Hose Assembly Construction
When working with fluid systems and aircraft maintenance, do not overlook the critical nature of hose assemblies. In addition to being integral components of several systems, they have their own specifications and require special attention.
Because hose assemblies are used extensively in pneumatic, vacuum, hydraulic, fuel, lube, vent, and drainage systems, they are rated according to listed specifications as it relates to a particular service environment. Many environmental factors include specified temperature, pressure, and impulse conditions. When hose assemblies are neglected or mishandled, the result may be a failure in the system.
Aerospace hoses fall into two basic categories: PTFE and Rubber
- Both are available in a variety of pressure ranges. Low-pressure hoses are designed for pressures up to 200 psi (13.79 bar), medium pressure hoses for pressures from 200 to 1500 psi (13.79 to 103.42 bar), and high-pressure hoses for pressures from 1500 to 3000 psi (103.42 to 206.84 bar).
- Temperature ranges vary depending on the pressure rating of the hose. For example, low-pressure rubber hoses have a temperature range from -65°F to +160°F (-53.89°C to +71.11°C). Medium pressure hoses are rated from a low range of -40°F to +250°F (-40°C to +121.11°C), to a high range of -65°F to +375°F (-53.89°C to +190.55°C). Finally, high-pressure rubber hoses are rated from a range of -40°F to 200°F (-40°C to +93.33°C), to a range of -65°F to +375°F (-53.89°C to +190.55°C).
The selection of the hose construction to fit the application is critical. Generally, a hose consists of three parts: (1) inner tube (2) reinforcement (3) cover.
- Some of the requirements the inner tube must meet to perform within spec include: cracking resistance, flexibility, and deterioration when exposed to specific temperature ranges. Other requirements include minimum porosity, smoothness, and chemical compatibility.
- Reinforcement is the hose’s strength and gives it its rated pressure capability. The pressure capability depends upon the type and quality of the materials used. A hose cover is placed over the reinforcement primarily as protection from environmental damage.
- The cover does not contribute to the pressure capability of the hose. Still, it protects the hose reinforcement from abrasion, rust, moisture, and other factors. In addition, chafe guards, firesleeves, and internal coils may be used to protect the hose under unusual external conditions.