BOILERS.
The first boilers were made as a single cylinder of wrought iron set in
brick work, with provision for a fire under one end. This was used for
many years, but it produced steam very slowly and with great waste of
fuel.
The first improvement to be made in this was a fire flue running the
whole length of the interior of the boiler, with the fire in one end of
the flue. This fire flue was entirely surrounded by water.
Then a boiler was made with two flues that came together at the
smoke-box end. First one flue was fired and then the other,
alternately, the clear heat of one burning the smoke of the other when
it came into the common passage.
The next step was to introduce conical tubes by which the water could
circulate through the main fire flue (Galloway boiler).
[Illustration: FIG. 1. ORR & SEMBOWER’S STANDARD HORIZONTAL BOILER,
WITH FULL-ARCH FRONT SETTING.]
The object of all these improvements was to get larger heating surface.
To make steam rapidly and economically, the heating surface must be as
large as possible.
[Illustration: FIG. 2. GAAR, SCOTT & CO.’S LOCOMOTIVE BOILER.]
But there is a limit in that the boiler must not be cumbersome, it must
carry enough water, and have sufficient space for steam.
The stationary boiler now most commonly used is cylindrical, the fire
is built in a brick furnace under the sheet and returns through fire
tubes running the length of the boiler. (Fig. 1.)
LOCOMOTIVE FIRE TUBE TYPE OF BOILER.
The earliest of the modern steam boilers to come into use was the
locomotive fire tube type, with a special firebox. By reference to
the illustration (Fig. 2) you will see that the boiler cylinder is
perforated with a number of tubes from 2 to 4 inches in diameter
running from the large firebox on the left, through the boiler cylinder
filled with water, to the smoke-box on the right, above which the
smokestack rises.
[Illustration: FIG. 3. THE HUBER FIRE BOX.]
It will be noticed that the walls of the firebox are double, and that
the water circulates freely all about the firebox as well as all about
the fire tubes. The inner walls of the firebox are held firmly in
position by stay bolts, as will be seen in Fig. 3, which also shows the
position of the grate.
[Illustration: FIG. 4. HUBER RETURN FLUE BOILER.]
RETURN FLUE TYPE OF BOILER.
The return flue type of boiler consists of a large central fire flue
running through the boiler cylinder to the smoke box at the front end,
which is entirely closed. The smoke passes back through a number of
small tubes, and the smokestack is directly over the fire at the rear
of the boiler, though there is no communication between the fire at the
rear of the boiler and it except through the main flue to the front and
back through the small return flues. Fig. 4 illustrates this type of
boiler, though it shows but one return flue. The actual number may be
seen by the sectional view in Fig. 5.
[Illustration: FIG. 5. SECTION VIEW OF HUBER RETURN FLUE BOILER.]
The fire is built in one end of the main flue, and is entirely
surrounded by water, as will be seen in the illustration. The long
passage for the flame and heated gases enables the water to absorb a
maximum amount of the heat of combustion. There is also an element of
safety in this boiler in that the small flues will be exposed first
should the water become low, and less damage will be done than if the
large crown sheet of the firebox boiler is exposed, and this large
crown sheet is the first thing to be exposed in that type of boiler.
WATER TUBE TYPE OF BOILER.
The special difference between the fire tube boiler and the water tube
boiler is that in the former the fire passes through the tubes, while
in the latter the water is in the tubes and the fire passes around them.
[Illustration: FIG. 6. FREEMAN VERTICAL BOILER.]
In this type of boiler there is an upper cylinder (or more than one)
filled with water; a series of small tubes running at an angle from the
front or fire door end of the upper cylinder to a point below and back
of the grates, where they meet in another cylinder or pipe, which is
connected with the other end of the upper cylinder. The portions of the
tubes directly over the fire will be hottest, and the water here will
become heated and rise to the front end of the upper cylinder, while to
fill the space left, colder water is drawn in from the back pipe, from
the rear end of the upper cylinder, down to the lower ends of the water
tubes, to pass along up through them to the front end again.
