BOULTON AND WATTROTATIVE STEAM ENGINE1785Sydney, AustraliaApril 17, 1986

An International Historic Mechanical Engineering Landmark

The American Society ofMechanical Engineers

This engine of 1785 srandsat the second beginning ofsteam power; it is the momentwhen the chain connection be-tween the piston and beam ofthe 73-year-old steam pumpwas replaced by two links thatformed a “parallel motion.”The piston could now add anupward push to the formerdown-only pull permitted bythe chain, giving an almostcontinuous flow of power fromthe two-fold or double actionon the piston that allowed theengine to be rotative and soturn the shafts of manufactur-ing industry to achieve a long-sought goal.

The steam engine’s transi-tion from pumping duty to itssecond and more versatile formcame slowly. Tracing the storyof the rotative engine meansreturning to the early eigh-teenth century when it was

known that: (1) given a ve-tical, open-topped cylinderwith piston, atmosphericpressure would drive the pistondown into a vacuum formedbeneath it; (2) such a vacuumcould be created by the con-densation of steam under thepiston. Thomas Newcomen(1663- 1729) of Devon, usingthese ideas and others, puttogether the first practicalsteam engine and pump fordraining distressed mines orsupplying water. This event of1712 was immortalized byThomas Barney’s engravingdated 1719 relating to a coa1mine in Staffordshire nearDudley Castle. Well-executed,the print includes a key to theparts of the “Steam Engine”and “A Scale of Feet &Inches” enabling the deter-mination of principal dimen-sions.

Newcomen’s InfluenceThis was the first beam

engine, a style that would carryon for long over a century. Theoverhead beam of wood withits arc ends was 24 ft (7.3 m)long and centrally pivoted onstout engine-house Wall 22 ft(6.7 m) above the floor. Inreality the beam was a partialpulley, for the chains to thereciprocating piston rods,steam at one end, pump at theother, were always tangent tothe ares of half-beam radius,thus providing rod guidance inthe vertical (or perpendicular,as was said two centuries ago)as the beam oscillated. It canbe read that the open-toppedcylinder had a diameter of 21in. (533 mm) with a length of7 ft 10 in. (2338 mm).

The boiler-really an enor-mous tea kettle of 5.5-ft(1.67 m) diameter - was direct-ly below the open-toppedcylinder and would furnishsteam at atmospheric pressureto the space under the piston,the piston having been hauledto the top of its cylinder by theweight of the pump rod and itsgear. Injection of cold water in-to the steam under the pistoncaused condensation with theformation of a vacuum intowhich atmospheric pressure,acting down, shoved thepiston. This was the powerstroke with which the pumprod at the other end of thebeam was hauled up.

If an incomplete (poor)vacuum of say 10 psia (68 kPa)is assumed, the force on the21-in. (533 mm) piston wouldhave been about 3400 lb(1542 kg), giving a pivot reac-

tion on the wall of twice that.Someone’s note on the engrav-ing remarks that 10 gallons ofwater were raised 51 yards“perpendicular” when run-ning at 12 strokes per minute.This works out at about 5.5horsepower (4.1 kW) for thewater end. A calculation forthe cylinder (assuming a 6.5 - ft[1981 mm] stroke) yields an in-dicated horsepower of about8.2 (6.1 kW). There are no realdata on the thermal efficiency,but by any guess it was appall-ing, one-half percent has beensuggested. In fact, these pump-ing engines that did a splen-did job in saving the drowningcoal mines could be affordedonly there, being run on thecoal that was so poor that itcouldn’t be sold. Mineralmines (non - coal regions) couldhardly take advantage of theengine because of the cost oftransporting coal.

Keep It HotJames Watt (1736-1819) was

born 24 years after that firstNewcomen engine went towork at Tipton. As instrumentmaker at the College ofGlasgow, he was brought intocontact with the steam enginein 1763 by being asked torepair a model Newcomenengine used in the “NaturalPhilosophy” class. The problemwas that the model, havinglarge boiler and small cylinder,would make but a few strokesbefore stopping for want ofsteam. He recognized that thecylinder cooled betweenstrokes, that several volumes ofsteam were therefore condens-ing idly before one remained

to be deliberately condensedfor the power stroke. This con-clusion led to his first patent in1769; it might be called the“Keep It Hot” patent, for cen-tral idea was to keep thecylinder hot, as close to 212° Fas possible, to discouragethat senseless steam -consuming initial condensationcaused by a cool system. This“coolness” stemmed from hav-ing the piston top and thecylinder wall in constant con-tact with ambient air, and acylinder bottom shockinglycooled everytime the condens-ing water was injected.

