ROUGH-AND-TUMBLE ENCINEEK 1OJ 



expansive force of the steam. By cutting off at l /i we 



e piston is driven half its stroke, or 6 



inches by live steam, and by the expansion of the 



i the remaining 6 inches; by # we mean that 

 live steam is used 9 inches before cutting off, and ex- 

 pansively the remaining 3 inches of stroke. 



Here is something for you to remember: "The ear- 



:i the stroke you cut off. the greater the economy, 

 but the less the power ; the later you cut off the less the 

 economy and the greater the po\ 



Suppose we go into this a little further. If you are 

 carrying 100 pounds pressure and cut off at % t you 



readily see the economy of fuel and water, for the 

 steam is only allowed to enter the cylinder during J4 

 of its stroke; but by reason of this, you only get an 



ige pressure on the piston head of 59 pounds 

 throughout the stroke. But if this is' sufficient to do 

 the work, why not take advantage of it and thereby 

 save your fuel and water? Now, with the same pres- 

 sure as before, and cutting off at J4, you have an aver- 

 age pressure on piston head of 84 pounds, a gain of 50 

 per cent in economy and a loss of 16 per cent in power. 

 Cutting off at }i gives you an average pressure of 96 

 pounds throughout the stroke. A gain on cutting off 

 of 75 per cent in economy, and a loss of nearly 

 46 per cent in power. This shows that the most ;>. 

 able point at which to work steam expansively i 



