Air scoop › Warning light Electrical connections to warning light Pressure gage Warning mechanism Contacts Adjustment screw To oil Y connection Carburetor dilution Diaphragm Inlet from valve Air Fuel tuel pump Location of units in the system Pressure waming mechanism FIGURE 4-22. Fuel pressure-indicating system.
be checked to determine when fuel temperatures are approaching those at which there may be danger of ice crystals forming in the fuel.
MULTIENGINE FUEL SYSTEMS The design of the fuel system for an aucraft having two or more engines presents problems not normally encountered in single-engine fuel systems. A large number of tanks are often required to carry the necessary fuel. These tanks may be located in widely separated parts of the aircraft, such as the fuselage and the inboard and outboard sections of the wings. The individual engine fuel systems must be interconnected so that fuel can be fed from the various tanks to any engine. In case of engine failure, the fuel normally supplied to the inoperative engine must be made available to the others.
Crossfeed System The twin-engine fuel system illustrated in figure 4-24 is the simple crossfeed type. As shown, the tank selector valves are set to supply fuel from the main tanks to the engines. These valves can also be positioned to supply fuel from the auxiliary tanks. The crossfeed valve is shown in the off position. It can also be set to supply fuel from the fuselage tank to either or both engines and to crossfeed. A few of the numerous combinations in which the three valves can be set are also illustrated.
Manifold System The main feature of the four-engine system % 45 55 shown in figure 4-25 is the fuel manifold. This FUEL CRUISE POWER 65 fuel manifold system is actually a variation of the crossfeed. As shown, fuel is being supplied from PRESSURE the main tanks directly to the engines. The mani- PSE fold valves can also be set so that all tanks feed 7000' into the manifold and each engine receives its fuel 5000 supply from this line. The auxiliary fuel supply SEA 3000' can be delivered to the engines only through the LEVEL manifold. The main advantage of this system is its flexibility. Should an engine fail, its fuel is 16 immediately available to the other engines. If a tank is damaged, the corresponding engine can be supplied with fuel from the manifold.
Another advantage of this system is that all FIGURE 4-23. Fuel pressure gage for fuel-injection fuel tanks can be serviced at the same time system. through a single line manifold connection. This 93
Left engine Right engine Fuselage tank Engine-driven pump Filter Crossfeed valve Main tank Auxiliary Auxiliary Main tank tank tank Boost pump Tank selector valve Main Aux. Main Aux. Main Aux sam Aux. Main Auxiliary tanks Right main tank Fuselage tank Fuselage tank to engines to both engines to left engine to both engines FIGURE 4-24. Twin-engine crossfeed system schematic.
method of fuel servicing has greatly reduced servicing time on large aircraft because fuel can be introduced into the fueling manifold under high pressure.
FUEL JETTISON SYSTEMS A fuel jettison system is required for transport category and general aviation aircraft if the maximum take-off weight exceeds the maximum landing weight. The maximum take-off and landing weights are design specifications and may be found in the Aircraft Type Certificate data sheets.
A fuel jettison system must be able to jettison enough fuel within 10 minutes for general aviation, or 15 minutes for transport category aircraft, to meet the requirements of the specifications and Federal Air Regulations. It must be operable under the conditions encountered during all operations of the aircraft.
Design requirements are that fuel jettisoning must be stopped with a minimum of fuel for 45 minutes of cruise at maximum continuous power for reciprocating engines. Turbine powered aircraft require enough fuel for take-off and landing and 45 minutes cruising time.
The fuel jettisoning system is usually divided into two separate, independent systems, one for each wing, so that lateral stability can be maintained by jettisoning fuel from the "heavy" wing if it is necessary to do so. Normally, if an unbalanced fuel load exists, fuel will be used from the "heavy" wing by supplying fuel to engines on the opposite wing.
The system consists of lines, valves, dump chutes and chute-operating mechanisms. Each wing contains either a fixed or an extendable dump chute depending upon system design. In either case the fuel must discharge clear of the airplane.
