Steam locomotive braking system
Steam locomotives have their own braking system, independent from the rest of the train. Locomotive brakes employ large shoes which press against the driving wheel treads.
With the help of air brakes, a separate system also allowed the driver to control the brakes on all cars. These systems require steam-powered compressors, which are mounted on the side of the boiler or on the smoke-box front.
An alternative to the air brake is the vacuum brake, in which a steam-operated ejector is mounted on the engine instead of the air pump, to create vacuum and release the brakes.
A Steam locomotive is usually always fitted with sandboxes from which sand can be delivered to the rails to improve traction and braking in wet or icy weather. On American locomotives the sandboxes, or sand domes, are usually mounted on top of the boiler.
When the locomotive is running under power, a draught on the fire is created by the exhaust steam directed up the chimney by the blast-pipe. Without draught, the fire will quickly die down and steam pressure will fall.
When the locomotive is stopped, or coasting with the regulator closed, there is no exhaust steam to create a draught, so the draught is maintained by means of the blower. This is a ring placed either around the base of the chimney, or around the blast pipe orifice, containing several small steam nozzles directed up the chimney.
These nozzles are fed with steam directly from the boiler, controlled by the blower valve. When the regulator is open, the blower valve is closed; when the driver intends to close the regulator, he will first open the blower valve.
It is important that the blower be opened before the regulator is closed, since without draught on the fire, there may be back-draught air from the atmosphere that blows down the chimney, causing the flow of hot gases through the boiler tubes to be reversed, with the fire itself being blown through the fire-hole onto the footplate, with serious consequences for the crew.
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