Pipes, Unions and Fittings PDF

Rigid Lines Rigid Lines Applications A single aircraft typically contains several different types of rigid fluid lines. Each type of line has a specific application. However, as a rule, rigid tubing is used in stationary applications and where long, relatively straight runs are possible. Systems tha...

Rigid Lines Rigid Lines Applications A single aircraft typically contains several different types of rigid fluid lines. Each type of line has a specific application. However, as a rule, rigid tubing is used in stationary applications and where long, relatively straight runs are possible. Systems that typically utilise rigid tubing include fuel, oil, oxygen and instrument systems. Many fluid lines used in early aircraft were made of copper tubing. However, copper tubing proved troublesome because it became hard and brittle from the vibration encountered during flight and eventually failed. Today, aluminium-alloy and corrosion-resistant steel lines have replaced copper in most applications. Aluminium tubing comes in a variety of alloys. For example, in low-pressure systems (below 1000 psi) such as those used for instrument air or ventilating air, commercially pure aluminium tubing made from 1100-H14 (half-hard) or aluminium alloy 3003-H14 (half-hard) is used. Low pressure aluminium tubing 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 204 of 229 Aluminium-alloy tubes are identified in a number of ways. For example, on larger tubes, the alloy designation is stamped directly on the tube’s surface. However, on small tubing, the alloy designation is typically identified by a coloured band. These coloured bands are no more than 4 in. wide and are painted on the tube’s ends and mid-section. When a band consists of two colours, half the width is used for each colour. Aviation Australia Aluminium alloy tube marking colour bands Steel tubing for aircraft use is normally identified by its part number from the aircraft manufacturer’s Maintenance Manual Illustrated Parts Catalogue. Occasionally, it may be necessary to manufacture aircraft fluid pipes. Replacement tubing should be of the same size and material as the original tubing and must be pressure tested before fitting to an aircraft. Although identification markings for steel tubing differ, each usually includes the manufacturer’s name or trademark, the Society of Automotive Engineers (SAE) number, and the physical condition of the metal with the outside diameter of the pipe, e.g. Titanium 3AL-2.5V and CRES 304-1/8-hard. Corrosion-resistant steel tubing, either annealed or quarter-hard, is used in high-pressure systems (3000 psi). Applications include high-pressure hydraulic, pneumatic and oxygen systems. Corrosionresistant steel is also used in areas that are subject to physical damage from dirt, debris and corrosion caused by moisture, exhaust fumes and salt air. Another benefit of corrosion-resistant steel tubing is that it has a higher tensile strength, which permits the use of tubing with thinner walls. As a result, its installation weight is similar to that of thicker-walled aluminium alloy tubing. 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 205 of 229 Steel tubing 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 206 of 229 Size Designations The size of rigid tubing is determined by its outside diameter in increments of 1/16 in. Therefore, a -4 B-nut tubing is 4/16 or 1/4 in. in diameter. A tube diameter is typically printed on all rigid tubing. Another important size designation is wall thickness, which determines a tube’s strength. Like the outside diameter, wall thickness is generally printed on the tube in thousandths of an inch. © Aviation Australia Rigid tube sizing One dimension that is not printed on rigid tubing is the inside diameter. However, since the outside diameter and wall thickness are indicated, the inside diameter is determined by subtracting twice the wall thickness from the outside diameter. For example, if you have a piece of -8 tubing with a wall thickness of 0.072 in. the inside diameter can be solved as follows. −8 tubing ⟹ 8/16 = 1/2 = 0.5 in. OD wall thickness = 0.072 in. ∴ I D = 0.5 − (2 × 0.072) = 0.356 in. 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 207 of 229 Rigid Line Fittings and Unions Tube Flaring Much of the rigid tubing used in modem aircraft is connected to components by flaring the tube ends and using flare-type fittings. A flared-tube fitting consists of a sleeve and a B-nut. Using this type of connector eliminates damage to the flare caused by the wiping or ironing action as the nut is tightened. The sleeve provides added strength and supports the tube so that vibration does not concentrate at the flare. The nut fits over the sleeve and, when tightened, draws the sleeve and flare tightly against a male fitting to form a seal. Tube flaring Two types of flares are used in aircraft plumbing systems: the single flare and the double flare. 