TROUBLESHOOTING THE FUEL SYSTEM In order to become proficient at the art of troubleshooting, one must be familiar with the complete system. To do this, one can become familiar with the schematics of various portions of the system, the nomenclature of the units, and their particular function within the system by studying aircraft and engine maintenance manuals.
Engine Engine Engine Engine No. 1 No. 2 No. 3 No. 4
• Filter Auxiliary tank Engine-driven Firewall Manifold Refueling pump shut-off valve • valves receptacle Tank Fuel manifold shut-off valve No. 1 tank No. 2 tank Auxiliary tank No. 3 tank No. 4 tank Boost pump Flow to engine Flow blocked FIGURE 4-25. A typical manifold crossfeed system.
Location of Leaks and Defects The location of leaks and defects within the internal portions of the fuel system is usually a matter of observation of the pressure gage and operation of the selector valves to determine where the trouble lies. Troubleshooting of the internal fuel system can be aided by visualizing the path of flow of the fuel from the fuel tank to the fuel-metering device, noting the location of the pump(s), selector valves, emergency shutoff valves, etc.
The location of leaks or defects in the external portions of the fuel system involves very little time in comparison to locating leaks within the internal system. Usually, fuel leaks are evidenced by stains or wet spots, if they are newly developed, and by the presence of fuel odor. The plumbing, clamps, gaskets, supports, etc., are to be examined carefully at each inspection period. Any defect or leak in the internal or external fuel system is a potential hazard.
Replacement of Gaskets, Seals, and Packings In order to prevent leakage of fuel, it is of utmost importance that all gaskets, seals, and packings be properly installed. Listed below are some of the general precautions that should always be observed.
When replacing units of the fuel system, it is necessary to check each part for cleanliness, ensure that all of the old gasket material is removed, and ensure that none of the old seal remains in the groove seat. Always replace old gaskets and seals with new ones, check the new gaskets and seals for cleanliness and integrity, and ensure that it is the right part for the job. Mating surfaces should be perfectly flat so that the gasket can do the job for which it is designed. Screws, nuts, and bolts that hold units together should be evenly tightened or torqued to prevent leakage past the gasket or seal.
FUEL TANK REPAIRS There are three basic type fuel cells used in aircraft. Welded sheet metal integral and fuel cell.
No fuel system is airworthy if it will not contain fuel. Inspection of the fuel tank bays or aircraft structure for evidence of fuel leaks is a very important part of the preflight inspection.
Welded Steel Tanks Welded tanks are most common in the smaller single and twin engine aircraft. If the access plates to the fuel tank compartment are discolored the tank should be inspected for leaks. When leaks are found, the tank must be drained and inerted. Fuel will be drained in accordance with 95
local instructions and the manufacturer's recommendations. Inerting the tank may be accomplished by slowly discharging a CO, fire extinguisher (5 lb. minimum size) into the tank.
Dry nitrogen may be used if it is available. If the tank is to be welded, removal is necessary.
Before welding, the tank must be steamed for a minimum of 8 hours. This is to remove all traces of fuel. Air pressure not over ½ psi may be used to detect the leaking area. Liquid soap or bubble solution brushed in the suspected area may identify the leak. Aluminum tanks are fabricated from weldable alloys. After riveting patches in place, the rivets may be welded to insure no leaks from that area. Pressure checks should be performed after repairs are completed to assure that all leaks were corrected.
Fuel Cells Fuel cell leaks will usually appear on the lower skin of the aircraft. A fuel stain in any area should be investigated immediately. Fuel cells suspected of leaking should be drained, removed from the aircraft and pressure checked. When performing a pressure check, ¾ to ½ psi air presure is adequate. All fuel cell maintenance must be accomplished in accordance with the manufacturer's specifications.
