STEAM ENGINES 



To read an indicator diagram for pressures. Whenever pos- 

 sible the scales should be divided into parts equivalent to the scale 

 of the spring, i. e., if the spring is 60 pounds to the inch the scales 

 should be divided into 60 parts. Whenever this is not possible a 

 tenths or hundredths scale may be used. The scale shown in Fig. 



FIG. 269 



FIG. 270 



270 is a tenths scale, and it now reads 1.7 inches with a 6o-pound 

 spring. This gives a steam pressure at that point of 



1.7 X 60= 102.0 pounds. 



If the scale is moved down to the point of release it reads 

 0.45 X 60 = 27.00 pounds. 



533- Governors. The object of a governor is to main- 

 tain as nearly as possible a uniform speed of rotation of 

 the engine. When the speed of the engine varies through 

 several revolutions because of variation of load or boiler 

 pressure, the governor will aid in regulating it, but if 

 the variation of speed is confined to a single revolution 

 or a part of a revolution, the variation must be cared for 

 in the flywheel. Since governors for steam engines are 

 attached to the engine, they cannot regulate the speed 

 exactly, for they cannot act until the engine does. In 

 other words, the engine has to commence to slow down 

 before the governor will be affected. It then takes the 

 governor a little time to act, and consequently the engine 

 has quite a chance to vary its speed of rotation. In 

 practice, however, when a slight change of speed takes 

 place, a good governor acts instantly and allows only a 



