to 37°. Under no circumstances is it permissible to use an automotive type flaring tool which produces a flare of 45°.
Single Flare A hand flaring tool similar to that shown in figure 5-13 is used for flaring tubing. The tool Tubing, grip die Tubing Grip die 00000 Flaring tool Steel pilots Top view plunger Side view FIGURE 5-13. Hand faring tool (single flare).
consists of a flaring block or grip die, a yoke, and a faring pin. The flaring block is a hinged double bar with holes corresponding to various sizes of tubing. These holes are countersunk on one end to form the outside support against which the flare is formed. The yoke is used to center the flaring pin over the end of the tube to be flared.
To prepare a tube for flaring, cut the tube squarely and remove all burrs. Slip the fitting nut and sleeve on the tube and place the tube in the proper size hole in the flaring tool. Center the plunger or flaring pin over the end of the tube.
Then project the end of the tubing slightly from the top of the flaring tool, about the thickness of a dime, and tighten the clamp bar securely to prevent slippage.
Make the flare by striking the plunger several light blows with a lightweight hammer or mallet.
Turn the plunger a half turn after each blow and be sure it seats properly before removing the tube from the flaring tool. Check the flare by sliding the sleeve into position over the flare.
the outside diameter of the flare should extend approximately one-sixteenth inch beyond the end of the sleeve, but should not be larger than the major outside diameter of the sleeve.
Double Flare A double flare should be used on 5052-0 and 6061-T aluminum alloy tubing for all sizes from ⅛- to g-inch outside diameter. This is necessary to prevent cutting off the flare and failure of the tube assembly under operating pressures. Double flaring is not necessary on steel tubing. See figure 5-14 for an illustration of single- and doublefared tubing. The double flare is smoother and more concentric than the single flare and, therefore, seals better. It is also more resistant to the shearing effect of torque.
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 A. Single-flared end 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 us. with large-diameter tubing, over 11¾6 inch, unk ss special rollers are supplied.
The grip-die method of beading is confined to small tubing.
Flareless-Tube Assemblies Although the use of flareless-tube fittings eliminates all tube flaring, another operation, referred to as presetting, is necessary prior to installation B. Double-flared end of a new flareless-tube assembly. Figure 5-15 (steps 1, 2, and 3) illustrates the presetting oper- FIGURE 5-14. Cutaway view of single- and ation, which is performed as follows:
double-flared tube ends.
(a.) Cut the tube to the correct length, with the ends perfectly square. Deburr the inside and outside of the tube. Slip the nut, then To make the double flare, separate the clamp the sleeve, over the tube (step 1).
blocks of the double-flaring tool and insert and (b.) Lubricate the threads of the fitting and clamp the tubing with the burred end flush with nut with hydraulic fluid. Place the fitting in the top of the clamp. Insert the starting pin into a vise (step 2), and hold the tubing firmly and the flaring pin guide and strike the pin sharply squarely on the seat in the fitting. (Tube with a hammer until the shoulder of the pin stops must bottom firmly in the fitting.) Tighten against the clamp blocks. Remove the starting pin the nut until the cutting edge of the sleeve and insert the finishing pin; hammer it until its grips the tube. This point is determined by shoulder rests on the clamp block. slowly turning the tube back and forth while tightening the nut. When the tube no longer Beading turns, the nut is ready for final tightening.
(c.) Final tightening depends upon the tub- Tubing may be beaded with a hand-beading ing. For aluminum alloy tubing up to and intool, with machine-beading rolls, or with grip dies. cluding ½-inch outside diameter, tighten the The method to be used depends on the diameter nut from one to one and one-sixth turns.
and wall thickness of the tube and the material For steel tubing and aluminum alloy tubing from which it was made. over ½-inch outside diameter, tighten from The hand-beading tool is used with tubing one and one-sixth to one and one-half turns.
having ¼- to 1-inch outside diameter. The bead is formed by using the beader frame with the After presetting the sleeve, disconnect the tubproper rollers attached. The inside and outside ing from the fitting and check the following points 112
Sleeve pilot Tube nut for aluminum alloy tubing or 0.015 inch for Fitting.
