Pipes, Hoses and Unions

• Rigid pipes


  Used in stationary applications and where long, relatively straight runs are possible
• Systems that typically use rigid tubing

  • Fuel
  • Oil
  • Oxygen
  • Instrument
• Aluminium-alloy tubing


  Used in low-pressure systems (below 1000 psi) such as instrument air or ventilating air
• Aluminium alloy tube marking

  Coloured bands on the tube's ends and mid-section

  
• Corrosion-resistant steel tubing


  Used in high-pressure systems (3000 psi) such as hydraulic, pneumatic and oxygen systems
• Rigid tube size


  Determined by outside diameter in increments of 1/16 in
• Rigid tube wall thickness


  Determines tube strength, printed on tube in thousandths of an inch
• Flared-tube fittings


  Consist of a sleeve and a B-nut, eliminate damage to the flare caused by tightening
• Types of flares


  • Single flare
  • Double flare
• Flared-tube fittings


  Identified by AN or MS number, made of aluminium alloy, steel or copper base alloys

  
• Flareless tube fittings


  Use an internal bevel of 24°, consist of a tube, sleeve and nut

  
• MS type flareless fittings

  Most commonly used, can withstand high system working pressures (up to 8000 psi)
• Flareless fitting identification


  Aluminium alloy fittings are yellow, steel fittings are cadmium plated

  
• Universal bulkhead fittings


  Used to support a line passing through a bulkhead, have straight machine threads
• Tapered pipe thread fittings

  Create a seal by wedging the tapered external male thread and the tapered internal female threads

  
• Banjo fittings


  Used to connect rigid and flexible lines
• Quick-disconnect couplings


  Allow rapid connection and disconnection of fluid lines
• Beading


  Process of forming a bead on the end of a rigid tube to provide a seat for a fitting
• Flexible fluid lines


  Used in applications where rigid lines are not practical, such as moving components
• Flexible line identification


  Colour coded outer cover, part number, size, and pressure rating
• Types of flexible hose

  • Braided hose
  • Convoluted hose
  • Teflon hose
• Flexible pipe fittings


  Swaged-end fittings and reusable fittings

  
• Blanks are used to seal off unused ports
• Use it to cut into the outside of the tube


  Heavy wall flareless fittings
• Universal Bulkhead Fittings


  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. Flared tube connections, crush washers or synthetic seals must be used to make these connections Fluid-tight.
• 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.

  
• 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.
• 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.
• 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.

  
• Bead forming


  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.
• Flexible Fluid Lines


  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.

  
• Inner liner materials


  • Neoprene
  • Buna-N
  • Butyl
  • Teflon
• Neoprene


  A form of synthetic rubber that is abrasion resistant and is used with petroleum-based Fluids.
• Buna-N


  A synthetic rubber compound that is also used to carry petroleum-based products. Buna-N is better suited to carry petroleum products than neoprene.
• Butyl


  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

  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, TeÙon experiences less volumetric expansion than rubber and has an almost limitless shelf and service life.
• Reinforcement layers


  Common reinforcement layers are made of cotton, rayon, polyester fabric, carbon-steel wire or a stainless steel wire braid. The proper design of the reinforcement layers can minimise dimensional changes when pressure is applied.
• 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.
• 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 five-digit code identifying the manufacturer. Hose suitable for use with phosphate ester-base hydraulic fluid will be marked 'SKYDROL'. To make the correct hose selection, always refer to the applicable aircraft maintenance or parts manual.
• Size designation


  The size of a flexible hose is determined by its inside diameter and is measured in increments of 1/16 in. A dash number indicates the tube diameter. For example, -10 identifies a 10/16- or 5/8-in. hose.