Boiler design question

[Glenn Brooks]

Hello All,

I am starting to work on replacing the original boiler on my antique 1904 Campbell 12 5/8” gauge 4-4-0 loco. It currently has a 14” diameter keyhole design. (See below)

This has been sort of an on agin, off again project. Mostly due to deciding best way to regauge down to 12” gauge.

This will require a firebox 1” narrower than the existing design- causing a loss of around 18 square inches of grate area.

My question is: is should I compensate for the smaller grate size by increasing, or decreasing, the total heating surface of the flues - given that I stay with a 14” boiler? Or does this decreased grate size even matter?

Thanks much for any suggestions or comments.

Glenn

[NP317]

Glenn:
Contact Keith Sternberg on Lopez Island.
He is extraordinarily well versed in firebox calculations for full sized and model steamers.
And nationally known as a marine steam engine restorer. He manages maintenance of the Virginia V's steam engine.
When he built his Allen Ten Wheeler he calculated the optimum grate area and ended up blanking off the forward third of the firebox grate.
Results are a coal burning steamer that is difficult to prevent the safety valves from exhausting! It steams exceptionally well.

So Keith might be able to assist you planning the new boiler firebox.
PM me and I'll put you in touch with him.
RussN

[Glenn Brooks]

Thanks Russ, I know Keith. I’ll contact him.

Glenn