THE PROCESS OF BOILING. Let it be remembered that the boiling spoken
of so often is really caused by the formation of the steam particles,
and that without the boiling there can be but a very slight quantity of
steam produced.
While pure water boils at 212°, if it is saturated with common salt,
it boils only on attaining 224°, alum boils at 220°, sal ammoniac at
236°, acetate of soda at 256°, pure nitric acid boils at 248°, and pure
sulphuric acid at 620°.
ON THE FIRST APPLICATION OF HEAT to water small bubbles soon begin to
form and rise to the surface; these consist of air, which all water
contains dissolved in it. When it reaches the boiling point the bubbles
that rise in it are principally steam.
IN THE CASE OF A NEW PLANT, or where the boiler has some time been
idle it is frequently advisable to build a small fire in the base of
the chimney before starting the boiler fires. This will serve to heat
the chimney and drive out any moisture that may have collected in the
interior and will frequently prevent the disagreeable smoking that
often follows the building of a fire in the furnace.
ALWAYS BEAR IN MIND that the steam in the boilers and engines is
pressing outward on the walls that confine it in every direction; and
that the enormous forces you are handling, warn you to be careful.
When starting fires close the gauge cocks and safety valve as soon as
steam begins to form.
GO SLOW. It is necessary to start all new boilers very slowly. The
change from hot to cold is an immense one in its effects on the
contraction and expansion of the boiler, the change of dimension
by expansion is a force of the greatest magnitude and cannot be
over-estimated. Leaks which start in boilers that were well made and
perfectly tight can be attributed to this cause. Something must give
if fires are driven on the start, and this entails trouble and expense
that there is no occasion for. This custom applies to engines and steam
pipes as well as to boilers. No one of any experience will open a stop
valve and let a full head of live steam into a cold line of pipe or a
cold engine.
To preserve the grate bars from excessive heat, when first firing a
boiler, it is well to sprinkle a thin layer of coal upon the grates
before putting in the shavings and wood for starting the fire. This
practice tends greatly to prolong the life of the grate-bars.
The fuel should generally be dry when used. Hard coal, however, may be
dampened a little to good advantage, as it is then less liable to crowd
and will burn more freely.
Air, high temperature and sufficient time are the principal points in
firing a steam boiler.
In first firing up make sure that the throttle valve is closed, in
order that the steam first formed may not pass over into the engine
cylinder and fill it with water of condensation. If the throttle valve
leak steam it should be repaired at the first opportunity.
Keep all heating surfaces free from soot and ashes.
Radiant rays go in all directions, yet they act in the most efficient
manner when striking a surface exactly at a right angle to their
line of movement. The sides of a fire-box are for that reason not
as efficient as the surface over the fire, and a flat surface over
the fire is the best that can be had, so far as that fact alone is
concerned.
When combustion is completed in a furnace, then the balance of the
boiler beyond the bridge wall can be utilized for taking up heat
from the gases. The most of this heat has to be absorbed by actual
contact; thus by the tubes the gases are finally divided, allowing that
necessary contact.
Combustion should be completed on the grates for the reason that
it can be effected there at the highest temperature. When this is
accomplished, the fullest benefit is had from radiant heat striking the
bottom of the boiler—_it is just there that the bulk of the work is
done_.
There must necessarily be some waste of heat by its passing up the
chimney to maintain draft. It is well to have the gases, as they enter
the chimney, as much below 600 deg. F. (down to near the temperature of
the steam) as you can and yet maintain perfect combustion.
Every steam engine has certain well-defined sounds in action which we
call noises, for want of a better term, and it is upon them and their
continuance that an engineer depends for assurance that all is going
well.
This remark also applies to the steam boiler, which has, so to speak,
a language of its own, varying in volume from the slight whisper which
announces a leaking joint to the thunder burst which terribly follows a
destructive explosion. The hoarse note of the safety-valve is none the
less significant because common.
The dampers and doors to the furnace and ash-pit should always be
closed after the fire has been drawn, in order to keep the heat of the
boiler as long as possible.
But the damper must never be entirely closed while there is fire on the
grate, as explosions dangerous in their character might occur in the
furnace from the accumulated gases.
Flues or tubes should often be swept, as soot, in addition to its
liability to becoming charged with a corroding acid, is a non-conductor
of heat, and the short time spent in cleaning them will be repaid by
the saving of labor in keeping up steam. In an establishment where they
used but half a ton of bituminous coal per day, the time of raising
steam in the morning was fifty per cent. longer when the tubes were
unswept for one week than when they were swept three times a week.
SMOKE will not be seen _if combustion is perfect_. Good firing will
abate most of the smoke.
Coals, at the highest furnace temperature, radiate much heat, whereas
gases ignited at and beyond the bridge wall radiate comparatively
little heat—it is a law in nature for a solid body highly heated to
radiate heat to another solid body.
DRY AND CLEAN is the condition in which the boiler should be kept,
_i.e._, dry outside and clean both inside and out.
To haul his furnace fire and open the safety valve before seeking his
own safety or the preservation of property, is the duty of the fireman
in the event of fire threatening to burn a whole establishment.
Many, now prominent, engineers have made their first reputation by
remembering to do this at a critical time.
WHEN WATER IS PUMPED into the boiler or allowed to run in, some opening
must be given for the escape of the contained air; usually the most
convenient way is to open the upper gauge cock after the fire has been
lighted until cloudy steam begins to escape.