Counter vapor barrier

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The counter- vapor brake is the use of the working principle of a steam cylinder with round slides on a steam locomotive, changing the direction of operation by changing the design direction of the control and thus the advance of the slide relative to the steam piston. Due to the inertia of the steam locomotive in the existing direction of movement, the changed working direction of the steam cylinder, contrary to the previous working direction, initially slows down the movement of the piston pushrod and the power transmission to the locomotive's engine until it comes to a standstill.

The counter- vapor brake works with steam, it is often confused with the counter-pressure brake , which, however, works with ambient air and is used as an inertia brake (dynamic brake) and is approved as a separate brake system.

Working principle

The counter-vapor brake is not actually a brake, but only the utilization of the functional principle of a steam engine to achieve a braking effect. It is therefore not a separate component on a steam locomotive.

However, the counter-vapor brake principle can only be achieved with round or piston valves. In the case of simple flat gate valves , due to their construction principle, no opposite steam application is possible, since the slide is only pushed open by the applied steam pressure; if the slide is charged with steam in opposite directions, it would immediately be lifted off the slide surface and the steam would escape without affecting the piston.

Experienced steam locomotive drivers can use the steam brake to reverse the steam locomotive from one direction of movement into the opposite direction, virtually without any noticeable stop, since the actual "switching moment" already takes place in the original direction of movement. However, this procedure requires precise knowledge and experience, since incorrect handling can also damage the engine of the locomotive .

In the case of steam locomotives without a second independent braking system (e.g. compressed air brakes , suction air brakes , vapor brakes ) for the locomotive, in addition to the throwing lever or parking brake that is generally always present, the counter-steam brake was used as a second braking system. Steam locomotives that exist today usually have two independent brake systems for approval reasons, so that the counter-vapor brake is not regarded as a brake system, but is used.

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  • Heym, Rudolf: How does it actually work, the steam locomotive? , Bruckmann, 2004, ISBN 3765472557