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 208 of 229 Single and double end flared tubing Flared-Tube Fittings Flared fittings are identified by an AN or MS number. However, prior to World War II, fittings were made to an AC standard. Since AC fittings are still used in some older aircraft, it is important to be able to identify the differences in fittings. For example, an AN fitting has a shoulder between the end of the threads and the flare cone. The AC fitting does not have this shoulder. Another difference between AC and AN fittings is the sleeve design. The AN sleeve is noticeably longer than the AC sleeve of the same size. Flared-tube fittings 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 209 of 229 Flared-tube fittings are made of aluminium alloy, steel or copper base alloys. For identification purposes, all AN steel fittings are coloured black, and all AN aluminium fittings are coloured blue. The AN 819 aluminium bronze sleeves are cadmium plated and are not coloured. AN fittings come in a variety of shapes and sizes, each with a specific use. As an aircraft technician, you must be familiar with the most common fittings used on aircraft. Flared-tube fittings variety 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 210 of 229 Flareless Tube Fittings Two different types of tube fittings are used on modern aircraft utilising high system pressures, although they both use the same thread, they are not interchangeable. AN fittings have a 37° external flare as previously stated, while the flareless fitting utilises an internal bevel of 24°. Flared fittings are used with a flared tube, sleeve and B-nut, while flareless fittings are used with an un-flared, straight-cut tube. The fitting consists of three parts: a tube, a sleeve and a nut. Flareless fittings 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 211 of 229 Identification of Flareless Fittings Identification of flareless fittings MS type fittings are the most commonly used type of plumbing fitting in service on large transport category aircraft today because they can withstand high system working pressures (Up to 8000 psi). Flareless fittings are made of aluminium alloy or steel. Aluminium alloy fittings can be identified visually by their yellow colour, which is caused by the anodising treatment. The cadmium plating on steel fittings is identified by letter-number codes such as MS21900-4, which is interpreted as follows: MS – prefix (military specification) 21900 – design part number (adapter, flareless tube to AN flared tube) 4 – size of fitting in sixteenths of an inch (4/16 in.) The material from which the fittings are made is indicated by the absence or presence of a letter at the end of the MS number. For example: MS21900-4 is made from carbon steel. MS21900-8-D is made from aluminium alloy. MS21900-8-S is made from corrosion-resistant steel, class 347. 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 212 of 229 Flareless Fittings The heavy wall tubing used in some high-pressure systems is difficult to flare. For these applications, the flareless fitting is designed to provide leak-free attachments without flares. Although the use of flareless fittings eliminates the need to flare the tube, a step referred to as pre-setting is necessary prior to installation of a new flareless tube assembly. Pre-setting is the process of applying enough pressure to the sleeve to cause it to cut into the outside of the tube. Heavy wall flareless fittings Heavy wall flareless fittings 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 213 of 229 Heavy wall flareless fittings Universal Bulkhead Fittings One specific type of fitting is the universal bulkhead fitting. As the name implies, a bulkhead fitting is used to support a line that passes through a bulkhead. Bulkhead fittings have straight machine threads similar to those on common nuts and bolts. Therefore, flared tube connections, crush washers or synthetic seals must be used to make these connections fluid-tight. Universal bulkhead fittings 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 214 of 229 Tapered Pipe Thread Fittings Fluid lines are commonly attached to components by tapered pipe thread fittings. Tapered pipe thread fittings create a seal by wedging the tapered external male thread and the tapered internal female threads. This is the same type of thread used in household plumbing and automotive applications. These threads taper 1/16 in. to the inch. Tapered pipe thread fittings 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 215 of 229 Banjo Fittings Banjo fittings are available in all standards and are used in many engine and airframe fluid systems. In some applications, O-rings are used in place of aluminium gaskets. The banjo is free to rotate before the bolt is torqued; this allows stress-free alignment of the fluid line to the component. Banjo fitting 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 216 of 229 Quick-Disconnect Couplings Couplings provide quick connect/disconnect capability with self-sealing action for use on Ground Support Equipment (GSE) and other aerospace applications. They require only simple one-hand operation to connect and disconnect, with positive visual and touch