Lancashire boilers (Fire-tube boilers)

      The Lancashire boiler is similar to the cornish , but has two large flues containing the fires. It was the invention of William Fairbairn in 1844 , from a theoretical consideration of the thermodynamics of more efficient boilers that led him to increase the furnace grate area  relative to the volume of water.
      Later developments added Galloway tubes (after their inventor , patented in 1848) , crosswise water tubes across the flue , thus increasing the heated surface area. As these are short tubes of large diameter and the boiler continues to use a relatively low pressure , this is still not considered to be a water-tube boiler. The tubes are tapered , simply to make their installation through the flue easier.

Lancashire boiler in Germany