Main air duct

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The main air line (abbreviation HL or HLL), called the main line in Switzerland , is the continuous connection line for the braking system of rail vehicles . It has two tasks, filling the auxiliary air reservoir in each connected vehicle for the single-line brake and applying and releasing the brake . Depending on the system, it supplies the vehicles with the necessary compressed air or vacuum. There is a shut-off valve on the vehicle's bumper to shut off the compressed air lines. In the case of vacuum brakes, the shut-off function is assumed by blind covers to which the coupling head attaches.

Screw coupling and main air line on a side tipping car

According to UIC541-03 " Driver's brake valves ", the normal operating pressure of the main air line is 5.00 bar ± 0.05 bar, but theoretically it can also be between 4 bar and 6 bar. At this pressure the brake is released and the auxiliary air tanks are filled. If the driver (train driver) initiates braking via the driver's brake valve, the pressure in the main air line is reduced. The normal service braking is initiated with a pressure reduction of 0.4 to 1.5 bar (full braking), the rapid, forced or emergency brake (NB) vents the main air line to ambient air pressure. To release the brake, the pressure is raised again to the normal operating pressure. The main air line is therefore the energy and information carrier of the automatic compressed air brake (railway) on a pneumatic basis. Since the transmission speed of the braking information plays a decisive role in long train compositions , the UIC540 writes a breakdown speed of min. 250 m / s, which results from the length of the main air line divided by the time ( breakthrough time ) from the triggering of an emergency brake to the start of the pressure increase in the brake cylinder of the last car. Theoretically, pressure waves propagate at the speed of sound (343 m / s), about 270 m / s to 300 m / s can be reached in rail vehicles. For this reason, the clear width of the main air duct is prescribed in UIC541; for passenger coaches 25 mm and for longer freight trains 32 mm; In addition, no sharp bends or even 90 ° screw connections are permitted in this pipeline . Furthermore, the pipeline should be laid on one level so that there is no risk of freezing due to condensation in the pipe bends below in winter . When coupling, the main air line is first connected with brake couplings (hoses), then the stop cocks are opened. After a new train formation , the continuity of the main air line and the function of the brake must be checked with a full brake test before departure .

See also

Individual evidence

  1. a b Swiss Driving Regulations (FDV) A2016 Federal Office of Transport (FOT), July 1, 2016 (PDF; 3 MB). R 300.14 Appendix 1, Section 5.1.1 Main line (main air line HLL)