244 Kansas Academy of Science. 



will be less noticeable in the earlier part of expansion because the 

 difference in pressure is slight, but will become more and more ap- 

 parent on the expansion line as the pressure becomes more unbal- 

 anced in the latter part of the stroke. The presence of entrained 

 moisture will also cause the terminal pressure to be high to some 

 extent. 



A leaky piston or exhaust valve, on the other hand, will give too 

 low an expansion curve. 



When release occurs too early the expansion line will drop sud- 

 denly before the end of the stroke is reached, to the back-pressure 

 line, or very near it. Too late a release will cause the back pressure 

 to be high at the beginning of the return stroke. A slow- opening 

 exhaust valve will tend to slope the back-pressure line from release. 



Cramped exhaust openings will raise the back-pressure line, 

 which should not be at a height equal to more than two or three 

 pounds above the atmospheric line. Compression should begin at 

 a point that will bring the pressure in the cylinder up to one-third 

 to two-thirds the distance to the top of the card when admission 

 takes place. If less than this, the compression will not overcome 

 the inertia of the reciprocating parts. If the line rises too high, 

 compression takes place too early, and power is lost. 



