ion gradually
carries the fuel as it is burned toward the rear and bottom of the
furnace. At the bottom of the grates flat dumping sections are supplied
for completing the combustion and for cleaning. The fuel is partly
burned or coked on the upper portion of the grates, the volatile gases
driven off in this process for a perfect action being ignited and burned
in their passage over the bed of burning carbon lower on the grates, or
on becoming mixed with the hot gases in the furnace chamber. In the
second class the fuel is fed from the sides of the furnace for its full
depth from front to rear onto grates inclined toward the center of the
furnace. It is moved by rocking bars and is gradually carried to the
bottom and center of the furnace as combustion advances. Here some type
of a so-called clinker breaker removes the refuse.

Underfeed Stokers are either horizontal or inclined. The fuel is fed
from underneath, either continuously by a screw, or intermittently by
plungers. The principle upon which these stokers base their claims for
efficiency and smokelessness is that the green fuel is fed under the
coked and burning coal, the volatile gases from this fresh fuel being
heated and ignited in their passage through the hottest portion of the
fire on the top. In the horizontal classes of underfeed stokers, the
action of a screw carries the fuel back through a retort from which it
passes upward, as the fuel above is consumed, the ash being finally
deposited on dead plates on either side of the retort, from which it can
be removed. In the inclined class, the refuse is carried downward to the
rear of the furnace where there are dumping plates, as in some of the
overfeed types.

Underfeed stokers are ordinarily operated with a forced blast, this in
some cases being operated by the same mechanism as the stoker drive,
thus automatically meeting the requirements of various combustion rates.

Traveling Grates are of the class best illustrated by chain grate
stokers. As implied by the name these consist of endless grates composed
of short sections of bars, passing over sprockets at the front and rear
of the furnace. Coal is fed by gravity onto the forward end of the
grates through suitable hoppers, is ignited under ignition arches and is
carried with the grate toward the rear of the furnace as its combustion
progresses. When operated properly, the combustion is completed as the
fire reaches the end of the grate and the refuse is