Me Compound Condensing

8/4/2019 Me Compound Condensing

1/16

January 3, 1924 The Model Engineer and Electrician. 5A Model Compound Condensing Engine.

By C. S. BAHRETT.

( With Coloured S upplement Presented w ith th is

AB O U TIssue.)

1902, when I was serving myappren-

ticeship with a f i rm of l i f t engineers, a

bed plate and fitting main bearings, machining

iend, who was serving his with the Thames crankshaft (from forging) and cylinderc o v e r s ,

on Works, became fired with the ambition to

whilst I prepared drawiags and patterns for the

uild a decent-sized compound engine. He \vasair pump.

After about twelve months on it (at intervals)

ot particularly keen on a purely marine engines I had expec ted h im to be , bu t though t he

h i s en thus iasm began to wane , and h i s fancyturned to gas engines; the poor o ld compound

I_Fig. I.-The Completed Model Compound Condensing Engine.

o u l d m a k e it a n o n - r e v e r s i n g e n g i n e fory n a mo d r i v i n g . W i t h t h i s end i n v i ew, an d

lth t h e e x p e r i e n c e g a i n e d i n constructingeveral simpler models, I prepared a set of draw-

gs for him and had the patterns made for theng ine p roper ; the condenser was no t dec idedn till later.

A set of castings was made b y t he Cannonoundry, of Goswell Road, and he got to work,

ompleting the boring of the cylinders, p lan ing

was put on the shelf, and the new love gained

a l l his attention.

He thenwent to sea for a year or two, and Iheard no th ing fu r ther o f the compound un t i l

1909, when he had g iven up model work alto-gether. I was at his home one evening lookmg

over a quantity of odds and ends, a n d we cameacross the pieces and patterns of the compound,when he asked me if I would like to take them

over a n d f i n i s h t h e j o b ; n e e d l e s s t o s a y , I


2/16

6 The Model Engineer and Electrician.

VJ

i

t-7kHktt-r

i I


3/16

The Model Engineer and Electrician. 7

jumped at the opportunity and took the lot home. boxes. Pistons are of magnalium, and in twoThe first thing I did was to examine every- parts, with a s ing le cas t - i ron ring 1/4-in. wide

thing thoroughly and scrap the following parts : between them.all cylinder covers, both steam chests and covers,and piston rods, procuring new castings and

The rings were turned from a bush castingheld in the chuck, and were first bored to a

Eleva t ion (Condaaser S i d e ) of_Model C o mp o u n d C o n d e n s i n g E n g i n e .

forgings for these; then I Prepared a new setof drawings, as the old ones had disappeared.

size which would give the correct diameter when

split and closed, then the outside was rough-The cylinders were lapped out, ports trimmed turned to I-32nd in. over finished size, afterup and one or two incorrect stud holes plugged; shifting the bush in the chuck to give the

the new chests and covers were faced up in the required eccentricity. The next operation waslathe and bored for rods and double stuffing to part the ring off the bush, and face the sides


4/16

8 The Model Engineer and Electrician. J a n u a r y 3, 1924


5/16

J a n u a r y 3,pg. The Model Engineer and Electrician. 9o correct fit between the flanges of the piston;hen the ring was split at 45 degs. at its thinnest

gart and the joint carefully filed to close fit. Aig was then prepared (see nest issue for sketch).

A spigot was turned on a piece of material A toit the bore of the ring when closed, its width

being slightly less than that of the ring, a thickwasher B made and attached by setscrew C. Alip of thin springy material D wasmade, placed

labour well paid, as the rings are absolutelysteamtight.

The piston rods were made fr om forging s,machined to dimensions shown on drawing, andfitted with G.M. split brasses. Connecting rodsare also made from forgings, the G.M. brassesbeing machined on ali faces in the lathe toensure accuracy, the exterior being finished on a

mandrel after all parts were bolted together.

Fig. 2.-Front View of Model Compcund Condensing Engine.

over the ring and tightened up by the bolt, soas to draw the split in the ring quite close ;finally, setscrew C tightened up and the ringturned to exactlv fit the cylinder. Of course,the spigot on A is set slightly eccentric to suit

the r ing and when released the ring opened out,and on the first insertion in the cylinder therewas a good bearing equallv all round the outersurface. The above may seem a very elaboratemethod of making a simple article, but it is

Crosshead pins are driven in and secured by asmall screw each ; the low pressure pin isextended to form journals for the air pumplinks.

