A. Black smoke consists of small particles of carbon suspended in the
gases of combustion and indicates incomplete combustion. Black smoke is
not combustible, it is like lampblack and cannot be burned after having
been produced. The production of it can be prevented by suitable
arrangements and manipulation.
32. Q. Should the gas not burn in the fire-box, will it burn after it
enters the flues? Why?
A. Gas will not burn only a short distance in the flues of a boiler, as
the water absorbs the heat so quickly that the temperature of gas is
lowered below the igniting point.
33. Q. What is the effect on the flow of air through the fire from
opening the door? What on the burning of the gases? What on the flues
and sheets of the fire-box?
A. When the furnace door is opened, the flow of air through the grate is
stopped in proportion to the amount that passes through the door. The
vacuum will be filled from the quickest source and the door is closer
than some parts of the grate. The gases mix with the air from the door
and pass out through the flues; no combustion takes place, as the air
is not hot enough to unite with the gas. The flues and sheets of the box
will be caused to leak on account of the rapid contraction.
34. Q. Can the firing be done more effectively if the water level is
observed closely?
A. Yes, in order to know how much water there is in the boiler and
whether it is necessary to hurry the fire; if the boiler is full, it is
possible to prevent the pops opening by delaying the fire.
35. Q. How should the fire and water be handled in starting from a
terminal or other station?
A. The steam pressure should be near the maximum and there should be
sufficient water in the boiler to last until such time as the fire is
burning well so that the pressure will not be reduced when water is put
into the boiler. There should be a moderately heavy bed of fire well
burned and distributed evenly over the grates. After the fire is burning
well, the injector should be started lightly; the feed being gradually
increased so as not to cause any decrease of steam pressure.
36. Q. What is the purpose of a safety valve on a locomotive boiler? Why
are more than one used?
A. A safety valve is used to limit the maximum pressure in the boiler by
opening and allowing steam to escape. More than one safety valve are
used as additional protection against excessive pressure; one is set at
the maximum pressure and the others are set at two or three pounds above
the maximum pressure.
37. Q. What is usually the reason for steam being wasted from the safety
valve? What can be done to prevent this waste?
A. Careless firing, careless running. Both engineer and fireman work in
harmony to obtain the best results.
38. Q. What is the estimated waste of coal for each minute the safety
valve is open?
A. About fifteen pounds. The estimated waste of steam when an engine
pops equals every second all the heat obtained from a quarter pound of
coal. Safety valves usually remain open about half a minute, resulting
in the loss of about eight pounds of coal.
39. Q. What should be the condition of the fire on arriving at a station
where a stop is to be made?
A. On approaching the station where a stop is to be made, firing should
be stopped far enough back to allow the carbon gases to be consumed
before the throttle is closed, so there will be little or no black smoke
from the stack and yet have sufficient fire that it will not be
necessary to feed the fire again if a short stop is to be made until the
train is started and the engine cut back or nearly to the running
cut-off.
40. Q. How should you build up the fire when at stations in order to
avoid black smoke?
A. Put in small quantities of coal at a time, have the door slightly
open and have the blower on lightly; good judgment must be exercised by
the fireman.
41. Q. Why is it that if there is a thin fire with a hole in it the
steam pressure will fall at once?
A. Because too much cold air is drawn into the fire-box and through the
tubes, retarding combustion and cooling the fire-box and tubes.
42. Q. If the injector is to be used after throttle is shut off, how
should the fire be maintained?
A. A sufficient quantity of coal should be placed on the grates to
maintain the maximum steam pressure and the blower used to keep the fire
burning brightly.
43. Q. What would be the result of starting a heavy train or allowing
drivers to slip with the fire too thin on the grates?
A. The fire would be pulled off the grates and into the tubes, leaving
the fire bed full of holes and some of the fire remaining on the grates
turned over. Large quantities of cold air would be drawn in, resulting
in a rapid decrease of temperature and pressure. The tubes would
possibly start leaking and the fire would be in such condition that it
could not be built up properly in a long distance. Possibly the grates
would become clogged up with green coal--an excellent opportunity for
forming clinkers. In this condition, the engine would fail to make steam
for the entire trip.