1. Initial data
The specifications of the machine manufacturers indicate the maximum allowable air pressure on the compressor side: for the CBS Tornado - 12 bar (or 1.2 MPa), for the Plumett CableJet - 14 bar (1.4 MPa). The friction coefficient of a standard protective polyethylene pipe with an inner solid layer of lubricant reaches 0.08 (for example, the requirement of KaR-Tel LLP). A typical blowing cable has the following parameters: diameter 10 mm, weight 90 kg / km (for example, cable of the OKG brand from the Saranskkabel-Optics plant). We calculate the derived parameters of the cable: the cross-sectional area will be 78.5 * 10-6 m2, the weight will be 0.9 N / m.
2. Calculation of the load that the blowing machine exerts on the cable passing through it
Cable load = compressor air pressure * cable cross-section.
On CableJet: Load = 1.4 ∙ 106 Pa * 75.5 ∙ 10-6 m2 ≈ 110 N.
In Tornado: load = 1.2 ∙ 106 Pa * 75.5 ∙ 10-6 m2 ≈ 94 N.
3. Calculation of the effort required to pull the cable in the pipe
Force = coefficient of friction of the pipe * weight of the cable * length of the cable length.
For a 1.0 km segment: 0.08 * 0.9 N / m * 1000 m ≈ 72 N.
For a 1.5 km segment: 0.08 * 0.9 N / m * 1500 m ≈ 108 N.
For a 2.0 km segment: 0.08 * 0.9 N / m * 2000 m ≈ 144 N.
4. Intermediate results
The results show that with these machines (delivered load up to 110 N), it is possible to blow in up to 1.5 km of a typical cable (required force 108 N).
5. Additional example
As an additional example, consider the blowing of a cable armored with round wires. It is empirically clear that such a cable, relatively heavy and inflexible and not intended for this installation method, will have a short blowing range. Let's check this by calculation. Parameters of an armored cable of the OKB brand of the same plant: diameter 14 mm (cross-sectional area 15.4 ∙ 10-5 m2), weight 300 kg / km (weight 3 N / m).
On CableJet: Load = 1.4 ∙ 106 Pa * 15.4 ∙ 10-5 m2 ≈ 216 N.
In Tornado: load = 1.2 ∙ 106 Pa * 15.4 ∙ 10-5 m2 ≈ 185 N.
For a 1.0 km segment: 0.08 * 3 N / m * 1000 m ≈ 240 N.
For a 0.75 km segment: 0.08 * 3 N / m * 750 m ≈ 180 N.
As you can see, the blowing range in this case is really small, it reaches only 750 m.
6. Conclusion
In conclusion, we note that the requirements for the maximum load on the cable for blowing, which are often prescribed in technical specifications, equal to 1.7 kN or even 2.7 kN, after the above examples can be considered overestimated.
7. Materials used
Rules for the construction of fiber-optic lines of railway communication with the laying of cables in plastic pipelines (approved by the Order of the Ministry of Railways of the Russian Federation No. A-1062u of June 16, 1999)http://www.docload.ru/Basesdoc/8/8597/index.htm#i1361837http://proelectro.ru/lib/kabel/46.htmlhttp://www.cbsproducts.com/tornado.htmhttp://www.plumettaz.com/web.nsf/produit_details.xsp?lang=en&documentId=0F590BC51DA741BBC1257ACA005788A3http://sarko.ru/new/volokonno-opticheskiy-kabel/kabel-okg.htmlhttp://sarko.ru/new/volokonno-opticheskiy-kabel/kabel-okb.html
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