Each
alteration in the position of the reversing lever or screw, as well as in
the degree of opening of the steam regulator or the blast pipe, requires a
corresponding alteration of the fire. Generally the driver generally
passes the word when he intends shutting off steam, so that the alteration
in the firing can be effected before the steam is actually shut off; and
in this way the regulation of the fire and that of the steam are virtually
done together. All this care is necessary to prevent smoke, which is
nothing less than a waste of fuel. When, for instance, the train arrives
at the top of a bank, which it has to go down with the brakes on, exactly
at the moment of the driver shutting off the steam and shifting the
reversing lever into full forward gear, the petroleum and steam are shut
off from the spray injector, the ash-pan doors are closed, and if the
incline be a long one, the revolving iron damper over the chimney top is
moved into position, closing the chimney, though not hermetically. The
accumulated heat is thereby retained in the fire-box; and the steam even
rises in pressure, from the action of the accumulated heat alone. As soon
as the train reaches the bottom of the incline and steam is again
required, the first thing done is to uncover the chimney top; then the
steam is turned on to the spray injector, and next a small quantity of
petroleum is admitted, but without opening the ash-pan doors, a small fire
being rendered possible by the entrance of air around the spray injector,
as well as by possible leakage past the ash-pan doors.
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