Patent No. 913, January 9,1769, for “a new Method ofLessening the Consumption ofSteam and Fuel in FireEngines” featured a three-point program of direct con-cern: (1) reduce condensationat the piston by closing the topof the cylinder, letting thepiston rod come through agland, and use hot steam at at-mospheric pressure instead ofcool ambient air to force thepiston down; (2) arrange for asteam jacket around thecylinder; (3) have a seperatevessel or “external condenser”connected to the cylinder bot-tom, and carry out the conden-sation in this remote vessel,thus keeping the cold condens-ing water and condensate awayfrom the cylinder.

Some seven years wouldelapse before the merits of thepatent could be demonstrated,for development costs posed aproblem. Watt had his livingto earn, doing so as civilengineer and surveyor; his pa-tent sponsor, an industrialistwith two-thirds interest in

whatever profits might bemade, went bankrupt. Greatgood fortune brought Watt theengineer into partnership withMatthew Boulton (1728-1809)the astute industrialist. It was1776 before the propositions ofthe 1769 patent were reducedto successful practice.

Public achievement camewith a mine pumping enginehaving a 50-in. (1270 mm)diameter cylinder and a blow-ing engine (for an iron works)with 38-in. (965 mm) cylinder.Their most satisfactory perfor-mance was in part due to theaccurate steam cylinders finish-ed on ironmaster Wilkinson’snewly contrived boring mill.Fuel consumption of theseengines was third of that nor-mal for the time. Word gotaround, and enquiries from thelong-suffering metal mines ofCornwall were followed byorders from there and otherplaces as well.

The Industrial PushWith the ever-increasing in-

dustrial activity of theburgeoning eighteenth cen-tury, especially in England,rotational power beyond thatderived from animals, water, orwind was desperately needed.Animal power was bulky andtroublesome what with feedingand stabling; wind power wasuncertain except in favoredareas and hardly suited to theregularity of industry; andwater power could only be ex-ploited further by going fartheraway from the cities to tap theremoter portions of alreadywell-populated streams. Minedrainage and water supply tomunicipalities and canal

feeders (canals constituted themain transportation system,the roads being wretched) werehandled by Newcomen (at-mospheric) pumping engines,but here the heavy cost of fuelfor the primitive engine setlimits. More and moremillwork and machinery,dependent upon shaft power,was in the making but falteringfor lack of adequate drives.The need was met, in smallpart, by the awkward arrange-ment of having an enginepump water over a waterwheelfrom a reservoir to which thewater returned to be againpumped over the wheel.

That a rotative engine wouldhave unlimited industrial ap-plication was very clear toBoulton who began to urgeWatt to take the matter inhand, as by letter in 1781, June21: “The people in London,Manchester, and Birminghamare steam mill mad. I don’tmean to hurry you but weshould determine to take out apatent for certain methods ofproducing rotative motionfrom the fire engine.”

The basic problem at thisstage was to convert the beam’soscillation into rotation, readilydone with a connecting rod toa crank, an idea unfortunatelypatented by someone else.However, the crank arrange-ment and the single-actingengine weren’t the best ofpartners, for it may be imag-ined that the rotational motionwas non-uniform despiteflywheel and often ill-suited ifnot unacceptable to machineoperations of sensitivity, as intextile mills.

Watt devised substitutes for

the crank, in Patent No. 1306,October 25, 1781, “circularmotion round an axis.”Of the several schemes thesun- and- planet gear (epicyclic)was chosen and would be useduntil 1802, even though thecrank patent expired in 1794.With a large flywheel, this arrange-ment worked well-enough forsome purposes in the mannerof the crank. After all, theengine was single-acting—power on only the downstroke,the piston being returned tothe top of the cylinder by iner-tia from the wheelwork. Dou-ble action, or power from theupstroke too, a notion Watthad been toying with since1775, came into view again.

Watt addressed the problemwith his next patent, No.1321, March 12, 1782, inwhich he presented a numberof “new improvements”: theexpansive principle; double ac-tion to double the power andget a more regular motion; acompound engine in whichsteam used in a first cylinderwould act expansively in asecond; a rack-and-sectorrelating piston rod to beam topermit “push” as well as“pull” for double action; anda steam wheel or rotativeengine. Pertinent is the rackpiston-rod engaging a gear sec-tor on the beam end. The ob-vious solution of constrainingthe piston rod with a crossheadin a vertical guide was imprac-tical then for manufacturingreasons: straight guides severalfeet in length would have hadto be worked out by chippingand filing, prohibitively expen-sive for anticipated productionengines.

