The punctuation and spelling from the original text have been faithfully preserved.Onlyobvioustypographicalerrorshavebeencorrected.
IBEGtothankthefollowinggentlemenandfirmsforthehelptheyhavegivenme inconnectionwiththeletterpressandillustrationsof"HowItWorks"— Messrs.F.J.C.PoleandM.G.Tweedie(forrevisionofMS.);W.Lineham;J.F. Kendall; E. Edser; A.D. Helps; J. Limb; The Edison Bell Phonograph Co.; Messrs.HolmesandCo.;ThePeltonWheelCo.;Messrs.BabcockandWilcox; Messrs.Siebe,Gorman,andCo.;Messrs.NegrettiandZambra;Messrs.Chubb; The Yale Lock Co.; The Micrometer Engineering Co.; Messrs. Marshall and Sons;TheMaignenFilterCo.;Messrs.BroadwoodandCo.
and old that I have at last decided to answer it in such a manner that a much largerpublicthanthatwithwhichIhavepersonalacquaintancemaybeableto satisfythemselvesastotheprinciplesunderlyingmanyofthemechanismsmet withineverydaylife. Inordertoincludesteam,electricity,optics,hydraulics,thermics,light,anda variety of detached mechanisms which cannot be classified under any one of theseheads,withinthecompassofabout450pages,Ihavetobecontentwitha comparativelybrieftreatmentofeachsubject.Thisbrevityhasinturncompelled me to deal with principles rather than with detailed descriptions of individual devices—thoughinseveralcasesrecognizedtypesareexamined.Thereaderwill 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 alltelescopes,motors,andsteam-engines sofarastheyareatpresentdeveloped,whichIthinkmaybeofgreaterultimate profittotheuninitiated. While careful to avoid puzzling the reader by the use of mysterious phraseologyIconsiderthatthepartsofamachineshouldbegiventheirtechnical names wherever possible. To prevent misconception, many of the diagrams accompanyingtheletterpresshavewordsaswellasletterswrittenonthem.This coursealsoobviatesthewearisomereferencefromtexttodiagramnecessitated bytheuseofsolitarylettersorfigures. Imayadd,withregardtothediagramsofthisbook,thattheyarepurposely somewhat unconventional, not being drawn to scale nor conforming to the canons of professional draughtsmanship. Where advisable, a part of a machine hasbeenexaggeratedtoshowitsdetails.Asarulesolidblackhasbeenpreferred
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 diagramsforwhichhewasresponsible. Four organs of the body—the eye, the ear, the larynx, and the heart—are noticedinappropriateplaces.Theeyeiscomparedwiththecamera,thelarynx withareedpipe,theheartwithapump,whiletheearfitlyopensthechapteron acoustics.Thereaderwhoisunacquaintedwithphysiologywillthusbeenabled toappreciatethebetterthesemarvellousdevices,farmoremarvellous,byreason oftheirabsolutelyautomaticaction,thananycreationofhumanhands. A.W. UPLANDS,STOKEPOGES,BUCKS.
IF ice be heated above 32° Fahrenheit, its molecules lose their cohesion, and movefreelyroundoneanother—theiceisturnedintowater.Heatwaterabove 212°Fahrenheit,andthemoleculesexhibitaviolentmutualrepulsion,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 beatmoreandmoreviolentlyagainsttheirprisonwalls,sothateverysquareinch ofthevesselissubjectedtoarisingpressure.Wemaycomparetheactionofthe steammoleculestothatofbulletsfiredfromamachine-gunataplatemounted on a spring. The faster the bullets came, the greater would be the continuous compressionofthespring. THEMECHANICALENERGYOFSTEAM.
Ifsteamisletintooneendofacylinderbehindanair-tightbutfreely-moving piston,itwillbombardthewallsofthecylinderandthepiston;andiftheunited pushofthemoleculesontheonesideofthelatterisgreaterthantheresistance ontheothersideopposingitsmotion,thepistonmustmove.Havingthuspartly 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 molecularactivity—thatis,pressure—wouldberestored.Wearehereassuming thatnoheathaspassedthroughthecylinderorpistonandbeenradiatedintothe air;foranylossofheatmeanslossofenergy,sinceheatisenergy. THEBOILER.