Sleeve • Tube steel tubing.
(c.) A slight collapse of the tube at the sleeve cut is permissible. No movement of the sleeve pilot, except rotation, is permissible.
REPAIR OF METAL TUBE LINES Sleeve cutting edge Scratches or nicks no deeper than 10 percent Step 1 of the wall thickness in aluminum alloy tubing may be repaired, if they are not in the heel of a bend. Replace lines with severe die marks, seams, or splits in the tube. Any crack or deformity in a flare is also 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. Dents can be removed by drawing a bullet of proper size through the tube by means of a length of cable.
A severely damaged line should be replaced.
However, the line can 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. If the damaged portion is short enough, omit the insert tube and repair by using one union and two sets of con- Step 2 necting fittings.
3/32 to When repairing a damaged line, be very careful 1/8 inch to remove all chips and burrs. Any open line that is to be left unattended for some time should be sealed, using metal, wood, rubber, or plastic plugs or caps.
When repairing a low-pressure line using a flexible fluid connection assembly, position the Step 3 hose clamps carefully in order to prevent overhang Slight deformation permissible of the clamp bands or chafing of the tightening screws on adjacent parts. If chafing can occur, .005 inch maximum - aluminum the hose clamps should be repositioned on the alloy tubing hose. Figure 5-16 illustrates the design of a flexible 015 inch maximum - corrosion fluid connection assembly and gives the maximum resistant steel tubing allowable angular and dimensional offset.
FIGURE 5-15. Presetting flareless-tube assembly. Layout of Lines (illustrated in step 3):
(a.) The tube should extend ⅔2 to ⅛ inch beyond the sleeve pilot; otherwise blowoff may occur.
(b.) The sleeve pilot should contact the tube or have a maximum clearance of 0.005 inch Remove the damaged or worn assembly, taking care not to further damage or distort it, and use it as a forming template for the new part. If the old length of tubing cannot be used as a pattern, make a wire template, bending the pattern by hand as required for the new assembly. Then bend the tubing to match the wire pattern.
Never select a path that does not require bends 113
Clamps 1/4" Min.
Ref.
Nut Socket Fitting Hose Tubing Nipple 3° Max.
Angular deviation 1/16" Max offset Minimum gap "G" shall be 1/2" or Tube OD/4, whichever is greater.
Maximum gap "G" is not limited except on suction lines using other than self-sealing hose. On such suction lines, maximum G shall be 1-1/2 inch or one tube diameter, whichever is greater.
FIGURE 5-16. Flexible fluid connection assembly.
in the tubing. A tube cannot be cut or flared accurately enough so that it can be installed without bending and still be free from mechanical strain. Bends are also necessary to permit the tubing to expand or contract under temperature changes and to absorb vibration. If the tube is small (under one-fourth inch) and can be hand formed, casual bends may be made to allow for this. If the tube must be machine formed, definite bends must be made to avoid a straight assembly.
Start all bends a reasonable distance from the fittings, because the sleeves and nuts must be slipped back during the fabrication of flares and during inspections. In all cases the new tube assembly should be so formed prior to installation that it will not be necessary to pull or deflect the assembly into alignment by means of the coupling nuts.
FABRICATION AND REPLACEMENT OF
FLEXIBLE HOSE Hose and hose assemblies should be checked for deterioration at each inspection period. Leakage, separation of the cover or braid from the inner tube, cracks, hardening, lack of flexibility, and FIGURE 5-17. Sleeve-type fittings.
excessive "cold flow" are apparent signs of deterioration and reason for replacement. The term "cold flow" describes the deep, permanent impressions in the hose produced by the pressure of hose clamps or supports.
When failure occurs in a flexible hose equipped with swaged end fittings, the entire assembly must be replaced. Obtain a new hose assembly of the correct size and length, complete with factoryinstalled end fittings.
When failure occurs in hose equipped with reusable end fittings, a replacement line can be fabricated with the use of such tooling as may be necessary to comply with the assembly instructions of the manufacturer.
