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[Hedd_Jones]

Hello Hedd.
We have seen sparks coming out the chimney at the Great Dorset Steam Fair. Maybe just putting on a show!
https://www.youtube.com/watch?v=Dm_5cizZwZ8
Adrian.

The exhaust steam goes into the bottom of the chimney, creating a vacuum behind it, thus 'pulling' the fire. The harder the engine works, the harder it pulls the fire. The 'puffer' principle.

But a steamer is direct drive, no clutch, so if the engine is stationary, no exhaust to pull the fire, certainly no sparks. Particularly if there is a damper on the chimney.

An engine working very hard will throw sparks, at the GDSF there is a lot of showing off so you will have seen it (as have I). In real use you try to avoid it for obvious reasons, we generally carry £5,000,000.00 insurance policies against damage caused by sparks. And have to fit 'spark arrestors'. Its not at all difficult to drive in such a way where they are minimized. There was a lot of discussion on various groups on Facebook over the summer about this given the dry spell we had.