Uploaded February 2020 | Updated September 2026, 3 minutes ago
When we were gifted this roberts type water tube boiler by the Thompsons of Lee's Mills, it was missing fire grates which delayed trials. Construction of fire grates meant a long awaited test run, 200 PSI steam pressure attained meant we could run engines of a very large size compared to the capacity of the boiler itself. The Sirocco engine has a cylinder bore equal to that of the steam drum diameter on this boiler.
An illustration of the sizes of steam power and what you can pull off if you have an intuitive understanding. Some interesting numbers: using a tiny steam driven duplex feedwater pump for a 3.5 inch gauge model locomotive with water piston bores of less than 5/8 of an inch, at 200 PSI, a boiler with only 10 square feet of heating surface, no superheat and a 5" diameter steam drum can run an engine with a 5" bore 4" stroke cylinder at normal speed while maintaining the water level and steam pressure.
When we were gifted this roberts type water tube boiler by the Thompsons of Lee's Mills, it was missing fire grates which delayed trials. Construction of fire grates meant a long awaited test run, 200 PSI steam pressure attained meant we could run engines of a very large size compared to the capacity of the boiler itself. The Sirocco engine has a cylinder bore equal to that of the steam drum diameter on this boiler.
An illustration of the sizes of steam power and what you can pull off if you have an intuitive understanding. Some interesting numbers: using a tiny steam driven duplex feedwater pump for a 3.5 inch gauge model locomotive with water piston bores of less than 5/8 of an inch, at 200 PSI, a boiler with only 10 square feet of heating surface, no superheat and a 5" diameter steam drum can run an engine with a 5" bore 4" stroke cylinder at normal speed while maintaining the water level and steam pressure.