3/4 DIA 1-1/2 DI/
A - SLOW SEEP
B - SEEP Integral Fuel Tanks The integral tank is a nonremovable part of the aircraft. Because of the nature of an integral tank, some leaks allow fuel to escape directly to the atmosphere. This makes it completely feasible to disregard certain minute leaks that do not represent a fire hazard or too great a loss of fuel. In order to standardize the procedures for integral tank fuel storage maintenance, the various rates of fuel leakage are classified.
Fuel Leak Classification The size of the surface area that a fuel leak moistens in a 30-minute period is used as the classification standard. Wipe the leak area completely dry with clean cotton cloths. Compressed air may also be used to dry the leak areas that are difficult to wipe. Wear goggles when using compressed air to dry the leak area. Dust the leak area with dyed red talcum powder. The talcum powder turns red as the fuel wets it, making the wet area easier to see.
At the end of 30 minutes, each leak is classified into one of four classes cake The four classes of heavy seep, or running leak.
leaks are shown in figure 4-26. A slow seep is a leak in which the fuel wets an area around the
- AREA WHERE FUEL
APPEARS TO FLOW
OR RUN, FOLLOWING
CONTOUR OF SKIN
WHEN THIS AREA IS WIPED DRY.
C - HEAVY SEEP
D - RUNNING LEAK FIGURE 4-26. Fuel leak classification.
leak source not over ¾ of an inch in diameter.
A seep is a leak that wets an area from ¾ inches to 1½ inches in diameter. A heavy seep is a fuel leak that wets an area around the leak source from 1½ inches to 3 inches in diameter. In none of these three leak classifications does the fuel run, flow, drip, or resemble any of these conditions at the end of the 30-minute time period.
The last classification, a running leak, is the most severe and the most dangerous. It may drip from the aircraft surface, it may run down vertical surfaces, or it may even run down your finger when you touch the wet area. The aircraft is unsafe for flight and must be grounded for repair.
When possible, the fuel from the leaking tank should be removed after you mark the leak location.
If it is impossible to defuel the tank immediately, the aircraft should be isolated in an approved area.
Place appropriate warning signs around the aircraft until qualified personnel can defuel the leaking tank.
Grounding of the aircraft for slow seeps, seeps, and heavy seeps, is determined by the applicable aircraft handbook. This determination may depend on the location of the fuel leak. For example, can the leakage progress to a potential fire source?
The number of fuel leaks in a given area is also a contributing factor. There is no rule of thumb for determining if the aircraft is to be grounded.
Running leaks ground the aircraft regardless of location.
You may only have to make appropriate entries on the aircraft forms and periodically observe the progress of the fuel leak if it is determined that the aircraft is airworthy and no repair is required.
When repair is required, you must find the cause of the fuel leak and make an effective repair.
Leak Repairs Repair of leaks in integral fuel tanks must be accomplished in accordance with the aircraft manufacturer's specifications. No attempt will be made in this handbook to discuss integral tank repairs further.
Fire Safety The first and most difficult step in the achievement of fire safety is to correct the misconceptions about the "safety" of turbine fuels. At the time these fuels were first introduced many people said, "fire problems in aircraft are over, turbine fuel is completely safei This is obviously nonsense but it has been persistent nonsense.
Flight line personnel have agreed that aviation gasoline will burn, and therefore they have exercised reasonable care and caution in handling it.
However, it has been difficult to convince them that under some circumstances turbine fuels are just as dangerous from the fire standpoint.
The characteristics of turbine fuel do vary from those of gasoline. Kerosene, for example, has a slow flame propagation and burning rate, which makes it less hazardous in the event of spill or a ground accident. However, it does ignite readily when vaporized or when misted, as when sprayed through a small leak in a service hose.
One disadvantage of the low volatility fuels is that they will not evaporate readily and completely if spilled on the ramp, so special treatment of the spill area is required. Small spills of kerosene should be removed with a commercial absorbent cleaning agent. On large spils it is better to apply an approved emulsifier and then flush away the resulting mixture with large volumes of water.
