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The Waggon Boiler

wp93799b36_06wp0f0bee94_06The Waggon Boiler (so called because its shape was similar to the American Pioneer Waggon) was used by James Watt in the 1700’s to power his stationary steam engines. It was one of the earlier designs of steam boiler. Like James Watt’s Engines, Waggon Boilers were not designed to run at a significant steam pressure. This was because little was known about pressure vessel design and because suitable material for their manufacture was only available in small sheets of variable quality. Thus Waggon boilers only provided steam at pressures of about 0.3 bar (5 psi) or less.
The diagram on the left illustrates the basic shape of the Waggon boiler (ignore the lightly drawn inner tube – that was a later development). Essentially, it was a rectangular box with a rounded top. It was fired underneath with return flues along the sides. Ash from the fire dropped into arched chambers below the boiler from which it was removed by wheelbarrow.
Originally Crofton had 3 Waggon boilers running at  0.3 bar (5 psi).These were replaced in 1844 by 3 three Cornish Boilers running at 1.4 bar (20 psi). The ash pits for the Waggon Boilers still exist at Crofton (they are part of the ‘undercroft’) but they are not suitable for general public access as they are cramped and poorly lit.
The diagram on the right shows a Waggon boiler installed in its boiler house.


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