"Overfiring" a steam locomotive

[Redwards]

I've seen this term in a few threads recently and was hoping to get some clarification on what it means.  Is it as simple as creating a fire that would exceed what would be considered optimal for the operation of the locomotive (e.g. using too much fuel, resulting in higher firebox temperatures, etc.)?

--Reed

[PNWRMNM]

Overfiring is using more fuel than there is airflow to burn the fuel cleanly. The result is not excess firebox temperature, but black smoke from the stack and wasted fuel. With oil fired engines the condition can be cured very quickly by reducing the oil flow to the atomizer in the firebox.

With coal fired engines it is possible to put a slug of coal in a portion of the firebox that is so large that the mass of coal will not burn immediately. I do not know if this too is called overfiring.

Mac McCulloch

[Redwards]

Thank you Mac for your explanation.  Aside from putting on a show for railfans on a photo line, is there another scenario where this would be done on purpose?

--Reed

[PNWRMNM]

No. It has always been considered a waste of fuel and bad practice.

Mac

[BigJim]

is there another scenario where this would be done on purpose?

Yes there is.
When the shifter worked the cement plant near here, before starting switching operations at the plant the fireman would fill the firebox with a hefty amount of coal and let it simmer, so to speak. Not a lot of steam pressure was needed during switching operations. When it was known that it was close to time to leave the fireman would then start cleaning up his fire and getting the pressure up for the trip home.

[Anonymous]

I have heard of cases where damage to locomotive boilers was said to have been caused by overfiring.  How can overfiring cause boiler damage?