Thecombustionoffuelinafurnacecausesthewallsofthefurnacetobecome hot, which means that the molecules of the substance forming the walls are thrownintoviolentagitation.Ifthewallsarewhatarecalled"goodconductors" of heat, they will transmit the agitation through them to any surrounding substance.Inthecaseoftheordinaryhousestovethisistheair,whichitselfis 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) through the furnace plates to the water until the point is reached when steam generates.Atatmosphericpressure—thatis,ifnotconfinedinanyway—steam would fill 1,610 times the space which its molecules occupied in their watery formation. If we seal up the boiler so that no escape is possible for the steam molecules, their motion becomes more and more rapid, and pressure is developed by their beating on the walls of the boiler. There is theoretically no limit to which the pressure may be raised, provided that sufficient fuelcombustionenergyistransmittedtothevaporizingwater. To raise steam in large quantities we must employ a fuel which develops greatheatinproportiontoitsweight,isreadilyprocured,andcheap.Coalfulfils all these conditions. Of the 800 million tons mined annually throughout the world,400milliontonsareburntinthefurnacesofsteam-boilers. A good boiler must be—(1) Strong enough to withstand much higher pressuresthanthatatwhichitisworked;(2)sodesignedastoburnitsfueltothe greatestadvantage. Eveninthebest-designedboilersalargepartofthecombustionheatpasses through the chimney, while a further proportion is radiated from the boiler. Professor John Perry considers that this waste amounts, under the best conditions at present obtainable, to eleven-twelfths of the whole. We have to
Ifyouplaceapotfilledwithwateronanopenfire,andwatchitwhenitboils, you will notice that the water heaves up at the sides and plunges down at the centre. This is due to the water being heated most at the sides, and therefore beinglightestthere.Therisingsteam-bubblesalsocarryitup.Onreachingthe surface, the bubbles burst, the steam escapes, and the water loses some of its heat,andrushesdownagaintotaketheplaceofsteam-ladenwaterrising. Fig.1. Fig.2. FIG.1. FIG.2. Ifthefireisveryfierce,steam-bubblesmayrisefromallpointsatthebottom, andimpededownwardcurrents(Fig.1).Thepotthen"boilsover." Fig. 2 shows a method of preventing this trouble. We lower into our pot a vesselofsomewhatsmallerdiameter,withaholeinthebottom,arrangedinsuch a manner as to leave a space between it and the pot all round. The upward currents are then separated entirely from the downward, and the fire can be forcedtoaverymuchgreaterextentthanbeforewithoutthewaterboilingover. This very simple arrangement is the basis of many devices for producing free circulationofthewaterinsteam-boilers. We can easily follow out the process of development. In Fig. 3 we see a simple U-tubedependingfromavesselofwater.Heatisappliedtotheleftleg, and a steady circulation at once commences. In order to increase the heating surfacewecanextendtheheatedlegintoalongincline(Fig.4),beneathwhich threelampsinsteadofonlyoneareplaced.Thedirectionofthecirculationisthe same,butitsrateisincreased. Fig.3. FIG.3.
Fig.4. Fig.5. FIG.4. FIG.5. Still,alotoftheheatgetsaway.Inasteam-boilertheburningfuelisenclosed eitherbyfire-brickora"water-jacket,"formingpartoftheboiler.Awater-jacket signifiesadoublecoatingofmetalplateswithaspacebetween,whichisfilled withwater(seeFig.6).Thefireisnowenclosedmuchasitisinakitchenrange. But our boiler must not be so wasteful of the heat as is that useful household fixture.Ontheirwaytothefunneltheflamesandhotgasesshouldactonavery large metal or other surface in contact with the water of the boiler, in order to giveupadueproportionoftheirheat. Fig.6. FIG.6.—Diagrammaticsketchofalocomotivetypeofboiler.Water indicatedbydottedlines.Thearrowsshowthedirectiontakenbytheair andhotgasesfromtheair-doortothefunnel. THEMULTITUBULARBOILER.
