Cornish Boiler

When volunteers commenced restoring the mill in 1978 they determined that they wanted the engine to operate using steam rather then be driven by a motor or by compressed air and for the steam to be raised in a traditional manner rather than by a modern generator. This was a fortunate decision as they soon realized that the design of the 1820s engine called for a high volume of low pressure steam which a traditional boiler provides. The boiler is approximately 2m in diameter and 7m long. After lighting using house coal, Welsh steam coal is used. It takes 5 days from lighting to safely bring the temperature of the boiler and flues to to the point where sufficient steam is provided to run the mill.   

Boiler Operation

The present boiler is of a ‘Cornish’ type built at the nearby Cliff Vale Boiler Works in 1903. It is hand fired with coal and contains about 2,500 gallons (11,000 litres) of water,  indicated in two water gauge frames. It has one fire tube which travels the length of  the boiler with the first 2m being fire grate.  The flue gases travel down the fire tube to the back then return under the boiler and are then directed into the side flues where they travel to the back of the boiler and then to the chimney. This gives the time and thermal contact to pass their heat into the boiler and so boil the water.  Steam pressure is indicated by a Bourdon gauge. The dead weight safety valve releases pressure at 60 pounds per square inch (4.2 kg force per sq. cm), although the boiler is operated at about half that pressure. Steam is taken from the top of the boiler to the engine room and other parts of the building.

Boiler Water Replenishment

Water is fed to the boiler from the large iron tank in the roof. It is probable that originally canal water was used and would have been pumped in, against boiler pressure, by two Weir steam pumps similar to the ones seen against the side wall. They are operational but not connected to the boiler. Today treated mains water and twin electric pumps are used. 

Boiler History

When the mill last operated commercially, steam was generated by a ‘Lancashire’ boiler built in the 1930s and installed in the early 1950s. Originally it would probably have been a ‘Cornish’ boiler larger than the one installed at present. After the mill ceased operating commercially in 1972 and during the redevelopment of the site the end which protruded beyond the rear wall of the boiler room into the yard was cut off. A replacement was required and the present boiler was located locally at Tunstall swimming baths where it was used to heat water for the slipper baths. Fortunately it had recently been taken out of service, was acquired and moved to the mill in 1988.