This type of boiler gives great heating surface, and since the tubes
are small they will have ample strength with much thinner walls. Great
freedom of circulation is important in this type of boiler, there being
no contracted cells in the passage. This is not adapted for a portable
engine.
UPRIGHT OR VERTICAL TYPE OF BOILER.
In the upright type of boiler the boiler cylinder is placed on end,
the fire is built at the lower end, which is a firebox surrounded by a
water jacket, and the smoke and gases of combustion rise straight up
through vertical fire flues. The amount of water carried is relatively
small, and the steam space is also small, while the heating surface is
relatively large if the boiler is sufficiently tall. You can get up
steam in this type of boiler quicker than in any other, and in case of
the stationary engine, the space occupied is a minimum. The majority
of small stationary engines have this type of boiler, and there is a
traction engine with upright boiler which has been widely used, but
it is open to the objection that the upper or steam ends of the tubes
easily get overheated and so become leaky. There is also often trouble
from mud and scale deposits in the water leg, the bottom area of which
is very small.
DEFINITION OF TERMS USED IN CONNECTION WITH BOILERS.
_Shell_--The main cylindrical steel sheets which form the principal
part of the boiler.
_Boiler-heads_--The ends of the boiler cylinder.
_Tube Sheets_--The sheets in which the fire tubes are inserted at each
end of the boiler.
_Fire-box_--A nearly square space at one end of a boiler, in which the
fire is placed. Properly it is surrounded on all sides by a double
wall, the space between the two shells of these walls being filled with
water. All flat surfaces are securely fastened by stay bolts and crown
bars, but cylindrical surfaces are self-bracing.
_Water-leg_--The space at sides of fire-box and below it in which water
passes.
_Crown-sheet_--The sheet of steel at the top of the firebox, just under
the water in the boiler. This crown sheet is exposed to severe heat,
but so long as it is covered with water, the water will conduct the
heat away, and the metal can never become any hotter than the water
in the boiler. If, however, it is not covered with water, but only by
steam, it quickly becomes overheated, since the steam does not conduct
the heat away as the water does. It may become so hot it will soften
and sag, but the great danger is that the thin layer of water near this
overheated crown sheet will be suddenly turned into a great volume
of steam and cause an explosion. If some of the pressure is taken
off, this overheated water may suddenly burst into steam and cause an
explosion, as the safety valve blows off, for example (since the safety
valve relieves some of the pressure).
_Smoke-box_--The space at the end of the boiler opposite to that of the
fire, in which the smoke may accumulate before passing up the stack in
the locomotive type, or through the small flues in the return type of
boiler.
_Steam-dome_--A drum or projection at the top of the boiler cylinder,
forming the highest point which the steam can reach. The steam is taken
from the boiler through piping leading from the top of this dome, since
at this point it is least likely to be mixed with water, either through
foaming or shaking up of the boiler. Even under normal conditions the
steam at the top of the dome is drier than anywhere else.
_Mud-drum_--A cylindrical-shaped receptacle at the bottom of the boiler
similar to the steam-dome at the top, but not so deep. Impurities in
the water accumulate here, and it is of great value on a return flue
boiler. In a locomotive boiler the mud accumulates in the water leg,
below the firebox.
_Man-holes_--Are large openings into the interior of a boiler, through
which a man may pass to clean out the inside.
_Hand-holes_--Are smaller holes at various points in the boiler into
which the nozzle of a hose may be introduced for cleaning out the
interior. All these openings must be securely covered with steam-tight
plates, called man-hole and hand-hole plates.
_A boiler jacket_--A non-conducting covering of wood, plaster, hair,
rags, felt, paper, asbestos or the like, which prevents the boiler
shell from cooling too rapidly through radiation of heat from the
steel. These materials are usually held in place against the boiler by
sheet iron. An intervening air-space between the jacket and the boiler
shell will add to the efficiency of the jacket.
_A steam-jacket_--A space around an engine cylinder or the like which
may be filled with live steam so as to keep the interior from cooling
rapidly.
