Tài liệu HOW IT WORKS ppt

HOW IT WORKS AUTHOR'S NOTE. I beg to thank the following gentlemen and firms for the help they have given me in connection with the letterpress and illustrations of "How It Works"— Messrs. F.J.C. Pole and M.G. Tweedie (for revision of MS.); W. Lineham; J.F. Kendall; E. Edser; A.D. Helps; J. Limb; The Edison Bell Phonograph Co.; Messrs. Holmes and Co.; The Pelton Wheel Co.; Messrs. Babcock and Wilcox; Messrs. Siebe, Gorman, and Co.; Messrs. Negretti and Zambra; Messrs. Chubb; The Yale Lock Co.; The Micrometer Engineering Co.; Messrs. Marshall and Sons; The Maignen Filter Co.; Messrs. Broadwood and Co. ON THE FOOTPLATE OF A LOCOMOTIVE. How It Works Dealing in Simple Language with Steam, Electricity, Light, Heat, Sound, Hydraulics, Optics, etc. and with their applications to Apparatus in Common Use By ARCHIBALD WILLIAMS Author of "The Romance of Modern Invention," "The Romance of Mining," etc., etc. THOMAS NELSON AND SONS London, Edinburgh, Dublin, and New York PREFACE. How does it work? This question has been put to me so often by persons young and old that I have at last decided to answer it in such a manner that a much larger public than that with which I have personal acquaintance may be able to satisfy themselves as to the principles underlying many of the mechanisms met with in everyday life. In order to include steam, electricity, optics, hydraulics, thermics, light, and a variety of detached mechanisms which cannot be classified under any one of these heads, within the compass of about 450 pages, I have to be content with a comparatively brief treatment of each subject. This brevity has in turn compelled me to deal with principles rather than with detailed descriptions of individual devices—though in several cases recognized types are examined. The reader will look in vain for accounts of the Yerkes telescope, of the latest thing in motor cars, and of the largest locomotive. But he will be put in the way of understanding the essential nature of all telescopes, motors, and steam-engines so far as they are at present developed, which I think may be of greater ultimate profit to the uninitiated. While careful to avoid puzzling the reader by the use of mysterious phraseology I consider that the parts of a machine should be given their technical names wherever possible. To prevent misconception, many of the diagrams accompanying the letterpress have words as well as letters written on them. This course also obviates the wearisome reference from text to diagram necessitated by the use of solitary letters or figures. I may add, with regard to the diagrams of this book, that they are purposely somewhat unconventional, not being drawn to scale nor conforming to the canons of professional draughtsmanship. Where advisable, a part of a machine has been exaggerated to show its details. As a rule solid black has been preferred to fine shading in sectional drawings, and all unnecessary lines are omitted. I would here acknowledge my indebtedness to my draughtsman, Mr. Frank Hodgson, for his care and industry in preparing the two hundred or more diagrams for which he was responsible. Four organs of the body—the eye, the ear, the larynx, and the heart—are noticed in appropriate places. The eye is compared with the camera, the larynx with a reed pipe, the heart with a pump, while the ear fitly opens the chapter on acoustics. The reader who is unacquainted with physiology will thus be enabled to appreciate the better these marvellous devices, far more marvellous, by reason of their absolutely automatic action, than any creation of human hands. A.W. Uplands, Stoke Poges, Bucks. CONTENTS. Chapter I.—THE STEAM-ENGINE. What is steam?— The mechanical energy of steam—The boiler— The circulation of water in a boiler—The enclosed furnace—The multitubular boiler—Fire-tube boilers— Other types of boilers—Aids to combustion—Boiler fittings— The safety-valve—The water-gauge—The steam- gauge—The water supply to a boiler 13 Chapter II.— THE CONVERSION OF HEAT ENERGY INTO MECHANICAL MOTION. Reciprocating engines—Double- cylinder engines—The function of the fly-wheel— The cylinder—The slide-valve—The eccentric— "Lap" of the valve: expansion of steam—How the cut- off is managed—Limit of expansive working— Compound engines— Arrangement of expansion 44 engines—Compound locomotives— Reversing gears—"Linking-up"—Piston-valves—Speed governors—Marine-speed governors— The condenser Chapter III.—THE STEAM TURBINE. How a turbine works—The De Laval turbine— The Parsons turbine— Description of the Parsons turbine— The expansive action of steam in a Parsons turbine—Balancing the thrust— Advantages of the marine turbine 74 Chapter IV.—THE INTERNAL- COMBUSTION ENGINE. The meaning of the term—Action of the internal- combustion engine—The motor car—The starting- handle—The engine—The carburetter— Ignition of the charge—Advancing the spark— Governing the engine—The clutch—The gear-box— The compensating gear—The silencer—The brakes— Speed of cars 87 Chapter V.—ELECTRICAL APPARATUS. What is electricity?—Forms of electricity— Magnetism—The permanent magnet— Lines of force—Electro-magnets—The electric bell— The induction coil—The condenser— Transformation of current—Uses of the induction coil 112 Chapter VI.