271 

 The value ©f the steam piph within the smoke box op a locomotive, as a 



MEANS OF SUPERHEATING. By Wm. F. M. GoSS. 



The pipe connection, by which steam is conveyed from the boiler to the 

 engines of an American locomotive, begins at the throttle valve within the 

 dome of the boiler, and extends forward along the inside of the boiler 

 until it finally passes out through forward head into the smoke box. Here 

 it receives a fitting known as the " T-head," from which branch pipes lead- 

 ing to the cylinders on either side of the machine. The T-head and the 

 two branch pipes are exposed to the temperature of the smoke box, which, 

 when the engine is in action, is several hundred degrees higher than the 

 temperature of the steam within the pipes, and it is therefore evident 

 that the latter must receive some heat from the smoke box in its passage 

 through these pipes. The amount of heat thus transmitted, however, has 

 always been a matter of speculation. 



Designers of compound locomotives have often arranged an enlarged 

 pipe within the smoke box to serve in the double capacity of receiver and 

 re-heater, the expectation being that the steam exhausted from the high 

 pressure cylinder would be dried, or even superheated, by its passage 

 through this pipe in its course to the lower pressure cylinder. To throw 

 some light on the extent of the drying or superheating effect, as well as 

 to settle another question at issue, the following experiment was made 

 upon the Purdue experimental locomotive : 



A thermometer having been inserted in the T-head, another in the mid- 

 dle of one branch of the steam pipe, and a third in the saddle close to the 

 valve-box, the locomotive was run with the throttle partially open, the 

 drop in pressure from the boiler to the pipe being sufficient to superheat 

 all of the steam at the lower pressure. It is evident that a change in the 

 quality of the steam as it passed from one thermometer to another in its 

 course to the cylinders woald be at once detected by a change of tem- 

 perature. 



The conditions of the test were maintained for half an hour or more be- 

 fore observations were taken, after which time the thermometers were 

 read and other observations taken simultaneously at five minute intervals 

 for a second half hour. The following is a summary of results : 



Smoke box temperature 700. ° F 



Increase of smoke box temperature over temperature of steam in 



the boiler 345. ° F 



Temperature in T-head 335.30° F 