Fig.7. FIG.7.—TheBabcockandWilcoxwater-tubeboiler.Onesideofthebrick seatinghasbeenremovedtoshowthearrangementofthewater-tubesand furnace. To save room, boilers which have to make steam very quickly and at high pressuresarelargelycomposedofpipes.Suchboilerswecallmultitubular.They areoftwokinds—(1)Water-tubeboilers;inwhichthewatercirculatesthrough tubes exposed to the furnace heat. The Babcock and Wilcox boiler (Fig. 7) is typicalofthisvariety.(2)Fire-tubeboilers;inwhichthehotgasespassthrough tubes surrounded by water. The ordinary locomotive boiler (Fig. 6) illustrates thisform. TheBabcockandWilcoxboileriswidelyusedinmines,powerstations,and, inamodifiedform,onshipboard.Itconsistsoftwomainparts—(1)Adrum, H,
intheupperpartofwhichthesteamcollects;(2)agroupofpipesarrangedon theprincipleillustratedbyFig.5.Theboilerisseatedonarectangularframeof fire-bricks.Atoneendisthefurnacedoor;attheothertheexittothechimney. From the furnace F the flames and hot gases rise round the upper end of the slopingtubes TT into thespace A,wheretheyplayupontheundersurfaceof H before plunging downward again among the tubes into the space B. Here the temperature is lower. The arrows indicate further journeys upwards into the space Contherightofafire-brickdivision,andpastthedowntubes SSinto D, whencethehotgasesfindanescapeintothechimneythroughtheopening E.It willbenoticedthatthegreatestheatisbroughttobearon TTneartheirjunction with UU, the "uptake" tubes; and that every succeeding passage of the pipes bringsthegraduallycoolinggasesnearertothe"downtake"tubesSS. Thepipes TTareeasilybrushedandscrapedaftertheremovalofplugsfrom the"headers"intowhichthetubeendsareexpanded. Otherwell-knownwater-tubeboilersaretheYarrow,Belleville,Stirling,and Thorneycroft,allusedfordrivingmarineengines. FIRE-TUBEBOILERS.
Fig. 6 shows a locomotive boiler in section. To the right is the fire-box, surroundedonallsidesbyawater-jacketindirectcommunicationwiththebarrel of the boiler. The inner shell of the fire-box is often made of copper, which withstandsthefierceheatbetterthansteel;theouter,liketherestoftheboiler,is of steel plates from ½ to ¾ inch thick. The shells of the jacket are braced togetherbyalargenumberofrivets, RR;andthetop,orcrown,isstrengthened byheavylongitudinalgirdersrivetedtoit,orisbracedtothetopoftheboilerby longbolts.Alargenumberoffire-tubes(onlythreeareshowninthediagramfor the sake of simplicity) extend from the fire-box to the smoke-box. The most powerful "mammoth" American locomotives have 350 or more tubes, which, with the fire-box, give 4,000 square feet of surface for the furnace heat to act upon. These tubes are expanded at their ends by a special tool into the tubeplatesofthefire-boxandboilerfront.GeorgeStephensonandhispredecessors experiencedgreatdifficultyinrenderingthetube-endjointsquitewater-tight,but theinventionofthe"expander"hasremovedthistrouble.
Thefire-brickarchshown(Fig.6)inthefire-boxisusedtodeflecttheflames towards the back of the fire-box, so that the hot gases may be retarded somewhat,andtheircombustionrenderedmoreperfect.Italsohelpstodistribute theheatmoreevenlyoverthewholeoftheinsideofthebox,andpreventscold airfromflyingdirectlyfromthefiringdoortothetubes.InsomeAmericanand Continental locomotives the fire-brick arch is replaced by a "water bridge," whichservesthesamepurpose,whilegivingadditionalheatingsurface. Thewatercirculationinalocomotiveboileris—upwardsatthefire-boxend, where the heat is most intense; forward along the surface; downwards at the smoke-boxend;backwardsalongthebottomofthebarrel. OTHERTYPESOFBOILERS.
