Blown Fiber and Jetted Fiber are two new terms we're hearing in wireless networking industry regarding DAS installations. These terms are used to describe the use of compressed air when placing microfiber cable. Both these terms suggest that the microfiber is being pushed or propelled by air through a microduct; However, "air lubrication" would possibly be a more appropriate phrase. Jetted Fibers and Blown Fibers in distributed antenna systems (DAS) help push fiber deeper into the network to increase bandwidth and keep construction costs down to allow for future expansion.
Air is used as a means of reducing friction between the inner wall of the microduct and the microfiber cable jacket. Like when the air is off a puck on an air hockey table, the puck has difficulty overcoming the friction between its surface and the hockey table's surface. Static Friction and Dynamic Friction are the two types of friction the microfiber (or puck) must overcome in order to move forward efficiently.
When an object is not in motion, static friction is the existing force between the contact surfaces. Static friction tells us how much force is required to start moving that object.
When an object is in motion, dynamic friction is the existing force between the contact surfaces. Dynamic friction tells us how much applied force is required to maintain movement of that object.
The friction is greater when the object is heavier, which means that when the microduct contains more microfiber it must overcome more friction. This friction-issue between the two surfaces can be lessened by lubricants, such as air. Using a lubricant means that friction resistance is not dependent on surface materials but is almost entirely independent on the force between both surfaces. Friction and temperature are still related, and the viscosity of the lubricant is affected by the temperature with lubrication.
Air pressure, pounds or bars per-square-inch (PSI), is more important than air volume, which is generally referred to in CFM (cubic feet per minute). The maximum and ideal pressure to be used is 15 bars (217 PSI) at 35 CFM; while the minimum pressure is 10 bars (145 PSI) at 180 CFM.
There's less likelihood the surface of the microfiber will come into contact with the surface of the microduct when the air pressure is greater. Therefore, the air acts as a lubricant by raising the microfiber away from the microduct's wall. This allows operators to easily push fiber deeper into the network; which means that the fiber goes where it is needed to increase bandwidth to subscribers, and it also keeps construction costs down by allowing for future expansion.
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