32 FARM MOTORS 



the cylinder is doing more work than the other, and as 

 a result there is excessive vibration and unequal strain 

 in the parts. It is impossible to change the connecting 

 rod, but there are now valve gears on the market which 

 partly rectify the defect by the manner in which they 

 admit the steam. Owing to mechanical complications 

 which arise, it is still a question as to the advisability 

 of putting these valves on small engines. 



529. The indicator diagram. Fig. 264 is an ideal indicator dia- 

 gram and can be described as follows : The line xy is traced on the 

 paper with no pressure in the cylinder, i.e., it is the atmospheric line. 



B, C 



FIG. 264 FIG. 265 



The point A shows when steam commences to enter the cylinder. 

 Point B is the maximum pressure and the time when the steam port 

 is opened its full amount. From B to C the port is open, and the 

 pressure is the same as B. At C the cut-off takes place and the 

 steam works on expansion. At D the exhaust port opens, and from 

 D to E the pressure drops to the pressure at which the steam exhausts 

 to the air. From E to F is back pressure, due to exhaust. At F com- 

 pression takes place and lasts until A is reached. 

 The different parts of the diagram are known as follows : 

 xy. Atmospheric line, 



AB. Admission line, 



BC. Steam line, 



CD. Expansion line, 



DE. Exhaust line, 



EF. Back pressure line, 



FA. Compression line, 

 A. Point of admission, 



C. Point of cut-off, 



D. Point of release, 



F. Point of compression. 





