THE ENGINE PROPER. 



nately comes opposite the two ports leading to the ends 

 of the small or high pressure cylinder. The valve in mov- 

 ing also alternately uncovers these ports, allowing the high- 

 pressure cylinder to exhaust into the steam chest. The low- 

 pressure cylin- 

 der receives the 

 steam from the 

 steam chest, 

 and exhausts, 

 (through the 

 heater), into 

 the stack, i n 



FIG. 19. FACE OF VALVE. 



exactly the same manner as a simple engine. The valve is 

 "balanced" because high-pressure steam is under and tending 

 to lift it, while the low-pressure steam is on top, and pressing 



it against its seat. When 

 the engine is running with 

 a light load, the pressure 

 is sometimes insufficient 

 to hold the valve against 

 its seat, in which case a 

 loud clattering noise is 

 made by the valve as it 

 raises from and returns to 

 FIG. 20. its seat. To prevent this, 



SHOWING PIPE TO STEAM PLUGS, two steam plugs are placed 



