_THE STEAM-ENGINE OF TO-DAY._
... "And, last of all, with inimitable power, and 'with whirlwind
sound,' comes the potent agency of steam. In comparison with the
past, what centuries of improvement has this single agent comprised
in the short compass of fifty years! Everywhere practicable,
everywhere efficient, it has an arm a thousand times stronger than
that of Hercules, and to which human ingenuity is capable of fitting
a thousand times as many hands as belonged to Briareus. Steam is
found in triumphant operation on the seas; and, under the influence
of its strong propulsion, the gallant ship--
'Against the wind, against the tide,
Still steadies with an upright keel.'
It is on the rivers, and the boatman may repose on his oars; it is
on highways, and exerts itself along the courses of land-conveyance;
it is at the bottom of mines, a thousand feet below the earth's
surface; it is in the mills, and in the workshops of the trades. It
rows, it pumps, it excavates, it carries, it draws, it lifts, it
hammers, it spins, it weaves, it prints. It seems to say to men, at
least to the class of artisans: 'Leave off your manual labor; give
over your bodily toil; bestow but your skill and reason to the
directing of my power, and I will bear the toil, with no muscle to
grow weary, no nerve to relax, no breast to feel faintness!' What
further improvement may still be made in the use of this astonishing
power it is impossible to know, and it were vain to conjecture. What
we do know is, that it has most essentially altered the face of
affairs, and that no visible limit yet appears beyond which its
progress is seen to be impossible."--DANIEL WEBSTER.
THE PERIOD OF REFINEMENT--1850 TO DATE.
By the middle of the present century, as we have now seen, the
steam-engine had been applied, and successfully, to every great
purpose for which it was fitted. Its first application was to the
elevation of water; it next was applied to the driving of mills and
machinery; and it finally became the great propelling power in
transportation by land and by sea.
At the beginning of the period to which we are now come, these
applications of steam-power had become familiar both to the engineer
and to the public. The forms of engine adapted to each purpose had
been determined, and had become usually standard. Every type of the
modern steam-engine had assumed, more or less closely, the form and
proportions which are now familiar; and the most intelligent designers
and builders had been taught--by experience rather than by theory, for
the theory of the steam-engine had then been but little investigated,
and the principles and laws of thermo-dynamics had not been traced in
their application to this engine--the principles of construction
essential to successful practice, and were gradually learning the
relative standing of the many forms of steam-engine, from among which
have been preserved a few specially fitted for certain specific
methods of utilization of power.
During the years succeeding the date 1850, therefore, the growth of
the steam-engine had been, not a change of standard type, or the
addition of new parts, but a gradual improvement in forms,
proportions, and arrangements of details; and this period has been
marked by the dying out of the forms of engine least fitted to succeed
in competition with others, and the retention of the latter has been
an example of "the survival of the fittest." This has therefore been a
Period of Refinement.
During this period invention has been confined to details; it has
produced new forms of parts, new arrangements of details; it has
devised an immense variety of valves, valve-motions, regulating
apparatus, and a still greater variety of steam-boilers and of
attachments, essential and non-essential, to both engines and boilers.
The great majority of these peculiar devices have been of no value,
and very many of the best of them have been found to have about equal
value. All the well-known and successful forms of engine, when equally
well designed and constructed and equally well managed, are of very
nearly equal efficiency; all of the best-known types of steam-boiler,
where given equal proportions of grate to heating-surface and equally
well designed, with a view to securing a good draught and a good
circulation of water, have been found to give very nearly equally good
results; and it has become evident that a good knowledge of principles
and of practice, on the part of the designer, the constructor, and the
manager of the boiler, is essential in the endeavor to achieve
economical success; that good engineering is demanded, rather than
great ingenuity. The inventor has been superseded here by the
engineer.
The knowledge acquired in the time of Watt, of the essential
principles of steam-engine construction, has since become generally
familiar to the better class of engineers. It has led to the selection
of simple, strong, and durable forms of engine and boiler, to the
introduction of various kinds of valves and of valve-gearing, capable
of adjustment to any desired range of expansive working, and to the
attachment of efficient forms of governor to regulate the speed of the
engine, by determining automatically the point of cut-off which will,
at any instant, best adjust the energy exerted by the expanding steam
to the demand made by the work to be done.
The value of high pressures and considerable expansion was recognized
as long ago as in the early part of the present century, and Watt, by
combining skillfully the several principal parts of the steam-engine,
gave it very nearly the shape which it has to-day. The compound
engine, even, as has been seen, was invented by contemporaries of
Watt, and the only important modifications since his time have
occurred in details. The introduction of the "drop cut-off," the
attachment of the governor to the expansion-apparatus in such a manner
as to determine the degree of expansion, the improvement of
proportions, the introduction of higher steam and greater expansion,
the improvement of the marine engine by the adoption of
surface-condensation, in addition to these other changes, and the
introduction of the double-cylinder engine, after the elevation of
steam-pressure and increase of expansion had gone so far as to justify
its use, are the changes, therefore, which have taken place during
this last quarter-century. It began then to be generally understood
that expansion of steam produced economy, and mechanics and inventors
vied with each other in the effort to obtain a form of valve-gear
which should secure the immense saving which an abstract consideration
of the expansion of gases according to Marriotte's law would seem to
promise. The counteracting phenomena of internal condensation and
reevaporation, of the losses of heat externally and internally, and of
the effect of defective vacuum, defective distribution of steam, and
of back-pressure, were either unobserved or were entirely overlooked.
It was many years, therefore, before engine-builders became convinced
that no improvement upon existing forms of expansion-gear could secure
even an approximation to theoretical efficiency.
The fact thus learned, that the benefit of expansive working has a
limit which is very soon reached in ordinary practice, was not then,
and has only recently become, generally known among our steam-engine
builders, and for several years, during the period upon which we now
enter, there continued the keenest competition between makers of rival
forms of expansion-gear, and inventors were continually endeavoring to
produce something which should far excel any previously-existing
device.
In Europe, as in the United States, efforts to "improve" standard
designs have usually resulted in injuring their efficiency, and in
simply adding to the first cost and running expense of the engines,
without securing a marked increase in economy in the consumption of
steam.
SECTION I.--STATIONARY ENGINES.
"STATIONARY ENGINES" had been applied to the operation of
mill-machinery, as has been seen, by Watt and by Murdoch, his
assistant and pupil; and Watt's competitors, in Great Britain and
abroad, had made considerable progress before the death of the great
engineer, in its adaptation to its work. In the United States, Oliver
Evans had introduced the non-condensing high-pressure stationary
engine, which was the progenitor of the standard engine of that type
which is now used far more generally than any other form. These
engines were at first rude in design, badly proportioned, rough and
inaccurate as to workmanship, and uneconomical in their consumption of
fuel. Gradually, however, when made by reputable builders, they
assumed neat and strong shapes, good proportions, and were well made
and of excellent materials, doing their work with comparatively little
waste of heat or of fuel.
One of the neatest and best modern designs of stationary engine for
small powers is seen in Fig. 93, which represents a "vertical
direct-acting engine," with base-plate--a form which is a favorite
with many engineers.
The engine shown in the engraving consists of two principal parts, the
cylinder and the frame, which is a tapering column having openings in
the sides, to allow free access to all the working parts within. The
slides and pillow-blocks are cast with the column, so that they cannot
become loose or out of line; the rubbing surfaces are large and easily
lubricated. Owing to the vertical position, there is no tendency to
side wear of cylinder or piston. The packing-rings are self-adjusting,
and work free but tight. The crank is counterbalanced; the crank-pin,
cross-head pin, piston-rod, valve-stem, etc., are made of steel; all
the bearing surfaces are made extra large, and are accurately fitted;
and the best quality of Babbitt-metal only used for the
journal-bearings.
[Illustration: FIG. 93.--Vertical Stationary Steam-Engine.]
The smaller sizes of these engines, from 2 to 10 horse-power, have
both pillow-blocks cast in the frame, giving a bearing each side of
the double cranks. They are built by some constructors in quantities,
and parts duplicated by special machinery (as in fire-arms and
sewing-machines), which secures great accuracy and uniformity of
workmanship, and allows of any part being quickly and cheaply
replaced, when worn or broken by accident. The next figure is a
vertical section through the same engine.
[Illustration: FIG. 94.--Vertical Stationary Steam-Engine. Section.]
Engines fitted with the ordinary rigid bearings require to be erected
on a firm foundation, and to be kept in perfect line. If, by the
settling of the foundation, or from any other cause, they get out of
line, heating, cutting, and thumping result. To obviate this, modern
engines are often fitted with self-adjusting bearings throughout; this
gives the engine great flexibility and freedom from friction. The
accompanying cuts show clearly how this is accomplished. The
pillow-block has a spherical shell turned and fitted into the
spherically-bored pillow-block, thus allowing a slight angular motion
in any direction. The connecting-rod is forged in a single piece,
without straps, gibs, or key, and is mortised through at each end for
the reception of the brass boxes, which are curved on their backs, and
fit the cheek-pieces, between which they can turn to adjust themselves
to the pins, in the plane of the axis of the rod. The adjustment for
wear is made by wedge-blocks and set screws, as shown, and they are so
constructed that the parts cannot get loose and cause a break-down.
The cross-head has adjustable gibs on each side, turned to fit the
slides, which are cast solidly in the frame, and bored out exactly in
the line with the cylinder. This permits it freely to turn on its
axis, and, in connection with the adjustable boxes in the
connecting-rod, allows a perfect self-adjustment to the line of the
crank-pin. The out-board bearing may be moved an inch or more out of
position in any direction, without detriment to the running of the
engine, all bearings accommodating themselves perfectly to whatever
position the shaft may assume.
The ports and valve-passages are proportioned as in locomotive
practice. The valve-seat is adapted to the ordinary plain slide or
D-valve, should it be preferred, but the balanced piston slide-valve
works with equal ease whether the steam-pressure is 10 or 100 pounds,
and at the same time gives double steam and exhaust openings, which
greatly facilitates the entrance of the steam to, and its escape from,
the cylinder, thus securing a nearer approach to boiler-pressure and a
less back-pressure, saving the power required to work an ordinary
valve, and reducing the wear of valve-gear.
This is a type of engine frequently seen in the United States, but
more rarely in Europe. It is an excellent form of engine. The vertical
direct-acting engine is sometimes, though rarely, built of very
considerable size, and these large engines are more frequently seen in
rolling-mills than elsewhere.
Where much power is required, the stationary engine is usually an
horizontal direct-acting engine, having a more or less effective
cut-off valve-gear, according to the size of engine and the cost of
fuel. A good example of the simpler form of this kind of engine is the
small horizontal slide-valve engine, with independent cut-off valve
riding on the back of the main valve--a combination generally known
among engineers as the Meyer system of valve-gear. This form of
steam-engine is a very effective machine, and does excellent work when
properly proportioned to yield the required amount of power. It is
well adapted to an expansion of from four to five times. Its
disadvantages are the difficulty which it presents in the attachment
of the regulator, to determine the point of cut-off by the heavy work
which it throws upon the governor when attached, and the rather
inflexible character of the device as an expansive valve-gear. The
best examples of this class of engine have neat heavy bed-plates,
well-designed cylinders and details, smooth-working valve-gear, the
expansion-valve adjusted by a right and left hand screw, and
regulation secured by the attachment of the governor to the
throttle-valve.