This will prevent or appreciably lessen any oily residue.
Just as with gasoline, an electrostatic charge may be built up in pumping turbine fuel through a service hose. In fact, the amount of the charge is higher in kerosene because of the higher specific gravity and wider boiling range, Also, the amount of the charge increases with high linear rate of fuel flow, such as is required for servicing turbine powered aircraft.
In consequence, all of the fire safety precautions observed in the handling of gasoline must be followed with equal care in the handling of turbine fuels. These precautions are well known and have been detailed by the National Fire Protection Association in its bulletin No. 407. It is recommended that this bulletin be made required reading for all personnel handling turbine fuel.
CHAPTER 5
FLUID LINES AND FITTINGS
GENERAL The term "aireraft plumbing" refers not only to the hose, tubing, fittings, and connectors used in the aircraft, but also to the processes of forming Occasionally it may be necessary to repair or replace damaged aircraft plumbing lines. Very often the repair can be made simply by replacing the tubing. However, if replacements are not available, the needed parts may have to be fabricated. Replacement tubing should be of the same size and material as the original line. All tubing is pressure tested prior to initial installation, and is designed to withstand several times the normal operating pressure to which it will be subjected.
If a tube bursts or cracks, it is generally the result of excessive vibration, improper installation, or damage caused by collision with an object.
All tubing failures should be carefully studied and the cause of the failure determined.
PLUMBING LINES Aircraft plumbing lines usually are made of metal tubing and fittings or of flexible hose. Metal tubing is widely used in aircraft for fuel, oil, cooloxygen, instrument, and hydraulic lines.
Flexible hose is generally used with moving parts or where the hose is subject to considerable vibra- Generally, aluminum alloy or corrosion-resistant steel tubing have replaced copper tubing: The high fatigue factor of copper tubing is the chief reason for its replacement. It becomes hard and brittle from vibration and finally breaks, however it may be restored to its soft annealed state by heating it red hot and quenching it in cold water.
Cooling in air will result in a degree of softness but not equal to that obtained with the cold water quench: This annealing process must be accomplished if copper tubing is removed for any reason.
Inspection of copper tubing for cracks, hardness, brittleness and general condition should be accomplished at regular intervals to preclude failure. The workability, resistance to corrosion, and lightweight of aluminum alloy are major factors in its adoption for aircraft plumbing.
In some special high-pressure (3,000 p.s.i.)
hydraulic installations, corrosion-resistant steel tubing, either annealed or ¼-hard, is used. Corrosionresistant steel tubing does not have to be annealed for flaring or forming; in fact, the flared section is somewhat strengthened by the cold working and strain hardening during the flaring process.
higher tensile strength permits the use of tubing with thinner walls; consequently the final installation weight is not much greater than that of the thicker-wall aluminum alloy tubing.
IDENTIFICATION OF MATERIALS Before making repairs to any aircraft plumbing, it is important to make accurate identification of plumbing materials. Aluminum alloy or steel tubing can be identified readily by sight where it is used as the basic plumbing material. However, it is difficult to determine whether a material is carbon steel or stainless steel, or whether it is 1100, 3003, 5052-0, or 2024-T aluminum alloy.
It may be necessary to test samples of the material for hardness by filing or scratching with a scriber. The magnet test is the simplest method for distinguishing between the annealed austenitic and the ferritic stainless steels. The austenitic types are nonmagnetic unless heavily cold worked, whereas the straight chromium carbon and low alloy steels are strongly magnetic. Figure 5-1 gives the methods for identifying five common Magnet Nitric acid Material test test Carbon steel- - Strongly Slow chemical magnetic. action, brown.
18-8_. Nonmagnetic. No action.
Pure nickel. Strongly Slow action, magnetic. pale green.
Monel-- Slightly Rapid action, magnetic. greenish blue.
Nickel steel__. Nonmagnetic. Rapid action, greenish bluę.