_Ash-pit_--The space directly under the grates, where the ashes
accumulate.
_Dead-plates_--Solid sheets of steel on which the fire lies the same as
on the grates, but with no openings through to the ash-pit. Dead-plates
are sometimes used to prevent cold air passing through the fire into
the flues, and are common on straw-burning boilers. They should seldom
if ever be used on coal or wood firing boilers.
_Grate Surface_--The whole space occupied by the grate-bars, usually
measured in square feet.
_Forced Draft_--A draft produced by any means other than the natural
tendency of the heated gases of combustion to rise. For example, a
draft caused by letting steam escape into the stack.
_Heating Surface_--The entire surface of the boiler exposed to the heat
of the fire, or the area of steel or iron sheeting or tubing, on one
side of which is water and on the other heated air or gases.
_Steam-space_--The cubical contents of the space which may be occupied
by steam above the water.
_Water-space_--The cubical contents of the space occupied by water
below the steam.
_Diaphragm-plate_--A perforated plate used in the domes of locomotive
boilers to prevent water dashing into the steam supply pipe. A dry-pipe
is a pipe with small perforations, used for taking steam from the
steam-space, instead of from a dome with diaphragm-plate.
THE ATTACHMENTS OF A BOILER.[1]
Before proceeding to a consideration of the care and management of
a boiler, let us briefly indicate the chief working attachments of
a boiler. Unless the nature and uses of these attachments are fully
understood, it will be impossible to handle the boiler in a thoroughly
safe and scientific fashion, though some engineers do handle boilers
without knowing all about these attachments. Their ignorance in many
cases costs them their lives and the lives of others.
Footnote 1: Unless otherwise indicated, cuts of fittings show those
manufactured by the Lunkenheimer Co., Cincinnati, Ohio.
The first duty of the engineer is to see that the boiler is filled with
water. This he usually does by looking at the glass water-gauge.
THE WATER GAUGE AND COCKS.
[Illustration: TWO-ROD WATER GAUGE.]
There is a cock at each end of the glass tube. When these cocks are
open the water will pass through the lower into the glass tube, while
steam comes through the other. The level of the water in the gauge will
then be the same as the level of the water in the boiler, and the water
should never fall out of sight below the lower end of the glass, nor
rise above the upper end.
Below the lower gauge cock there is another cock used for draining
the gauge and blowing it off when there is a pressure of steam on. By
occasionally opening this cock, allowing the heated water or steam to
blow through it, the engineer may always be sure that the passages
into the water gauge are not stopped up by any means. By closing the
upper cock and opening the lower, the passage into the lower may be
cleared by blowing off the drain cock; by closing the lower gauge cock
and opening the upper the passage from the steam space may be cleared
and tested in the same way when the drain cock is opened. If the glass
breaks, both upper and lower gauge cocks should be closed instantly.
[Illustration: GAUGE OR TRY COCK.]
In addition to the glass water gauge, there are the try-cocks for
ascertaining the level of the water in the boiler. There should be two
to four of these. They open directly out of the boiler sheet, and by
opening them in turn it is possible to tell approximately where the
water stands. There should be one cock near the level of the crown
sheet, or slightly above it, another about the level of the lower gauge
cock, another about the middle of the gauge, another about the level of
the upper gauge, and still another, perhaps, a little higher. But one
above and one below the water line will be sufficient. If water stands
above the level of the cock, it will blow off white mist when opened;
if the cock opens from steam-space, it will blow off blue steam when
opened.
The try-cocks should be opened from time to time in order to be sure
the water stands at the proper level in the boiler, for various things
may interfere with the working of the glass gauge. Try-cocks are often
called gauge cocks.
[Illustration: TRY COCK.]
THE STEAM GAUGE.
The steam gauge is a delicate instrument arranged so as to indicate by
a pointer the pounds of pressure which the steam is exerting within the
boiler. It is extremely important, and a defect in it may cause much
damage.
[Illustration: PRESSURE GAUGE.]
The steam gauge was invented in 1849 by Eugene Bourdon, of France.