Forsmallstationarylandenginestheverticalboilerismuchused.InFig.8 wehavethreeformsofthistype—AandBwithcrosswater-tubes;Cwithvertical fire-tubes.Thefurnaceineverycaseissurroundedbywater,andfedthrougha dooratoneside. Fig.8. FIG.8.—Diagrammaticrepresentationofthreetypesofverticalboilers. TheLancashireboilerisoflargesize.Ithasacylindricalshell,measuringup to30feetinlengthand7feetindiameter,traversedfromendtoendbytwolarge flues,intherearpartofwhicharesituatedthefurnaces.Theboilerisfixedona seatingoffire-bricks,sobuiltupastoformthreeflues,AandBB,shownincross section in Fig. 9. The furnace gases, after leaving the two furnace flues, are deflected downwards into the channel A, by which they pass underneath the boilertoapointalmostunderthefurnace,wheretheydividerightandleftand travel through cross passages into the side channels BB, to be led along the boiler'sflanksto thechimneyexit C. By this arrangement the effective heating surface is greatly increased; and the passages being large, natural draught generallysufficestomaintainpropercombustion.TheLancashireboilerismuch usedinfactoriesand(inamodifiedform)onships,sinceitisasteadysteamer andiseasilykeptinorder. Fig.9.
FIG.9.—CrossandlongitudinalsectionsofaLancashireboiler. In marine boilers of cylindrical shape cross water-tubes and fire-tubes are oftenemployedtoincreasetheheatingsurface.Returntubesarealsoledthrough thewatertothefunnels,situatedatthesameendasthefurnace. AIDSTOCOMBUSTION.
We may now turn our attention more particularly to the chemical process calledcombustion,uponwhichaboilerdependsforitsheat.Ordinarysteamcoal containsabout85percent.ofcarbon,7percent.ofoxygen,and4percent.of hydrogen, besides traces of nitrogen and sulphur and a small incombustible residue.Whenthecoalburns,thenitrogenisreleasedandpassesawaywithout combiningwithanyoftheotherelements.Thesulphuruniteswithhydrogenand formssulphurettedhydrogen(alsonamedsulphurousacid),whichisinjuriousto steelplates,andislargelyresponsibleforthedecayoftubesandfunnels.More ofthehydrogenuniteswiththeoxygenassteam. Themostimportantelementincoalisthecarbon(knownchemicallybythe symbol C). Its combination with oxygen, called combustion, is the act which heats the boiler. Only when the carbon present has combined with the greatest possible amount of oxygen that it will take into partnership is the combustion complete and the full heat-value (fixed by scientific experiment at 14,500 thermalunitsperpoundofcarbon)developed. Now, carbon may unite with oxygen, atom for atom, and form carbon monoxide (CO); or in the proportion of one atom of carbon to two of oxygen, and form carbon dioxide (CO2). The former gas is combustible—that is, will admit another atom of carbon to the molecule—but the latter is saturated with oxygen, and will not burn, or, to put it otherwise, is the product of perfect combustion.Aproperlydesignedfurnace,suppliedwithadueamountofair,will causenearlyallthecarboninthecoalburnttocombinewiththefullamountof oxygen. On the other hand, if the oxygen supply is inefficient, CO as well as CO2willform,andtherewillbeaheatloss,equalinextremecasestotwo-thirds ofthewhole.Itisthereforenecessarythatafurnacewhichhastoeatupfuelata greatpaceshouldbeartificiallyfedwithairintheproportionoffrom12to20
