GWR four-cylinder arrangement?

Well no, it rather suggests that you have reached the limits of gigantism in steam locos and need to think of diesels or electrics if you want to increase power! The only places which seemed to be able to make giant steam locos work was where coal was cheap. That tells you something.

My wider point is that there seems to be a cult of Chapelonism which is vey partial to quoting selected statistics about locos, without considering the whole picture. So you get magic power outputs from the cylinders, but much less discussion of how the steam was to be supplied, or whether the mechanical structure of the loco could deal with those power outputs. My feeling is that once you get above about 2,500hp with a coal-fired steam loco, you have to start accepting much reduced efficiency, from a machine that is already inefficient. At that point the rationale for moving away from steam starts to become inevitable.

Tom

 

The phenomenon of carryover was and remains a serious issue. It was addressed but needed further development work. It achieved the result of reducing lineside fires and the cost of associated insurance claims which was the leverage to get the ideas applied. Fuel consumption was reduced for a given power output and as an extension of this power output went up which was what the creators of the system wanted to test.

 

25%? It's powered by a small steam engine! You will find that the figure is somewhere between 3 and 5%.

 

Two firemen?

 

It's not the steam to power the stoker that is the issue, it is that large amount of coal disappears straight up the chimney unburnt.

Tom

 

Perhaps you should take a look at the 5,500hp N&W Y6s? They had cast frames and roller bearings throughout. Since they were equipped with roller bearings and automatic lubricators, the amount of time and expense required to maintain a Y6 was akin to diesel locomotives. In 1952, N&W tested its A class and Y6b class locomotives against a four-unit Electro-Motive Division F7 diesel set. The tests indicated that fuel costs and similar items were roughly the same, and the test was considered a tie. The Y6s lasted until 1961, long after most US railroads had given up steam. However, diesels eventually won out for lower maintenance and other operational costs.

 

For some the rationale for moving away from steam is at a very much lower power level. Apart from heritage applications, of course.

 

And the overall financial efficiency of that?

You are falling into the same trap as everyone else, finding ever more elaborate workarounds to enable one technological option while ignoring the total cost of operation.

Tom

 

But where do you get the figure of 25%? Unburnt coal going up the chimney? Char maybe.

 

According to Bill Withuhn in his book American Steam Locomotives Design and Development 1880-1960, the Pennsylvania Railroad ran a series of tests at the Altoona Test Plant on two otherwise identical locomotives. The stoker-fired engine burned about five percent more coal throughout its power range, due to the fact that a stoker grounds up the coal, injecting more of the coal as powder that was lost out of the stack.

So it would appear that 3 to 5% figure does include dust lost to the chimney.

 

Unburnt coal going up the chimney; plain and simple. You need to define what you mean by char but, in my book it is unburnt coal or, more exactly, partially burnt coal which has lost its volatile content but still contains unburnt carbon. That’s the sort of stuff you get in a smokebox and, if there is a leak in the smokebox which allows air to be drawn in, will continue to burn in there, hence the reason locos can get burnt smokeboxes from time to time. Tom will no doubt give chapter and verse but I think the SECR used to collect smokebox char and send it to Ashford for burning in the works boilers.

 

Depends on the circumstances. Picking up a second fireman at Bromsgrove or Tebay would be far cheaper than a banker, if that solution works with the locomotive.