A high pressure watertube boiler is a type of boiler in which water circulates in tubes heated externally by fire. Fuel is burned inside the furnace, creating hot gas which boils water in the steam-generating tubes. In smaller boilers, additional generating tubes are separate in the furnace, while larger utility boilers rely on the water-filled tubes that make up the walls of the furnace to generate steam.
Swiss locomotive rebuilt with a Brotan boiler in 1907.
Brotan boiler
Babcock & Wilcox boiler
End-view of a Yarrow boiler
A boiler is a closed vessel in which fluid is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central heating, boiler-based power generation, cooking, and sanitation.
A moveable (mobile) boiler (preserved, Historic Silver Mine in Tarnowskie Góry Poland).
A stationary boiler (United States).
1950s design steam locomotive boiler, from a Victorian Railways J class
A superheated boiler on a steam locomotive