THE STEAM TRACTOR 53 



is four and one half inches in diameter, as compared with 

 three and one half inches on a steam tractor developing 140 

 b.h.p. A cross-section of the two shows the gas engine shaft 

 to be nearly two thirds larger than the corresponding part on 

 a steam engine of the same number of cylinders and double 

 the power. 



The Governor 



One of the most vital points of the engine is the governor, 

 which may be likened to the human heart in its importance 

 and action, regulating as it does the energy delivered in ac- 

 cordance with the need. The farm tractor never enjoys 

 absolutely uniform working conditions. In fact, in plowing 

 the variation in soil in single field, to say nothing of grades and 

 other obstructions, creates enormous differences in the power 

 required. In order to prevent the outfit from stalling on the 

 one hand, or from running at an abnormal and dangerous 

 speed on the other, a sensitive governor must be employed. 



The speed regulation is effected by means of a flywheel 

 attached to the crankshaft, and a governor, usually of the 

 throttling type, which regulates the admission of steam accord- 

 ing to the needs of the load. The governor consists of two 

 or more weights which are free to swing outward by centrif- 

 ugal force, and in doing so pull down upon a spindle which 

 operates the throttle valve, controlling the opening in the 

 steam admission pipe. The governor may be set to maintain 

 various speeds. If the governor permits considerable fluctua- 

 tion of speed under a constant load, it is either of poor design, 

 poorly lubricated, or driven by a slipping belt. 



Valves 



The steam passes through the throttle valve to the steam 

 chest and thence through a valve to the cylinder. The ordi- 

 nary type of valve on traction engines used in America is the 

 slide valve. However, remarkably economical engines using 



