Transportation on Land 295 



127. The condenser. It was formerly the practice to ex- 

 haust the used steam into the open air or, in the case of loco- 

 motives, into the smokestack to increase the draft through 

 the fire box. In many modern engines, the stationary, marine, 

 and locomotive, the used steam is saved by being discharged 

 into condensers. 



The condenser promotes two kinds of economy and thus in- 

 creases the efficiency of the engine and the saving of fuel. In 

 the first place, the condenser chamber receives the exhaust 

 steam into a pressure which is somewhat less than that of the 

 atmosphere, or a partial vacuum (page 301 ff.). When exhaust 

 steam is expelled into the air, against atmospheric pressure, it 

 uses up energy which might well be given to the piston stroke ; 

 for the live steam has to drive out the used steam as well as 

 drive the piston. With the low pressure condenser the used 

 steam is taken from the cylinder with practically no help from 

 the live steam. Consequently the live steam expends its energy 

 upon the piston or in doing useful work. This is economical 

 of energy and in turn means a saving of fuel. 



The condenser effects another important saving. Steam in 

 condensing gives up a large amount of heat energy (page 307), 

 but the water of condensed steam retains also a large quantity 

 of heat, its temperature being just a little below that of boil- 

 ing water. It must therefore be evident that to collect and 

 condense steam and to return the water with its heat content 

 to the boilers is a saving of fuel that is quite worth while. 

 One may calculate what such a system of saving means in 

 terms of money from the actual cost of fuel and labor neces- 

 sary to bring a given quantity of water to the boiling tem- 

 perature. 



Condensers have been used on marine engines for years, and 

 recently have come into wide use on stationary engines. On 

 locomotives the adoption has been slower because of almost 

 unchangeable conditions, such as the size and weight of the 

 engine, and the limited quantity of cold water available for 



