Standards for Air-blown Optical Cable Laying

Air blowing (or jetting) of optical fiber cables requires proper conduit sizing, low-friction cables, suitable blowing equipment, and careful testing to ensure safe and efficient installation.

Cable and Conduit Requirements

• Cable Type: Use optical fiber cables with a low friction coefficient to minimize resistance between the cable outer surface and the duct inner wall. Both standard cables (uni-tube, multi-tube, armored, unarmored) and microduct cables can be installed using this method .
• Conduit Size: Select a conduit slightly larger than the cable diameter to allow smooth movement and reduce the required air pressure .
• Bend Radius: Respect the minimum bend radius of the cable to avoid damage during installation .
• Microducts: For microcables, microducts must be compatible with the cable size and designed for air-assisted installation as per ITU-T L.156 standards .

Equipment Requirements

• Blowing Machine: Modern fiber blowing machines include a cable drive system, air control system, duct clamps, seals, and speed/pressure controls for precise installation .
• Compressor: Provides high-speed airflow to push the cable through the duct.
• Pushing Device: A tractor mechanism or traction rollers apply initial pushing force to feed the cable into the duct before air is applied .
• Lubricants: Optional blowing lubricants can reduce friction and facilitate longer installation distances .

Installation Procedure

1. Preparation: Inspect ducts for debris, moisture, and integrity. Verify cable specifications and environmental conditions .
2. Crash Test: Perform a short test by pushing the cable into a sealed duct section to determine the maximum safe pushing force without damaging the cable or causing buckling .
3. Cable Feeding: Feed the cable into the blowing head and apply initial pushing force using the tractor mechanism .
4. Air Blowing: Introduce compressed air to create a jetting effect, allowing the cable to float inside the duct and reduce friction .
5. Monitoring: Track cable movement, adjust airflow and pushing force as needed, and avoid over-pressurization .

Factors Affecting Performance

• Route Shape: Multiple bends or undulations increase friction and reduce maximum blowing distance .
• Cable Stiffness: Stiffer cables perform better in straight ducts, while flexible cables handle complex routes with multiple bends .
• Environmental Conditions: High temperatures can deform polyethylene ducts, and high humidity can dilute lubricants, increasing friction .
• Blowing Distance: Depending on duct route and cable type, continuous lengths of over 1000 meters are achievable, with some field installations exceeding 2000 meters .

Safety and Best Practices

• Wear protective gear and ensure equipment is well-maintained .
• Avoid excessive pushing force to prevent cable damage or buckling .
• Conduct trial runs and monitor installation speed and air pressure to maintain safe and efficient operation .
• Use cables that have been validated on manufacturer or independent test tracks to maximize installation success . By following these requirements and procedures, optical fiber cables can be efficiently and safely installed using the air blowing method, minimizing damage, reducing labor, and achieving longer installation distances.