indicating full engagement. They are commonly used on fuel, hydraulic and water/waste servicing adaptors. A built-in shutoff valve provides no-spill connection and disconnection. Some have a multi-start thread, quarter-turn attachment, while others have a sliding collar, snap-lock attachment. Quick-disconnect couplings 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 217 of 229 Beading Large-diameter lines carrying low-pressure fluids such as engine return oil and cooling air are typically joined by a rubber hose that is slipped over the tube ends and held in place with screw-type hose clamps. However, for this to be effective, the tube must be beaded first. Beading Beading 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 218 of 229 This can be accomplished with either a power header or a hand beading tool. The diameter and wall thickness of the tube being beaded determine which is used. Bead forming 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 219 of 229 Flexible Fluid Lines Flexible Fluid Lines Application Flexible hose is used in aircraft fluid systems to connect moving parts with stationary parts in locations subject to vibration or where extensive flexibility is needed. It can also serve as a connector in metal tubing systems. Flexible fluid lines Flexible hose construction generally consists of an inner liner covered with layers of reinforcement to provide strength and an outer cover to protect from physical damage. The materials and manufacturing process of each layer determine the suitability of a specific hose for a particular application. 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 220 of 229 Inner Liners The inner liner of a flexible hose carries the fluid and therefore must have a minimum porosity and be chemically compatible with the material being carried. Furthermore, the liner must be smooth to offer the least resistance to flow and must remain flexible throughout an entire range of operating temperatures. Four different synthetic compounds are used in the construction of the inner liner: neoprene, BunaN, butyl and Teflon. Each of these compounds has different characteristics and is compatible with different types of fluid. Neoprene is a form of synthetic rubber that is abrasion resistant and is used with petroleum-based fluids. Buna-N is a synthetic rubber compound that is also used to carry petroleum-based products. In fact, Buna-N is better suited to carry petroleum products than neoprene. Butyl is a synthetic rubber compound made from petroleum raw materials and therefore breaks down if used with petroleum products. However, butyl is excellent as an inner liner for fluid lines carrying phosphate ester-base hydraulic fluids such as Skydrol®. Teflon is the DuPont trade name for tetrafluoroethylene resin. Teflon® has an extremely broad operating temperature range (-65 °F to 450 °F) and is compatible with nearly every liquid used. Furthermore, its unique wax-like surface offers minimum resistance to fluid flow. Because of its unique chemical structure, Teflon experiences less volumetric expansion than rubber and has an almost limitless shelf and service life. Flexible fluid lines 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 221 of 229 Reinforcement Layers The reinforcement layers placed over an inner liner determine the strength of a hose. Common reinforcement layers are made of cotton, rayon, polyester fabric, carbon-steel wire or a stainless steel wire braid. Since hose tends to increase in diameter and decrease in length when pressure is applied, the design of the reinforcement is critical. The proper design of the reinforcement layers can minimise these dimensional changes. Outer Cover A protective outer cover, usually made of rubber-impregnated fabric or stainless steel braid, is put over the reinforcement to protect the hose from physical damage. In areas of high heat, the outer cover is often designed as an integral fire-sleeve to provide extra protection. The outer cover of almost all aircraft flexible hose is marked with a lay line, which consists of a yellow, red or white stripe running the length of the hose. In addition to a stripe, the outer cover shows the information needed to identify the hose, such as the MIL-SPEC number, the manufacturer’s name or symbol, the dash number representing the hose size and, in some cases, the manufacturer’s part number along with the year and quarter the hose was manufactured. In addition to identifying a hose, the lay line shows if a hose is twisted when it is installed. When a hose is installed properly, the lay line runs straight with no twists. Outer cover aromatic resistant hose 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 222 of 229 Flexible Line Identification Lay lines and identification markings consisting of lines, letters and numbers are printed on the hose. Most hydraulic hose is marked to identify its type, the quarter and year of manufacture, and a fivedigit code identifying the manufacturer. These markings appear in contrasting coloured letters and numerals which indicate the natural lay (no twist) of the hose and are repeated at intervals of not more than 9 in. along the length of the hose. Code markings assist in replacing a hose with one of the same specifications or a recommended substitute. Hose suitable for use with phosphate ester-base hydraulic fluid will be marked ‘SKYDROL’. In some instances, several types of hose may be suitable for the same use. Therefore, to make the correct hose selection, always refer to the applicable aircraft maintenance or parts manual. Flexible line identification Size Designation The size of a flexible hose is determined by its inside diameter and is measured in increments of 1/16 in. Like rigid tubing, a dash number indicates the tube diameter. For example, -10 identifies a 10/16or 5/8-in. hose. 