With the rack-and-sectorhookup, a rigid rack replacedthe flexible chain as an exten-sion of the piston rod. Whenkept in engagement with thegear sector that replaced thearch head around which thechain had wrapped, the rackheld the piston rod to the samevertical as the chain would,with the advantage of beingable to transmit not only thepull of the conventional single-acting piston, but also thepush from a double-actingpiston. Although akinematically sound idea,workmanship and materials ofthe day weren’t up to it, thecast teeth of sector and rack be-ing troubled by the shockloading on reversal of thepiston’s motion. Furthermore,the headroom for the rack add-ed perhaps five feet to theheight of the engine house.Some other mechanism wasneeded.

Perpendicular MotionWatt puzzled mightily overthe problem, and in a letterof June 30, 1784, reports toBoulton that he “got a glimpseof a method of causinga piston rod to move up anddown perpendicularly by onlyfixing to it a piece of iron uponthe beam, without chains orperpendicular guides or on.towardly frictions, arch headsor other pieces of clumsiness.”

About a week later (July11th) he reports that he ispleased with tests on a “verylarge model of the newsubstitute for racks andsectors. . . It is a perpendicularmotion derived from a com-bination of motions aboutcentres.”

Early kinematicians wouldcall this the “three-bar mo-tion,” recognizing the threeconnected bars or links thatwere in play. (For “motion,”one may at times read“mechanism” and even“bar,” depending upon thecircumstances). Retaining thebasic beam as one of the “mo-tions about centres,” Wattadded an outboard radius rodof half-beam length (another“motion about centres”) andjoined the two by a link towhose midpoint the piston rodattached. This special pointdescribed a practically straightline in the vertical or perpen-dicular. Because of this, thewhole linkage—the three-barmotion or mechasnism — wasalso called a “perpendicularmotion.” This mechanism isthe mechanical invention ofwhich Watt would say that hewas proudest. It and two otherlinkages doing similar jobs

were protected by Patent No.1432 dated August 24, 1784.

This three-bar motion was abit awkward, for the radius rodlengthened the engine by halfagain, thus calling for anenlargement of the enginehouse. After building twoengines with the three-bar mo-tion, Watt held the length ofsubsequent engines down tobeam length by halving thethree-bar motion (the radiusbar was tucked under the outerhalf of the beam), and addingtwo links to form a panto-graph, the farthest joint ofwhich had a motion that wasan enlargement of the perpen-dicular motion’s uniquestraight-line point: it wouldtake the piston rod. In sum-mary, there were two points,the first located on the smallthree-bar motion, with the se-cond or parallel point beingthe far joint of the pantograph:the motion of this second pointwas parallel to that of the first,hence the quite proper name“parallel motion” for the pan-tograph configuration.

It is now that “our” engineenters history somewhatcautiously. Samuel Whitbread,a London brewer had orderedan engine with a 24-in.(610 mm) cylinder, 6-ft(1829 mm) stroke, in 1784.Although single-acting, it wasto be rotative, and a drawing(in the Boulton & Watt Collec-tion in Birmingham) datedNovember 1784 shows aparallel motion, almost certain-ly the first application of thatmechanism. This parallel mo-tion had followed hard on thethree-bar motion of the Coatesand Jarrett oil mill engine

ordered in 1783. A drawing ofJune 1784 shows that enginelaid out with rack and sector —but a three-bar motion sketch-ed over it and actually sup-plied. The Whitbread drawingof a few months later shows themore elegant parallel motion.

It has been said that whenfirst installed, the single-actingengine did the work of 24horses. This probably meantthe total number of animals re-quired during a day, not thenumber in use at one time, fora conservative calculation leadsto about 17 indicatedhorsepower, (12.7 kW), assum-ing a mean effective pressure of10 psia (69 kPa) and a speed of20 to 21 strokes per minute.When the engine was madedouble-acting in 1795, thepower developed by its cylinderwas of course doubled, to anIHP of perhaps 35 (26 kW) forthe rest of its working life thatextended to 1887: 102 years ofservice. The re- build in 1795did not replace the originalwood beam nor add a cen-trifugal governor, for theseitems are not shown on the of-ficial drawing of the time. Thepresent cast iron beam withproper counterweights appearsto have been fitted about 1805.

