Spark Arrestor

A problem besetting steam traction on British Railways for decades - fire risk, caused by sparks from the chimneys and cinders from the ashpan - has been made worst in recent years by hot and dry summers.

The risk from the ashpan is often consider to present the worst risk, because it may cause fires in the "cess", at the side of the track, burning signal cables etc. The is not difficult to combat on "The Duke", because it lends itself to being covered underneath by meshes or trays.

Preventing the emission of sparks from the chimney is a different matter:

• Over the years the usual method of "spark arresting" has been to place steel meshes around the blastpipe and chimney assembly in the smokebox, and maximum sizes have been set for the apertures in the mesh.
• Unfortunately, nothing so far has been completely successful. The main problem is that because the blastpipe creates the draught for the fire,by sucking exhaust gases through the boiler tubes, care has to be taken not to obstruct the gas flow and adversely affect the steaming. Reducing the size of the apertures in the mesh often decreases the amount of air space, and can bring the risk of clogging with particles of ash and char.

We investigated the problems and experimented with different meshes. It soon became apparent that other factors were also important e.g. the size of the smokebox, its length, the position of the chimney in it and the angle of the spark arrestor meshes. Nevertheless we came to the conclusion with regard to the mesh itself that there must be:

1. An aperture size small enough to ensure that any particles passing through would be too small to survive as sparks in the atmosphere.
2. A wire gauge thin enough to allow good air space and thus good gas flow.
3. A possibility that such a combination might resist clogging by causing fragmentation of most particles and ejection of them in tiny pieces.

Eventually we found such a mesh, in stainless steel. Tests carried out on The East Lancashire Railway, over six days of steaming with two totally different types of coal, simulated operating conditions as diverse as possible. They proved 100% successful. Then we fitted an intermediate mesh to the rear of the main one to give double protection.

Since then the system has been tried on the mainline with identical results.

This system is not currently installed in the locomotive because the current management do not understand it and have replaced it with the original system thus reintroducing the problems that the new system had eliminated.