Lancashire Boilers are related to, and derived from, the Cornish boiler in that they have tubular metal furnaces passing through a horizontal cylindrical water space with external multiple pass flues. However they differ from Cornish boilers in that they have an additional furnace tube, a different gas path and they are much larger. Crofton uses a Lancashire boiler, and has a spare shell on site held for the future. Both of these boilers are some 2.3 m (7½ ft) in diameter and 8.5 m (28 ft) long and weigh about 22 tonnes. They have a working water capacity of some 18,000 litres (4,000 gallons/18 tons). These dimensions are typical for boilers of this type.
The two cylindrical furnaces can be seen, they are 70 cm (2 ft 4 inches) in diameter. They have two functions:-
1. to transfer the heat from the hot fire gasses to the water surrounding them;
2. to help prevent the end plates of the boiler from bulging outwards.
The fire itself is only about 1.8 m (6 ft) long with a total grate area of 2.8 m2 (30 sq ft) and sits upon firebars made of cast iron. It is retained by a low firebrick wall. The external flues are made of brick and the top, exposed part of the boiler shell is covered in special insulating fire bricks.
From these diagrams, it can be seen that the gas path of a Lancashire boiler differs from that of its predecessor, the Cornish boiler, in that the hot gasses from the fire pass under the boiler first, then back down the sides. With the Cornish boiler, they go down the sides first then back down under it. Thus, a Lancashire boiler has two fire damper plates, one in each side flue, compared to the Cornish boiler’s single damper plate in the under-
The original Lancashire boilers at Crofton differed slightly from the above design, in that they had corrugated furnace tubes which were not able to act as end reinforcements. These boilers were therefore fitted with massive nutted stays that ran their length. These stays can be seen on the cut up example at the entrance to Crofton’s cafe. This latter boiler is particularly interesting, in that it has a ‘Cornish’ gas path (i.e. it has only one, central damper plate). This modification was probably adopted because the boiler was installed over the bed of the Cornish boiler that preceded it.
Corrugated furnace tubes were introduced on some later boilers to help prevent crushing as working steam pressures increased. Another type of design, that was introduced for the same reason, was the use of short, flanged tube segments, known as Adamson Rings, after their inventor.