STEAM BOILERS 323 



general use. With only a few changes, it is the same 

 now. By referring to Fig. 218, it will be noticed that 

 the fire box is practically built into the rear end of the 

 boiler barrel. Extending from the rear tube sheet and 

 through the entire length of boiler barrel are the fire 

 tubes, which are generally about two inches in diameter. 

 Surrounding the fire box and fire tubes is the water. 

 This gives abundance of heating surface, also freedom of 

 circulation. As the sides of the fire box are nearly flat, 

 they will easily collapse under the pressure of the steam 



FIG. 217 RETURN-FLUE TYPE OF INTERNALLY FIRED BOILER 



unless supported by stay bolts at intervals of every few 

 inches. 



The steam dome can be located anywhere, but it is 

 generally placed about midway between front and rear 

 ends. A pipe takes the steam from the top of the dome, 

 carries it down through the steam space, where it is dried, 

 then out wherever convenient. 



Generally the blow r -off is at the bottom and in front 

 of the fire box. The water glass is placed about on a 