The crankshaft forging was turned up in the

usual way, with centre plates attached by set-screws for turning the pins ; it is drilled throughwith a 3-32nd-in. hole for lubrication from mainbearings to crank-pins as shown on drawings,and a 1/8-in. keyway was end-miiled in the lathe,


6/16

1 0 The Model Engineer and Electrician. January 3, 1924.

with shaft bolted on slide-rest. The bed platecalls for no special comment, except that theholes for the sloping columns were drilled withthe aid of a wood block, which was cut to thecorrect angle on the drawing. This job, by theway, was carried out in the workshop at theearlier M.E. Exhibitions, as were the flywheeland the planing of the back columns.

The valves were certainly unorthodox, but

give a maximum of length with a minimum ofsteam chest, without any tipping action in thedriving. They are of cast-iron and were milledout of a piece of broken hydraulic cylinder.Eccentrics are of mild steel, secured by gib headkeys in sunk keyways, those in the shaft beingmilled in the lathe, and those in the sheaves cutwith a 1/8-in. wide parting tool set sideways in aboring bar, whilst the sheave was held in thechuck. The top ends of the eccentric rods arefitted with split brasses, embracing a 3-16th-in.diameter pin, and they were faced on sides in

the lathe after being bolted to rods.There is a small by-pass starting valve fitted,consisting of a 3-32nd-in. diameter needle valveand hand-wheel , which opens a I-16th-in.diameter drilled port leading from the H.P.steam chest to the H.P. exhaust port, and thenceto the eduction pipe to the L.P. steam chest,thus passing sufficient steam to start the engine,should the H.P. crank be on the dead centre.

A 1/16-in. clear way screw down steam stop valveis also fitted. details of which are shown onp. 14-15. Thi body casting for this was obtainedfrom Messrs. Stuart. Turner, and the hand-wheei was turned from mild steel, five spokescut out with drill and file, and notches on squarerim cut in the lathe, using change wheel asdivision plate. Cylinders are lagged with thinblue lagging steel secured with 1-16th-in. round-he ad steel scre ws A good tip for fitting this,if of an awkward shape, is to cut out a tem-porary sheet in thin tin, bend into place, cut allnecessary corners, etc., then flatten the wholepiece out and use it as a template to cult thelagging sheet. I found it very successful.

Top and bottom cylinders and both steam

chests are fitted with drain cocks, which areconnected by unions to 3-32nd-in. diametercopper pipes, three of which, from the highpressure end, meet in a small junction piecefixed to the back of one column, and thence bya single 1/8-in. diameter pipe down the columnto the underside of the bedplate; the three fromthe low pressure end being similarly arrangedand meeting the common pipe, thence out of theside of the bedplate. These details are clearlyshown in one of the photographs appearingwith these notes, and in another which will bereproduced next week. The condenser, of whichdetail drawings will also be given in the

January 10 issue, is of brass tube, 3 1/2 ins.diameter, and No. 16 gauge.

(To be continued.)

Model Engineers and theiror

Mr. J . C . Creb b in .

MUCH water has flowed under the bridges

s in c e the publication of the issue of theM O D E L E N G I N E E R for July, 1899. In its pages

is a short article by James C. Cretbin, entitled Some Models I Have Made, illustrated byphotographs of a single-driver model locomotiveof Great Western type, and which he terms hisNo. 3. The portrait accompanying the article isthe presentment of a young man, but he hadalready been recognised as worthy to be a vice.president of the (then) Soc ie ty of Model Engi-neers. He occupied this position from October,

1898, to November, 1901, a n d h a s b e e nmember of the committee from December, 1913,to November, 1915; again elected in December,

1921, an d h as been e lec ted c h a i r m an a tthe las t A.G.M. H e h a s assisted w i t hhi s locomotive, the now celebrated CosmoBonsor, at every one of the six MODE L ENGI-

NFER Exhibitions, giving pleasure to thousandsof people and demonstrating what a wonderfulthing a model locomotive can be. This uniqueand welcome record has been acknowledged bythe presentation, from the organisers, of aMODEL ENG I NE E R silver medal of honour, oneof the first two such medals which have everbeen given.

