14/06/2026
Regular fans may have noticed that Mad Bess running dates have not been published for June. Bess unfortunately is currently unavailable, due to a leak on one of the superheater elements - the process of repairing this is ongoing, and we hope to have Bess back in operation by the middle of July.
As on the 'full sized' version, Linda & Blanche , the boiler on Mad Bess is superheated, a relatively rare feature on locomotives of this gauge - indeed Bess is the only superheated 12/12.25" steam locomotive in the country.
Steam produced in the boiler on 'wet' or 'saturated', non-superheated steam locomotives will pass straight to the cylinders when the regulator demands steam. This steam still contains a high moisture content, and thus, if heated further, this moisture content can be converted to steam, increasing the temperature and volume of the steam supplied to the cylinders.
On a superheated locomotive, instead of passing straight to the cylinders, steam arrives at the superheater 'wet' header, after being demanded by the regulator. This steam is then sent down superheater elements. These elements pass back towards the firebox, housed inside large boiler tubes at the top of the tube stack, before returning back to the superheater header. The steam in these elements is therefore further heated, after the period of exposure to further heat. From here it is sent to the cylinders, where the higher temperature, more expansive steam is of greater use. Superheated steam has 30% more volume than wet steam, and therefore results in a water and fuel saving by reducing the demand on the boiler to produce steam.
Combined with a 180psi boiler and large cylinders, the superheating helps cement Bess as the 3rd most powerful 12/12.25" steam loco in the country.
A pinhole leak in one of the superheater elements allows steam to escape into the smokebox before it has reached the cylinders, and thus out of the chimney - significantly reducing the available power on the locomotive.
Removing the superheaters to effect the repair requires the removal of the smokebox, which requires the removal of the steam driven air pump, and significant associated plumbing. The welding will be undertaken locally by a specialist coded welder, and after hydraulic testing to ensure no further leaks are present, the process of reassembly can commence.
While the locomotive is unavailable, work will take place on the pony truck to restore the wheel profiles. The pony truck underneath the smokebox at the front of the loco, helping to guide the loco into curves and reduce fl**ge wear on the driving wheels. Being inside framed, the pony truck is more complex than a standard wheelset to set up on the lathe for turning, but it is light work for our master machinist Paul.