Vapor barrier (railway)

A steam brake is a type of brake for steam locomotives and their tender , in which a steam cylinder acts directly on the brake linkage.

Steam brakes were mainly used on railways that used the suction air brake as a brake for the train car and did not have their own suction air brake cylinder on the steam locomotive, such as. B. in Great Britain , or only one on the car train acting cable brake (z. B. Leberleinbremse ) had such. B. in Saxony with the narrow-gauge railways .

Vapor retarders can only be found on a few museum vehicles today.

functionality

Steam from the locomotive boiler is fed to the steam brake cylinder via a valve (brake valve) that can be regulated in stages or by a continuously variable valve in the driver's cab of the locomotive . The introduced steam sets the piston in the steam cylinder in motion, the piston rod transmits the braking force via a corresponding linkage to the brake pads of the vehicle , whereby the braking effect is achieved. A return spring returns the piston to its idle state as soon as the steam supply is interrupted. The relaxed and condensing steam is led out of the steam cylinder via a drain valve.

The vapor barrier works directly and immediately. Opening the brake valve too suddenly can easily result in overbraking with locking of the wheels. The operation of the vapor barrier therefore required a lot of experience on the part of the locomotive driver .

The vapor barrier can be operated either directly via a lever (valve) or indirectly together with the suction air brake. In the latter case, a control valve connected to the suction air line regulates the steam supply to the brake cylinder, so that the steam brake can also be activated automatically in the event of emergency braking or train separation (so-called automatic steam brake ).

literature

• Hodgson, Lake: Locomotive Management (9th Edition, 1948) . The St Margaret's Technical Press Ltd