The engine shown in the accompanying illustration (Fig. 95) is an
example of an excellent British stationary steam-engine. It is simple,
strong, and efficient. The frame, front cylinder-head, cross-head
guides, and crank-shaft "plumber-block," are cast in one piece, as has
so generally been done in the United States for a long time by some of
our manufacturers. The cylinder is secured against the end of the
bed-plate, as was first done by Corliss. The crank-pin is set in a
counterbalanced disk. The valve-gear is simple, and the governor
effective, and provided with a safety-device to prevent injury by the
breaking of the governor-belt. An engine of this kind of 10 inches
diameter of cylinder, 20 inches stroke of piston, is rated by the
builders at about 25 horse-power; a similar engine 30 inches in
diameter of cylinder would yield from 225 to 250 horse-power. In
this example, all parts are made to exact size by gauges standardized
to Whitworth's sizes.
[Illustration: FIG. 95.--Horizontal Stationary Steam-Engine.]
[Illustration: FIG. 96.--Horizontal Stationary Steam-Engine.]
In American engines (as is seen in Fig. 96), usually, two supports are
placed--the one under the latter bearing, and the other under the
cylinder--to take the weight of the engine; and through them it is
secured to the foundation. As in the vertical engine already
described, a valve is sometimes used, consisting of two pistons
connected by a rod, and worked by an ordinary eccentric. By a simple
arrangement these pistons have always the same pressure inside as out,
which prevents any leakage or blowing through; and they are said
always to work equally as well and free from friction under 150 pounds
pressure as under 10 pounds per square inch, and to require no
adjustment. It is more usual, however, to adopt the three-ported valve
used on locomotives, with (frequently) a cut-off valve on the back of
this main valve, which cut-off valve is adjusted either by hand or by
the governor.
Engines of the class just described are especially well fitted, by
their simplicity, compactness, and solidity, to work at the high
piston-speeds which are gradually becoming generally adopted in the
effort to attain increased economy of fuel by the reduction of the
immense losses of heat which occur in the expansion of steam in the
metallic cylinders through which we are now compelled to work it.
One of the best known of recent engines is the Allen engine, a
steam-engine having the same general arrangement of parts seen in the
above illustration, but fitted with a peculiar valve-gear, and having
proportions of parts which are especially calculated to secure
smoothness of motion and uniformity of pressure on crank-pin and
journals, at speeds so high that the inertia of the reciprocating
parts becomes a seriously-important element in the calculation of the
distribution of stresses and their effect on the dynamics of the
machine.
In the Allen engine,[85] the cylinder and frame are connected as in
the engine seen above, and the crank-disk, shaft-bearings, and other
principal details, are not essentially different. The valve-gear[86]
differs in having four valves, one at each end on the steam as well as
on the exhaust side, all of which are balanced and work with very
little resistance. These valves are not detachable, but are driven by
a link attached to and moved by an eccentric on the main shaft, the
position of the valve-rod attachment to which link is determined by
the governor, and the degree of expansion is thus adjusted to the work
of the engine. The engine has usually a short stroke, not exceeding
twice the diameter of cylinder, and is driven at very high speed,
generally averaging from 600 to 800 feet per minute.[87] This high
piston-speed and short stroke give very great velocity of rotation.
The effect is, therefore, to produce an exceptional smoothness of
motion, while permitting the use of small fly-wheels. Its short stroke
enables entire solidity to be attained in a bed of rigid form, making
it a very completely self-contained engine, adapted to the heaviest
work, and requiring only a small foundation.
[85] The invention of Messrs. Charles T. Porter and John F. Allen.
[86] Invented by Mr. John F. Allen.
[87] Or not far from 600 times the cube root of the length of
stroke, measured in feet.
The journals of the shaft, and all cylindrical wearing surfaces, are
finished by grinding in a manner that leaves them perfectly round. The
crank-pin and cross-head pin are hardened before being ground. The
joints of the valve-gear consist of pins turning in solid ferrules in
the rod-ends, both hardened and ground. After years of constant use
thus, no wear occasioning lost time in the valve-movements has been
detected.
High speed and short strokes are essential elements of economy. It is
now well understood that all the surfaces with which the steam comes
in contact condense it.
Obviously, one way to diminish this loss is to reduce the extent of
surface to which the steam is exposed. In engines of high speed and
short stroke, the surfaces with which the steam comes in contact,
while doing a given amount of work, present less area than in ordinary
engines running at low speed. Where great steadiness of motion is
desired, the expense of coupled engines is often incurred.
Quick-running engines do not require to be coupled; a single engine
may give greater uniformity of motion than is usually obtained with
coupled engines at ordinary speeds. The ports and valve-movements, the
weight of the reciprocating parts, and the size and weight of the
fly-wheels, should be calculated expressly for the speeds chosen.
The economy of the engine here described is unexcelled by the best of
the more familiar "drop cut-off" engines.
An engine reported upon by a committee of the American Institute, of
which Dr. Barnard was chairman, was non-condensing, 16 inches in
diameter of cylinder, 30 inches stroke, making 125 revolutions per
minute, and developed over 125 horse-power with 75 pounds of steam in
the boiler, using 25-3/4 pounds of steam per indicated horse-power,
and 2.87 pounds of coal--an extraordinarily good performance for an
engine of such small power.
The governor used on this engine is known as the Porter governor. It
is given great power and delicacy by weighting it down, and thus
obtaining a high velocity of rotation, and by suspending the balls
from forked arms, which are given each two bearing-pins separated
laterally so far as to permit considerable force to be exerted in
changing speeds without cramping those bearings sufficiently to
seriously impair the sensitiveness of the governor. This engine as a
whole may be regarded as a good representative of the high-speed
engine of to-day.
Since this change in the direction of high speeds has already gone so
far that the "drop cut-off" is sometimes inapplicable, in consequence
of the fact that the piston would, were such a valve-gear adopted,
reach the end of its stroke before the detached valve could reach its
seat; and since this progress is only limited by our attainments in
mechanical skill and accuracy, it seems probable that the
"positive-motion expansion-gear" type of engine will ultimately
supersede the now standard "drop cut-off engine."
The best known and most generally used class of stationary engines at
the present time is, however, that which has the so-called "drop
cut-off," or "detachable valve-gear." The oldest well-known form of
valve-motion of this description now in use is that known as the
Sickels cut-off, patented by Frederick E. Sickels, an American
mechanic, about the year 1841, and also built by Hogg, of New York,
who placed it upon the engine of the steamer South America. The
invention is claimed for both Hogg and Sickels. It was introduced by
the inventor in a form which especially adapted it to use with the
beam-engine used on the Eastern waters of the United States, and was
adapted to stationary engines by Messrs. Thurston, Greene & Co., of
Providence, R. I., who made use of it for some years before any other
form of "drop cut-off" came into general use. The Sickels cut-off
consisted of a set of steam-valves, usually independent of the
exhaust-valves, and each raised by a catch, which could be thrown out,
at the proper moment, by a wedge with which it came in contact as it
rose with the opening valve. This wedge, or other equivalent device,
was so adjusted that the valve should be detached and fall to its seat
when the piston reached that point in its movement, after taking
steam, at which expansion was to commence. From this point, no steam
entering the cylinder, the piston was impelled by the expanding vapor.
The valve was usually the double-poppet. Sickels subsequently invented
what was called the "beam-motion," to detach the valve at any point in
the stroke. As at first arranged, the valve could only be detached
during the earlier half-stroke, since at mid-stroke the direction of
motion of the eccentric rod was reversed and the valve began to
descend. By introducing a "wiper" having a motion transverse to that
of the valve and its catch, and by giving this wiper a motion
coincident with that of the piston by connecting it with the beam or
other part of the engine moving with the piston, he obtained a
kinematic combination which permitted the valve to be detached at any
point in the stroke, adding a very simple contrivance which enabled
the attendant to set the wiper so that it should strike the catch at
any time during the forward movement of the "beam-motion."
On stationary engines, the point of cut-off was afterward determined
by the governor, which was made to operate the detaching mechanism,
the combination forming what is sometimes called an "automatic"
cut-off. The attachment of the governor so as to determine the degree
of expansion had been proposed before Sickels's time. One of the
earliest of these contrivances was that of Zachariah Allen, in 1834,
using a cut-off valve independent of the steam-valve. The first to so
attach the governor to a _drop cut-off_ valve-motion was George H.
Corliss, who made it a feature of the Corliss valve-gear in 1849. In
the year 1855, N. T. Greene introduced a form of expansion-gear, in
which he combined the range of the Sickels beam-motion device with the
expansion-adjustment gained by the attachment of the governor, and
with the advantages of flat slide-valves at all ports--both steam and
exhaust.
Many other ingenious forms of expansion valve-gear have been invented,
and several have been introduced, which, properly designed and
proportioned to well-planned engines, and with good construction and
management, should give economical results little if at all inferior
to those just named. Among the most ingenious of these later devices
is that of Babcock & Wilcox, in which a very small auxiliary
steam-cylinder and piston is employed to throw the cut-off valve over
its port at the instant at which the steam is to be cut off. A very
beautiful form of isochronous governor is used on this engine, to
regulate the speed of the engine by determining the point of cut-off.
In Wright's engine, the expansion is adjusted by the movement, by the
regulator, of cams which operate the steam-valves so that they shall
hold the valve open a longer or shorter time, as required.
Since compactness and lightness are not as essential as in portable,
locomotive, and marine engines, the parts are arranged, in stationary
engines, with a view simply to securing efficiency, and the design is
determined by circumstances. It was formerly usual to adopt the
condensing engine in mills, and wherever a stationary engine was
required. In Europe generally, and to some extent in the United
States, where a supply of condensing water is obtainable, condensing
engines and moderate steam-pressures are still employed. But this type
of engine is gradually becoming superseded by the high-pressure
condensing engine, with considerable expansion, and with an
expansion-gear in which the point of cut-off is determined by the
governor.
[Illustration: FIG. 97.--Corliss Engine.]
[Illustration: FIG. 98--Corliss Engine Valve-Motion.]
The best-known engine of this class is the Corliss engine, which is
very extensively used in the United States, and which has been copied
very generally by European builders. Fig. 97 represents the Corliss
engine. The horizontal steam-cylinder is bolted firmly to the end of
the frame, which is so formed as to transmit the strain to the main
journal with the greatest directness. The frame carries the guides for
the cross-head, which are both in the same vertical plane. The valves
are four in number, a steam and an exhaust valve being placed at each
end of the steam-cylinder. Short steam-passages are thus secured, and
this diminution of clearance is a source of some economy. Both sets of
valves are driven by an eccentric operating a disk or wrist-plate, _E_
(Fig. 98), which vibrates on a pin projecting from the cylinder. Short
links reaching from this wrist-plate to the several valves, _D D_, _F
F_, move them with a peculiarly varying motion, opening and closing
them rapidly, and moving them quite slowly when the port is either
nearly open or almost closed. This effect is ingeniously secured by so
placing the pins on the wrist-plate that their line of motion becomes
nearly transverse to the direction of the valve-links when the limit
of movement is approached. The links connecting the wrist-plate with
the arms moving the steam-valves have catches at their extremities,
which are disengaged by coming in contact, as the arm swings around
with the valve-stem, with a cam adjusted by the governor. This
adjustment permits the steam to follow the piston farther when the
engine is caused to "slow down," and thus tends to restore the proper
speed. It disengages the steam-valve earlier, and expands the steam to
a greater extent, when the engine begins to run above the proper
speed. When the catch is thrown out, the valve is closed by a weight
or a strong spring. To prevent jar when the motion of the valve is
checked, a "dash-pot" is used, invented originally by F. E. Sickels.