Assembly of Sleeve-Type Fittings Sleeve-type end fittings for flexible hose are detachable and may be reused if determined to be serviceable. The inside diameter of the fitting is the same as the inside diameter of the hose to which it is attached. Common sleeve-type fittings are shown in figure 5-17.
To make a hose assembly, select the proper size hose and end fittings. Cut the hose to the correct length using a fine-tooth hacksaw. Place the socket in a vise. Screw the hose into the socket counterclockwise until the hose bottoms on the shoulder of the socket (figure 5-18); then back off one-quarter turn. Lubricate inside of hose and nipple threads liberally. Mark the hose position 114
assembly prior to tightening the cap or plug.
Hose tests, using a gas, are conducted underwater.
In all cases follow the hose manufacturer's instructions for proof-test pressure and fluid to be used when testing a specific hose assembly.
Place the hose assembly in a horizontal position and observe for leakage while maintaining the test pressure. Proof-test pressures should be maintained for at least 30 seconds.
<I T FIGURE 5-18. Assembly of MS fitting to flexible hose.
around the hose at the rear of the socket using a grease pencil or painted line. Insert the nipple into the nut and tighten the nipple and nut on the assembly tool. If an assembly tool is not available, a mating AN815 adapter may be used.
Using a wrench on the assembly tool, screw the nipple into the socket and hose. A ½2- to %-inch clearance between the nut and sleeve is required so that the nut will swivel freely when the assembly tool is removed. After assembly, always make sure all foreign matter is removed from inside the hose by blowing out with compressed air.
Proof-test After Assembly All flexible hose must be proof-tested after assembly by plugging or capping one end of the hose and applying pressure to the inside of the hose assembly. The proof-test medium may be a liquid or a gas. For example, hydraulic, fuel, and oil lines are generally tested using hydraulic oil or water, whereas air or instrument lines are tested with dry, oil-free air or nitrogen. When testing with a liquid, all trapped air is bled from the Instaliation of Flexible Hose Assemblies Flexible hose must not be twisted on installation, since this reduces the life of the hose considerably and may also loosen the fittings. Twisting of the hose can be determined from the identification stripe running along its length. This stripe should not spiral around the hose.
Flexible hose should be protected from chafing by wrapping it with tape, but only where necessary.
The minimum bend radius for flexible hose varies according to size and construction of the hose and the pressure under which the hose is to operate. Bends that are too sharp will reduce the bursting pressure of flexible hose considerably below its rated value (figure 5-19).
Flexible hose should be installed so that it will be subject to a minimum of flexing during operation. Although hose must be supported at least every 24 inches, closer supports are desirable. A flexible hose must never be stretched tightly between two fittings. From 5 percent to 8 percent of its total length must be allowed for freedom of movement under pressure. When under pressure, flexible hose contracts in length and expands in diameter.
Protect all flexible hose from excessive temperatures, either by locating the lines so they will not be affected or by installing shrouds around them.
INSTALLATION OF RIGID TUBING 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 and Torque Never apply compound to the faces of the fitting or the flare, for it will destroy the metal-to-metal contact between the fitting and fare, a contact 115
PLANNING HOSE LINE INSTALLATIONS WRONG
WRONG RIGHT
2... observe linear stripe. The hose must not be twisted. High pressures applied to a twisted hose may cause failure or loosen the nut.
RIGHT
1... provide slack or bend in the hose line to provide for changes in length that will occur when pressure is applied.
WRONG
WRONG RIGHT RIGHT
3.., relieve sharp bends, avoid strain or hose collapse nd make cleaner installations by using Aeroquir elbows or other adapter fittings. Provide as large a bend radius as possible. Never use less than the recommended minimum bend radius specified for the hose.
4... provide additional bend radius when lines are subject to flexing and remember that the metal end fittings are not flexible. Place line support clamps so as not to restrict hose flexing.
