Steam Engines. 



519 



Fio. 250.- Portable steam engine. 



in this position assists the high pressure steam in driving 

 the piston toward G. On the opposite side of the large 

 piston, in the low pressure cylinder B, is the steam which 

 has spent its available energy in driving the large piston in 

 the opposite direction and this is being 

 forced out through the passage 4,4 into 

 the exhaust 5. At the proper timCj when 

 the pistons are Hearing the ends of the 

 cylinders toward G, the eccentric reverses 

 the action of the rod F and pushes the 

 slide valve until 6 stands over 4 and 7 

 over 2, which permits the high pressure 

 steam to enter A through 2,2 and the 

 partly expanded steam to enter B by way 

 of O to C and from thence through 4,4 to 

 B, when the direction of motion of the pis- 

 ton is reversed. 



The construction of the piston head with^etai packing, 

 with its self adjusting metal packing rings 

 are shown in Fig. 251. 