This is a vessel having a nicely-fitted piston, which is received by a
"cushion" of water or air when the piston suddenly enters the cylinder
at the end of the valve-movement. In the original water dash-pot of
Sickels, the cylinder is vertical, and the plunger or piston descends
upon a small body of water confined in the base of the dash-pot.
Corliss's air dash-pot is now often set horizontally.
[Illustration: FIG. 99.--Greene Engine.]
In the Greene steam-engine (Fig. 99), the valves are four in number,
as in the Corliss. The cut-off gear consists of a bar, _A_, moved by
the steam-eccentric in a direction parallel with the centre-line of
the cylinder and nearly coincident as to time with the piston. On this
bar are tappets, _C C_, supported by springs and adjustable in height
by the governor, _G_. These tappets engage the arms _B B_, on the ends
of rock-shafts, _E E_, which move the steam-valves and remain in
contact with them a longer or shorter time, and holding the valve open
during a greater or less part of the piston-stroke, as the governor
permits the tappets to rise with diminishing engine-speed, or forces
them down as speed increases. The exhaust-valves are moved by an
independent eccentric rod, which is itself moved by an eccentric set,
as is usual with the Corliss and with other engines generally, at
right angles with the crank. This engine, in consequence of the
independence of the steam-eccentric, and of the contemporary movement
of steam valve-motion and steam-piston, is capable of cutting off at
any point from beginning to nearly the end of the stroke. The usual
arrangement, by which steam and exhaust valves are moved by the same
eccentric, only permits expansion with the range from the beginning to
half-stroke. In the Corliss engine the latter construction is
retained, with the object, in part, of securing a means of closing the
valve by a "positive motion," should, by any accident, the closing not
be effected by the weight or spring usually relied upon.
[Illustration: FIG. 100.--Thurston's Greene-Engine Valve-Gear.]
The steam-valve of the Greene engine, as designed by the author, is
seen in Fig. 100, where the valve, _G H_, covering the port, _D_, in
the steam-cylinder, _A B_, is moved by the rod, _J J_, connected to
the rock-shaft, _M_, by the arm, _L K_. The line, _K I_, should, when
carried out, intersect the valve-face at its middle point, under _G_.
The characteristics of the American stationary engine, therefore, are
high steam-pressure without condensation, an expansion valve-gear with
drop cut-off adjustable by the governor, high piston-speed, and
lightness combined with strength of construction. The pressure most
commonly adopted in the boilers which furnish steam to this type of
engine is from 75 to 80 pounds per square inch; but a pressure of 100
pounds is not infrequently carried, and the latter pressure may be
regarded as a "mean maximum," corresponding to a pressure of 60 pounds
at about the commencement of the period here considered--1850.
Very much greater pressures have, however, been adopted by some
makers, and immensely "higher steam" has been experimented with by
several engineers. As early as 1823, Jacob Perkins[88] commenced
experimenting with steam of very great tension. As has already been
stated, the usual pressure at the time of Watt was but a few pounds--5
or 7--in excess of that of the atmosphere. Evans, Trevithick, and
Stevens, had previously worked steam at pressures of from 50 to 75
pounds per square inch, and pressures on the Western rivers and
elsewhere in the United States had already been raised to 100 or 150
pounds, and explosions were becoming alarmingly frequent.
[88] Perkins was a native of Newburyport, Mass. He was born July 9,
1766, and died in London, July 30, 1849. He went to England when
fifty-two years of age, to introduce his inventions.
Perkins's experimental apparatus consisted of a copper boiler, of a
capacity of about one cubic foot, having sides 3 inches in thickness.
It was closed at the bottom and top, and had five small pipes leading
from the upper head. This was placed in a furnace kept at a high
temperature by a forced combustion. Safety-valves loaded respectively
to 425 and 550 pounds per square inch were placed on each of two of
the steam-pipes.
Perkins used the steam generated under these great pressures in a
little engine having a piston 2 inches in diameter and a stroke of 1
foot. It was rated at 10 horse-power.[89]
[89] It was when writing of this engine that Stuart wrote, in 1824:
"Judging from the rapid strides the steam-engine has made _during
the last forty years_ to become a universal first-mover, and from
the experience that has arisen from that extension, we feel
convinced that every invention which diminishes its size without
impairing its power brings it a step nearer to the assistance of the
'world's great laborers,' the husbandman and the peasant, for whom,
as yet, it performs but little. At present, it is made occasionally
to tread out the corn. What honors await not that man who may yet
direct its mighty power to plough, to sow, to harrow, and to reap!"
The progress of the steam-engine during those forty years does not
to-day appear so astounding. The sentiment here expressed has lost
none of its truth, nevertheless.
In the year 1827, Perkins had attained working pressures, in a
single-acting, single-cylinder engine, of upward of 800 pounds per
square inch. At pressures exceeding 200 pounds, he had much trouble in
securing effective lubrication, as all oils charred and decomposed at
the high temperatures then unavoidably encountered, and he finally
succeeded in evading this seemingly insurmountable obstacle by using
for rubbing parts a peculiar alloy which required no lubrication, and
which became so beautifully polished, after some wear, that the
friction was less than where lubricants were used. At these high
pressures Perkins seems to have met with no other serious difficulty.
He condensed the exhaust-steam and returned it to the boiler, but did
not attempt to create a vacuum in his condenser, and therefore needed
no air-pump. Steam was cut off at one-eighth stroke.
In the same year, Perkins made a compound engine on the Woolf plan,
and adopted a pressure of 1,400 pounds, expanding eight times. In
still another engine, intended for a steam-vessel, Perkins adopted, or
proposed to adopt, 2,000 pounds pressure, cutting off the admission at
one-sixteenth, in single-acting engines of 6 inches diameter of
cylinder and 20 inches stroke of piston. The steam did not retain
boiler-pressure at the cylinder, and this engine was only rated at 30
horse-power.[90]
[90] Galloway and Hebert, on the Steam-Engine. London, 1836.
Stuart follows a description of Perkins's work in the improvement of
the steam-engine and the introduction of steam-artillery by the
remark:
" ... No other mechanic of the day has done more to illustrate an
obscure branch of philosophy by a series of difficult, dangerous,
and expensive experiments; no one's labors have been more deserving
of cheering encouragement, and no one has received less. Even in
their present state, his experiments are opening new fields for
philosophical research, and his mechanism bids fair to introduce
a new style into the proportions, construction, and form, of
steam-machinery."
Perkins's experience was no exception to the general rule, which
denies to nearly all inventors a fair return for the benefits which
they confer upon mankind.
Another engineer, a few years later, was also successful in
controlling and working steam under much higher pressures than are
even now in use. This was Dr. Ernst Alban, a distinguished German
engine-builder, of Plau, Mecklenburg, and an admirer of Oliver Evans,
in whose path he, a generation later, advanced far beyond that great
pioneer. Writing in 1843, he describes a system of engine and boiler
construction, with which he used steam under pressures about equal to
those experimentally worked by Jacob Perkins, Evans's American
successor. Alban's treatise was translated and printed in Great
Britain,[91] four years later.
[91] "The High-Pressure Steam-Engine," etc. By Dr. Ernst Alban.
Translated by William Pole, F. R. A. S. London, 1847.
Alban, on one occasion, used steam of 1,000 pounds pressure. His
boilers were similar in general form to the boiler patented by Stevens
in 1805, but the tubes were horizontal instead of vertical. He
evaporated from 8 to 10 pounds of water into steam of 600 to 800
pounds pressure with each pound of coal. He states that the
difficulty met by Perkins--the decomposition of lubricants in the
steam-cylinder--did not present itself in his experiments, even when
working steam at a pressure of 600 pounds on the square inch, and he
found that less lubrication was needed at such high pressures than in
ordinary practice. Alban expanded his steam about as much as Evans, in
his usual practice, carrying a pressure of 150 pounds, and cutting off
at one-third; he adopted greatly increased piston-speed, attaining 300
feet per minute, at a time when common practice had only reached 200
feet. He usually built an oscillating engine, and rarely attached a
condenser. The valve was the locomotive-slide.[92] The stroke was made
short to secure strength, compactness, cheapness, and high speed of
rotation; but Alban does not seem to have understood the principles
controlling the form and proportions of the expansive engine, or the
necessity of adopting considerable expansion in order to secure
economy in working steam of great tension, and therefore was,
apparently, not aware of the advantages of a long stroke in reducing
losses by "dead-space," in reducing risk of annoyance by hot journals,
or in enabling high piston-speeds to be adopted. He seems never to
have attained a sufficiently high speed of piston to become aware that
the oscillating cylinder cannot be used at speeds perfectly
practicable with the fixed cylinder.
[92] Invented by Joseph Maudsley, of London, 1827.
Alban states that one of his smallest engines, having a cylinder 4-1/2
inches in diameter and 1 foot stroke of piston, with a piston-speed of
but 140 to 160 feet per minute, developed 4 horse-power, with a
consumption of 5.3 pounds of coal per hour. This is a good result for
so small an amount of work, and for an engine working at so low a
speed of piston. An engine of 30 horse-power, also working very
slowly, required but 4.1 pounds of coal per hour per horse-power.
The work of Perkins and of Alban, like that of their predecessors,
Evans, Stevens, and Trevithick, was, however, the work of engineers
who were far ahead of their time. The general practice, up to the time
which marked the beginning of the modern "period of refinement," had
been but gradually approximating that just described. Higher pressures
were slowly approached; higher piston-speeds came slowly into use;
greater expansion was gradually adopted; the causes of losses of heat
were finally discovered, and steam-jacketing and external
non-conducting coverings were more and more generally applied as
builders became more familiar with their work. The "compound engine"
was now and then adopted; and each experiment, made with higher steam
and greater expansion, was more nearly successful than the last.
Finally, all these methods of securing economy became recognized, and
the reasons for their adoption became known. It then remained, as the
final step in this progression, to combine all these requisites of
economical working in a double-cylinder engine, steam-jacketed, well
protected by non-conducting coverings, working steam of high pressure,
and with considerable expansion at high piston-speed. This is now done
by the best builders.
One of the best examples of this type of engine is that constructed by
the sons of Jacob Perkins, who continued the work of their father
after his death. Their engines are single-acting, and the small or
high-pressure cylinder is placed on the top of the larger or
low-pressure cylinder. The valves are worked by rotating stems, and
the loss of heat and burning of packing incident to the use of the
common method are thus avoided. The stuffing-boxes are placed at the
end of long sleeves, closely surrounding the vertical valve-stems
also, and the water of condensation which collects in these sleeves is
an additional and thorough protection against excessively high
temperature at the packing. The piston-rings are made of the alloy
which has been found to require no lubrication.
