Copyright
John Bourne.

A Catechism of the Steam Engine online

. (page 1 of 34)
Online LibraryJohn BourneA Catechism of the Steam Engine → online text (page 1 of 34)
Font size
QR-code for this ebook


Produced by Robert Connal and PG Distributed Proofreaders from images
generously provided by the Digital & Multimedia Center, Michigan State
University Libraries.





A CATECHISM OF THE STEAM ENGINE

IN ITS VARIOUS APPLICATIONS TO MINES,
MILLS, STEAM NAVIGATION, RAILWAYS,
AND AGRICULTURE.

WITH

PRACTICAL INSTRUCTIONS FOR THE MANUFACTURE
AND MANAGEMENT OF ENGINES OF EVERY CLASS.


BY

JOHN BOURNE, C.E.


_NEW AND REVISED EDITION._


[Transcriber's Note: Inconsistencies in chapter headings and numbering
of paragraphs and illustrations have been retained in this edition.]


PREFACE

TO THE FOURTH EDITION.

For some years past a new edition of this work has been called for, but I
was unwilling to allow a new edition to go forth with all the original
faults of the work upon its head, and I have been too much engaged in the
practical construction of steam ships and steam engines to find time for
the thorough revision which I knew the work required. At length, however, I
have sufficiently disengaged myself from these onerous pursuits to
accomplish this necessary revision; and I now offer the work to the public,
with the confidence that it will be found better deserving of the favorable
acceptation and high praise it has already received. There are very few
errors, either of fact or of inference, in the early editions, which I have
had to correct; but there are many omissions which I have had to supply,
and faults of arrangement and classification which I have had to rectify. I
have also had to bring the information, which the work professes to afford,
up to the present time, so as to comprehend the latest improvements.

For the sake of greater distinctness the work is now divided into chapters.
Some of these chapters are altogether new, and the rest have received such
extensive additions and improvements as to make the book almost a new one.
One purpose of my emendations has been to render my remarks intelligible to
a tyro, as well as instructive to an advanced student. With this view, I
have devoted the first chapter to a popular description of the Steam
Engine - which all may understand who can understand anything - and in the
subsequent gradations of progress I have been careful to set no object
before the reader for the first time, of which the nature and functions are
not simultaneously explained. The design I have proposed to myself, in the
composition of this work, is to take a young lad who knows nothing of steam
engines, and to lead him by easy advances up to the highest point of
information I have myself attained; and it has been a pleasing duty to me
to smooth for others the path which I myself found so rugged, and to
impart, for the general good of mankind, the secrets which others have
guarded with so much jealousy. I believe I am the first author who has
communicated that practical information respecting the steam engine, which
persons proposing to follow the business of an engineer desire to possess.
My business has, therefore, been the rough business of a pioneer; and while
hewing a road through the trackless forest, along which all might hereafter
travel with ease, I had no time to attend to those minute graces of
composition and petty perfection of arrangement and collocation, which are
the attribute of the academic grove, or the literary parterre. I am,
nevertheless, not insensible to the advantages of method and clear
arrangement in any work professing to instruct mankind in the principles
and practice of any art; and many of the changes introduced into the
present edition of this work are designed to render it less exceptionable
in this respect. The woodcuts now introduced into the work for the first
time will, I believe, much increase its interest and utility; and upon the
whole I am content to dismiss it into circulation, in the belief that those
who peruse it attentively will obtain a more rapid and more practical
acquaintance with the steam engine in its various applications, than they
would be likely otherwise to acquire.

I have only to add that I have prepared a sequel to the present work, in
the shape of a Hand-Book of the Steam Engine, containing the whole of the
rules given in the present work, illustrated by examples worked out at
length, and also containing such useful tables and other data, as the
engineer requires to refer to constantly in the course of his practice.
This work may be bound up with the "Catechism," if desired, to which it is
in fact a Key.

I shall thankfully receive from engineers, either abroad or at home,
accounts of any engines or other machinery, with which they may become
familiar in their several localities; and I shall be happy, in my turn, to
answer any inquiries on engineering subjects which fall within the compass
of my information. If young engineers meet with any difficulty in their
studies, I shall be happy to resolve it if I can; and they may communicate
with me upon any such point without hesitation, in whatever quarter of the
world they may happen to be.


JOHN BOURNE.
9 BILLITER STREET,
LONDON,

_March 1st, 1856_.




