Page 46 - Market Analysis Report of Optical Communications Field in China & Global market 2020

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Discussion on Laying Method of Air Blowing Cable

Hu Yong Yangtze Optical Fibre and Cable Joint Stock Limited Company
Dai Guangchong China Mobile Group Design Institute Co., Ltd.
Zhai Rui China Mobile Group Design Institute Co., Ltd.
I n the past, long distance trunk lines were basically The selection of pipelines for air blowing cable laying

directly buried. Even though the cable laying
communication pipeline has developed from cement pipe
through pipeline traction was realized later, the cable laying involves the material and diameter of pipeline. China’s
eventually failed due to the quality of pipeline connection, to PVC pipe, from silicon core pipe to micro plastic pipe,
the friction coefficient of pipeline inner wall and pipeline and finally to the cluster pipe that combines silicon core
laying quality (with/without bending). As a new laying pipe with micro plastic pipe. However, the best application
technology of cable, air blowing not only greatly increases scenario of the latest cluster pipe is expressway, for the
the laying length of cable, but also allows long-distance groove of expressway is flat and straight, so it is beneficial
cable laying to reduce joints. Air blowing is less sensitive to the deployment of cluster pipes and the long-distance
to the bending of line and friction coefficient than the air blowing of micro cables. However, for field lines,
traction laying. Therefore, in the pipeline with the same not only mechanical grooving is required, but also the
laying conditions, the laying distance of air blowing is construction contractor should strictly follow the technical
much longer than that of traction, so it covers a wider range requirements of pipe laying, so as to ensure the final laying
of applications. quality. Otherwise, the air blowing distance will only be
shortened. Hence, the selection and laying of pipeline is
I. Principle of Air Blowing Cable Laying very important. Once wrong pipelines are selected and the
In terms of the principle of air blowing cable laying, there laying is not carried out according to the specifications, it
is high-velocity airflow in the pipeline, which pushes the will not only affect the construction period, but also waste
cable to advance together with the pipeline, and there a lot of manpower and materials.
is thrust outside the pipeline to feed the cable into the
pipeline, thus overcoming the resistance when the optical According to the theory of air blowing, the larger the ratio
cable enters the pipeline. Compared with the traditional of pipeline’s inner diameter to cable’s outer diameter, the
direct burial, the air blowing technique provides the smaller the attenuation of air flow, the greater the drag
trunk cable with pipeline protection, thereby solving the force of air blowing on the cable surface, and the longer
problems of tight construction period of long distance trunk the cable laying length. Nonetheless, in terms of cost-
lines, difficulty in finding the insulation of cable to ground, effectiveness, the larger the pipeline diameter is, the
and poor cable protection. Moreover, compared with higher the procurement and transportation costs of the
traction cable laying, air blowing has lower requirements pipeline will be; from the perspective of construction, the
for pipelines, and the number of splice closures and points larger the pipeline diameter is, the greater demand for
with reserved cables is reduced, making operation easier. the displacement of the air compressor will have, and the
Therefore, the air blowing laying technique has so far volume and weight of the air compressor will increase too,
become the main choice for laying long distance trunk thus causing higher procurement and construction costs and
lines. transportation problem; from the perspective of safety, the
Fig1 Schematic Diagram of Air Blowing Cable Laying larger the pipeline diameter, the smaller the cable diameter
and the lower the cable hardness, the easier it is for the
cable to bend and break in the pipeline. Therefore, it is also
vital to select an appropriate pipeline diameter according
to the requirements on pipeline selection and laying. This
helps avoid that the machine operator breaks the cable
while he increases the thrust of the machine on the cable
when the speed of air blowing cable laying decreases at the
construction site. The air blowing speed is mainly increased
by increasing the airflow velocity, not by increasing the
thrust of the machine. Thus, it is better to set the optimal
ratio of the pipeline’s inner diameter to the cable diameter
at 50%~70%.
II. Important Indicators of Air Blowing Cable
Laying 2. Pipeline Laying Quality
The most important indicators of air blowing cable laying For air blowing cable, the main characteristics of the
pipeline include: It can withstand the high pressure
include pipeline selection, laying quality of pipeline and continuously output by the air compressor; the pipeline is
coefficient of internal friction of pipeline.
continuous; the friction coefficient is small. For field lines,
1. Pipeline Selection the air blowing distance is mainly affected by the laying
quality of the pipeline, followed by the friction coefficient.
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