368 FARM MOTORS 



part of the stroke, more 

 work can b e obtained 

 from the same amount of 

 steam. 



In Fig. 246 let the dis- 

 tance OV 2 represent the 

 length of stroke, OP 1 the 

 pressure of steam as it en- 

 ters the cylinder and while in communication with the 

 boiler. If the piston starts at the point O and travels to 

 Fj with the valve wide open, steam will continue in the 

 cylinder at the pressure of the boiler, i.e., the pressure at 

 A will be the same as at P and the line P^A will be paral- 

 lel to the line OF . Now, if steam is cut off at V^ and no 

 more allowed to enter, the pressure will fall as fast as the 

 steam expands and the line AB is formed. During this 

 part of the stroke all the work which is done in the cylin- 

 der is due to the expansion of the steam which was ad- 

 mitted during the first part of the stroke. When the piston 

 reaches V 2 the steam is exhausted against a back pressure 

 of OP 2 . 



The work done during the admission of steam is repre- 

 sented by the area OP^AV^, and is all the work this 

 amount of steam would do if it had not been allowed to 

 expand. 



The work done during expansion is represented by the 

 area V^ABV 2 . 



The total work done by the steam is the sum of these 

 two areas, or OP V ABV 2 . 



Then, of the total work done by the steam that repre- 

 sented by the area V \ABV ' 2 is gained by using the steam 

 expansively. 



512. Losses in a steam engine cylinder. Only 2 to 10 

 per cent of the total heat supplied to a non-condensing 