— THE ELECTRIC TELEGRAPH. Needle instruments—Influence of current on the 127 magnetic needle— Method of reversing the current—Sounding instruments—Te legraphic relays—Recording telegraphs—High- speed telegraphy Chapter VII.—WIRELESS TELEGRAPHY. The transmitting apparatus— The receiving apparatus—Syntonic transmission—The advance of wireless telegraphy 137 Chapter VIII.—THE TELEPHONE. The Bell telephone—The Edison transmitter— The granular carbon transmitter— General arrangement of a telephone circuit—Double-line circuits— Telephone exchanges—Submarine telephony 147 Chapter IX.— DYNAMOS AND ELECTRIC MOTORS. A simple dynamo Continuous-current dynamos Multipolar dynamos Exciting the field magnets Alternating current dynamos The transmission of power The electric motor Electric lighting The incandescent lamp Arc lamps "Series" and "parallel" arrangement of lamps Current for electric lamps Electroplating 159 Chapter X.—RAILWAY BRAKES. The Vacuum Automatic brake— The Westinghouse air-brake 187 Chapter XI.—RAILWAY SIGNALLING. The block system—Position of signals— Interlocking the signals—Locking gear—Points— 200 Points and signals in combination— Working the block system—Series of signalling operations— Single line signals—The train staff— Train staff and ticket—Electric train staff system— Interlocking—Signalling operations— Power signalling—Pneumatic signalling— Automatic signalling Chapter XII.—OPTICS. Lenses—The image cast by a convex lens— Focus—Relative position of object and lens— Correction of lenses for colour— Spherical aberration—Distortion of image— The human eye—The use of spectacles—The blind spot 230 Chapter XIII.—THE MICROSCOPE, THE TELESCOPE, AND THE MAGIC-LANTERN. The simple microscope— Use of the simple microscope in the telescope— The terrestrial telescope—The Galilean telescope— The prismatic telescope—The reflecting telescope— The parabolic mirror—The compound microscope— The magic-lantern—The bioscope— The plane mirror 253 Chapter XIV.— SOUND AND MUSICAL INSTRUMENTS. Nature of sound—The ear— Musical instruments—The vibration of strings— The sounding-board and the frame of a piano— The strings—The striking mechanism—The quality of 270 a note Chapter XV.—WIND INSTRUMENTS. Longitudinal vibration—Columns of air— Resonance of columns of air—Length and tone— The open pipe—The overtones of an open pipe— Where overtones are used—The arrangement of the pipes and pedals—Separate sound-boards— Varieties of stops—Tuning pipes and reeds— The bellows—Electric and pneumatic actions— The largest organ in the world—Human reeds 287 Chapter XVI.—TALKING-MACHINES. The phonograph—The recorder— The reproducer—The gramophone— The making of records—Cylinder records—Gramophone records 310 Chapter XVII.—WHY THE WIND BLOWS. Why the wind blows—Land and sea breezes— Light air and moisture—The barometer— The column barometer—The wheel barometer— A very simple barometer—The aneroid barometer— Barometers and weather—The diving-bell— The diving-dress—Air-pumps—Pneumatic tyres— The air-gun—The self-closing door-stop— The action of wind on oblique surfaces—The balloon— The flying-machine 322 Chapter XVIII.— HYDRAULIC MACHINERY. The siphon—The bucket pump—The force- pump—The most marvellous pump— The blood 350 channels—The course of the blood— The hydraulic press—Household water- supply fittings—The ball-cock—The water-meter— Water-supply systems—The household filter— Gas traps—Water engines— The cream separator—The "hydro" Chapter XIX.—HEATING AND LIGHTING. The hot-water supply—The tank system— The cylinder system—How a lamp works—Gas and gasworks—Automatic stoking—A gas governor— The gas meter—Incandescent gas lighting 386 Chapter XX.—VARIOUS MECHANISMS. Clocks and Watches:— A short history of timepieces—The construction of timepieces— The driving power—The escapement— Compensating pendulums—The spring balance— The cylinder escapement—The lever escapement— Compensated balance-wheels— Keyless winding mechanism for watches—The hour hand train. Locks:—The Chubb lock— The Yale lock. The Cycle:—The gearing of a cycle— The free wheel—The change- speed gear. Agricultural Machines:—The threshing-machine—Mowing- machines. Some Natural Phenomena:—Why sun- heat varies in intensity—The tides—Why high tide varies daily 410 [Pg 13] HOW IT WORKS. Chapter I. THE STEAM-ENGINE. What is steam?—The mechanical energy of steam—The boiler—The circulation of water in a boiler—The enclosed furnace—The multitubular boiler—Fire-tube boilers—Other types of boilers—Aids to combustion—Boiler fittings—The safety- valve—The water-gauge—The steam-gauge—The water supply to a boiler. WHAT IS STEAM? If ice be heated above 32° Fahrenheit, its molecules lose their cohesion, and move freely round one another—the ice is turned into water. Heat water above 212° Fahrenheit, and the molecules exhibit a violent mutual repulsion, and, like dormant bees revived by spring sunshine, separate and dart to and fro. If confined in an air- tight vessel, the molecules have their flights curtailed, and beat more and more violently against their prison walls, so that every square inch of the[Pg 14] vessel is subjected to a rising pressure. We may compare the action of the steam molecules to that of bullets fired from a machine-gun at a plate mounted on a spring. The faster the bullets came, the greater would