Pipes and Unions

The different systems in an aircraft require the services of pipes and hoses, in a range of sizes. These can include fuel, oxygen, lubrication, hydraulic, instruments, heating, fire extinguishing, air conditioning and water systems. Loss of integrity in any of these systems could put the aircraft at risk.

The pressures inside the pipes can vary from negative (suction) through ambient in instrument piping to as much as 4000 psi (27.58 x 10³ kN/m²) in a hydraulic system. Low-pressure fluid lines can be manufactured from metal or plastic (pipes and tubes) or from various forms of rubber (hoses). High-pressure fluid line can be made from a variety of materials, including aluminium alloy, stainless steel, copper, titanium and also reinforced flexible hoses.

Fluid lines are made of rigid, semi-rigid and flexible tubes, depending on their use. A rigid fluid line would be one that is not normally bent to shape or flared. Direction changes and connections are made by the use of threaded end-fittings.

Semi-rigid fluid lines are bent and formed to shape and have a relatively thin wall thickness in comparison to rigid lines. A variety of end-fittings may be used to make connections between semi-rigid tubes.

Flexible fluid lines are made from rubber or synthetic materials and are usually called hoses. Depending on the pressure, they are designed to carry hoses may have reinforcing materials wrapped around them. Various types of end-fittings are used to attach hoses to each other and to other components.