FIGURE 5-1. Identification of metallic materials.
metallic materials by using the magnet and concentrated nitric acid tests.
By comparing code markings of the replacement tubing with the original markings on the tubing being replaced, it is possible to identify definitely the material used in the original installation.
The alloy designation is stamped on the surface of large aluminum alloy tubing. On small aluminum alloy tubing, the designation may be stamped on the surface, but more often it is shown by a color code. Bands of the color code, not more than 4 inches in width, are painted at the two ends and approximately midway between the ends of some tubing. When the band consists of two colors, one-half the width is used for each color.
Painted color codes used to identify aluminum alloy tubing are:
Aluminum aloy number 1100 3003 Green 2014 Gray 2024 Red 5052 Purple 6053 Black 6061 7075 Aluminum alloy tubing, 1100 (/½-hard) or 3003 (½-hard), is used for general purpose lines of low or negligible fluid pressures, such as instrument lines and ventilating conduits. The 2024-T and 5052-0 aluminum alloy materials are used in general purpose systems of low and medium pressures, such as hydraulic and pneumatic 1,000 to 1,500
p.s.i. systems and fuel and oil lines. Occasionally, these materials are used in high-pressure (3,000
p.s.i.) systems.
Tubing made from 2024-T and 5052-0 materials will withstand a fairly high pressure before bursting. These materials are easily flared and are soft enough to be formed with handtools. They must be handled with care to prevent scratches, dents, Corrosion-resistant steel tubing, either annealed or ¼-hard, is used extensively in high-pressure hydraulic systems for the operation of landing gear, flaps, brakes, and the like. External brake lines should always be made of corrosion-resistant steel to minimize damage from rocks thrown by the tires during takeoff and landing, and from careless ground handling. Although identification markings for steel tubing differ, each usually includes the manufacturer's name or trademark, the SAE number, and the physical condition of the metal.
Metal tubing is sized by outside diameter, which is measured fractionally in sixteenths of an inch.
Thus Number 6 tubing is 16 (or ⅜ inch) and Number 8 tubing is 16 (or ½ inch), etc.
In addition to other classification or means of identification, tubing is manufactured in various wall thicknesses. Thus, it is important when installing tubing to know not only the material and outside diameter, but also the thickness of the wall.
FLEXIBLE HOSE Flexible hose is used in aircraft plumbing to connect moving parts with stationary parts in locations subject to vibration or where a great amount of flexibility is needed. It can also serve as a connector in metal tubing systems.
Synthetics Synthetic materials most commonly used in the manufacture of flexible hose are: Buna-N, Neoprene, Butyl and Teflon (trademark of DuPont Corp.). Buna-N is a synthetic rubber compound which has excellent resistance to petroleum products. Do not confuse with Buna-S. Do not use for phosphate ester base hydraulic fluid (Skyrol ®).
Neoprene is a synthetic rubber compound which has an acetylene base. Its resistance to petroleum products is not as good as Buna-N but has better Do not use for phosphate ester base hydraulic fluid (Skydrol ®). Butyl is a synthetic rubber compound made from petroleum raw materials. It is an excellent material to use with phosphate ester based hydraulic fluid (Skydrol ® ).
Do not use with petroleum products. Teflon is the DuPont trade name for tetrafluoroethylene resin.
It has a broad operating temperature range (-65° F. to +450° F.). It is compatible with nearly every substance or agent used. It offers little resistance to flow; sticky viscous materials will not adhere to it. It has less volumetric expansion than rubber and the shelf and service life is practically limitless.
Rubber Hose Flexible rubber hose consists of a seamless synthetic rubber inner tube covered with layers of cotton braid and wire braid, and an outer layer of rubber-impregnated cotton braid. This type of hose is suitable for use in fuel, oil, coolant, and hydraulic systems. The types of hose are normally classified by the amount of pressure they are designed to withstand under normal operating conditions.
1. Low pressure, any pressure below 250 p.s.i.
Fabric braid reinforcement.