be the continuous compression of the spring. THE MECHANICAL ENERGY OF STEAM. If steam is let into one end of a cylinder behind an air-tight but freely-moving piston, it will bombard the walls of the cylinder and the piston; and if the united push of the molecules on the one side of the latter is greater than the resistance on the other side opposing its motion, the piston must move. Having thus partly got their liberty, the molecules become less active, and do not rush about so vigorously. The pressure on the piston decreases as it moves. But if the piston were driven back to its original position against the force of the steam, the molecular activity—that is, pressure— would be restored. We are here assuming that no heat has passed through the cylinder or piston and been radiated into the air; for any loss of heat means loss of energy, since heat is energy. THE BOILER. [...]... forming the walls are thrown into violent agitation If the walls are what are called "good conductors" of heat, they will transmit the agitation through them to any surrounding substance In the case of the ordinary house stove this is the air, which itself is agitated, or grows warm A steam-boiler has the furnace walls surrounded by water, and its function is to transmit molecular movement (heat, or energy)... combustion, upon[Pg 27] which a boiler depends for its heat Ordinary steam coal contains about 85 per cent of carbon, 7 per cent of oxygen, and 4 per cent of hydrogen, besides traces of nitrogen and sulphur and a small incombustible residue When the coal burns, the nitrogen is released and passes away without combining with any of the other elements The sulphur unites with hydrogen and forms sulphuretted hydrogen... 170° Fahrenheit or more, and the poor stokers have a very bad time of it Fig 10.— Sketch showing how the "forced draught" is produced in a stokehold and how it affects the furnaces [Pg 30] SCENE IN THE STOKEHOLD OF A BATTLE-SHIP [Pg 31] The second system is that of the induced draught Here air is sucked through the furnace by creating a vacuum in the funnel and in a chamber opening into it Turning to... to the same writer, a cubic foot of heated water under a pressure of from 60 to 70 lbs per square inch has about the same energy as one pound of gunpowder Steam is a good servant, but a terrible master It must be kept under strict control However strong a boiler may be, it will burst if the steam pressure in it be raised to a certain point; and some device must therefore be fitted on it which will... filling the boilers quite full and (1) by heating the water, which expands slightly, but with great pressure; (2) by forcing in additional water with a powerful pump In either case a rupture[Pg 34] would not be attended by an explosion, as water is very inelastic The days when an engineer could "sit on the valves"—that is, screw them down—to obtain greater pressure, are now past, and with them a considerable... straightens itself, and assumes the position indicated by the dotted lines Hang an empty "inner tube" of a pneumatic tyre over a nail and inflate it, and you will get a good illustration of the principle Fig Showing the principle of the steam-gauge [Pg 38] 13.— Fig 14.—Bourdon steam-gauge Part of dial removed to show mechanism In Fig 14 we have a Bourdon gauge, with part of the dial face broken away to show... valve V As it rushes through the nozzle of the cone A it takes up water and projects it into the "mixing cone" B, which can be raised or lowered by the pinion D (worked by the hand-wheel wheel shown) so as to regulate the amount of water admitted to B.[Pg 42] At the centre of B is an aperture, O, communicating with the overflow The water passes to the boiler through the valve on the left It will be... greatest "limit of error" allowed Fig 23.—The eccentric and its rod THE ECCENTRIC is used to move the slide-valve to and fro over the steam ports (Fig 23) It consists of three main parts—the sheave, or circular plate S, mounted on the crank shaft; and the two straps which encircle it, and in which it revolves To one strap is bolted the "big end" of the eccentric rod, which engages at its other end with the... soldered at one end into a hollow casting, into which screws a tap connected with the boiler The other end (closed) is attached to a link, L, which works an arm of a quadrant rack, R, engaging with a small pinion, P, actuating the pointer As the steam pressure rises,[Pg 39] the tube T moves its free end outwards towards the position shown by the dotted lines, and traverses the arm of the rack, so shifting... shifting the pointer round the scale As the pressure falls, the tube gradually returns to its zero position The Schäffer-Budenberg gauge depends for its action on the elasticity of a thin corrugated metal plate, on one side of which steam presses As the plate bulges upwards it pushes up a small rod resting on it, which operates a quadrant and rack similar to that of the Bourdon gauge The principle . A LOCOMOTIVE. How It Works Dealing in Simple Language with Steam, Electricity, Light, Heat, Sound, Hydraulics, Optics, etc. and with their applications. When the coal burns, the nitrogen is released and passes away without combining with any of the other elements. The sulphur unites with hydrogen and forms