IO2 K QE AND-TUMBLE ENGINEERING 



although various other devices are used with more or 

 less success. As they all accomplish the same pur- 

 pose it is not necessary for us to discuss the merits or 

 demerits of either. 



The main object is to enable the operator to run his 

 engine either backward or forward at will, but the link 

 is also a great source of economy, as it enables the en- 

 gineer to use the steam more or less expansively, as 

 he may use more or less power, and, especially is this 

 true, while the engine is on the road, as the power re- 

 quired may vary in going a short distance, anywhere 

 from nothing in going down hill, to the full power of 

 your engine in going up. 



By using steam expansively, we mean the cutting 

 off of the steam from the cylinder, when the piston 

 has traveled a certain part of its stroke. The earlier 

 in the stroke this is accomplished the more benefit 

 you get from the expansive force of the steam. 



The reverse on traction engines is usually arranged 

 to cut off at J4, J^ r M* To illustrate what is meant 

 by "cutting off' at *4 J4 or J4, we will suppose the 

 engine has a 12 inch stroke. The piston begins its 

 stroke at the end of the cylinder, and is driven by live 

 steam through an open port, 3 inches or one quarter 

 of the stroke, when the port is closed by the valve 

 shutting the steam from the cylinder, and the piston 

 is driven the remaining 9 inches of its stroke by the 