Steam is usually worked at from 250 to 450 pounds, and is generated in
boilers composed of small tubes three inches in diameter and
three-eighths of an inch thick, which are tested under a pressure of
2,500 pounds per square inch. The safety-valve is usually loaded to
400 pounds. The boiler is fed with distilled water, obtained
principally by condensation of the exhaust-steam, any deficiency being
made up by the addition of water from a distilling apparatus. Under
these conditions, but 1-1/4 pound of coal is consumed per hour and per
horse-power.
THE PUMPING-ENGINE in use at the present time has passed through a
series of changes not differing much from that which has been traced
with the stationary mill-engine. The Cornish engine is still used to
some extent for supplying water to towns, and is retained at deep
mines. The modern Cornish engine differs very little from that of the
time of Watt, except in the proportions of parts and the form of its
details. Steam-pressures are carried which were never reached during
the preceding period, and, by careful adjustment of well-set and
well-proportioned valves and gearing, the engine has been made to work
rather more rapidly, and to do considerably more work. It still
remains, however, a large, costly, and awkward contrivance, requiring
expensive foundations, and demanding exceptional care, skill, and
experience in management. It is gradually going out of use. This
engine, as now constructed by good builders, is shown in section in
Fig. 101.
A comparison with the Watt engine of a century earlier will at once
enable any one to appreciate the extent to which changes may be made
in perfecting a machine, even after it has become complete, so far as
supplying it with all essential parts can complete it.
[Illustration: FIG. 101.--Cornish Pumping-Engine, 1880.]
In the figure, _A_ is the cylinder, taking steam from the boiler
through the steam-passage, _M_. The steam is first admitted above the
piston, _B_, driving it rapidly downward and raising the pump-rod,
_E_. At an early period in the stroke the admission of steam is
checked by the sudden closing of the induction-valve at _M_, and the
stroke is completed under the action of expanding steam assisted by
the inertia of the heavy parts already in motion. The necessary weight
and inertia is afforded, in many cases, where the engine is applied to
the pumping of deep mines, by the immensely long and heavy pump-rods.
Where this weight is too great, it is counterbalanced, and where too
small, weights are added. When the stroke is completed, the
"equilibrium valve" is opened, and the steam passes from above to the
space below the piston, and an equilibrium of pressure being thus
produced, the pump-rods descend, forcing the water from the pumps and
raising the steam-piston. The absence of the crank, or other device
which might determine absolutely the length of stroke, compels a very
careful adjustment of steam-admission to the amount of load. Should
the stroke be allowed to exceed the proper length, and should danger
thus arise of the piston striking the cylinder-head, _N_, the movement
is checked by buffer-beams. The valve-motion is actuated by a
plug-rod, _J K_, as in Watt's engine. The regulation is effected by a
"cataract," a kind of hydraulic governor, consisting of a
plunger-pump, with a reservoir attached. The plunger is raised by the
engine, and then automatically detached. It falls with greater or less
rapidity, its velocity being determined by the size of the
eduction-orifice, which is adjustable by hand. When the plunger
reaches the bottom of the pump-barrel, it disengages a catch, a weight
is allowed to act upon the steam-valve, opening it, and the engine is
caused to make a stroke. When the outlet of the cataract is nearly
closed, the engine stands still a considerable time while the plunger
is descending, and the strokes succeed each other at long intervals.
When the opening is greater, the cataract acts more rapidly, and the
engine works faster. This has been regarded until recently as the most
economical of pumping-engines, and it is still generally used in
freeing mines of water, and in situations where existing heavy
pump-rods may be utilized in counterbalancing the steam-pressure, and,
by their inertia, in continuing the motion after the steam, by its
expansion, has become greatly reduced in pressure.
In this engine a gracefully-shaped and strong beam, _D_, has taken
the place of the ruder beam of the earlier period, and is carried on a
well-built wall of masonry, _R_. _F_ is the exhaust-valve, by which
the steam passes to the condenser, _G_, beside which is the air-pump,
_H_, and the hot-well, _I_. The cylinder is steam-jacketed, _P_, and
protected against losses of heat by radiation by a brick wall, _O_,
the whole resting on a heavy foundation, _Q_.
The Bull Cornish engine is also still not infrequently seen in use.
The Cornish engine of Great Britain averages a duty of about
45,000,000 pounds raised one foot high per 100 pounds of coal. More
than double this economy has sometimes been attained.
[Illustration: FIG. 102.--Steam-Pump.]
A vastly simpler form of pumping-engine without fly-wheel is the now
common "direct-acting steam-pump." This engine is generally made use
of in feeding steam-boilers, as a forcing and fire pump, and wherever
the amount of water to be moved is not large, and where the pressure
is comparatively great. The steam-cylinder, _A R_, and feed-pump, _B
Q_ (Fig. 102), are in line, and the two pistons have usually one rod,
_D_, in common. The two cylinders are connected by a strong frame,
_N_, and two standards fitted with lugs carry the whole, and serve as
a means of bolting the pump to the floor or to its foundation.
The method of working the steam-valve of the modern steam-pump is
ingenious and peculiar. As shown, the pistons are moving toward the
left; when they reach the end of their stroke, the face of the piston
strikes a pin or other contrivance, and thus moves a small auxiliary
valve, _I_, which opens a port, _E_, and causes steam to be admitted
behind a piston, or permits steam to be exhausted, as in the figure,
from before the auxiliary piston, _F_, and the pressure within the
main steam-chest then forces that piston over, moving the main
steam-valve, _G_, to which it is attached, admitting steam to the
left-hand side of the main piston, and exhausting on the right-hand
side, _A_. Thus the motion of the engine operates its own valves in
such a manner that it is never liable to stop working at the end of
the stroke, notwithstanding the absence of the crank and fly-wheel, or
of independent mechanism, like the cataract of the Cornish engine.
There is a very considerable variety of pumps of this class, all
differing in detail, but all presenting the distinguishing feature of
auxiliary valve and piston, and a connection by which it and the main
engine each works the valve of the other combination.
[Illustration: FIG. 103.--The Worthington Pumping-Engine, 1876.
Section.]
[Illustration: FIG. 104.--The Worthington Pumping-Engine.]
In some cases these pumps are made of considerable size, and are
applied to the elevation of water in situations to which the Cornish
engine was formerly considered exclusively applicable. The
accompanying figure illustrates such a pumping-engine, as built for
supplying cities with water. This is a "compound" direct-acting
pumping-engine. The cylinders, _A B_, are placed in line, working one
pump, _F_, and operating their own air-pumps, _D D_, by a bell-crank
lever, _L H_, connected to the pump-buckets by links, _I K_. Steam
exhausted from the small cylinder, _A_, is further expanded in the
large cylinder, _B_, and thence goes to the condenser, _C_. The
valves, _N M_, are moved by the valve-gear, _L_, which is actuated by
the piston-rod of a similar pair of cylinders placed by the side of
the first. These valves are balanced, and the balance-plates, _R Q_,
are suspended from the rods, _O P_, which allow them to move with the
valves. By connecting the valves of each engine with the piston-rod
of the other, it is seen that the two engines must work alternately,
the one making a stroke while the other is still, and then itself
stopping a moment while the latter makes its stroke.
Water enters the pump through the induction-pipe, _E_, passes into the
pump-barrel through the valves, _V V_, and issues through the
eduction-valves, _T T_, and goes on to the "mains" by the pipe, _G_,
above which is seen an air-chamber, which assists to preserve a
uniform pressure on that side the pump. This engine works very
smoothly and quietly, is cheap and durable, and has done excellent
duty.
Beam pumping-engines are now almost invariably built with crank and
fly-wheel, and very frequently are compound engines. The accompanying
illustration represents an engine of the latter form.
[Illustration: FIG. 105.--Double-Cylinder Pumping-Engine, 1878.]
[Illustration: FIG. 106.--The Lawrence Water-Works Engine.]
_A_ and _B_ are the two steam-cylinders, connected by links and
parallel motion, _C D_, to the great cast-iron beam, _E F_. At the
opposite end of the beam, the connecting-rod, _G_, turns a crank,
_H_, and fly-wheel, _L M_, which regulates the motion of the engine
and controls the length of stroke, averting all danger of accident
occurring in consequence of the piston striking either cylinder-head.
The beam is carried on handsomely-shaped iron columns, which, with
cylinders, pump, and fly-wheel, are supported by a substantial stone
foundation. The pump-rod, _I_, works a double-acting pump, _J_, and
the resistance to the issuing water is rendered uniform by an
air-chamber, _K_, within which the water rises and falls when
pressures tend to vary greatly. A revolving shaft, _N_, driven from
the fly-wheel shaft, carries cams, _O P_, which move the lifting-rods
seen directly over them and the valves which they actuate. Between the
steam-cylinders and the columns which carry the beams is a well, in
which are placed the condenser and air-pump. Steam is carried at 60 or
80 pounds pressure, and expanded from 6 to 10 times.
[Illustration: FIG. 107.--The Leavitt Pumping-Engine.]
A later form of double-cylinder beam pumping-engine is that invented
and designed by E. D. Leavitt, Jr., for the Lawrence Water-Works, and
shown in Figs. 106 and 107. The two cylinders are placed one on each
side the centre of the beam, and are so inclined that they may be
coupled to opposite ends of it, while their lower ends are placed
close together. At their upper ends a valve is placed at each end of
the connecting steam-pipe. At their lower ends a single valve serves
as exhaust-valve to the high-pressure and as steam-valve to the
low-pressure cylinder. The pistons move in opposite directions, and
steam is exhausted from the high-pressure cylinder directly into the
nearer end of the low-pressure cylinder. The pump, of the
"Thames-Ditton" or "bucket-and-plunger" variety, takes a full supply
of water on the down-stroke, and discharges half when rising and half
when descending again. The duty of this engine is reported by a board
of engineers as 103,923,215 foot-pounds for every 100 pounds of coal
burned. The duty of a moderately good engine is usually considered to
be from 60 to 70 millions. This engine has steam-cylinders of 17-1/2
and 36 inches diameter respectively, with a stroke of 7 feet. The pump
had a capacity of about 195 gallons, and delivered 96 per cent. Steam
was carried at a pressure of 75 pounds above the atmosphere, and was
expanded about 10 times. Plain horizontal tubular boilers were used,
evaporating 8.58 pounds of water from 98 deg. Fahr. per pound of coal.
STEAM-BOILERS.--The steam supplied to the forms of stationary engine
which have been described is generated in steam-boilers of exceedingly
varied forms. The type used is determined by the extent to which their
cost is increased in the endeavor to economize fuel by the pressure of
steam carried, by the greater or less necessity of providing against
risk of explosion, by the character of the feed-water to be used, by
the facilities which may exist for keeping in good repair, and even by
the character of the men in whose hands the apparatus is likely to be
placed.
As has been seen, the changes which have marked the growth and
development of the steam-engine have been accompanied by equally
marked changes in the forms of the steam-boiler. At first, the same
vessel served the distinct purposes of steam-generator and
steam-engine. Later, it became separated from the engine, and was then
specially fitted to perform its own peculiar functions; and its form
went through a series of modifications under the action of the causes
already stated.
When steam began to be usefully applied, and considerable pressures
became necessary, the forms given to boilers were approximately
spherical, ellipsoidal, or cylindrical. Thus the boilers of De Caus
(1615) and of the Marquis of Worcester (1663) were spherical and
cylindrical; those of Savery (1698) were ellipsoidal and cylindrical.