PREFACE

TO THE FIFTH EDITION.

The last edition of the present work, consisting of 3,500 copies, having
been all sold off in about ten months, I now issue another edition, the
demand for the work being still unabated. It affords, certainly, some
presumption that a work in some measure supplies an ascertained want, when,
though addressing only a limited circle - discoursing only of technical
questions, and without any accident to stimulate it into notoriety, - it
attains so large a circulation as the present work has reached. Besides
being reprinted in America, it has been translated into German, French,
Dutch, and I believe, into some other languages, so that there is, perhaps,
not too much vanity in the inference that it has been found serviceable to
those perusing it. I can with truth say, that the hope of rendering some
service to mankind, in my day and generation, has been my chief inducement
in writing it, and if this end is fulfilled, I have nothing further to
desire.

I regret that circumstances have prevented me from yet issuing the
"Hand-Book" which I have had for some time in preparation, and to which, in
my Preface of the last year, I referred. I hope to have sufficient leisure
shortly, to give that and some other of my literary designs the necessary
attention. Whatever may have been the other impediments to a more prolific
authorship, certainly one of them has not been the coldness of the
approbation with which my efforts have been received, since my past
performances seem to me to have met with an appreciation far exceeding
their deserts.

JOHN BOURNE.

_February 2d, 1857_.




PUBLISHERS' NOTICE.


In offering to the American public a reprint of a work on the Steam Engine
so deservedly successful, and so long considered standard, the publishers
have not thought it necessary that it should be an exact copy of the
English edition; there were some details in which they thought it could be
improved, and better adapted to the use of American engineers. On this
account, the size of the page has been increased to a full 12mo, to admit
of larger illustrations, which in the English edition are often on too
small a scale; and some of the illustrations themselves have been supplied
by others equally applicable, more recent, and to us more familiar
examples. The first part of Chapter XI, devoted in the English edition to
English portable and fixed agricultural engines, in this edition gives
place entirely to illustrations from American practice, of steam engines as
applied to different purposes, and of appliances and machines necessary to
them. But with the exception of some of the illustrations and the
description of them, and the correction of a few typographical errors, this
edition is a faithful transcript of the latest English edition.




CONTENTS.


Classification of Engines.

Nature and uses of a Vacuum.

Velocity of falling Bodies and Momentum of moving Bodies.

Central Forces.

Centres of Gravity, Gyration, and Oscillation.

The Pendulum and Governor.

The Mechanical Powers.

Friction.

Strength of materials and Strains subsisting in Machines.


CHAP. I. - GENERAL DESCRIPTION OF THE STEAM ENGINE.

The Boiler.

The Engine.

The Marine Engine.

Screw Engines.

The Locomotive Engine.


CHAP. II. - HEAT, COMBUSTION, AND STEAM.

Heat.

Combustion.

Steam.


CHAP. III. - EXPANSION OF STEAM AND ACTION OF THE VALVES.


CHAP. IV. - MODES OF ESTIMATING THE POWER AND PERFORMANCE OF
ENGINES AND BOILERS.

Horses Power.

Duty of Engines and Boilers.

The Indicator.

Dynamometer, Gauges, and Cataract.


CHAP. V. - PROPORTIONS OF BOILERS.

Heating and Fire Grate Surface.

Calorimeter and Vent.

Evaporative Power of Boilers.

Modern Marine and Locomotive Boilers.

The Blast in Locomotives.

Boiler Chimneys.

Steam Room and Priming.

Strength of Boilers.

Boiler Explosions.


CHAP. VI. - PROPORTIONS OF ENGINES.

Steam Passages.

Air Pump, Condenser, and Hot and Cold Water Pumps.

Fly Wheel.

Strengths of Land Engines.

Strengths of Marine and Locomotive Engines.


CHAP. VII. - CONSTRUCTIVE DETAILS OF BOILERS.

Land and Marine Boilers.

Incrustation and Corrosion of Boilers.

Locomotive Boilers.


CHAP. VIII. - CONSTRUCTIVE DETAILS OF ENGINES.

Pumping Engines.

Various forms of Marine Engines.

Cylinders, Pistons, and Valves.

Air Pump and Condenser.

Pumps, Cocks, and Pipes.

Details of the Screw and Screw Shaft.

Details of the Paddles and Paddle Shaft.

The Locomotive Engine.


CHAP. IX. - STEAM NAVIGATION.

