LOCOMOTIVE FIRE TUBE TYPE OF BOILER.
The earliest of the modern steam boilers to come into use was the locomotive fire tube type, with a special firebox. By reference to the illustration ([Fig. 2]) you will see that the boiler cylinder is perforated with a number of tubes from 2 to 4 inches in diameter running from the large firebox on the left, through the boiler cylinder filled with water, to the smoke-box on the right, above which the smokestack rises.
FIG. 3. THE HUBER FIRE BOX.
It will be noticed that the walls of the firebox are double, and that the water circulates freely all about the firebox as well as all about the fire tubes. The inner walls of the firebox are held firmly in position by stay bolts, as will be seen in [Fig. 3], which also shows the position of the grate.
FIG. 4. HUBER RETURN FLUE BOILER.