After the invention of the steam-engine of Newcomen, the pressures
adopted were again very low, and steam-boilers were given irregular
forms until, at the beginning of the present century, they were again
of necessity given stronger shapes. The material was at first
frequently copper; it is now usually wrought-iron, and sometimes
steel.
The present forms of steam-boilers may be classified as plain, flue,
and tubular boilers. The plain cylindrical or common cylinder boiler
is the only representative of the first class in common use. It is
perfectly cylindrical, with heads either flat or hemispherical. There
is usually attached to the boiler a "steam-drum" (a small cylindrical
vessel), from which the steam is taken by the steam-pipe. This
enlargement of the steam-space permits the mist, held in suspension by
the steam when it first rises from the surface of the water, to
separate more or less completely before the steam is taken from the
boiler.
[Illustration: FIG. 108.--Babcock & Wilcox's Vertical Boiler.]
Flue-boilers are frequently cylindrical, and contain one or more
cylindrical flues, which pass through from end to end, beneath the
water-line, conducting the furnace-gases, and affording a greater area
of heating-surface than can be obtained in the plain boiler. They are
usually from 30 to 48 inches in diameter, and one foot or less in
length for each inch of diameter. Some are, however, made 100 feet and
more in length. The boiler is made of iron 1/4 to 3/8 of an inch in
thickness, with hemispherical or carefully stayed flat heads, and
without flues. The whole is placed in a brickwork setting. These
boilers are used where fuel is inexpensive, where the cost of
repairing would be great, or where the feed-water is impure. A
cylindrical boiler, having one flue traversing it longitudinally, is
called a Cornish boiler, as it is generally supposed to have been
first used in Cornwall. It was probably first invented by Oliver Evans
in the United States, previous to 1786, at which time he had it in
use. The flue has usually a diameter 0.5 or 0.6 the diameter of the
boiler. A boiler containing two longitudinal flues is called the
Lancashire boiler. This form was also introduced by Oliver Evans. The
flues have one-third the diameter of the boiler. Several flues of
smaller diameter are often used, and when a still greater proportional
area of heating-surface is required, tubes of from 1-1/4 inch to 4 or
5 inches in diameter are substituted for flues. The flues are usually
constructed by riveting sheets together, as in making the shell or
outer portion. They are sometimes welded by British manufacturers, but
rarely if ever in the United States. Tubes are always "lap-welded" in
the process of rolling them. Small tubes were first used in the United
States, about 1785. In portable, locomotive, and marine steam-boilers,
the fire must be built within the boiler itself, instead of (as in the
above described stationary boilers) in a furnace of brickwork exterior
to the boiler. The flame and gases from the furnace or fire-box in
these kinds of boiler are never led through brick passages en route to
the chimney, as often in the preceding case, but are invariably
conducted through flues or tubes, or both, to the smoke-stack. These
boilers are also sometimes used as stationary boilers. Fig. 108
represents such a steam-boiler in section, as it is usually exhibited
in working drawings. Provision is made to secure a good circulation of
water in these boilers by means of the "baffle-plates," seen in the
sketch, which compel the water to flow as indicated by the arrows.
The tubes are frequently made of brass or of copper, to secure rapid
transmission of heat to the water, and thus to permit the use of a
smaller area of heating-surface and a smaller boiler. The steam-space
is made as large as possible, to secure immunity from "priming" or the
"entrainment" of water with the steam. This type of steam-boiler,
invented by Nathan Read, of Salem, Mass., in 1791, and patented in
April of that year, was the earliest of the tubular boilers. In the
locomotive boiler (Fig. 109), as in the preceding, the characteristics
are a fire-box at one end of the shell and a set of tubes through
which the gases pass directly to the smoke-stack. Strength,
compactness, great steaming capacity, fair economy, moderate cost, and
convenience of combination with the running parts, are secured by the
adoption of this form. It is frequently used also for portable and
stationary engines. It was invented in France by M. Seguin, and in
England by Booth, and used by George Stephenson at about the same
time--1828 or 1829.
[Illustration: FIG. 109.--Stationary "Locomotive" Boiler.]
Since the efficiency of a steam-boiler depends upon the extent of
effective heating-surface per unit of weight of fuel burned in any
given time--or, ordinarily, upon the ratio of the areas of heating and
grate surface--peculiar expedients are sometimes adopted, having for
their object the increase of heating-surface, without change of form
of boiler and without proportionate increase of cost.
One of these methods is that of the use of Galloway conical tubes
(Fig. 110). These are very largely used in Great Britain, but are
seldom if ever seen in the United States. The Cornish boiler, to which
they are usually applied, consists of a large cylindrical shell, 6
feet or more in diameter, containing one tube of about one-half as
great dimensions, or sometimes two of one-third the diameter of the
shell each. Such boilers have a very small ratio of heating to grate
surface, and their large tubes are peculiarly liable to collapse. To
remove these objections, the Messrs. Galloway introduced stay-tubes
into the flues, which tubes are conical in form, and are set in either
a vertical or an inclined position, the larger end uppermost. The area
of heating-surface is thus greatly increased, and, at the same time,
the liability to collapse is reduced. The same results are obtained by
another device of Galloway, which is sometimes combined with that just
described in the same boiler. Several sheets in the flue have
"pockets" worked into them, which pockets project into the
flue-passage.
[Illustration: FIG. 110.]
Another device is that of an American engineer, Miller, who surrounds
the furnace of cylindrical and other boilers with water-tubes. The
"fuel-economizers" of Greene and others consist of similar collections
of tubes set in the flues, between the boiler and the chimney.
"_Sectional_" boilers are gradually coming into use with high
pressures, on account of their greater safety against disastrous
explosions. The earliest practicable example of a boiler of this class
was probably that of Colonel John Stevens, of Hoboken, N. J. Dr.
Alban, who, forty years later, attempted to bring this type into
general use, and constructed a number of such boilers, did not
succeed. Their introduction, like that of all radical changes in
engineering, has been but slow, and it has been only recently that
their manufacture has become an important branch of industry.
A committee of the American Institute, of which the author was
chairman, in 1871, examined several boilers of this and the ordinary
type, and tested them very carefully. They reported that they felt
"confident that the introduction of this class of steam-boilers will
do much toward the removal of the cause of that universal feeling of
distrust which renders the presence of a steam-boiler so objectionable
in every locality. The difficulties in thoroughly inspecting these
boilers, in regulating their action, and other faults of the class,
are gradually being overcome, and the committee look forward with
confidence to the time when their use will become general, to the
exclusion of older and more dangerous forms of steam-boilers."
The economical performance of these boilers with a similar ratio of
heating to grate surface is equal to that of other kinds. In fact,
they are usually given a somewhat higher ratio, and their economy of
fuel frequently exceeds that of the other types. Their principal
defect is their small capacity for steam and water, which makes it
extremely difficult to obtain steady steam-pressure. Where they are
employed, the feed and draught should be, if possible, controlled by
automatic attachments, and the feed-water heated to the highest
attainable temperature. Their satisfactory working depends, more than
in other cases, on the ability of the fireman, and can only be secured
by the exercise of both care and skill.
Many forms of these boilers have been devised. Walter Hancock
constructed boilers for his steam-carriage of flat plates connected by
stay-bolts, several such sections composing the boiler; and about the
same time (1828) Sir Goldsworthy Gurney constructed for a similar
purpose boilers consisting of a steam and a water reservoir, placed
one above the other, and connected by triangularly-bent water-tubes
exposed to the heat of the furnace-gases. Jacob Perkins made many
experiments looking to the employment of very high steam-pressures,
and in 1831 patented a boiler of this class, in which the
heating-surfaces nearest the fire were composed of iron tubes, which
tubes also served as grate-bars. The steam and water space was
principally comprised within a comparatively large chamber, of which
the walls were secured by closely distributed stay-bolts. For
extremely high pressures, boilers composed only of tubes were used.
Dr. Ernst Alban described the boiler already referred to, and its
construction and operation, and stated that he had experimented with
pressures as high as 1,000 pounds to the square inch.
The Harrison steam-boiler, which has been many years in use in the
United States, consists of several sections, each of which is made up
of hollow globes of cast-iron, communicating with each other by necks
cast upon the spheres, and fitted together with faced joints. Long
bolts, extending from end to end of each row, bind the spheres
together. (_See_ Fig. 111.)
[Illustration: FIG. 111.--Harrison's Sectional Boiler.]
An example of another modern type in extensive use is given in Fig.
112, a semi-sectional boiler, which consists of a series of inclined
wrought-iron tubes, connected by T-heads, which form the vertical
water-channels, at each end. The joints are faced by milling them, and
then ground so perfectly tight that a pressure of 500 pounds to the
square inch is insufficient to produce leakage. No packing is used.
The fire is made under the front and higher end of the tubes, and the
products of combustion pass up between the tubes into a
combustion-chamber under the steam and water drum; hence they pass
down between the tubes, then once more up through the space between
the tubes, and off to the chimney. The steam is taken out at the top
of the steam-drum near the back end of the boiler. The rapid
circulation prevents to some extent the formation of deposits or
incrustations upon the heating-surfaces, sweeping them away and
depositing them in the mud-drum, whence they are blown out. Rapid
circulation of water, as has been shown by Prof. Trowbridge, also
assists in the extraction of the heat from the gases, by the
presentation of fresh water continually, as well as by the prevention
of incrustation.
[Illustration: FIG. 112.--Babcock and Wilcox's Sectional Boiler.]
Attempts have been made to adapt sectional boilers to marine engines;
but very little progress has yet been made in their introduction. The
Root sectional boiler (Fig. 113), an American design, which is in
extensive use in the United States and Europe, has also been
experimentally placed in service on shipboard. Its heating-surface
consists wholly of tubes, which are connected by a peculiarly formed
series of caps; the joints are made tight with rubber "grummets."
[Illustration: FIG. 113.--Root Sectional Boiler.]
SECTION II.--PORTABLE AND LOCOMOTIVE ENGINES.
Engines and boilers, when of small size, are now often combined in one
structure which may be readily transported. Where they have a common
base-plate simply, as in Fig. 114, they are called, usually,
"semi-portable engines." These little engines have some decided
advantages. Being attached to one base, the combined engine and boiler
is easily transported, occupies little space, and may very readily be
mounted upon wheels, rendering it peculiarly well adapted for
agricultural purposes.
[Illustration: FIG. 114.--Semi-Portable Engine, 1878.]
The example here shown differs in its design from those usually seen
in the market. The engine is not fastened to or upon the boiler, and
is therefore not affected by expansion, nor are the bearings
overheated by conduction or by ascending heat from the boiler. The
fly-wheel is at the base, which arrangement secures steadiness at the
high speed which is a requisite for economy of fuel. The boilers are
of the upright tubular style, with internal fire-box, and are
intended to be worked at 150 pounds pressure per inch. They are fitted
with a baffle-plate and circulating-pipe, to prevent priming, and also
with a fusible plug, which will melt and prevent the crown-sheet of
the boiler burning, if the water gets low.
[Illustration: FIG. 115.--Semi-Portable Engine, 1878.]