Two cotton braids - impregnated with synthetic compound MIL H-8794 Size 6-2/68 Mfg Symbol
- Yellow Single wire braid - Synthetic inner tube A. Flame- and aromatic-resistant hose White numerals, letters and stripe - RED 7 MIL-H-6000-Size- 3-4/68 to Sanbole as (Views showing opposite sides of hose) B. Nonself-sealing, Aromatic and Heat-resistant hose White T Mfg Symbol:
Red numerals and letters C. Flame-, Aromatic-, and Oil-resistant hose Yellow numerals, letters and stripe Red numerals, letters and stripe IL H-5593- D. Nonself-sealing, Aromatic-resistant hose.
E. Self-sealing, Aromatic-resistant hose FIGURE 5-2. Hose identification markings.
2. Medium pressure, pressures up to 3,000
p.s.i. ap One wire braid reinforcement.
Smaller sizes carry pressure up to 3,000
p.s.i.
Larger sizes carry pressure up to 1,500
p.s.i.
3. High pressure (all sizes up to 3,000 p.s.i.
operating pressures).
Identification markings consisting of lines, letters, and numbers are printed on the hose. (See figure
5-2.) These code markings show such information as hose size, manufacturer, date of manufacture, and pressure and temperature limits. Code markings assist in replacing a hose with one of the same specification or a recommended substitute.
Hose suitable for use with phosphate ester base hydraulic fluid will be marked "Skydrol " use". AULIC In some instances several types of hose may be suitable for the same use. Therefore, in order to AULIC make the correct hose selection, always refer to the maintenance or parts manual for the particular airplane.
Teflon Hose ROC Teflon hose is a flexible hose designed to meet LUBRICATION CATA the requirements of higher operating temperatures and pressures in present aircraft systems. It can ILUBRICATION ROC generally be used in the same manner as rubber hose. Teflon hose is processed and extruded into LUBRICATION tube shape to a desired size. It is covered with stainless steel wire, which is braided over the tube for strength and protection.
Teflon hose is unaffected by any known fuel, petroleum, or synthetic base oils, alcohol, coolants, or solvents commonly used in aircraft. Although D D it is highly resistant to vibration and fatigue, the principle advantage of this hose is its operating Size Designation The size of flexible hose is determined by its inside diameter. Sizes are in one-sixteenth-inch increments and are identical to corresponding sizes of rigid tubing, with which it can be used.
Identification of Fluid Lines 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, as well as the direction of fluid flow. Figure 5-3 illustrates the various color codes and symbols used to designate the type of system and its contents.
In most instances, fluid lines are marked with 1-inch tape or decals, as shown in figure 5-4 (A).
WARNING SYMBOL FIGURE 5-3. Identification of aircraft fluid lines.
On lines 4 inches 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, as shown in figure 5-4 (B). 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.
FUEL FLAM VEL Red FUEL Red FLAM (B) FIGURE 5-4. Fluid line identification using:
(A) tape and decals and (B) metal tags.
In addition to the above-mentioned markings, certain lines may be further identified as to specific function within a system; for example, DRAIN, VENT, PRESSURE, or RETURN.
Lines conveying fuel may be marked FLAM;
lines containing toxic materials are marked TOXIC in place of FLAM. Lines containing physically dangerous materials, such as oxygen, nitrogen, or freon, are marked PHDAN.
The aircraft and engine manufacturers are responsible for the original installation of identification markers, but the aviation mechanic is responsible for their replacement when it becomes necessary.
Generally, tapes and decals are placed on both ends of a line and at least once in each compartment through which the line runs. In addition, identification markers are placed immediately adjacent to each valve, regulator, filter, or other accessory within a line. Where paint or tags are used, location requirements are the same as for tapes and decals.
PLUMBING CONNECTORS Plumbing connectors, or fittings, attach one piece of tubing to another or to system units.
There are four types: (1) Flared fitting, (2) flareless fitting, (3) bead and clamp, and (4) swaged.