Early High - TechThe engine was high

technology for its day, muchmore commanding than theother mechanical marvels ofthe time, the windmill andclock. King George III, a manof plain and practical tastesand amusements, partial tohunting and mechanical con-trivances, brought QueenCharlotte and their four

children to the brewery in Mayof 1797 to inspect the “won-drous works to be seen there,”the moving and excitingengine being a key attraction.Although of modest capacity,it had set a good example, forby 1796, eleven other Boultonand Watt engines were amiablyat work in London. A secondengine came to Whitbread’s in1841.

In 1887 a compound engineby Messrs. Simpson & Co. fit-ted with Cowper’s inter-mediate steam reservoirreplaced “our” engine. Thenew machine, with high andlow pressure cylinders, wouldhave operated on steampressure a good deaal higherthan the perhaps 3 psig (21kPa) of the Boulton and Wattengine it superseded. And itwould have been compact-one thinks of the old enginestanding 30 ft (9.1 m) tall andswinging a 14-ft (4.2 m)flywheel, all for an IHP ofmaybe 35 (26 kW). At anyrate, the engine wasdismantled.

Archibald Liversidge, Pro-fessor of Engineering at SydneyUniversity and trustee of theSydney Technological Museum(founded 1880), happened tobe in London at this timevisiting his friend theengineer of the Brewery.Samuel Whitbread kindlydonated the engine to theMuseum where it arrived in1889. In course it was housedin a special building behindthe Museum in Harris Streetand given an electric turningmotor in 1930.

In 1983 the engine wasremoved to the Castle Hill site

and with loving care wasbrought to steaming conditionto celebrate its bicentenary inJuly of 1985.

As mentioned earlier, theengine is 30 ft (9.14 m) tall,and has about the same length,with an overall weight of 33tonnes. The cast iron beam, 18ft 4 in. (5.6 m) center to centerweighs about 9.2 tonnes; thewood beam of the 1795 draw-ing might have weighed about1.5 tonnes if of oak. Built ofsections of cast iron, the 14-ft(4.26 m) flywheel weighs,together with its shaft, some 8tonnes. Finally, the connec-ting rod is 18 ft (5.5 m) centerto center.

Mention must be made ofthe next-in-age survivor, the“Lap” engine of 1788 now inthe Science Museum, London,of which faithful copies havebeen made for museums inMunich, West Germany, andDearborn, Michigan, U.S.A.This engine drove the laps orpolishing buffs for steel or-naments in Boulton’s SohoManufactory, delivering 70years of service. It was the firstengine to be fitted with cen-trifugal governor. Smaller thanthe Whitbread engine, its boreand stroke are 18.75 in.(476 mm) and 4 ft (1219 mm).Watt rated it at 10 horsepower(7.5 kW), but put on test whenthe museum acquired it in1858, some 13.75 horsepower(10.3 kW) could be noted.Power was taken off theflywheel rim that carried 296inserted gear teeth.

June 1986R.S. HartenbergF. ASME, F. I Mech E, VDI

The American Society ofMechanical Engineers is mostgrateful to the officers and staff atthe Power House Museum andthe Institution of Engineers,Australia, for their assistance andsupport of this designation,and to Professor RichardS. Hartenberg, who wrote thetext for this brochure.

The Boulton and Watt RotativeSteam engine is the twentiethInternational Historic MechanicalEngineering landmark to bedesignated by ASME, and thefifth to be designated outside ofthe United States. The others arein Puerto Rico, Great Britain andFrance. For a complete list andinformation on the Society’sHistory and Heritage Programwrite:

ASME Public Information Dept.,345 East 47th St.New York, NY 10017

The American Society of Mechanical Engineers

Dr. L.S. Fletcher, PresidentPaul F. Allmendinger Executive DirectorWilliam J. Warren, International Affairs Committee

ASME National History and Heritage Committee

Dr. R. Carson Dalzell, ChairmanRobert M. Vogel-Smithsonian InstitutionDr. Richard S. HartenbergDr. J. Paul HartmanDr. Euan F. C. SomerscalesJoseph P. Van Overveen

The Institution of Engineers, Australia

W. J. Rourke, Chief ExecutiveM. H. Thomas, Chairman, College of Mechanical Engineers

Power House Museum

Dr. Lindsay Sharp, Director

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