Resistance of Vessels in Water.

Experiments on the Resistance of Vessels.

Influence of the size of Vessels upon their Speed.

Structure and Operation of Paddle Wheels.

Configuration and Action of the Screw.

Comparative Advantages of Paddle and Screw Vessels.

Comparative Advantages of different kinds of Screws.

Proportions of Screws.

Screw Vessels with full and auxiliary Power.

Screw and Paddles combined.


CHAP. X. - EXAMPLES OF ENGINES OF RECENT CONSTRUCTION.

Oscillating Paddle Engines.

Direct acting Screw Engine.

Locomotive Engine.


CHAP. XI. - ON VARIOUS FORMS AND APPLICATIONS OF THE STEAM ENGINE.

Governor.

Donkey Pumps.

Portable Steam Engines.

Stationary Engines.

Steam Fire Engines.

Steam Excavator.


CHAP. XII. - MANUFACTURE AND MANAGEMENT OF STEAM ENGINES.

Construction of Engines.

Erection of Engines.

Management of Marine Boilers.

Management of Marine Engines.

Management of Locomotives.




MECHANICAL PRINCIPLES OF THE STEAM ENGINE.



CLASSIFICATION OF ENGINES.


1. _Q._ - What is meant by a vacuum?

_A._ - A vacuum means an empty space; a space in which there is neither
water nor air, nor anything else that we know of.

2. _Q._ - Wherein does a high pressure differ from a low pressure engine?

_A._ - In a high pressure engine the steam, after having pushed the piston
to the end of the stroke, escapes into the atmosphere, and the impelling
force is therefore that due to the difference between the pressure of the
steam and the pressure of the atmosphere. In the condensing engine the
steam, after having pressed the piston to the end of the stroke, passes
into the condenser, in which a vacuum is maintained, and the impelling
force is that due to the difference between the pressure of the steam above
the piston, and the pressure of the vacuum beneath it, which is nothing;
or, in other words, you have then the whole pressure of the steam urging
the piston, consisting of the pressure shown by the safety-valve on the
boiler, and the pressure of the atmosphere besides.

3. _Q._ - In what way would you class the various kinds of condensing
engines?

_A._ - Into single acting, rotative, and rotatory engines. Single acting
engines are engines without a crank, such as are used for pumping water.
Rotative engines are engines provided with a crank, by means of which a
rotative motion is produced; and in this important class stand marine and
mill engines, and all engines, indeed, in which the rectilinear motion of
the piston is changed into a circular motion. In rotatory engines the steam
acts at once in the production of circular motion, either upon a revolving
piston or otherwise, but without the use of any intermediate mechanism,
such as the crank, for deriving a circular from a rectilinear motion.
Rotatory engines have not hitherto been very successful, so that only the
single acting or pumping engine, and the double acting or rotative engine
can be said to be in actual use. For some purposes, such, for example, as
forcing air into furnaces for smelting iron, double acting engines are
employed, which are nevertheless unfurnished with a crank; but engines of
this kind are not sufficiently numerous to justify their classification as
a distinct species, and, in general, those engines may be considered to be
single acting, by which no rotatory motion is imparted.

4. _Q._ - Is not the circular motion derived from a cylinder engine very
irregular, in consequence of the unequal leverage of the crank at the
different parts of its revolution?

_A._ - No; rotative engines are generally provided with a fly-wheel to
correct such irregularities by its momentum; but where two engines with
their respective cranks set at right angles are employed, the irregularity
of one engine corrects that of the other with sufficient exactitude for
many purposes. In the case of marine and locomotive engines, a fly-wheel is
not employed; but for cotton spinning, and other purposes requiring great
regularity of motion, its use with common engines is indispensable, though
it is not impossible to supersede the necessity by new contrivances.

5. _Q._ - You implied that there is some other difference between single
acting and double acting engines, than that which lies in the use or
exclusion of the crank?

_A._ - Yes; single acting engines act only in one way by the force of the
steam, and are returned by a counter-weight; whereas double acting engines
are urged by the steam in both directions. Engines, as I have already said,
are sometimes made double acting, though unprovided with a crank; and there
would be no difficulty in so arranging the valves of all ordinary pumping
engines, as to admit of this action; for the pumps might be contrived to
raise water both by the upward and downward stroke, as indeed in some mines
is already done. But engines without a crank are almost always made single
acting, perhaps from the effect of custom, as much as from any other
reason, and are usually spoken of as such, though it is necessary to know
that there are some deviations from the usual practice.