Last March we received a let ter from abroad,

in which the writer asked us to publish accountsof celebrities in the mode1 engineering world.Amongst others, he ment ioned Mr. J . C .Crebbin, and remarked, I, for one, am veryinterested, and continually wondering what hisordinary every-day occupation is. For all Iknow he may be president of a railway orgreaser on a Thames steamboat. But what-ever he is, I will lay that he knows his job.If we were going to write Mr. Crebbin into astory for a cinema film, we should entitle it Big Heart, for this is his main characteristic

-whether as a model engineer or in his dealingswith other men. He was sent to Australiawhen ten years of age, owing to reasons ofhealth, in a five-masted clipper sailing ship, andberthed with the bosun, carpenter and thedonkeyman. He knew no one on board theship. He remained in Australia until he was14, then returned to London and went to schoolat Owens College, Islington, where he surprisedeveryone by making a cylinder frictional electricmachine with a gin bottle. The hair for therubber was given to him by a carman from a

horses tail. He pass ed the Science and ArtExaminations in Physics, Mathematics andChemistry, but terms himself the biggest dufferat languages who ever existed. He obtained


7/16


8/16


9/16

34 The Model Engineer and Electrician. J a n u a r y 10, 1924.

indefatigable labour on behalf of the Club hehas reached the presidential chair, a positionwhich he has now adorned for some years. Hehas often been on duty at the Lake sideadjudicating at the races, etc., against doctorsorders, and his services at these events area l w a ys highlv v a l u ed a nd h i s ju d gm en tsrespected. Ve ry often I have seen himshoulder responsibilities when all others fail andmany times this has occurred when he has notbeen physically fit. He is a bluff old diamondwho looks as if he had just stepped off the bridgeof a P. and 0. liner, and being one of the boyshimself he understands theirfailings and goodpoints as no other can. It would not be too

_IFig. S.-Another Deck View o! Danube II.

fulsome to say that W e love him. It has beena principle with him to set the boys a goodexample by owning the best boats he could get.and Danube II. is a fitting unit in the Piersonfleet.

THE City of York has had a most unfortunateexperience in adapting two Diesel engines froma German submarine for use in its electric lightplant. These engines were purchased in 1920,the cost being little m o r e than half that of a

corresponding steam plant, but the engines haveproved most unsatisfactory in use, the cost ofrenewals having been very great, and strong-complaints have been received of t he excessivevibration when running. The experience atYork has been similar in these respects to thatof another borough in the South of England,and it is reported that the Electric LightingCommittee has decided to scrap the engines.

A Model Compound

Condensing Engine.

By C. S. BARRETT.

The condenser is constructed of a piece of3-1/2in. diameter I6-gauge brass tube, with thetube plates (16 G) turned to fit and sweated in,5/8 in. from the end of the barrel, after drillingthem a good fit for the 86 1/4in. diameter thin

Showing Method of Machining the Piston Rings.

brass tubes, the thinner the better. The 1/4in.tubes are then cut off all exactly the samelength; a good method of doing this, provideda ho l l o w mandrel lathe is available, is as

follows:

Hold the length of tube in a self-centring chuck and adjust the poppet (with pre-ferably a drilling pad on the end of the barrel)so that the required length is outside the chuck

jaws, leaving enough to allow the slide-rest to


10/16

J an u a r y I O, 1924. The Model Engineer and Electrician. 35come close to them. Then mount a parting tool the tubes are as thin as they should be. A divi-made of a thin saw blade on edge in the slide- sion plate of 1-16th-in. brass is now fitted, asrest, and adjust lengthways so as to cut off the i shown at Y on drawing, to ensure the flow ofexact length ; run lathe at high speed and part I ci rculat ing water passing through the bot tomthrough. Release chuck, push tube up to poppet, / half of the tubes, and back through the top half.tighten chuck and repeat, and provided neitherthe slide-rest nor the poppet is moved, the n-hole

, Then the cast angle ends are turned a good fit

batch of tubes can be cut off dead to length in

1 in the barrel, a few brass screws put in radialiy,

the rings sweated in, and the ends of the barrelless time than it takes to write the description. with the rings faced in the lathe to ensure a flat

The next operation i s t o r e a d e r t h e t u b e swater t ight ; th is may be done by sweat ing i f preferred, but mine were expanded in with anexpander of the three-roller type, as shown in

sketch on p. 40. If this tool IS c a r e f u l l y m a d eand the rollers are free to move slightly radiaily,

it is surprising how quickly the tubes can berendered abso lu t e ly water t i gh t , as i t r equ i res

only a few turns with the thumb and finger, if

joint for the covers. The latter are a straight-

f o r war d t u r ni n g j o b , an d ar e s ecu r ed to t h eb a r r e l b y 12 3-32nd-in. s t u d s t a p p e d i n t o r h eangle r ings , an oiled brown paper join t being

inserted when finally assembling. The follow-ing facings are attached by countersunk screwswith paint and paper joints, as shown on thedrawings : In let f rom L.P. exhaust wi th castelbow piece, outlet to air pump, circulating water


11/16

36 The Model Engineer and Electrician. January I O, 1924.inlet, and circulating water outlet.An extra facing may be fitted at thebottom of the condenser if desired tolake a 3/8n. clear bore stop valve simi-lar to the main stop valve, so that theengine map be run non-condensing.