He discovered that a flat tube bent in a simple curve, held fast at
one end, would expand and contract if made of proper spring material,
through the pressure of the water within the tube. The free end
operates a clock-work that moves the pointer.
It is important that the steam gauge be attached to the boiler by a
siphon, or with a knot in the tube, so that the steam may operate on
water contained in the tube, and the water cannot become displaced by
steam, since steam might interfere with the correct working of the
gauge by expanding the gauge tube through its excessive heat.
Steam gauges frequently get out of order, and should be tested
occasionally. This may conveniently be done by attaching them to a
boiler which has a correct gauge already on it. If both register alike,
it is probable that both are accurate.
[Illustration: STEAM GAUGE SIPHON.]
[Illustration: FRONT CYLINDER COCK.]
There are also self-testing steam gauges. With all pressure off,
the pointer will return to 0. Then a series of weights are arranged
which may be hung on the gauge and cause the pointer to indicate
corresponding numbers. The chief source of variation is in the
loosening of the indicator needle. This shows itself usually when the
pressure is off and the pointer does not return exactly to zero.
SAFETY VALVE.
The safety valve is a valve held in place by a weighted lever[2] or
by a spiral spring (on traction engines) or some similar device, and
is adjustable by a screw or the like so that it can be set to blow
off at a given pressure of steam, usually the rated pressure of the
boiler, which on traction engines is from 110 to 130 pounds. The valve
is supplied with a handle by which it can be opened, and it should
be opened occasionally to make sure it is working all right. When it
blows off the steam gauge should be noted to see that it agrees with
the pressure for which the safety valve was set. If they do not agree,
something is wrong; either the safety valve does not work freely, or
the steam gauge does not register accurately.
Footnote 2: This kind of safety valve is now being entirely discarded
as much more dangerous than the spring or pop valve.
[Illustration: SECTIONAL VIEW OF KUNKLE POP VALVE.]
[Illustration: SAFETY VALVE.]
The cut shows the Kunkle safety valve. To set it, unscrew the jam nut
and apply the key to the pressure screw. For more pressure, screw
down; for less, unscrew. After having the desired pressure, screw the
jam nut down tight on the pressure screw. To regulate the opening
and closing of the valve, take the pointed end of a file and apply it
to the teeth of the regulator. If valve closes with too much boiler
pressure, move the regulator to the left. If with too little, move the
regulator to the right.
This can be done when the valve is at the point of blowing off.
[Illustration: PHANTOM VIEW OF MARSH INDEPENDENT STEAM PUMP.]
Other types of valves are managed in a similar way, and exact
directions will always be furnished by the manufacturers.
FILLING THE BOILER WITH WATER.
There are three ways in which a boiler is commonly filled with water.
First, before starting a boiler it must be filled with water by hand,
or with a hand force-pump. There is usually a filler plug, which must
be taken out, and a funnel can be attached in its place. Open one of
the gauge cocks to let out the air as the water goes in.
When the boiler has a sufficient amount of water, as may be seen by
the glass water gauge, replace the filler plug. After steam is up the
boiler should be supplied with water by a pump or injector.
THE BOILER PUMP.
There are two kinds of pumps commonly used on traction engines, the
Independent pump, and the Cross-head pump.
The Independent pump is virtually an independent engine with pump
attached. There are two cylinders, one receiving steam and conveying
force to the piston; the other a water cylinder, in which a plunger
works, drawing the water into itself by suction and forcing it out
through the connection pipe into the boiler by force of steam pressure
in the steam cylinder.
[Illustration: STRAIGHT GLOBE VALVE.]
[Illustration: ANGLE GLOBE VALVE.]
It is to be noted that all suction pumps receive their water by reason
of the pressure of the atmosphere on the surface of the water in the
supply tank or well. This atmospheric pressure is about 15 pounds to
the square inch, and is sufficient to support a column of water 28 to
33 feet high, 33 feet being the height of a column of water which the
atmosphere will support theoretically at about sea level. At greater
altitudes the pressure of the atmosphere decreases. Pumps do not work
very well when drawing water from a depth over 20 or 22 feet.