Another illustration of this form of engine, as built in small sizes,
is seen below. The peculiarity of this engine is, that the cylinder is
placed in the top of the boiler, which is upright. By this arrangement
the engine is constantly drawing from the boiler the hottest and
driest steam, and there is thus no liability of serious loss by
condensation, which is rapid, even in a short pipe, when the engine is
separate from the boiler.
The engine illustrated is rated at 10 horse-power, and makers are
always expected to guarantee their machines to work up to the rated
power. The cylinder is 7 by 7 inches, and the main shaft is directly
over it. On this shaft are three eccentrics, one working the pump, one
moving the valves, and the third one operating the cut-off. The
driving-pulley is 20 inches in diameter, and the balance-wheel 30
inches. The boiler has 15 1-1/4-inch flues. It is furnished with a
heater in its lower portion. The boiler of this engine is tested up to
200 pounds, and is calculated to carry 100 pounds working pressure,
though that is not necessary to develop the full power of the engine.
The compactness of the whole machine is exceptional. It can be set up
in a space 5 feet square and 8 feet high. The weight of the 10
horse-power engine is 1,540 pounds, and of the whole machine 4,890
pounds, boxed for shipment. Every part of the mechanism usually fits
and works with the exactness of a gun-lock, as each piece is carefully
made to gauge.
Portable engines are those which are especially intended to be moved
conveniently from place to place. The engine is usually attached to
the boiler, and the feed-pump is generally attached to the engine. The
whole machine is carried on wheels, and is moved from one place to
another, usually by horses, but sometimes by its own engine, which is
coupled by an engaging and disengaging apparatus to the rear-wheels.
English builders have usually excelled in the construction of this
class of steam-engine, although it is probable that the best American
engines are fully equal to them in design, material, and construction.
The later work of the best-known English builders has given economical
results that have surprised engineers. The annual "shows" of the Royal
Agricultural Society have elicited good evidence of skill in
management as well as of excellence of design and construction. Some
little portable engines have exhibited an economical efficiency
superior to that of the largest marine engines of any but the compound
type, and even closely competing with that form. The causes of this
remarkable economy are readily learned by an inspection of these
engines, and by observation of the method of managing them at the
test-trial. The engines are usually very carefully designed. The
cylinders are nicely proportioned to their work, and their pistons
travel at high speed. Their valve-gear consists usually of a plain
slide-valve, supplemented by a separate expansion-slide, driven by an
independent eccentric, and capable of considerable variation
in the point of cut-off. This form of expansion-gear is very
effective--almost as much so as a drop cut-off--at the usual grade of
expansion, which is not far from four times. The governor is usually
attached to a throttle-valve in the steam-pipe, an arrangement which
is not the best possible under variable loads, but which produces no
serious loss of efficiency when the engine is driven, as at
competitive trials, under the very uniform load of a Prony strap-brake
and at very nearly the maximum capacity of the machine. The most
successful engines have had steam-jacketed cylinders--always an
essential to maximum economy--with high steam and a considerable
expansion. The boilers are strongly made, and are, as are also all
other heated surfaces, carefully clothed with non-conducting material,
and well lagged over all. The details are carefully proportioned, the
rods and frames are strong and well secured together, and the bearings
have large rubbing-surfaces. The connecting-rods are long and
easy-working, and every part is capable of doing its work without
straining and with the least friction.
In handling the engines at the competitive trial, most experienced and
skillful drivers are selected. The difference between the performances
of the same engine in different hands has been found to amount to from
10 to 15 per cent., even where the competitors were both considered
exceptionally skillful men. In manipulating the engine, the fires are
attended to with the utmost care; coal is thrown upon them at regular
and frequent intervals, and a uniform depth of fuel and a perfectly
clean fire are secured. The sides and corners of the fire are looked
after with especial care. The fire-doors are kept open the least
possible time; not a square inch of grate-surface is left unutilized,
and every pound of coal gives out its maximum of calorific power, and
in precisely the place where it is needed. Feed-water is supplied as
nearly as possible continuously, and with the utmost regularity. In
some cases the engine-driver stands by his engine constantly, feeding
the fire with coal in handfuls, and supplying the water to the heater
by hand by means of a cup. Heaters are invariably used in such cases.
The exhaust is contracted no more than is absolutely necessary for
draught. The brake is watched carefully, lest irregularity of
lubrication should cause oscillation of speed with the changing
resistance. The load is made the maximum which the engine is designed
to drive with economy. Thus all conditions are made as favorable as
possible to economy, and they are preserved as invariable as the
utmost care on the part of the attendant can make them.
These trials are usually of only three or five hours' duration, and
thus terminate before it becomes necessary to clean fires. The
following are results obtained at the trial of engines which took
place in July, 1870, at the Oxford Agricultural Fair:
KEY:
A: Number.
B: Diameter.
C: Stroke.
D: Nominal.
E: Dynamometric.
F: Point of cut off.
G: Revolutions per minute.
H: Pounds coal per horse-power per hour.
---------------+-------------+-----+--------------+------+------+----
MAKERS' NAME | CYLINDERS. | | HORSE-POWER. | | |
AND +-----+-------+ +-------+------+ | |
RESIDENCE. | A | B | C | D | E | F | G | H
---------------+-----+-------+-----+-------+------+------+------+----
| |Inches.| In. | | | | |
Clayton, | | | | | | | |
Shuttleworth | 1 | 7 | 12 | 4 | 4.42 | ... |121.65|3.73
& Co., Lincoln | | | | | | | |
| | | | | | | |
Brown & May, | | | | | | | |
Devizes | 1 | 7-3/16| 12 | 4 | 4.19 | 11.48|125.65|4.44
| | | | | | | |
Reading Iron- | | | | | | | |
Works Company, | 1 | 5-3/4 | 14 | 4 | 4.16 | ... |145.7 |4.65
Reading | | | | | | | |
---------------+-----+-------+-----+-------+------+------+------+----
These were horizontal engines, attached to locomotive boilers.
At a similar exhibition held at Bury, in 1867, considerably better
results even than these were reported, as below, from engines of
similar size and styles:
KEY:
A: Number.
B: Diameter.
C: Stroke.
D: Nominal.
E: Dynamometric.
F: Point of cut off.
G: Revolutions per minute.
H: Pounds coal per horse-power per hour.
---------------+-------------+-----+--------------+------+------+----
MAKERS' NAME | CYLINDERS. | | HORSE-POWER. | | |
AND +-----+-------+ +-------+------+ | |
RESIDENCE. | A | B | C | D | E | F | G | H
---------------+-----+-------+-----+-------+------+------+------+----
| |Inches.| In. | | | | |
Clayton, | | | | | | | |
Shuttleworth | 1 |10 | 20 | 10 | 11.00| 3.10 | 71.5 | 4.13
& Co., Lincoln | | | | | | | |
| | | | | | | |
Reading Iron- | | | | | | | |
Works Company, | 1 | 8-5/8 | 20 | 10 | 10.43| 1.4 |109.4 | 4.22
Reading | | | | | | | |
---------------+-----+-------+-----+-------+------+------+------+----
With all these engines steam-jackets were used; the feed-water was
highly and uniformly heated by exhaust-steam; the coal was selected,
finely broken, and thrown on the fire with the greatest care; the
velocity of the engines, the steam-pressure, and the amount of
feed-water, were very carefully regulated, and all bearings were run
quite loose; the engine-drivers were usually expert "jockeys."
The next illustration represents the portable steam-engine as built by
one of the oldest and most experienced manufacturers of such engines
in the United States.
In the boilers of these engines the heating-surface is given less
extent than in the stationary engine-boiler, but much greater than in
the locomotive, and varies from 10 to 20 square feet per horse-power.
The boilers are made very strong, to enable them to withstand the
strains due to the attached engine, which are estimated as equivalent
to from one-tenth to one-fifth that due to the steam-pressure. The
boiler is sometimes given even double the strength usual with
stationary boilers of similar capacity. The engine is mounted, in this
example, directly over the boiler, and all parts are in sight and
readily accessible to the engineer.
[Illustration: FIG. 116.--The Portable Steam-Engine, 1878.]
One of these engines, of 20 horse-power, has a steam-cylinder 10
inches in diameter and 18 inches stroke of piston, making 125
revolutions per minute, and has 9 square feet of grate-surface and 288
feet of heating-surface. It weighs about 4-1/2 tons. Steam is carried
at 125 pounds.
In the class of engines just described, the draught is obtained by the
blast of the exhaust-steam which is led into the chimney. Such engines
are now sold at from $120 to $150 per horse-power, according to size
and quality, the smaller engines costing most. The usual consumption
of fuel is from 4 to 6 pounds per hour and per horse-power, burning
from 15 to 20 pounds on each square foot of grate, and each pound
evaporating about 8 pounds of water. A usual weight is, for the larger
sizes, 500 pounds per horse-power.
[Illustration: FIG. 117.--The Thrashers' Road-Engine, 1878.]
These engines are sometimes arranged to propel themselves, as in the
Mills "Thrashers'" road-engine or locomotive, of which the
accompanying engraving is a good representation. This engine is
proportioned for hauling a tank containing 10 barrels, or more, of
water and a grain-separator over all ordinary roads, and to drive a
thrashing-machine or saw-mill, developing 20 or 25 horse-power. This
example of the road-engine has a boiler built to work at 250 pounds of
steam; the engine is designed for a maximum power of 30 horses.
This engine has a balanced valve and automatic cut-off, and is fitted
with a reversing-gear for use on the road. The driving-wheels are of
wrought-iron, 56 inches diameter and 8 inches wide, with cast-iron
driving-arms. Both wheels are drivers on curves as well as on straight
lines. The engine is guided and fired by one man, and the total weight
is so small that it will pass safely over any good country bridge. A
brake is attached, to insure safety when going down-hill. Although
designed to move at a speed of about three miles per hour, the
velocity of the piston may be increased so that four miles per hour
may be accomplished when necessary.
[Illustration: FIG. 118.--Fisher's Steam-Carriage.]
This is an excellent example of this kind of engine as constructed at
the present time. The strongly-built boiler, with its heater, the
jacketed cylinder, and light, strong frame of the engine, the steel
running-gear, the carefully-covered surfaces of cylinder and boiler,
and excellent proportions of details, are illustrations of good modern
engineering, and are in curious contrast with the first of the class,
built a century earlier by Smeaton.
Steam-carriages for passengers are now rarely built. Fig. 118
represents that designed by Fisher about 1870 or earlier. It was only
worked experimentally.
[Illustration: FIG. 119.--Road and Farm Locomotive.]
The above is an engraving of a road and farm locomotive as built by
one of the most successful among several British firms engaged in this
work.
The capacity of these engines has been determined by experiment by the
author in the United States, and abroad by several distinguished
engineers.
The author made a trial of one of these engines at South Orange, N.
J., to determine its power, speed, and convenience of working and
man[oe]uvring. The following were the principal dimensions:
Weight of engine, complete, 5 tons 4 cwt. 11,648 pounds.
Steam-cylinder--diameter 7-3/4 inches.
Stroke of piston 10 inches.
Revolution of crank to one of driving-wheels 17
Driving-wheels--diameter 60 inches.
" breadth of tire 10 inches.
" weight, each 450 pounds.
Boiler--length over all 8 feet.
" diameter of shell 30 feet.
