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  Air Brakes - Preface



Everybody, even if he/she knows something about technology, swears stone and leg that a heavy truck, possibly even fully loaded, has a longer braking distance than a car. And when it comes to the showdown, everyone is amazed at how well such a vehicle performs.

Anyone who hasn't experienced it will hardly believe it. A heavy truck with a fully loaded semi-trailer and a standard car drive side by side at 80 km/h, both brake fully at the same point and come to a standstill after roughly the same stopping distance.

Is it the large contact area or the enormous weight or both? In any case, a motorcyclist should be careful if he/she has to brake hard behind a truck. Better enough distance beforehand, otherwise it might not be enough.

Not only the 40 tons permissible total weight are impressive, but maybe even more the performance balance. We already know that 294 kW (400 hp) is easily possible with a truck, and we think a little less about the torque of up to 3000 Nm. But who would have ever heard of up to ten times the braking power of such a vehicle?

How fortunate that the inner shoe brake was invented early on, with which the enormous forces of an estimated 10,000 N fully benefit the friction between the brake shoes and drum. In the meantime, however, internally ventilated brake discs are also consistently jammed in trucks by smaller pads and heavy pliers.

Even with car disc brakes, this cannot be achieved with foot force alone. Even in the days when trucks were only equipped with drum brakes, that wasn't possible. Here, too, there is already a significant difference to the car, because in this case the foot force is stronger than the assistant, while in the truck it only has a steering function.

That doesn't exactly simplify the thoughts about a possible failure of such a system. You can get a car to a standstill with difficulty, but you can still stop it if the brake booster fails, but not a truck. Therefore, the safety precautions for the latter are significantly greater.

For example, it is a mandatory part of driver training here to pay more attention to decreasing braking efficiency, e.g. due to fading. In the case of a car, this actually only applies to excessive loads. In the case of a truck, this is quite possible when driving downhill with a heavily laden trailer, if the driver behaves just a little unwisely.

We're talking about an external force braking system here and maybe you're already familiar with a dual-circuit system in principle. However, since a trailer or even a semi-trailer that may be heavier than the towing vehicle must also be considered, a so-called 'dual-line system' is added to the truck.

We will also have to talk about the legally required tests of the system. It is not enough just to have to take note of its effect, e.g. on the test bench. You listen deep into the system and, for example, load is simulated. Of course, the individual exam dates are also getting partly much closer to each other.

Such a brake even has its own symbols from the pneumatics kit, just as you may have first become acquainted with the modular system of hydraulics with the ABS systems in cars. In order to explain the structure, simplified signs (symbols) are used, which, together with dashes for the air lines, make the whole thing clearer.

And then these numbers to mark the connections. And then these numbers to identify the connections. One digit seems to be sufficient, if there were not also those on a component that have to be numbered consecutively. And then there is the number to identify the respective component, ten digits for device (3), type (3), modification (3) and condition (1).








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