pounds of air for every pound of fuel. There are two methods of creating a violentdraughtthroughthefurnace.Thefirstis— Theforceddraught;verysimplyexemplifiedbytheordinarybellowsusedin every house. On a ship (Fig. 10) the principle is developed as follows:—The boilersaresituatedinacompartmentorcompartmentshavingnocommunication withtheouterair,exceptforthepassagesdownwhichairisforcedbypowerful fansatapressureconsiderablygreaterthanthatoftheatmosphere.Thereisonly one "way out"—namely, through the furnace and tubes (or gas-ways) of the boiler,andthefunnel.Sothroughtheseitrushes,raisingthefueltowhiteheat. As may easily be imagined, the temperature of a stokehold, especially in the tropics,isfarfrompleasant.IntheRedSeathethermometersometimesrisesto 170°Fahrenheitormore,andthepoorstokershaveaverybadtimeofit. Fig.10. FIG.10.—Sketchshowinghowthe"forceddraught"isproducedina stokeholdandhowitaffectsthefurnaces. SCENEINTHESTOKEHOLDOFABATTLE-SHIP. SCENEINTHESTOKEHOLDOFABATTLE-SHIP. Thesecondsystemisthatoftheinduceddraught.Hereairissuckedthrough thefurnacebycreatingavacuuminthefunnelandinachamberopeningintoit. Turning to Fig. 6, we see a pipe through which the exhaust steam from the locomotive's cylinders is shot upwards into the funnel, in which, and in the smoke-box beneath it, a strong vacuum is formed while the engine is running. Now,"natureabhorsavacuum,"soairwillgetintothesmoke-boxiftherebea way open. There is—through the air-doors at the bottom of the furnace, the furnace itself, and the fire-tubes; and on the way oxygen combines with the carbonofthefuel,toformcarbondioxide.Thepowerofthedraughtissogreat that,asoneoftennoticeswhenatrainpassesduringthenight,red-hotcinders, pluckedfromthefire-box,anddraggedthroughthetubes,arehurledfarintothe air.Itmightbementionedinparenthesisthattheso-called"smoke"whichpours fromthefunnelofamovingengineismainlycondensingsteam.Asteamship,on the other hand, belches smoke only from its funnels, as fresh water is far too precioustowasteassteam.Weshallrefertothislateron(p.72).
The most important fittings on a boiler are:—(1) the safety-valve; (2) the water-gauge;(3)thesteam-gauge;(4)themechanismsforfeedingitwithwater. THESAFETY-VALVE.
ProfessorThurston,aneminentauthorityonthesteam-engine,hasestimated that a plain cylindrical boiler carrying 100 lbs. pressure to the square inch containssufficientstoredenergytoprojectitintotheairaverticaldistanceof3½ miles.InthecaseofaLancashireboileratequalpressurethedistancewouldbe 2½miles;ofalocomotiveboiler,at125lbs.,1½miles;ofasteamtubularboiler, at 75 lbs., 1 mile. According to the same writer, a cubic foot of heated water underapressureoffrom60to70lbs.persquareinchhasaboutthesameenergy asonepoundofgunpowder. Steam is a good servant, but a terrible master. It must be kept under strict control.Howeverstrongaboilermaybe,itwillburstifthesteampressureinit beraisedtoacertainpoint;andsomedevicemustthereforebefittedonitwhich willgivethesteamfreeegressbeforethatpointisreached.Adeviceofthiskind iscalledasafety-valve.Itusuallyblowsoffatlessthanhalfthegreatestpressure thattheboilerhasbeenprovedbyexperimenttobecapableofwithstanding. Inprinciplethesafety-valvedenotesanorificeclosedbyanaccurately-fitting plug,whichispressedagainstitsseatontheboilertopbyaweightedlever,orby a spring. As soon as the steam pressure on the face of the plug exceeds the counteracting force of the weight or spring, the plug rises, and steam escapes untilequilibriumoftheopposingforcesisrestored. Onstationaryenginesaleversafety-valveiscommonlyemployed(Fig.11). Theblowing-offpointcanbevariedbyshiftingtheweightalongthearmsoasto give it a greater or less leverage. On locomotive and marine boilers, where shocks and movements have to be reckoned with, weights are replaced by springs,settoacertaintension,andlockedupsothattheycannotbetampered with. Fig.11.
