The pneumatic brake




The pneumatic brake is today the most widely used braking system over the wold, but also  the most ancient one as its principles have not been so much modified since the invention of George WESTINGHOUSE (see page on railway braking history).

Nevertheless, technical progresses - in particular for pneumatic components - and the contribution of electricity have made it possible to dramatically improve the performances of this type of brake.

 

Basic principles

The basic principle of the pneumatic brake consists in transferring the brake demands issued by the driver by means of a phneumatic pipe  installed all long the train. This pipe is called the Brake Pipe (BP).

Two principles have coexisted during dozens of years:

Both types of pneumatic brakes intrinsically meet one of the base golden rules of railway braking, i.e. brake automaticity (see page corresponding to braking principles): any break in the BP leads to a pressure drop or increase (according to the configuration) on both portions of the train on each side of the breaking point, thus leading to brake application on these both portions (the latters remaining mechanically coupled or not).

The vacuum brake has been used for a long time in some European countries (in particualr in the UK) as well as in Africa and in Asia. But it low usable pressure range - due to the difficulty to create vacuum) - required the installation of very large brake cylinders. Moreover, tolerance to leakages is far lower than for the compressed air pneumatic brake. This is the reason why this brake is disappearing - it is used only sporadically in Africa and Asia - the operators progressively modifying the recent rolling stock with the compressed air pneumatic brake and scrapping the old one.


The main standards

The compressed air pneumatic brake has thus became a universal system used all over the world. Very quickly, three standards have been issued in order to ensure interoperability of rolling stocks from one coutry to the other in the same area. These three standards are:

The UIC (Union Internationale des Chemins deFer) standard: it is used essentially in Europe and in Africa, as well as in India.

The AAR (Association of American Railways) standard: it is used on the American continent (from Alaska to Tierra del Fuego...) as well as often in Asia and Oceania.

The Russian standard (Matrosov brake): it is only used in the former USSR republics.

The different standards essentially differ by the minimum required performances and vehicles physical coupling requirements, the operating principles being identical. Couplability between the UIC brake and the AAR brake is even possible without so much restrictions in case for rescue operations.

 

 

We'll provide here details mainly for the UIC brake, as it is the one used in Europe (and in particular in SNCF, France). It shall be noted that UIC requirements are generally met integrally only for vehicles operated in the frame of international traffic (RIC passenger cars  and wagons). For the other rolling stocks used for national operation or(and) of EMU/DMU type, the pneumatic brake is only "UIC type", its operating principles globaly complying with UIC standards but the detailled operation presneting operating modes that are not compatible with a full interoperability: this is in particular the case for EMU/DMU rolling stocks (such as TGV, Z2N, XTER, ATER, TER2N in France).

After having explored the operating principles of the main components of the compressed air pneumatic brake, we'll provide a little more details about the typical brake architecture of each type of rolling stock. Attention ! The purpose is neither to be exhaustive here nor to pretend that all vehicles of the same type are equipped with the same brake equipment... But the given explanations will enable you to better understand the typical brake quipment.