鍋爐

鍋爐是蒸汽機車上的大型圓筒狀水箱。它的內部由許多稱為「煙管」的管道貫穿兩端，使鍋爐後端的火箱與前端的煙箱互通。來自火箱的熱空氣和煙霧通過煙管，加熱鍋爐內的水，最終使其沸騰轉化為蒸汽。蒸汽為能夠被壓縮的氣體，因此蒸汽會在鍋爐中積聚，從而增加壓力。水的沸點溫度取決於鍋爐內的壓力大小。壓力愈大，沸點愈高。鍋爐中的蒸汽冷卻下來後將會凝結再度轉化為水。

大多數蒸汽機都有一個安全閥，可以在鍋爐超壓時自動釋放過量蒸汽。建議不要產生超過車輛運轉時所需的蒸汽，產生過量蒸汽僅會浪費燃料。

Water is fed to the boiler from storage using an injector . Since stored water is cold, adding it to the boiler can condense steam back into water, resulting in pressure drop, so it needs to be done carefully.

The boiling point temperature of water depends on the amount of pressure in the boiler. The higher the pressure, the higher the boiling point.