Blowing in is a special procedure for the subsequent laying of fibre optic cables. For this purpose, empty pipes or speed
pipes are laid during cable laying, into which fibre optic cables can be blown with compressed air. The glass fibres
are blown into micro
pipes, which arelaid in the empty pipes or directly into the ground. These microducts are also known as speed pipes and have a diameter of 3 mm to about 20 mm. They have a slippery inner coating, as do the FO cores, which have a special coating that allows them to slide in the empty conduit, overcoming even tight bends with small bending radii
Due to the high sliding ability, there is only little friction, which makes high laying lengths of several kilometres possible. To blow in the fibres, a fibre-optic blow-in device is required, with which compressed air is forced through the speed pipe. Theglass fibre lies on the air cushion and there is hardly any friction on the inner wall of the Speedpipe.
A significant advantage of the blow-in technique is that older glass fibres that no longer meet the requirements can be blown out using compressed air and replaced with new ones.