The mud drum should be periodically examined and the sediment removed; blow-off cocks and check valves should be examined each time the boiler is cleaned; when surface blow-cocks are used they should be often opened for a few minutes at a time; be sure that all openings for air to boiler or flues except through the fire, are carefully stopped.
If a boiler is not required for some time, empty and dry it thoroughly. If this is impracticable, fill it quite full of water and put in a quantity of washing soda; and external parts exposed to dampness should receive a coating of linseed oil. Avoid all dampness in seatings or coverings and see that no water comes in contact with the boiler from any cause.
Although this form of boiler is not liable to destructive explosion, the same care should be exercised to avoid possible damage to boilers and expensive delays.
SECTIONAL BOILERS.
Probably one of the first sectional boilers brought into practical use is one made of hollow cast iron spheres, each 8 inches in diameter, externally, and 3⁄8 of an inch thick, connected by curved necks 31⁄2 inches in diameter. These spheres are held together by wrought iron bolts and caps, and in one direction are cast in sets of 2 or 4, which are afterwards drawn together so as to give more or less heating surface to the boiler according to the number used.
NOTE.
Owing to their multiplication of parts all sectional, including water tube boilers, should be made with unusual care in their details of construction, setting, fittings and proportions. It is to the attention paid to these “points” that the sectional boilers are now coming into more general favor.
LOCOMOTIVE BOILERS.
The essential features of locomotive boilers are dictated by the duties which they have to perform under peculiar conditions. The size and the weight are limited by the fact that the boiler has to be transported rapidly from place to place, and also that it has to fit in between the frames of the locomotive; while at the same time, the pressure of the steam has to be very great in order that with comparatively small cylinder the engine may develop great power; moreover, the quantity of water which has to be evaporated in a given time is very considerable. To fulfil these latter conditions a large quantity of coal must be burned on a fire grate of limited area; hence intense combustion is necessary under a forced blast. To utilize advantageously the heat thus generated, a large heating surface must be provided and this can only be obtained by passing the products of combustion through a great number of tubes of small diameter.