BBC's Top Gear stokes a steamer

[Fluesheet]

O.S. Nock says in the Railway Enthusiasts Encyclopedia that mechanical firing is not as efficient as manual firing. Some of the coal arrives in the firebox as 'slack' which is immediatly carried away by the blast.

I'd never heard that, and I can see the point. I'd always understood that opening the firedoor was an impediment to efficiency as doing so disrupts the draft coming through the firebed. I'd also suspect that if the firebox was large enough and you weren't running full throttle (i.e. draft wasn't at it's max), the slack would have time to combust and provide some heat to the whole process.

But when it comes right down to it, the combination of the grate area and required firing rate would have been the determining factor - at some point you're going to need more coal than a man can throw. I once read that the rule of thumb was that a locomotive could be hand-fired up to about 1500 horsepower, beyond that, you had to start doubling up your stokers (this was not uncommon on some U.S. railroads) or provide mechanical assistance.

I read a fascinating article in the Pennsylvania Railroad Historical and Technical Society Magazine (the Keystone) about boiler theory, especially as it related to draft. Throughout the thesis, the writers referred to front end designs and tube / flue designs of European locomotives (especially British and German designs) as (generally) being closer to being "correct". They theoretically had a lower resistance to gas flow through the tubes, which meant less draft was needed, which meant the fire could burn slower, and therefore have more time to transfer heat into the furnace and superheater tubes. I've read of American designs that had such a high draft that the firebed would jump off the grates (not just the slack!). An engineer that did often was NOT going to be popular with his fireman!

Matt