Steam Question

[NW Mailing List]

Hi Christopher. The altitude question came up a few months ago. 

My educated guess is that higher elevations probably did not affective starting tractive force as the steam pressure inside the boiler would be constant (subject to safety valve settings), regardless of the external air pressure. Potentially the ability to generate steam rapidly under high loadings (i.e., power) could be reduced since there isn’t as much oxygen for the fuel to interact with and would therefore generate less heat for given amount of fuel. Alternatively, the fueling might have to be forced (i.e., more fuel) to get the same amount of heat.  Dad’s technical books - specifically  “The Steam Locomotive” by M.E. Johnson (Baldwin’s Chief Engineer) - doesn’t mention the topic at all. It could be that steam locomotives were so inefficient that any performance changes / fuel consumption rates related to altitude just weren’t noticeable. 

Along those lines, the book “The Steam Locomotive Energy Story” covers some of the efficiency questions, and is available at the N&WHS Commissary. 

Additives for boiler water and their ratios depended on the water source being used. External methods (softening plants) mixed chemicals into the raw water, then piped it to a settling tank to get various solids out of suspension before the water ever got to a tender. The materials used were lime, soda ash, and sodium aluminate. In another process (called the Zeolite Method) that exchanged salts that tended to cause scale with those that didn’t used aluminum, sodium, calcium and potassium. The downside to external plants was their expense in operation, so they were most often used in heavy traffic areas. 

In locations that didn’t warrant a water softening plant, an internal treatment  was used. This used soda ash, sodium aluminate and tannin to get the solids to precipitate out in the boiler. This was not a preferred method since the chemical ratios were harder to control (especially if applied by the engine crew) and by it’s nature allowed all the solids to get into the boiler, creating more sludge, foaming and other downsides. 

All of this (and much more) from the Johnson book noted above. 

Matt Goodman
Columbus, Ohio, US

> On Nov 28, 2021, at 1:27 PM, NW Mailing List <nw-mailing-list at nwhs.org> wrote:
> 
> Does the ambient outside temperature and or pressure affect the power produced by a steam locomotive?  I know the less the ambient pressure the lower the boiling temperature of water.  Did the engineers have to adjust their operating procedures in winter vs. summer?
> 
> Additionally, what additives did they add to boiler water to avoid scaling, and approximately when did railroads start doing this?
> 
> Christopher J. Bunsey
> 
> 
> 
> 
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