The air pump is of the Edwards

type, 1-in. bore, I-in. stroke, and hasonly one valve, the delivery. On thedown stroke a vacuum is created onthe top of the piston or bucket unt i lit nears the bottom of i ts st ro ke ,when the ports open and air passesfrom chamber in the body to the topof the bucket; at the same time, theconical bottom of the bucket hits thewater in the chamber, without shockand projects it round the curved sides,through the ports on to the top of thebucket, which, rising, closes the portsand takes the ai r and water throughthe delivery valve to the discharge, at

Elevation and Plan of Piston Rod Gland.

the same time drawing further quan-t i t ie s o f ai r a nd wa te r f ro m t hecondenser.

The principal points at which careis necessary are the machining o f theinterior of the body to a smooth and

even curve, and the accurate machin-ing of the top cover with its boredguide; the re s t i s straightforwardl a t h e work. T h e b u c k e t i s n o tpacked, two or more water groovesare turned in it, and it must be a goodfit in the barrel. T h e p u m p i sattached to the side of the bedplateby four 1/8-i,n. steel studs (care beingtaken to ensure that it is vertical),and it is driven bya pair o f s i d el e v e rs from the L.P. cosshead pin ;the bearing bracket for these is fixedto rear column by four 3-32nd-in.studs. The four connecting links areeach f i t ted with sp l i t gun-meta lbrasses, working o n 5-32nd-in.diameter pins, and held together with


12/16

J an u a r y I O, 1924. The Model Engineer and Electrician. 37

GUND.avcut-r -z-00 vi& SEA71

DET AIL S OF EDW ARDS AIR PUM P FOR M ODEL COM POUND CONDENS ING ENGINE.


13/16

38 The Model Engineer and Electrician. J a n u a r y 10 , 1924.

Main B earing 4 OFF

Brasses G.M. Caps M.S .

THE FRONT COLUMNS , MAIN BEARIN GS, ECCENTR IC SH EAVES AN D CRANKS HAFT FOR MODEL

COMPOUND CONDENS ING ENGINE.


14/16

J a nua ry 10, 1924. The Model Engineer and Electrician. 391-16th-in. diameter columns or distance pieces.These little bearings had their sides faced inthe lathe, after being fitted with the distancepieces.

Up to the time of writing the engine has hadbut one t e s t run, and that under rather adverseconditions. It was coupled up to a verticalmulti-tubular boiler fired with anthracite andfitted with slide crank steam feed pump, while

to a somewhat alarming figure, without anyload, and priming commenced. The dynamo-meter brake mas then rigged on the flywheeland a few test runs taken, with the resultsshown below. It is, at first glance, curious thatthe revolutions and power should fall off above60 lbs. pressure, but this was entirely due topriming, as I had my hands too full to keep asteady pressure and water level. There are so

the condenser circulating water was taken fromthe main tap by means of the garden hose, and

the condensate passed into the household bucket.When 50 lbs. pressure showed on the gauge, alldrains were opened, and the starting and mainsteam valves eased, when I was surprised atthe quantity of water which passed from thedrains before the engine moved away gently. Onopening out the main steam valve the speed rose

many things to be attended to, viz., firing, feedpump, brake adjustment, stop valve, revolution

counter and watch. The help that I anticipateddid not materialise, as the morning started wetand the run was out of doors. However, thetest results show some very good figures, and Ihope at higher pressure to obtain better; nearlyhalf-horsepower at 60 lbs. pressure is good forso small an engine.


15/16

The Model Engineer and Eleotrioian.

/IThe following are the results of the tests :-{I]q$revs.3 lbs. brake pull, Boiler pressure 45 Lbs.=.210 b.h.p.2 ,, 3 a1 ,, 8, 55 ,, .354 ,,(3) 1040 ?> 3 ,, ,, .II:; !?;z ,I 3 I, I, 1. 60 ,/ 4 4 5 ,,3 ,, =.411 ,>

J a n u a r y 10,1924.

