In the back counties of England for many generations before the steam
engine was evolved from the brains of Trevithick, Watt and Stephenson,
the word “stoke” was used, meaning to “stir the fire.” The word was
derived from an ancient word, stoke, meaning a stick, stock or post.
To-day there are very many men who are called “stokers,” employed
principally on locomotive engines, steam vessels, etc., and then there
is the “stoke hole,” so-called, in which they do their work.
[Illustration: Mechanical Stoker]
But, now comes the “mechanical stoker,” which is well named, as its
office is to feed and “stir the fire” by a machine, thus relieving
the fireman from much excessively hard toil and allowing the time and
energy thus saved to be more profitably used elsewhere. The figure
shows a view of the American Stoker which is a device of the most
advanced type.
The principal parts of the machine are: 1, the Hopper, which may
be filled either by hand shoveling or by elevating and conveying
machinery; 2, the Conveyor Screw, which forces the coal, or indeed, any
description of fuel, forward to the 3, Magazine, shown in the figure
to the left; 4, a Driving Mechanism, which is a steam motor arranged
conveniently in front of the hopper; 5, the Retort, so called from its
being the place (above the conveyor) where the coal is distilled into
gas.
NOTE.—An illustrated printed description of this machine is issued and
sent free upon application by the makers. The American Stoker Co.,
Washington Life Building, Cor. Broadway and Liberty St., New York.
The rate of feeding coal is controlled by the speed of the motor, this
being effected by the simple means of throttling the steam in the
supply pipe to the motor. The shields covering the motor effectually
protect the mechanism from dirt and dust. The motor has a simple
reciprocating piston; its piston rod carries a crosshead, which, by
means of suitable connecting links, operates a rocker arm having a pawl
mechanism, which in turn actuates the ratchet wheel attached to the
conveyor shaft. The stoker is thus entirely self-contained and complete
in itself.
A screw conveyor or worm is located in the conveyor pipe and extends
the entire length of the magazine. Immediately beneath the conveyor
pipe is located the wind-box, having an opening beneath the hopper.
At this point is connected the piping for the air supply, furnished at
low pressure by a volume blower. The other end of the wind-box opens
into the air space between the magazine and outer casing. The upper
edge of the magazine is surrounded by tuyeres, or air blocks, these
being provided with openings for the discharge of air, inwardly and
outwardly.
The stoker rests on the front and rear bearing bars; the space between
the sides of the stoker and side walls is filled with iron plates,
termed “dead grates.” Steam is carried to the motor by a 3/4-inch steam
pipe. The exhaust steam from the motor is discharged into the ash pit.
In operation the coal is fed into the hopper, carried by the conveyor
into the magazine, which it fills, “overflows” on both sides, and
spreads upon the sides of the grates. The coal is fed slowly and
continuously, and, approaching the fire in its upward course, it is
slowly roasted and coked, and the gases released from it are taken up
by the fresh air entering through the tuyeres, which explodes these
gases and delivers the coal as coke on the grates above. The continuous
feeding gives a breathing motion to this coke bed, thus keeping it open
and free for the circulation of air.
It will be noted that in this machine the fuel is introduced from the
bottom of the bed of fuel, technically speaking, upon the principle of
“underfeeding.”