I N N O V A T I O N A N D F L E X I B I L I T Y
9.5 Blowing through unequal m/d Sizes
Fibre is normally blown through a constant size of micro duct be it 3/2.1mm, 5/3.5mm or 8/6mm. It is not possible to combine two micro ducts of
different size and expect to achieve the same blowing performance because the airflow in the larger m/d falls to a useless level i.e. with almost no
fibre driving force. If one of the lengths is only 50m or so, connected to several hundred metres of a different size, then blowing from one through the
other may well work. Refer to the figures below.
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Mid Point Changes
1. m/d increases
The sudden drop in pressure at the mid-point shortens the
pressure gradient, making the first half of the blow easier.
But there is only 1 bar air left in the second half, and the
fibre unit, now only ‘pushed’ will buckle and stop at the
pushing limit point ’X’.
2. m/d decreases.
The restriction at mid point causes the first half of the route
to ‘fully pressurise’, killing the pressure gradient, and the
fibre unit, now only ‘pushed’ will buckle and stop at the
pushing limit point ‘X’. It never reaches the ‘good’ 2nd
portion of the route where the pressure drop is very good.
Far End Changes
3. m/d increases near the end
As with case #1, the portion of the route with the small m/d
performs well. The pressure gradient dies in the larger m/d.
Now if the push limit distance is less that the remaining
m/d, the fibre unit will stop before emerging. If this part of
the route is bendy, the failure is more likely still
4. m/d decreases near the end
Similar to case #2 but much worse. The length of the larger
m/d may as well not exist, as it may have only a 1 bar
pressure drop. The FU will stop after a short distance (the
pushing limit).
The very good part of the route is inaccessible.
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9 Fibre blowing
“This document is intended as a guide only. Whilst the information it contains is believed to be correct, Emtelle can take no responsibility for actions taken based on the information contained in this document. Emtelle reserves the
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I N N O V A T I O N A N D F L E X I B I L I T Y
