Butterley Boiler

The Butterley or "whistle mouth" boiler is a little-known design derived from the Cornish pattern, produced by the noted Butterley boilerworks of Derbyshire. It is basically a Cornish boiler with the lower half of the shell around the furnace removed, so as to permit a large fire to be lit. This made it popular in the textile mills of the Pennines, where the hard Northern coal was of less calorific value than the Welsh coal used in the South West and required a larger fire. Alternatively it may be considered as a shortened Cornish boiler with a waggon boiler placed in front of it with a larger fire beneath that. It suffers the same drawback as the wagon boiler: the concave firebox plate is mechanically weak and this either limits the working pressure or requires extra mechanical staying.