Thimble tube boiler

Niven of Newcastle upon Tyne were granted a patent in 1935, some decades after Clarkson began manufacture, for a relatively small improvement.

[2] As boiling is random, the boiler is limited in both its evaporative capacity and also its maximum furnace temperature.

The majority have a large vertical central flue, with the thimble tubes protruding into it from a surrounding water jacket.

These thimble tubes are formed by deep drawing of steel – a process that was not available in Victorian times, but that became a cheap means of production once available.

A 1954 patent by Clarksons describes a boiler shell with a sliding shutter on the outside to access the central flue.

[3] An alternate form had a central water tank with outward-pointing thimbles, surrounded by a dry sheetmetal casing.

This system was used where a large amount of steam was required even when in port, such as for heated cargoes like banana boats and passenger liners.

One rare use of the thimble tube boiler as a directly fired power generator was an experiment fitting to Leyland steam wagons in 1920.