" thickness of shell 7/16 inch.
" fire-box sheets, outside, thickness 1/2 inch.
Load on driving-wheels, 4 tons 10 cwt. 10,080 pounds.
The boiler was of the ordinary locomotive type, and the engine was
mounted upon it, as is usual with portable engines.
The steam-cylinder was steam-jacketed, in accordance with the most
advanced practice here and abroad. The crank-shaft and other
wrought-iron parts subjected to heavy strains were strong and plainly
finished. The gearing was of malleableized cast-iron, and all
bearings, from crank-shaft to driving-wheel, on each side, were
carried by a single sheet of half-inch plate, which also formed the
sides of the fire-box exterior.
The following is a summary of the conclusions deduced by the author
from the trial, and published in the _Journal of the Franklin
Institute_: A traction-engine may be so constructed as to be easily
and rapidly man[oe]uvred on the common road; and an engine weighing
over 5 tons may be turned continuously without difficulty on a circle
of 18 feet radius, or even on a road but little wider than the length
of the engine. A locomotive of 5 tons 4 hundredweight has been
constructed, capable of drawing on a good road 23,000 pounds up a
grade of 533 feet to the mile, at the rate of four miles an hour; and
one might be constructed to draw more than 63,000 pounds up a grade of
225 feet to the mile, at the rate of two miles an hour.
It was further shown that the coefficient of traction with
heavily-laden wagons on a good macadamized road is not far from .04;
the traction-power of this engine is equal to that of 20 horses; the
weight, exclusive of the weight of the engine, that could be drawn on
a level road, was 163,452 pounds; and the amount of fuel required is
estimated at 500 pounds a day. The advantages claimed for the
traction-engine over horse-power are: no necessity for a limitation of
working-hours; a difference in first cost in favor of steam; and in
heavy work on a common road the expense by steam is less than 25 per
cent. of the average cost of horse-power, a traction-engine capable of
doing the work of 25 horses being worked at as little expense as 6 or
8 horses. The cost of hauling heavy loads has been estimated at 7
cents per ton per mile.
Such engines are gradually becoming useful in steam-ploughing. Two
systems are adopted. In the one the engine is stationary, and hauls a
"gang" of ploughs by means of a windlass and wire rope; in the other
the engine traverses a field, drawing behind it a plough or a gang of
ploughs. The latter method has been proposed for breaking up
prairie-land.
Thus, thirty years after the defeat of the intelligent, courageous,
and persistent Hancock and his coworkers in the scheme of applying the
steam-engine usefully on the common road, we find strong indications
that, in a new form, the problem has been again attacked, and at least
partially solved.
One of the most important of the prerequisites to ultimate success in
the substitution of steam for animal power on the highway is that our
roads shall be well made. As the greatest care and judgment are
exercised, and an immense outlay of capital is considered justifiable,
in securing easy grades and a smooth track on our railroad routes, we
may readily believe that similar precaution and outlay will be found
advisable in adapting the common road to the road-locomotive. It would
seem to the engineer that the natural obstacles generally supposed to
stand in the way have, after all, no real existence. The principal
inconvenience that may be anticipated will probably arise from the
carelessness or avarice of proprietors, which may sometimes cause them
to appoint ignorant and inefficient engine-drivers, giving them charge
of what are always excellent servants, but terrible masters.
Nevertheless, as the transportation of passengers on railroads is
found to be attended with less liability to loss of life or injury of
person than their carriage by stage-coach, it will be found, very
probably, that the general use of steam in transporting freight on
common roads may be attended with less risk to life or property than
to-day attends the use of horse-power.
The STEAM FIRE-ENGINE is still another form of portable engine. It is
also one of the latest of all applications of steam-power. The steam
fire-engine is peculiarly an American production. Although previously
attempted, their permanently successful introduction has only occurred
within the last fifteen years.
[Illustration: FIG. 120.--The Latta Steam Fire-Engine.]
As early as 1830, Braithwaite and Ericsson, of London, England, built
an engine with steam and pump cylinders of 7 and 6-1/2 inches
diameter, respectively, with 16 inches stroke of piston. This machine
weighed 2-1/2 tons, and is said to have thrown 150 gallons of water
per minute to a height of between 80 and 100 feet. It was ready for
work in about 20 minutes after lighting the fire. Braithwaite
afterward supplied a more powerful engine to the King of Prussia, in
1832. The first attempt made in the United States to construct a steam
fire-engine was probably that of Hodge, who built one in New York in
1841. It was a strong and very effective machine, but was far too
heavy for rapid transportation. The late J. K. Fisher, who throughout
his life persistently urged the use of steam-carriages and
traction-engines, designing and building several, also planned a
steam fire-engine. Two were built from his design by the Novelty
Works, New York, about 1860, for Messrs. Lee & Larned. They were
"self-propellers," and one of them, built for the city of
Philadelphia, was sent to that city over the highway, driven by its
own engines. The other was built for and used by the New York Fire
Department, and did good service for several years. These engines were
heavy, but very powerful, and were found to move at good speed under
steam and to man[oe]uvre well. The Messrs. Latta, of Cincinnati, soon
after succeeded in constructing comparatively light and very effective
engines, and the fire department of that city was the first to adopt
steam fire-engines definitely as their principal reliance. This change
has now become general.
The steam fire-engine has now entirely displaced the old hand-engine
in all large cities. It does its work at a fraction of the cost of the
latter. It can force its water to a height of 225 feet, and to a
distance of more than 300 feet horizontally, while the hand-engine can
seldom throw it one-third these distances; and the "steamer" may be
relied upon to work at full power many hours if necessary, while the
men at the hand-engine soon become fatigued, and require frequent
relief. The city of New York has 40 steam fire-engines. One engine to
every 10,000 inhabitants is a proper proportion.
In the standard steam fire-engine (Fig. 120) reciprocating engines and
pumps are adopted, as seen in section in Fig. 121, in which _A_ is the
furnace, and _B_ the set of closely-set vertical fire-tubes in the
boiler. _C_ is the combustion-chamber, _D_ the smoke-pipe, and _R_ the
steam-space. _E_ is the steam-cylinder, and _F_ the pump, which is
seen to be double-acting. There are two pairs of engines and pumps,
working on cranks, set at right angles, and turning a balance-wheel
seen behind them. _G_ is the feed-pump which supplies water to the
boiler, _H_ the air-chamber which equalizes the water-pressure, which
reaches it through the pipe, _I J_. _K_ is the feed-water tank, under
the driver's seat, _L_, which, with the engines and boiler, are
carried on the frame, _M M_. The fireman stands on the platform, _N_.
When it is necessary to move the machine, an endless chain connects
the crank-shaft with the rear-wheels, and the engine, with pumps shut
off, is thus made to drive the wheels at any desired speed.
[Illustration: FIG. 121.--The Amoskeag Engine. Section.]
[Illustration: FIG. 122.--The Silsby Rotary Steam Fire-Engine.]
A self-propelling engine by the Amoskeag Company had the following
dimensions and performance: Weight, 4 tons; speed, 8 miles per hour;
steam-pressure, 75 pounds per square inch; height of stream from
1-1/4-inch nozzle, 225 feet; 1-3/4-inch nozzle, 150 feet; distance
horizontally, 1-1/4-inch nozzle, 300 feet; 1-3/4-inch, 250 feet--a
performance which contrasts wonderfully with that of the hand-worked
fire-engine which these engines have now superseded.
It has recently become common to construct the steam fire-engine with
rotary engine and pump (Fig. 122). The superiority of a rotary motion
for a steam-engine is apparently so evident that many attempts have
been made to overcome the practical difficulties to which it is
subject. One of these difficulties, and the principal one, has been
the packing of the part which performs the office of the piston in the
straight cylinder. Robert Stephenson once expressed the opinion that a
rotary engine would never be made to work successfully, on account of
this difficulty of packing. The most palpable of the advantages of the
rotary engine are the reduction in the size of the engine, claimed to
result from the great velocity of the piston; the avoidance of great
accidental strains, especially noticed in propelling ships; and a
great saving of the power which is asserted to be expended in the
reciprocating engine in overcoming the inertia while changing the
direction of the motions. These advantages adapt the rotary engine, in
an especial manner, to the driving of a locomotive or steam
fire-engine.
[Illustration: FIG. 123.--Rotary Steam-Engine.]
[Illustration: FIG. 124.--Rotary Pump.]
In the Holly rotary engine, seen in Fig. 123, eccentrics and
sliding-cams, which are frequently used in rotary engines, and which
are objectionable on account of their great friction, are avoided.
Corrugated pistons, or irregular cams, _C D_, are adopted, forming
chambers within the cases. In the engine the steam enters at _A_, at
the bottom of the case, and presses the cams apart. The only packing
used is in the ends of the long metal cogs, which are ground to fit
the case and are kept out by the momentum of the cams, assisted by a
slight spring back of the packing-pieces. The friction on the pump
(Fig. 124) is said to be less than in the engine. This is the reason
given in support of the claim that the rotary engine forces water to a
given distance with from one-fourth to one-third the steam-pressure
necessary to drive all reciprocating engines. The smaller amount of
power necessary to do the work, the less strain and consequent wear
and tear upon the whole machine, are said to make it more durable and
reliable. The pump being chambered, its liability to injury by the use
of dirty or gritty water is lessened, and it is stated that it will
last for years, pumping gritty water that would soon cut out a
piston-pump. The pump used with this engine is, as shown in the above
illustration, somewhat similar to the rotary engine driving it. Each
of the revolving pistons has three long teeth bearing against the
cylinder, and packed, to prevent leakage, like the engine-cams. They
are carried on steel shafts coupled to the engine-shafts. The water
enters at _E_ and is discharged at _F_, and the passages are purposely
made large in order that sand, chips, and dirt, which may enter with
the water, may pass through.
The rotary engine is gradually coming into use for various special
purposes, where small power is called for, and where economy of fuel
is not important; but it has never yet competed, and may perhaps never
in the future compete, with the reciprocating-piston engine where
large engines are required, or where even moderate economy of fuel is
essential. This form of engine has assumed so little importance, in
fact, in the application of the steam-engine, that comparatively
little is known of its history. Watt invented a rotary engine, and
Yule many years afterward (1836) constructed such engines at Glasgow.
Lamb patented another in 1842, Behrens still another in 1847. Napier,
Hall, Massey, Holly, La France, and others, have built engines of this
class in later times. Nearly all consist either of cams rotating in
gear, as in those above sketched, or of a piston set radially in a
cylinder of small diameter, which turns on its axis within a much
larger cylinder set eccentrically, the piston, as the former turns,
sliding in and out of the smaller cylinder as its outer edge slides in
contact with the inner surface of the larger. In some forms of rotary
engine, a piston revolves on a central shaft, and a sliding abutment
in the external cylinder serves to separate the steam from the exhaust
side and to confine the steam expanding while doing work. Nearly all
of these combinations are also used as pumps.
Fire-engines, made by the best-known American builders of engines,
with reciprocating engines and pumps, such as are in general use in
the United States, have become standard in general plan and
arrangement of details. These are probably the best illustrations of
extreme lightness, combined with strength of parts and working power,
which have ever been produced in any branch of mechanical
engineering. By using a small boiler crowded with heating-surface,
very carefully proportioned and arranged, and with small water-spaces;
by adopting steel for running-gear and working parts wherever
possible; by working at high piston-speed and with high
steam-pressure; by selecting fuel with extreme care--by all these
expedients, the steam fire-engine has been brought, in this country,
to a state of efficiency far superior to anything seen elsewhere.
