Fig. 396.
The Fox Boiler with which the Metropolitan and other engines are equipped deserves an extended notice. It is shown in vertical section in Fig. [395], the arrows indicating the steam and water circulation. Its design, while simple, embodies some original ideas as to the arrangement of the tube surface method of circulation, etc.; it is a steam generator of the water tube type designed to meet the requirements peculiar to the fire service. The steam take-off and sectional view of shell with the tube system removed is shown in Fig. [397].
Note.—Working pressure can be generated in this boiler in six minutes from cold water, and the provisions for expansion are so near perfect that no bad effect is noticeable from such severe treatment. The manifold tube sections are tested to 600 pounds pressure, and are put together with great care; the manifolds are counter-bored to admit the full diameter of the tube, leaving none of the threaded portion exposed.
Plan showing Steam Take-Off.—Fig. 397.
Top View of Empty Shell, showing manifold Beam.—Fig. 398.
The boiler consists primarily of a simple annular shell heavily stay-bolted throughout, and constitutes a water-legged fire-box and steam reservoir; the principal heating surface of the boiler consists of straight water tubes, manifolded in sectional form and housed within the shell, the general scheme providing arrangements to make all connections readily accessible, and permitting the withdrawal from the boiler of any one or all of the several tube sections; the shell, being practically a permanent feature, need seldom be disturbed by reason of subsequent repairs or renewals of the tube systems.
It may be noted that the lower part, or water leg, of the shell is contracted for the purpose of facilitating the rapid generation of steam, and also providing the maximum grate area; at a point somewhat below the water line of the boiler, the inner shell is flanged inward, thereby enlarging the annular space between the inner and outer sheets for the purpose of providing a more copious reservoir.