The amount of pressure that the system carries is usually the deciding factor in selecting a connector. The beaded type of joint, which requires a bead and a section of hose and hose clamps, is AN819 AN818 nut sleeve Tubing FIGURE 5-5. Flared-tube fitting.
AC
AN FEATURE AC 37° ANGLE 35°
- BODY LENGTH YES RECESS NO BODY LENGTH
COARSER THREADS FINER
BLUE GRAY
OR COLOR OR
BLACK YELLOW BODY
LONGER LENGTH SHORTER
BLUE OR BLACK GRAY OR YELLOW FIGURE 5-6. AN and AC fitting differences.
used only in low- or medium-pressure systems, such as vacuum and coolant systems. The flared, flareless, and swaged types may be used as connectors in all systems, regardless of the pressure.
5-6.) The AC fitting does not have this shoulder.
Other differences between the AC and AN fittings include the sleeve design, the AC sleeve being noticeably longer than the AN sleeve of the same size. Although certain flared-tube fittings Flared-Tube Fittings are interchangeable, the pitch of the threads is A flared-tube fitting consists of a sleeve and a nut, as shown in figure 5-5. The nut fits over the sleeve and, when tightened, draws the sleeve and different in most cases. Figure 5-7 shows the AN and AC811 fittings that can be safely interchanged. Combinations of end connections, nuts, tubing flare tightly against a male fitting to form a seal. Tubing used with this type of fitting must Type End Type Typc be flared before installation. Sizes OD Tube Connection (Male (Female Sleeve Nut Type Flare Tub‹ The male fitting has a cone-shaped surface with Thread) Thread) the same angle as the inside of the flare. The sleeve supports the tube so that vibration does All Sizes All Sizes ANI 8112 ANI 8112 ANI 8112 AN 8112 not concentrate at the edge of the flare, and All Sizes AN AN AN 811 All Sizes AN AN 811 811 distributes the shearing action over a wider area All Sizes AN AN 811 for added strength. Tube flaring and the instal- All Sizes 811 811 811 All Sizes 811 811 AN lation of flared-tube fittings are discussed in detail All Sizes 811 811 AN 811 later in this chapter. AN 811 AN 811 The AC (Air Corps) flared-tube fittings have 78,16> 4. 516, 1¾, 2 16, 14, 2 AN AN 811 811 811 AN AN been replaced by the AN (Army/Navy) Standard 78, 16. 4, 16, 14, 2 AN 811 811 and MS (Military Standard) fittings. However, 1 This is the normal assembly of AN fittings.
since AC fittings are still in use in some of the 2 This is the normal assembly of AC811 fittings.
older aircraft, it is important to be able to identify them. The AN fitting has a shoulder between the FIGURE 5-7a. Interchangeability of AN and AC811 end of the threads and the flare cone. (See figure fittings.
TYPICAL CONNECTION CT 45 MT OT FIGURE 5-7 b. AC811 solderless fittings.
- AN744 to AN932 —- Material:
Aluminum alloy. (code D) Steel.. (code, absence of letter) Brass- (code B) Aluminum bronze. (code Z-for AN819 sleeve) Size:
The dash number following the AN number indicates the size of the tubing (or hose) for which the fitting is made, in 16ths of an inch. This size measures the O. D. of tubing and the I. D. of hose.
Fittings having pipe threads are coded by a dash number, indicating the pipe size in 8ths of an inch.
The material code letter, as noted above, follows the dash number.
BOLT AN775 ELBOW AN777 BOLT AN774 ELBOW AN776 ELBOW AN778 TEE AN779 PLUG AN806 TEE AN804 PLUG AN814 ADAPTOR AN807 UNION AN815 CAP AN820 NUT AM817 SLEEVE NUT AN818 AN819 NIPPLE AN816 ELBOW AN821 ELBOW AN822 ELBOW AN823 TEE AN824 FIGURE 5-8. AN plumbing fittings.