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 223 of 229 Types of Flexible Hose While aircraft hose is manufactured to meet a variety of applications, the types of hose are normally classified by the amount of pressure they are designed to withstand. These include low-pressure, medium-pressure and high-pressure. Low-Pressure Hose Most air or vacuum hoses and some aircraft instrument lines are not required to carry high pressures. Therefore, low-pressure rubber hose is typically used with these types of installations. These hoses have a seamless inner tube and a reinforcement made of a single layer of cotton braid. An outer cover of ribbed or smooth rubber is used to protect the reinforcement from physical abrasion. Low-pressure hose 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 224 of 229 Medium-Pressure Hose Medium-pressure hose is used with fluid pressures up to 3000 psi. However, its maximum operating pressure varies with its diameter. For example, smaller sizes carry pressure up to 3000 psi, while larger sizes are often restricted to lower pressures. Medium-pressure hose has a seamless inner liner with one layer of cotton braid and one layer of stainless-steel reinforcement. A braid of rough oil-resistant rubber-impregnated cotton is usually used as an outer cover. If the hose is used with a petroleum-based fluid, its inner liner is made of synthetic rubber and its outer braid is grey-black. However, if the hose is used with Skydrol or any phosphate ester-base hydraulic fluid, the inner liner is made of synthetic Butyl rubber and the outer braid is coloured green with SKYDROL written on it. Medium-pressure hose 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 225 of 229 High-Pressure Hose All high-pressure hose has a maximum operating pressure of at least 3000 psi and uses a synthetic rubber liner to carry petroleum products. This inner liner is wrapped with two or more steel braids as reinforcement. To help distinguish high-pressure hose from medium-pressure hose, the entire hose has a smooth outer cover. Most high-pressure hose is black with a yellow lay line. However, a hose designed to carry Skydrol has a Butyl rubber inner liner and a green outer cover with a white lay line. High-pressure hose 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 226 of 229 Flexible Pipe Fittings Introduction Fittings provide a convenient method of connecting flexible hoses to components. Flexible hose fittings are typically classified by the way they are attached to a hose and by the amount of pressure they can withstand. Swaged-End Fittings Hoses using swaged-end fittings are assembled on special machinery that is typically not found in the shop. These fittings cannot be removed and reused. Therefore, replacement lines with swaged fittings must be obtained from the manufacturer or a properly equipped hose assembly shop. Swaged-end fittings 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 227 of 229 Reusable Fittings Some hose assemblies incorporate reusable fittings consisting of a socket, a nipple and a nut. When a failure occurs in a hose with this type of fitting, a replacement assembly can generally be fabricated. However, before any fittings can be reused, they must be removed from the damaged hose assembly and carefully inspected. Any damage to the sealing surface or the threads is cause for rejection. Furthermore, the nut should be inspected for signs of cracking and damage caused by wrenches. Damaged components should not be reused. While all fittings used on aircraft must conform to MILSPEC, they are manufactured by several companies. Therefore, it is good practice not to mix components manufactured by different companies. Reusable fittings 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 228 of 229 Blanks When aircraft fluid lines are disconnected or removed, open ends of the lines and fittings must be covered. Blanks are closed fittings and can be made from plastic, metal, wood or even a plastic bag. This prevents the ingress of contaminants into the system under maintenance. An appropriate cap plug should be fitted to disconnected lines or fittings and lightly torqued to prevent fluid leakage, injury to personnel or damage to equipment if the open system is inadvertently energised. Blanks 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 229 of 229