TRACTION ENGINES 



449 



locked. In other words, when the clutch locks, the blocks 

 all are forced out against the rim of the belt wheel tight 

 enough so they stick to it and the whole mechanism re- 

 volves with the wheel. The clutch is a very important 

 part of the traction engine and requires very careful ad- 

 justment and care. Since the blocks DDD are continually 

 wearing off, the arms EE have to be constantly adjusted. 

 They should be so carefully adjusted that when thrown 

 in, the clutch will lock and hold itself in position. They 

 should also be adjusted so there will be no slip between 

 the clutch blocks and the clutch shoe. Fig. 333 



shows another type of 

 clutch, which has a metal 

 clutch block instead of 

 wood. 



588. Transmission gear- 

 ing. The steam engine for 

 traction engine work gen- 

 erally has a speed of 200 

 to 225 revolutions a min- 

 ute. If the drive wheels 

 were connected directly to 

 the engine shaft such a 

 speed would drive the out- 

 fit over the ground nearly 

 as fast as a locomotive travels. This is something that 

 could not be conceived of on country roads, hence the 

 speed has to be reduced to one which is permissible. For 

 this purpose a chain of gears such as is shown in Fig. 334 

 is utilized. Not only are these gears used to reduce the 

 speed of rotation from that of the drive wheel to that of 

 the engine, but since the engine is generally located some 

 distance from the traction wheel shaft, these gears con- 

 duct the power from the engine shaft to the shaft of the 



333 CLUTCH WITH METAL 

 BLOCKS 