Water can be forced to almost any height by pressure of steam on the
plunger, and it is taken from deep wells by deep well pumps, which suck
the water 20 to 25 feet, and force it the rest of the way by pressure
on a plunger.
The amount of water pumped is regulated by a cock or globe valve in the
suction pipe.
A Cross-head boiler pump is a pump attached to the cross-head of an
engine. The force of the engine piston is transmitted to the plunger of
the pump.
The pump portion works exactly the same, whether of the independent or
cross-head kind.
The cut represents an independent pump that uses the exhaust steam to
heat the water as it is pumped (Marsh pump).
[Illustration: VALVE WITH INTERNAL SCREW.]
Every boiler feed-pump must have at least two check valves.
A check valve is a small swinging gate valve (usually) contained in a
pipe, and so arranged that when water is flowing in one direction the
valve will automatically open to let the water pass, while if water
should be forced in the other direction, the valve will automatically
close tight and prevent the water from passing.
[Illustration: SECTIONAL VIEW OF SWING CHECK VALVE.]
There is one check valve in the supply pipe which conducts the water
from the tank or well to the pump cylinder. When the plunger is drawn
back or raised, a vacuum is created in the pump cylinder and the
outside atmospheric pressure forces water through the supply pipe
into the cylinder, and the check valve opens to let it pass. When the
plunger returns, the check valve closes, and the water is forced into
the feed-pipe to the boiler.
[Illustration: SECTIONAL VIEW OF CASE HEATER.]
There are usually two check valves between the pump cylinder and the
boiler, both swinging away from the pump or toward the boiler. In
order that the water may flow steadily into the boiler there is an air
chamber, which may be partly filled with water at each stroke of the
plunger. As the water comes in, the air must be compressed, and as it
expands it forces the water through the feed pipe into the boiler in
a steady stream. There is one check valve between the pump cylinder
and the air chamber, to prevent the water from coming back into the
cylinder, and another between the air chamber and the boiler, to
prevent the steam pressure forcing itself or the water from the boiler
or water heater back into the air chamber.
[Illustration: SECTIONAL VIEW OF PENBERTHY INJECTOR.]
[Illustration: U. S. AUTOMATIC INJECTOR.
(American Injector Co.)]
All three of these check valves must work easily and fit tight if the
pump is to be serviceable. They usually close with rubber facings which
in time will get worn, and dirt is liable to work into the hinge and
otherwise prevent tight and easy closing. They can always be opened for
inspection, and new ones can be put in when the old are too much worn.
Only cold water can be pumped successfully, as steam from hot water
will expand, and so prevent a vacuum being formed. Thus no suction will
take place to draw the water from the supply source.
There should always be a globe valve or cock in the feed pipe near the
boiler to make it possible to cut out the check valves when the boiler
is under pressure. _It is never to be closed except_ when required for
this purpose.
Before passing into the boiler the water from the pump goes through the
_heater_. This is a small cylinder, with a coil of pipe inside. The
feed pipe from the pump is connected with one end of this inner coil of
pipe, while the other end of the coil leads into the boiler itself. The
exhaust steam from the engine cylinder is admitted into the cylinder
and passes around the coil of pipe, afterwards coming out of the smoke
stack to help increase the draft. As the feed water passes through this
heater it becomes heated nearly to boiling before it enters the boiler,
and has no tendency to cool the boiler off. Heating the feed water
results in an economy of about 10 per cent.
[Illustration: AUTOMATIC INJECTOR.]
_The Injector_ is another means of forcing water from a supply tank or
well into the boiler, and at the same time heating it, by use of steam
from the boiler. It is a necessity when a cross-head pump is used,
since such a pump will not work when the engine is shut down. It is
useful in any case to heat the water before it goes into the boiler
when the engine is not working and there is no exhaust steam for the
heater.
