[Illustration: Sectional View Freeman Vertical Boiler.]
Q. How is a Vertical Tubular Boiler generally constructed?
A. A cylindrical fire box set into the lower part of a vertical
cylindrical shell, the space between forming an annular “water leg.” An
opening is formed in both sheets for the fire door. The top of the fire
box serves as a flue sheet for numerous tubes or flues which extend
through the closed top of the outside shell, and through which the
products of combustion pass to the smoke stack. The upper portions of
the tubes are surrounded by steam.
Where this style of boiler is made for marine purposes, the upper part
of the tubes is submerged, and is called a submerged-flue boiler.
Q. What advantages has the vertical type of boiler?
A. Minimum floor space, portability, low cost of setting, and a wide
allowable variation in the water level.
Q. What disadvantages has this type?
A. Liability to leakage in the exposed upper ends of flues where they
are not submerged, deposits from impure water in the “water leg,” in
small sizes insufficient heating surface, though the latter fault can
be corrected by making the boiler very tall. Some of the very large
vertical boilers are remarkably efficient.