FrcURE 5-19. Flexible hose installation.
which is necessary to produce the seal. Be sure Do not deflect into place that the line assembly is properly aligned before Replace tube assembly tightening the fittings. Do not pull the installation into place with torque on the nut. Correct and Incorrect - Will damage flare or threads, or cause sleeve to incorrect methods of installing flared-tube assemcrack under vibration if tight- blies are illustrated in figure 5-20. Proper torque ened values are given in figure 5-21. It must be remembered that these torque values are for flared- Incorrect - May pull off or type fittings only. Always tighten fittings to the distort flare if tightened correct torque value when installing a tube assembly. Overtightening a fitting may badly damage Correctly fitted or completely cut off the tube flare, or it may ruin and tightened the sleeve or fitting nut. Failure to tighten suf- .025 clearance between Flare and shoulder allow the line to blow out of the assembly or to ficiently also can be serious, as this condition may before tightening leak under system pressure.
The use of torque wrenches and the prescribed torque values prevents overtightening or under- FIGURE 5-20. Correct and incorrect methods of tightening. If a tube fitting assembly is tightened properly, it can be removed and retightened many tightening flared fittings. times before re-flaring is necessary.
Hose End Fittings Minimum bend and Hose Assemblies radii (inches) Aluminum Alloy Tubing, Bolt, Steel Tubing, Bolt MS28740 or Equivalent Alum.
Fitting or Nut Fitting or Nut End Fitting alloy Tubing Fitting Bolt Torque Torque 1100-H14 O.D. or Nut Size inch-Ibs. inch--Ibs. Minimum Maximum 5052-0 Steel 1/8 -2 3/8 20 - 30 3/16 -3 30 - 40 90 - 100 70 120 7/16 21/32 1/4 40 - 65 135 - 150 100 250 9/16 7/8 5/16 60 85 180 - 200 210 420 3/4 1 1/8 3/8 75 - 125 270 - 300 300 480 15/16 1 5/16 1/2 150 - 250 450 - 500 500 850 1 1/4 1 3/4 5/8 --10 200 - 350 650 - 700 700 1150 1 1/2 2 3/16 3/4 - 12 300 - 500 900 - 1000 1 3/4 2 5/8 7/8 -14 500 - 600 1000 - 1100
- 16 500 - 700 1200 - 1400 3 3 1/2 1-1/4 -20 600 - 900 1200 - 1400 3 3/4 4 3/8 1-1/2 -24 600-- 900 1500 - 1800 5 5 1/4 I -3/4 -28 850 - 1050 7 6 1/8 -32 950 - 1150 7 FIGURE 5-21. Flared fitting data.
Flareless Tube Installation Tighten the nut by hand until an incrcase 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.
With a wrench, turn the nut % 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. Should a connection leak, it is permissible to tighten the nut an additional % turn (making a total of ⅓ turn). If, after tightening the nut a total of ½ turn, leakage still exists, the assembly should be removed and the components of the assembly inspected for scores, cracks, presence of foreign material, or damage from overtightening.
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: Do not in any case tighten the nut beyond ⅓ 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 are:
1. Flare distorted into nut threads.
2. Sleeve cracked.
3. Flare cracked or split.
4. Flare out of round.
5. Inside of flare rough or scratched.
6. Fitting cone rough or scratched.
7. Threads of nut or union dirty, damaged or broken.
Some manufacturers service instructions will specify wrench torque values for flareless tubing installations (e.g., see figure 5-22).
PLUMBING ASSEMBLY PRECAUTIONS Make certain that the material in the fittings used is similar to that of the tubing; for example, use steel fittings with steel tubing and aluminum alloy fittings with aluminum alloy tubing. Brass fittings plated with cadmium may be used with aluminum alloy tubing.
For corrosion prevention, aluminum alloy lines and fittings are usually anodized. Steel lines and fittings, if not stainless steel, are plated to prevent rusting or corroding. Brass and steel fittings are usually cadmium plated, although some may come plated with nickel, chromium, or tin.
To ensure proper sealing of hose connections and to prevent breaking hose clamps or damaging the hose, follow the hose clamp tightening instructions carefully. When available, use the hose clamp torque-limiting wrench. These wrenches are available in calibrations of 15 and 25 inch-pounds. In the absence of torque-limiting wrenches, the fingertight-plus-turns method should be followed. Be- 117