When laying optical cables using the air blowing method

Air-blown optical cable installation requires proper cable selection, duct sizing, mechanical pushing, and controlled compressed air to ensure safe and efficient deployment.

Cable and Duct Requirements

Cable Types: Standard optical fiber cables (uni-tube, multi-tube, armored, unarmored) and microduct cables can be installed using this method. Cables should have low friction outer jackets to reduce resistance inside the duct. Cable Stiffness: Stiffer cables are preferred for straight ducts and longer distances, while more flexible cables are suitable for routes with multiple bends.

Duct Size: The duct should be slightly larger than the cable to allow smooth airflow and reduce friction. The Duct Fill Ratio (DFR) should ideally be between 30–80% depending on calculation method. Microducts: For microduct installations, cables with polyethylene (PE) sheaths and optimal stiffness are recommended to prevent buckling and facilitate navigation through bends.

Equipment and Installation Procedure

Blowing Device: A tractor mechanism with traction rollers is used to push the cable a few hundred meters into the duct before introducing compressed air. Compressed Air: Air is injected to “float” the cable, minimizing sidewall pressure and friction. Air pressure should be controlled to avoid cable damage, using the minimum required to move the cable.

Blowing Head: The cable is attached to a blowing head or piston that seals the duct and allows air to push the cable forward. For larger ducts, piston-assisted blowing is preferred. Crash Test: Before full installation, a crash test is performed by pushing the cable into a sealed duct section to determine the maximum safe pushing force and prevent jacket damage or buckling.

Environmental and Operational Considerations

Temperature: Avoid installing cables in extremely cold conditions, as the jacket may become brittle and more prone to damage. Route Planning: Straight trajectories allow longer blowing distances, while multiple bends or undulations may require mid-assist devices to extend cable reach. Lubrication: Optional low-friction lubricants can be applied to further reduce resistance and facilitate cable movement.

Performance and Distance

Typical Lengths: Single air-assisted devices can install 1,500–2,100 meters of cable under optimal conditions. Longer distances can be achieved using mid-assist devices along the route. Force Distribution: In blowing, the pulling force is distributed along the cable length due to air drag, unlike jetting which uses a reaction head.

By following these requirements—selecting the right cable, ensuring proper duct sizing, using controlled air pressure, and performing pre-installation tests—optical fiber cables can be efficiently and safely installed using the air-blowing method.