A steam brake is a type of brake for steam locomotive

Steam locomotive

A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...

s and their tenders, whereby a steam cylinder works directly on the brake linkages.

Steam brakes were primarily used on railways 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

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

, or where there was only a cable-operated brake (e.g. a Heberlein brake

Heberlein brake

Heberlein brake is a continuous railway brake used in Germany that is applied by means of a mechanical cable. Train braking is therefore initiated centrally from the locomotive using a winder. This causes the brake clips to be applied on individual wagons, assisted by a servo system which makes use...

) running along the train, like for example in Saxony

Kingdom of Saxony

The Kingdom of Saxony , lasting between 1806 and 1918, was an independent member of a number of historical confederacies in Napoleonic through post-Napoleonic Germany. From 1871 it was part of the German Empire. It became a Free state in the era of Weimar Republic in 1918 after the end of World War...

 on the narrow gauge

Narrow gauge

A narrow gauge railway is a railway that has a track gauge narrower than the of standard gauge railways. Most existing narrow gauge railways have gauges of between and .- Overview :...

 railways.

Steam brakes are usually found today on heritage steam locomotives.

Operation

Steam is supplied to the steam brake cylinders from the locomotive boiler

Boiler

A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Materials:...

 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

Piston rod

In a piston engine, a piston rod joins a piston to a connecting rod.Many internal combustion engines, and in particular all current automobile engines, do not have true piston rods, and the term piston rod is often used as a synonym for connecting rod in the context of these engines.All engines...

 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 result in a slight 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