P = spring balance in pounds, L = length oflever in feet, and R = revolutions per minute.

T a k i n g test (3 ) we get by substitution :

Tota l t ime under s team 1-1 /2 hours .70 ,, =.407 ,,

Evaporation, 16 lbs. of water (approx.).Co n d e n sa t e , 13.25 lbs. of water.

It was impossible to run long tests, as the fly-wheel overheated, so time was allowed betweeneach to allow it to cool.

The effect of the condenser was very marked;if the engine was throttled down to just tickover, while the circulating water was cut off(condenser by-pass being, of course, opened),then the water turned on again, and the by-passclosed, revolutions were immediately doubled,although the difference in speed was not somarked at higher speeds. It was necessary touse a considerable quantity of circulating waterto keep the condenser cool.

A sketch is given below of the brake gear used.The brake blocks A were of hardwood attachedby screws to the bars B, which bars were drilledto take the 1/4-in. screwed rods C and D, the rodC being provided with lock nuts inside the barsas shown, and D extended to take the hook boltE . R o u g h adjustment i s m a de w i t h t h elock nuts on rod C, and the brake pressure regu-lated while the engine is running by the wingnuts on rod D, the pull an the spring balance Fbeing adjusted by wing nut G.

The b.h.p. is arrived at as follows.-First

Three Roller Type Tube Expander

The Brake Gear Used for Testing the Engine.

measure exactly the distance radially between

the flywheel centre and the centre of the springbalance hook; in the present instance it is g ins.

PxLx2xRT h e f o r m u l a i s :

--, where33,000 , and this fraction worked12 x 7 x 33,000out gives .445 b.h.p.Care must be taken to measure length Lradially from wheel centre, and to see that the


16/16

J a nu a r y 10,1924. The Model Engineer and Electrician. 41.._

line of balance is at right angles to this line.The sketch will make this clear.

The photographic reproductions give a goodidea of the appearance of the engine, and show

interesting one throughout, and its performancewell repays the time and labour spent an it; itgrained a silver medal at the 1922 Exhibition.

Should anyone be desirous of building aa good deal of the exterior details. similar model, sets of castings will shortly be

The whole job has been an exceedingly

1

available.

A Large Spirit-Fired 2-1/2-in, Gauge ExperimentalLocomotive.

By HENRY GREENLY.

DURING the height of the discussion on solid

firing and the hauling of heavy loads byfreak performanccs on the short Exhibi t iontrack.

2-1/2-in. gauge locomotives, I was asked byMr. W. J. Bassett Lowke to suggest a designfo r a hauling model for the 1924 M O D E LENGINEER Exhibition, which by the time thesenotes will appear will be in progress. Whetherthe model will acquit itself in the manner thewriters paper calculations would show t o bepossible of accomplishment, and what will be

T o o b t a i n a h i g h drawbar p u l l w ha t i srequired is weight ADHESIVE: weight I may;repeat. S cale cylinders, scale pressures, sca ledrawbar pulls, scale everything else, is subser-vient. What is required to gain the plaudits ofthe observer is to obtain within the prescribedloading gauge limits the adhesive weight of aninch-scale locomotive,and having appropriated

Th e 2-8-2 Experimental 2-1/ 2-in. Gauge Three-Cylinder L ocomotive in Course of Construction.

the nature o f the mutual recr iminat ions o f avoirdupois in this illegitimate manner, t h e nextbuilders and designer, ca nn ot at th e moment portion of the problem is utilising it. Havingbe foretold. The final test, for good or ill, will arbi trar i ly fixed the steam pressure-a con-be its presence and work at the Exhibition. venient one based on practical experience, say,

Naturally, as the new goods locomotive foranything between 50 and 80 Ibs. per square inch

Eskdale was paramount in the writers mind at -the size of the cylinders can then be discussed.

the time of Mr. Bassett Lowkes request, the

The weight on the coupled wheels of the

design that was considered best for the service model as designed was estimated at about 28 to

there, where the maximum hauling capacity has30 lbs.* On a dry rail the maximum coefficient

to be maintained over a seven-mile non-stop runto time was thought to be sufficient for the

* A scale tonnage (with coefficient taken at 5)of 140 to 150 model tons

Me Compound Condensing

Documents

Transcript of Me Compound Condensing