From the sectional view of the boiler illustrated in Fig. The flues give to the boiler the largest part of its heating surface. It is the flues which largely affect the life of the boiler and, therefore, the life of the locomotive, for this reason it is quite necessary to properly install and maintain them. A large amount of the repair costs is directly traceable to the flues. These conditions cause the joints to break at the flue sheets.
Cold air entering the fire-box door is another source of flue trouble.
It is to these details that careful attention must be given in order to alleviate flue failures. Flues should be made of the best quality of charcoal iron, lap-welded, and subjected to severe tests before being used. They vary in length from about 15 to 20 feet, the length depending on the construction of the boiler and locomotive as a whole. The tubes are supported at each end by letting them extend through the tube sheets. It is in the setting of the tubes that great care should be exercised.