Steam is raised with wonderful promptness, even from cold water, and
water is thrown from the nozzle at the end of long lines of hose to
great distances. But this combination of lightness with power is only
attained at the expense of a certain regularity of action which can
only be secured by greater water and steam capacity in the boiler. The
small quantity of water contained within the boiler makes it necessary
to give constant attention to the feed, and the tendency, almost
invariably observed, to serious foaming and priming not only compels
unintermitted care while running, but even introduces an element of
danger which is not to be despised, even though the machine be in
charge of the most experienced and skillful attendants. Even the
greatest care, directed by the utmost skill, would not avail to
prevent frequent explosions, were it not for the fact that it rarely,
if ever, happens that accidents to such boilers occur from low water,
unless the boiler is actually completely emptied of water. In driving
them at fires, they frequently foam so violently that it is utterly
impossible to obtain any clew to the amount of water present, and the
attendant usually keeps his feed-pump on and allows the foaming to go
on. As long as water is passing into the boiler it is very unlikely
that any portion will become overheated and that accident will occur.
Such management appears very reckless, and yet accident from such a
cause is exceedingly rare.
The changes which have been made in LOCOMOTIVE-CONSTRUCTION during the
past few years have also been in the direction of the refinement of
the earlier designs, and have been accompanied by corresponding
changes in all branches of railroad-work. The adjustment of parts to
each other and proportioning them to their work, the modification of
the minor details to suit changes of general dimensions, the
improvement of workmanship, and the use of better material, have
signalized this latest period. Special forms of engine have been
devised for special kinds of work. Small, light tank-engines (Fig.
125), carrying their own fuel and water without "tenders," are used
for moving cars about terminal stations and for making up trains;
powerful, heavy, slow-moving engines, of large boiler-capacity and
with small wheels, are used on steep gradients and for hauling long
trains laden with coal and heavy merchandise; and hardly less powerful
but quite differently proportioned "express"-engines are used for
passenger and mail service.
[Illustration: FIG. 125.--Tank-Engine, New York Elevated Railroad.]
[Illustration: FIG. 126.--Forney's Tank-Locomotive.]
A peculiar form of engine (Fig. 126) has been designed by Forney, in
which the whole weight of engine, tender, coal, and water, is carried
by one frame and on one set of wheels, the permanent weight falling on
the driving-wheels and the variable load on the truck. These engines
have also a comparatively short wheel-base and high pulling-power. The
lightest tank-engines of the first class mentioned weigh 8 or 10 tons;
but engines much lighter than these, even, are built for mines, where
they are sent into the galleries to bring out the coal-laden wagons.
The heaviest engines of this class attain weights of 20 or 30 tons.
The heaviest engine yet constructed in the United States is said to be
one in use on the Philadelphia & Reading Railroad, having a weight of
about 100,000 pounds, which is carried on 12 driving-wheels.
[Illustration: FIG. 127.--British Express Engine.]
[Illustration: FIG. 128.--The Baldwin Locomotive. Section.]
[Illustration: FIG. 129.--The American Type of Express-Engine, 1878.]
A locomotive has two steam-cylinders, either side by side within the
frame, and immediately beneath the forward end of the boiler, or on
each side and exterior to the frame. The engines are non-condensing,
and of the simplest possible construction. The whole machine is
carried upon strong but flexible steel springs. The steam-pressure is
usually more than 100 pounds. The pulling-power is generally about
one-fifth the weight under most favorable conditions, and becomes as
low as one-tenth on wet rails. The fuel employed is wood in new
countries, coke in bituminous coal districts, and anthracite coal in
the eastern part of the United States. The general arrangement and the
proportions of locomotives differ somewhat in different localities.
In Fig. 127, a British express-engine, _O_ is the boiler, _N_ the
fire-box, _X_ the grate, _G_ the smoke-box, and _P_ the chimney. _S_
is a spring and _R_ a lever safety-valve, _T_ is the whistle, _L_ the
throttle or regulator valve, _E_ the steam-cylinder, and _W_ the
driving-wheel. The force-pump, _B C_, is driven from the cross-head,
_D_. The frame is the base of the whole system, and all other parts
are firmly secured to it. The boiler is made fast at one end, and
provision is made for its expansion when heated. Adhesion is
secured by throwing a proper proportion of the weight upon the
driving-wheel, _W_. This is from about 6,000 pounds on standard
freight-engines, having several pairs of drivers, to 10,000 pounds on
passenger-engines, per axle. The peculiarities of the American type
(Fig. 128) are the truck, _I J_, or bogie, supporting the forward part
of the engine, the system of equalizers, or beams which distribute the
weight of the machine equally over the several axles, and minor
differences of detail. The cab or house, _r_, protecting the
engine-driver and fireman, is an American device, which is gradually
coming into use abroad also. The American locomotive is distinguished
by its flexibility and ease of action upon even roughly-laid roads. In
the sketch, which shows a standard American engine in section, _A B_
is the boiler, _C_ one of the steam-cylinders, _D_ the piston, _E_ the
cross-head, connected to the crank-shaft, _F_, by the connecting-rod,
_G H_ the driving-wheels, _I J_ the truck-wheels, carrying the truck,
_K L_; _N N_ is the fire-box, _O O_ the tubes, of which but four are
shown. The steam-pipe, _R S_, leads the steam to the valve-chest, _T_,
in which is seen the valve, moved by the valve-gear, _U V_, and the
link, _W_. The link is raised or depressed by a lever, _X_, moved from
the cab. The safety-valve is seen at the top of the dome, at _Y_, and
the spring-balance by which the load is adjusted is shown at _Z_. At
_a_ is the cone-shaped exhaust-pipe, by which a good draught is
secured. The attachments _b_, _c_, _d_, _e_, _f_, _g_--whistle,
steam-gauge, sand-box, bell, head-light, and "cow-catcher"--are nearly
all peculiar, either in construction or location, to the American
locomotive. The cost of passenger-locomotives of ordinary size is
about $12,000; heavier engines sometimes cost $20,000. The locomotive
is usually furnished with a tender, which carries its fuel and water.
The standard passenger-engine on the Pennsylvania Railroad has four
driving-wheels, 5-1/2 feet diameter; steam-cylinders, 17 inches
diameter and 2 feet stroke; grate-surface 15-1/2 square feet, and
heating-surface 1,058 square feet. It weighs 63,100 pounds, of which
39,000 pounds are on the drivers and 24,100 on the truck. The
freight-engine has six driving-wheels, 54-5/8 inches in diameter. The
steam-cylinders are 18 inches in diameter, stroke 22 inches,
grate-surface 14.8 square feet, heating-surface 1,096 feet. It weighs
68,500 pounds, of which 48,000 are on the drivers and 20,500 on the
truck. The former takes a train of five cars up an average grade of 90
feet to the mile. The latter is attached to a train of 11 cars. On a
grade of 50 feet to the mile, the former takes 7 and the latter 17
cars. Tank-engines for very heavy work, such as on grades of 320 feet
to the mile, which are found on some of the mountain lines of road,
are made with five pairs of driving-wheels, and with no truck. The
steam-cylinders are 20-1/8 inches in diameter, 2 feet stroke;
grate-area, 15-3/4 feet; heating-surface, 1,380 feet; weight with tank
full, and full supply of wood, 112,000 pounds; average weight, 108,000
pounds. Such an engine has hauled 110 tons up this grade at the speed
of 5 miles an hour, the steam-pressure being 145 pounds. The adhesion
was about 23 per cent. of the weight.
In checking a train in motion, the inertia of the engine itself
absorbs a seriously large portion of the work of the brakes. This is
sometimes reduced by reversing the engine and allowing the
steam-pressure to act in aid of the brakes. To avoid injury by
abrasion of the surfaces of piston, cylinder, and the valves and
valve-seats, M. Le Chatelier introduces a jet of steam into the
exhaust-passages when reversing, and thus prevents the ingress of
dust-laden air and the drying of the rubbing surfaces. This method of
checking a train is rarely resorted to, however, except in case of
danger. The introduction of the "continuous" or "air" brake, which can
be thrown into action in an instant on every car of the train by the
engine-driver, is so efficient that it is now almost universally
adopted. It is one of the most important safeguards which American
ingenuity has yet devised. In drawing a train weighing 150 tons at the
rate of 60 miles an hour, about 800 effective horse-power is required.
A speed of 80 miles an hour has been often attained, and 100 miles has
probably been reached.
The American locomotive-engine has a maximum life which may be stated
at about 30 years. The annual cost of repairs is from 10 to 15 per
cent. of its first cost. On moderately level roads, the engine
requires a pint of oil to each 25 miles, and a ton of coal to each 40
or 50 miles run. One of the best-managed railroads in the United
States reports expenses as follows for one month:
Number "train-miles" run per ton of coal burned 53.95
" " " " quart of oil used 34.44
Passenger-cars hauled 1 mile per ton of coal 275.7
Other " " " " " 634.8
Cost repairs per mile run $2 43
" fuel " " 3 64
" oil and waste per mile run 62
" wages of engine-men per mile run 6 22
All other expenses per mile 1 91
Total cost per "train-mile" run 14 82
Although the above sketch and description represent the construction
and performance of the standard locomotive of the present time, there
are indications that the compound arrangement of engines will
ultimately be adopted. This will involve a considerable change of
proportions, greatly increasing the volume and weight of
steam-cylinders, but enabling the designer to more than proportionally
decrease the weight of boiler and the quantity of fuel carried. There
is no serious objection to their use, however, and no insuperable
difficulty in the construction of the "double-cylinder" type of engine
for the locomotive. A few such engines have already been put in
service. In these engines the high-pressure cylinder is placed on one
side and the larger low-pressure cylinder on the other side of the
locomotive, thus having but two cylinders, as in the older plan. The
valve-gear is the Stephenson link, as in the ordinary engine. At
starting, the steam is allowed to act on both pistons; but after a few
revolutions the course of the steam is changed, and the exhaust from
the smaller cylinder, instead of passing into the chimney, is sent to
the larger cylinder, which is at the same time cut off from the main
steam-pipe. When the engine is ascending a steep gradient the steam
may, if necessary, be taken from the boiler into both cylinders, as
when starting. Compound engines of this kind have been used on the
French line of railroad from Bayonne to Biarritz. They were designed
by Mallet and built at Le Creuzot. The steam-cylinders are of 9-1/2
and 15-3/4 inches diameter, and of 17-3/4 inches stroke of piston. The
four driving-wheels are 4 feet in diameter, and the total weight of
engine is 20 tons. The boiler has 484-1/2 square feet of
heating-surface, and is built to carry 10 atmospheres pressure. When
hauling trains of 50 tons at 25 miles an hour, these engines require
about 15 pounds of good coal per mile.
The total length of the railways in operation in the United States on
the 1st day of January, 1877, was 76,640 miles,[93] being an average
of one mile of railway for every 600 inhabitants. The railways are as
follows:
[93] January, 1884, over 120,000 miles.
Miles.