NATURE AND USES OF A VACUUM.

6. _Q._ - The pressure of a vacuum you have stated is nothing; but how can
the pressure of a vacuum be said to be nothing, when a vacuum occasions a
pressure of 15 lbs. on the square inch?

_A._ - Because it is not the vacuum which exerts this pressure, but the
atmosphere, which, like a head of water, presses on everything immerged
beneath it. A head of water, however, would not press down a piston, if the
water were admitted on both of its sides; for an equilibrium would then be
established, just as in the case of a balance which retains its equilibrium
when an equal weight is added to each scale; but take the weight out of one
scale, or empty the water from one side of the piston, and motion or
pressure is produced; and in like manner pressure is produced on a piston
by admitting steam or air upon the one side, and withdrawing the steam or
air from the other side. It is not, therefore, to a vacuum, but rather to
the existence of an unbalanced plenum, that the pressure made manifest by
exhaustion is due, and it is obvious therefore that a vacuum of itself
would not work an engine.

7. _Q._ - How is the vacuum maintained in a condensing engine?

_A._ - The steam, after having performed its office in the cylinder, is
permitted to pass into a vessel called the condenser, where a shower of
cold water is discharged upon it. The steam is condensed by the cold water,
and falls in the form of hot water to the bottom of the condenser. The
water, which would else be accumulated in the condenser, is continually
being pumped out by a pump worked by the engine. This pump is called the
air pump, because it also discharges any air which may have entered with
the water.

8. _Q._ - If a vacuum be an empty space, and there be water in the
condenser, how can there be a vacuum there?

_A._ - There is a vacuum above the water, the water being only like so much
iron or lead lying at the bottom.

9. _Q._ - Is the vacuum in the condenser a perfect vacuum?

_A._ - Not quite perfect; for the cold water entering for the purpose of
condensation is heated by the steam, and emits a vapor of a tension
represented by about three inches of mercury; that is, when the common
barometer stands at 30 inches, a barometer with the space above the mercury
communicating with the condenser, will stand at about 27 inches.

10. _Q._ - Is this imperfection of the vacuum wholly attributable to the
vapor in the condenser?

_A._ - No; it is partly attributable to the presence of a small quantity of
air which enters with the water, and which would accumulate until it
destroyed the vacuum altogether but for the action of the air pump, which
expels it with the water, as already explained. All common water contains a
certain quantity of air in solution, and this air recovers its elasticity
when the pressure of the atmosphere is taken off, just as the gas in soda
water flies up so soon as the cork of the bottle is withdrawn.

11. _Q._ - Is a barometer sometimes applied to the condensers of steam
engines?

_A._ - Yes; and it is called the vacuum gauge, because it shows the degree
of perfection the vacuum has attained. Another gauge, called the steam
gauge, is applied to the boiler, which indicates the pressure of the steam
by the height to which the steam forces mercury up a tube. Gauges are also
applied to the boiler to indicate the height of the water within it so that
it may not be burned out by the water becoming accidentally too low. In
some cases a succession of cocks placed a short distance above one another
are employed for this purpose, and in other cases a glass tube is placed
perpendicularly in the front of the boiler and communicating at each end
with its interior. The water rises in this tube to the same height as in
the boiler itself, and thus shows the actual water level. In most of the
modern boilers both of these contrivances are adopted.

12. _Q._ - Can a condensing engine be worked with a pressure less than that
of the atmosphere?

_A._ - Yes, if once it be started; but it will be a difficult thing to start
an engine, if the pressure of the steam be not greater than that of the
atmosphere. Before an engine can be started, it has to be blown through
with steam to displace the air within it, and this cannot be effectually
done if the pressure of the steam be very low. After the engine is started,
however, the pressure in the boiler may be lowered, if the engine be
lightly loaded, until there is a partial vacuum in the boiler. Such a
practice, however, is not to be commended, as the gauge cocks become
useless when there is a partial vacuum in the boiler; inasmuch as, when
they are opened, the water will not rush out, but air will rush in. It is
impossible, also, under such circumstances, to blow out any of the sediment
collected within the boiler, which, in the case of the boilers of steam
vessels, requires to be done every two hours or oftener. This is
accomplished by opening a large cock which permits some of the supersalted
water to be forced overboard by the pressure of the steam. In some cases,
in which the boiler applied to an engine is of inadequate size, the
pressure within the boiler will fall spontaneously to a point considerably
beneath the pressure of the atmosphere; but it is preferable, in such
cases, partially to close the throttle valve in the steam pipe, whereby the
issue of steam to the engine is diminished; and the pressure in the boiler
is thus maintained, while the cylinder receives its former supply.

