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Steam trains A-Z

“Big Boy” locomotives   A class of steam locomotives built in the US in the 1940s. At 40 metres (131 feet) long and 600 tonnes, Big Boys were the largest, heaviest and most powerful steam locomotives ever. 

Boiler   A tank containing water that, when heated, evaporates into steam. As more steam collects, its pressure builds, and it is fed to cylinders, where it pushes pistons that power the driving wheels.

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