There are various types of injectors, but they all work on practically
the same principle. The steam from the boiler is led through a tapering
nozzle to a small chamber into which there is an opening from a water
supply pipe. This steam nozzle throws out its spray with great force
and creates a partial vacuum in the chamber, causing the water to flow
in. As the pressure of the steam has been reduced when it passes into
the injector, it cannot, of course, force its way back into the boiler
at first, and finds an outlet at the overflow. When the water comes in,
however, the steam jet strikes the water and is condensed by it. At the
same time it carries the water and the condensed steam along toward the
boiler with such force that the back pressure of the boiler is overcome
and a stream of heated water is passed into it. In order that the
injector may work, its parts must be nicely adjusted, and with varying
steam pressures it takes some ingenuity to get it started. Usually
the full steam pressure is turned on and the cock admitting the water
supply is opened a varying amount according to the pressure.
First the valve between the check valve and the boiler should be
opened, so that the feed water may enter freely; then open wide the
valve next the steam dome, and any other valve between the steam supply
pipe and the injector; lastly open the water supply valve. If water
appears at the overflow, close the supply valve and open it again,
giving it just the proper amount of turn. The injector is regulated by
the amount of water admitted.
[Illustration: PLAIN WHISTLE.]
In setting up an injector of any type, the following rules should be
observed:
All connecting pipes as straight and short as possible.
The internal diameter of all connecting pipes should be the same or
greater than the diameter of the hole in the corresponding part of the
injector.
When there is dirt or particles of wood or other material in the source
of water supply, the end of the water supply pipe should be provided
with a strainer. Indeed, invariably a strainer should be used. The
holes in this strainer must be as small as the smallest opening in the
delivery tube, and the total area of the openings in the strainer must
be much greater than the area of the water supply (cross-section).
The steam should be taken from the highest part of the dome, to avoid
carrying any water from the boiler over with it. Wet steam cuts and
grooves the steam nozzle. The steam should not be taken from the pipe
leading to the engine unless the pipe is quite large.
Before using new injectors, after they are fitted to the boiler it is
advisable to disconnect them and clean them out well by letting steam
blow through them or forcing water through. This will prevent lead or
loose scale getting into the injector when in use.
Set the injector as low as possible, as it works best with smallest
possible lift.
_Ejectors and jet pumps_ are used for lifting and forcing water by
steam pressure, and are employed in filling tanks, etc.
BLAST AND BLOW-OFF DEVICES.
In traction engines there is small pipe with a valve, leading into
the smoke stack from the boiler. When the valve is opened, the steam
allowed to blow off into the smoke stack will create a vacuum and so
increase the draft. Blast or blow pipes are used only in starting the
fire, and are of little value before the steam pressure reaches 15
pounds or so.
The exhaust nozzle from the engine cylinder also leads into the smoke
stack, and when the engine is running the exhaust steam is sufficient
to keep up the draft without using the blower.
_Blow-off cocks_ are used for blowing sediment out of the bottom of a
boiler, or blowing scum off the top of the water to prevent foaming. A
boiler should never be blown out at high pressure, as there is great
danger of injuring it. Better let the boiler cool off somewhat before
blowing off.
SPARK ARRESTER.
Traction engines are supplied as a usual thing with spark arresters if
they burn wood or straw. Coal sparks are heavy and have little life,
and with some engines no spark arrester is needed. But there is great
danger of setting a fire if an engine is run with wood or straw without
the spark arrester.
[Illustration: DIAMOND SPARK ARRESTER.]
Spark arresters are of different types. The most usual form is a large
screen dome placed over the top of the stack. This screen must be kept
well cleaned by brushing, or the draft of the engine will be impaired
by it.
In another form of spark arrester, the smoke is made to pass through
water, which effectually kills every possible spark.
The _Diamond Spark Arrester_ does not interfere with the draft and
is so constructed that all sparks are carried by a counter current
through a tube into a pail where water is kept. The inverted cone, as
shown in cut, is made of steel wire cloth, which permits smoke and gas
to escape, but no sparks. There is no possible chance to set fire to
anything by sparks. It is adapted to any steam engine that exhausts
into the smoke stack.