372 



AGRICULTURAL ENGINEERING 



cylinder engine. If the engine is not in proper adjustment 

 there is no tendency to continue to operate it, as there is when 

 there are two or more cylinders, letting the remaining ones 

 furnish more than their share of the power. A multi- 

 plicity of cylinders, on the other hand, for a given power, 

 reduces the magnitude of the impulses and thus to a large 

 extent relieves the gearing of severe shocks. The multiple- 

 cylinder engine furnishes a steady power and is a little more 

 agreeable to operate for that reason. There seems to be 

 little doubt but that greater skill is required to keep the com- 

 plicated engine in proper adjustment and 

 repair. 



The Clutch. As the gas engine cannot 

 be started under load, it is necessary to 

 have a clutch to engage the engine with 

 gears or with chains and sprockets that 

 transmit the power to the drivers. This 



Fig. 238. One form i , -i . n 7 , n 



of clutch. The wood- clutch is generally used to engage a pulley 



en shoes are force;! * ,, . -, , > , 



outward against the when the engine is used to drive a station- 

 enlJarfpg Vt* by W frfc- ary machine with a belt, when the traction 



gearing is disengaged. 



In construction, the clutch consists of shoes usually made 

 of wooden blocks, which, by suitable levers, are made to bear 

 against a disk or other surface with sufficient pressure to 

 cause the power to be transmitted through the parts in 

 contact. The form and material of the friction surfaces 

 vary widely. Sometimes the clutch takes the form of two 

 cones, hence the name cone clutch. Again, the friction 

 may take place between a series of disks, one-half of which are 

 attached to the engine shaft and the other half to the trans- 

 mission. This type of clutch is called a multiple-disk clutch, 

 and the disks are usually engaged by the pressure of a spring 

 which may be brought to bear at the most suitable time. 



