A steam brake is a type of brake for
steam locomotive
A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, Fuel oil, oil or, rarely, Wood fuel, wood) to heat ...
s and their
tenders, whereby a steam
cylinder works directly on the brake linkages.
Steam brakes were primarily used on
railways
Rail transport (also known as train transport) is a means of transport using wheeled vehicles running in tracks, which usually consist of two parallel steel rails. Rail transport is one of the two primary means of land transport, next to roa ...
where
vacuum brakes were used to brake the train, but where there was no vacuum brake on the steam locomotive itself, as for example in the
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...
, or where there was only a cable-operated brake (e.g. a
Heberlein brake) running along the train, like for example in
Saxony
Saxony, officially the Free State of Saxony, is a landlocked state of Germany, bordering the states of Brandenburg, Saxony-Anhalt, Thuringia, and Bavaria, as well as the countries of Poland and the Czech Republic. Its capital is Dresden, and ...
on the
narrow gauge
A narrow-gauge railway (narrow-gauge railroad in the US) is a railway with a track gauge (distance between the rails) narrower than . Most narrow-gauge railways are between and .
Since narrow-gauge railways are usually built with Minimum railw ...
railways.
Steam brakes are usually found today on heritage steam locomotives.
Operation
Steam is supplied to the steam brake cylinders from the locomotive
boiler
A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, centra ...
via a valve (the brake valve) which may have several fixed settings or be infinitely variable. The piston in the steam cylinder is set in motion by the steam admitted, the
piston rod transfers the brake force via a system of rods to the
brake blocks of the vehicle, thus achieving the braking effect. A return spring returns the piston to its rest position as soon as the steam supply is interrupted. The expanded and condensed steam is drained from the steam cylinder through a drain valve (''Entwässerungsventil'').
Direct steam brake
A steam brake acts directly and immediately; the sudden opening of the brake valve can easily result in overbraking by locking the wheels. The operation of a steam brake therefore requires a great deal of experience from the
engine driver.
Vacuum controlled steam brake
A steam brake can be operated directly by a lever (valve) and also indirectly together with the vacuum brake. In the latter case, a control valve linked to the vacuum system controls the admission of steam to the brake cylinder, so that the steam brake can be activated automatically in an emergency or if the train separates (the so-called 'automatic steam brake').
Literature
* Hodgson, Lake: ''Locomotive Management (9th Edition, 1948)''. The St Margaret's Technical Press Ltd
{{Railway brakes
Railway brakes
Steam locomotive technologies