FIG.11.—ALEVERSAFETY-VALVE.V,valve;S,seating;P,pin;L,lever;F, fulcrum;W,weight.Thefiguresindicatethepositionsatwhichtheweight shouldbeplacedforthevalvetoactwhenthepressurerisestothatnumber ofpoundspersquareinch. Boilersaretestedbyfillingtheboilersquitefulland(1)byheatingthewater, which expands slightly, but with great pressure; (2) by forcing in additional waterwithapowerfulpump.Ineithercasearupturewouldnotbeattendedby anexplosion,aswaterisveryinelastic. 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 proportion of the dangers of high-pressure steam. The Factory Act of 1895, in forcethroughouttheBritishIsles,providesthateveryboilerforgeneratingsteam inafactoryorworkshopwheretheActappliesmusthaveapropersafety-valve, steam-gauge,andwater-gauge;andthatboilersandfittingsmustbeexaminedby a competent person at least once in every fourteen months. Neglect of these provisionsrenderstheownerofaboilerliabletoheavypenaltiesifanexplosion occurs. OneofthemostdisastrousexplosionsonrecordtookplaceattheRedcarIron Works,Yorkshire,inJune1895.Inthiscase,twelveoutoffifteenboilersranged side by side burst, through one proving too weak for its work. The flying fragmentsofthisboiler,strikingthesidesofotherboilers,explodedthem,andso thedamagewastransmitteddowntheline.Twentymenwerekilledandinjured; whilemassesofmetal,weighingseveraltonseach,werehurled250yards,and causedwidespreaddamage. Thefollowingistakenfromajournal,datedDecember22,1895:"Providence (Rhode Island).—A recent prophecy that a boiler would explode between December 16 and 24 in a store has seriously affected the Christmas trade. Shoppers are incredibly nervous. One store advertises, 'No boilers are being used;liftsrunningelectrically.'Allstoreshavehadtheirboilersinspected." THEWATER-GAUGE.
the level at which the water stands. The engineer must continually consult his gauge, for if the water gets too low, pipes and other surfaces exposed to the furnace flames may burn through, with disastrous results; while, on the other hand,toomuchwaterwillcausebadsteaming.Asectionofanordinarygaugeis seeninFig.12.Itconsistsoftwoparts,eachfurnishedwithagland,G,tomakea steam-tightjointroundtheglasstube,whichisinsertedthroughtheholecovered bytheplug P1.Thecocks T1T2arenormallyopen,allowingtheingressofsteam andwaterrespectivelytothetube.CockT3iskeptclosedunlessforanyreasonit is necessary to blow steam or water through the gauge. The holes C C can be cleanedoutiftheplugsP2P3areremoved. Fig.12. FIG.12.—Sectionofawater-gauge. Most gauges on high-pressure boilers have a thick glass screen in front, so thatintheeventofthetubebreaking,thesteamandwatermaynotblowdirectly ontotheattendants.Afurtherprecautionistoincludetwoball-valvesnearthe ends of the gauge-glass. Under ordinary conditions the balls lie in depressions clearoftheways;butwhenarushofsteamorwateroccurstheyaresuckedinto theirseatingsandblockallegress. On many boilers two water-gauges are fitted, since any gauge may work badlyattimes.Theglassesaretestedtoapressureof3,000lbs.ormoretothe squareinchbeforeuse. THESTEAM-GAUGE.
Itisoftheutmostimportancethatapersoninchargeofaboilershouldknow what pressure the steam has reached. Every boiler is therefore fitted with one steam-gauge; many with two, lest one might be unreliable. There are two principaltypesofsteam-gauge:—(1)TheBourdon;(2)theSchäffer-Budenberg. TheprincipleoftheBourdonisillustratedbyFig.13,inwhich Aisapieceof rubber tubing closed at one end, and at the other drawn over the nozzle of a cycletyreinflator.Ifbentinacurve,asshown,thesectionofthetubeisanoval. Whenairispumpedin,therubberwallsendeavourtoassumeacircularsection, because this shape encloses a larger area than an oval of equal circumference,
and therefore makes room for a larger volume of air. In doing so the tube straightensitself,andassumesthepositionindicatedbythedottedlines.Hangan empty"innertube"ofapneumatictyreoveranailandinflateit,andyouwillget agoodillustrationoftheprinciple.