334 FARM MOTORS 



some have two pumps, but the most common method is 

 a pump and injector. 



454. Feed-water heaters. The sudden change in tem- 

 perature of boilers puts them under a great deal of strain. 

 One of the principal reasons for this change in tempera- 

 ture is the admitting of cold feed water. This water may 

 be easily heated by passing the exhaust steam through 

 it. There are two methods of such heating: one is to 

 allow the exhaust steam to mingle with the water, thus 

 being condensed and carried back to the boiler, and the 

 other is to pass the feed water through pipes surrounded 

 by steam. By the former method the steam is returned 



FIG. 231 FEED- WATER HEATER 



to the boiler, and unless a filter is used all the cylinder 

 oil is carried into the boiler, to which it is detrimental. 

 In the latter case the steam does not return to the boiler, 

 but is sent up the stack, thus producing a forced draft. 

 Fig. 231 shows a heater of this type. 



As pumps and injectors will not operate with hot water, 

 and since the water from a heater is nearly as hot as the 

 exhaust steam, the heater must be located between pump 

 and boiler. 



455- Water columns. The purpose of the water col- 

 umn is to support the gauge glass and try cocks; it is 



