VIII 

 PERFORMANCE OF STEAM TRACTORS 



STEAM-PLOWING tractors range in size from 50 

 to 120 rated brake horsepower, and a general 

 ratio of brake horsepower to nominal rating is 

 about three to one. In other words, steam tractors 

 of the sizes used for plowing are rated at from 20 to 40 nominal 

 horsepower. Practically every steam engine will carry at 

 least 10 per cent, more load than is called for by the rating. 

 Three classes of 20, 25, and 30 to 35 nominal horsepower are 

 manufactured by most engine companies. These will handle, 

 roughly speaking, about seven, ten, and twelve or fourteen 

 plows, respectively. Ordinary steam-plowing engines, fully 

 equipped and ready for work, range in weight from ten to twenty- 

 five tons. They cost from $1800 to $3000 in the United States, 

 and possibly 30 per cent, more in Canada, owing to freight and 

 duty. Many smaller tractors are made for lighter work, but 

 since the steam engine is not so economical in small units for 

 plowing, the larger engines are practically the only ones which 

 have been constructed especially for this purpose. 



Some tractors are given only the brake rating, but it is cus- 

 tomary to use the term "nominal" in rating engines for sale. 

 This has no definite meaning, being simply the designation 

 adopted by the manufacturer in listing his various tractors. 

 Some tractors are rated on their actual drawbar horsepower 

 under what may be assumed as average conditions. Naturally 

 the matter of a tractive rating is very complex, since the con- 

 ditions over which the tractor must run are widely variable. 



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