Steam Traction Engine Horse Power Ratings

| July/August 1985

  • Case engine
    Case engine on the incline at the Winnipeg Fairgrounds in 1910.
  • Avery 30 HP

  • Case engine
  • Avery 30 HP

131 Robin Road, Blackwell, OK 74631

There seems to be a lot of confusion on horse power ratings. I am not going into how you figure brake horsepower because I think most everyone understands this. If a steam traction engine is tested on a prony brake and the brake is correctly built and operated, it will give you a correct answer.

The big problem seems to be in the old 'Nominal ' horse power ratings. Some seem to think the nominal rating as used on steam traction engines was a boiler horse power rating, while others have said it's a draw bar rating. Both are wrong.

Just what is 'Nominal' horse power? In Steam Engine Catechism by Robert Grimshaw, M. E. and I quote:

Nominal horse power does not mean anything in particular. It corresponds to 'as long as a piece of string,' or 'as big as a lump of chalk.'

Mr. Webster says 'Nominal'-- named as a mere matter of form, being trifling in comparison with the actual value.


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