13. _Q._ - If a hole be opened into a condenser of a steam engine, will air
rush into it?

_A._ - If the hole communicates with the atmosphere, the air will be drawn
in.

14. _Q._ - With what Velocity does air rush into a vacuum?

_A._ - With the velocity which a body would acquire by falling from the
height of a homogeneous atmosphere, which is an atmosphere of the same
density throughout as at the earth's surface; and although such an
atmosphere does not exist in nature, its existence is supposed, in order to
facilitate the computation. It is well known that the velocity with which
water issues from a cistern is the same that would be acquired by a body
falling from the level of the head to the level of the issuing point; which
indeed is an obvious law, since every particle of water descends and issues
by virtue of its gravity, and is in its descent subject to the ordinary
laws of falling bodies. Air rushing into a vacuum is only another example
of the same general principle: the velocity of each particle will be that
due to the height of the column of air which would produce the pressure
sustained; and the weight of air being known, as well as the pressure it
exerts on the earth's surface, it becomes easy to tell what height a column
of air, an inch square, and of the atmospheric density, would require to
be, to weigh 15 lbs. The height would be 27,818 feet, and the velocity
which the fall of a body from such a height produces would be 1,338 feet
per second.



VELOCITY OF FALLING BODIES AND MOMENTUM OF MOVING BODIES.

15. _Q._ - How do you determine the velocity of falling bodies of different
kinds?

_A._ - All bodies fall with the same velocity, when there is no resistance
from the atmosphere, as is shown by the experiment of letting fall, from
the top of a tall exhausted receiver, a feather and a guinea, which reach
the bottom at the same time. The velocity of falling bodies is one that is
accelerated uniformly, according to a known law. When the height from which
a body falls is given, the velocity acquired at the end of the descent can
be easily computed. It has been found by experiment that the square root of
the height in feet multiplied by 8.021 will give the velocity.

16. _Q._ - But the velocity in what terms?

_A._ - In feet per second. The distance through which a body falls by
gravity in one second is 16-1/12 feet; in two seconds, 64-4/12 feet; in
three seconds, 144-9/12 feet; in four seconds, 257-4/12 feet, and so on. If
the number of feet fallen through in one second be taken as unity, then the
relation of the times to the spaces will be as follows: -

Number of seconds | 1| 2| 3| 4| 5| 6|
Units of space passed through | 1| 4| 9|16|25|36| &c.

so that it appears that the spaces passed through by a falling body are as
the squares of the times of falling.

17. _Q._ - Is not the urging force which causes bodies to fall the force of
gravity?

_A._ - Yes; the force of gravity or the attraction of the earth.

18. _Q._ - And is not that a uniform force, or a force acting with a uniform
pressure?

_A._ - It is.

19. _Q._ - Therefore during the first second of falling as much impelling
power will be given by the force of gravity as during every succeeding
second?

_A._ - Undoubtedly.

20. _Q._ - How comes it, then, that while the body falls 64-4/12 feet in two
seconds, it falls only 16-1/12 feet in one second; or why, since it falls
only 16-1/12 feet in one second, should it fall more than twice 16-1/12
feet in two?

_A._ - Because 16-1/12 feet is the average and not the maximum velocity
during the first second. The velocity acquired _at the end_ of the 1st
second is not 16-1/12, but 32-1/6 feet per second, and at the end of the 2d
second a velocity of 32-1/6 feet has to be added; so that the total
velocity at the end of the 2d second becomes 64-2/6 feet; at the end of the
3d, the velocity becomes 96-3/6 feet, at the end of the 4th, 128-4/6 feet,
and so on. These numbers proceed in the progression 1, 2, 3, 4, &c., so
that it appears that the velocities acquired by a falling body at different
points, are simply as the times of falling. But if the velocities be as the
times, and the total space passed through be as the squares of the times,
then the total space passed through must be as the squares of the velocity;



Online LibraryJohn BourneA Catechism of the Steam Engine → online text (page 1 of 34)