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 6 
 
^anadion ^ocicty of ^ioil (^nginccrs. 
 
 IKCURPOHATED 1887. 
 
 ADVANCE PROOF— (Suhjecl to revision). 
 
 N.B.— This Sooiely, as a body, does not hold itself responsible for the fact* 
 and opinions stftteJ in any of its publications. 
 
 IMPULSE WATER WHEKLS. 
 
 To bo read Thursday, January 20ih, 1898. 
 
 J. T. Farmer, Ma.E. 
 
 The development of power by means of impulse water wheels hat 
 been rccfivins; considerable attention during the past ten years. 
 Water power . ' > be met with under varying conditions and in various 
 surroundiags ; and the means best adapted for the utilization of the 
 power vary with those conditions and surroundings. 
 
 Among the means devised by man at different times before the 
 advent of the impulse wheel for utilizing the water power that was 
 going to waste around him, one has easily taken the foremost place and, 
 indeed, has, by a process of the survival of the fittest, practically ousted 
 all other methodH from a position of being worthy of serious consider- 
 ation. The turbine has at the present day almost entirely taken the 
 place of the earlier devices in use, which have either been consigned to 
 museums as curiosities or are regarded as picturesque additions to the 
 landscape. 
 
 r(|.i 
 
 The impulse water wheel probably differs as much from the various 
 forms of turbiue in construction and in action ns the turbine does from 
 an overshot or breast water wheel. The previous statement with 
 regard to the turbine must thenforc be further modified so far as it is 
 found that the impulse motor is finding favour with those who utilise 
 water power. 
 
 PtLTON BucutT 
 
It lioB been 8aid that "countless wealth is being squandered .d al 
 the torrents and water eourses of the world." But it might be added 
 that unless the proper means arc taken for its ul.l.zat.on that wealth 
 of encr.'y avails little more to man than that of the tides m Jupiter. 
 
 It seeuis at first sight a very simple matter to place a wheel in posi- 
 uon to take ;.p the energy of water; but in praetiee that arrangemen 
 is generally found to involve more or less eostly eonstruetion .n the 
 .ay of dams, basins, eanals, flumes and even tunnels. Tub ,s pa t - 
 euhily the ease where the use of turbines is contemplated, and th. 
 consideration is frequently sufficient to annihilate the expediency o 
 Ls attempting to utilize a known and otherwise available source ol 
 
 ^Thcso adverse conditions are forcibly illustrated in the mountainous 
 districts of the North American Continent. Water power .s there u, 
 rndance but it is that of mountain torrents ; as a rule inconsiderable 
 „ vot^e of water, but, on account of the contiguration of the coun-ry 
 affordin- large head.. The latter circumstance makes any construct- 
 W^work very costly, and in most instances would put the use of an 
 ordinary turbine out of the question. 
 
 It was from such causes that the Western States became . he b t 
 Place of that system of water power of which the essential feature . 
 mp le water wheel. The simplification made possible in th. 
 yjn is that of the substitution of a pipe an nozzle of .nsign.fic 
 diinensions for the mas.ive head race and wheel pit associated with the 
 
 "^ The Vri: impure wheels brought into use were of the very crudest 
 desciption;with the increasing use of the system howevor cam Ih, 
 drelopmen which attends every invontion which has a large h Id of 
 u et ness ope n to it. The impulse .heel of the present day ranks as 
 S efficient mnong the various means of utilizing -^ural energy 
 
 A this stage it becomes a question to what extent ,t may be des.r b 
 
 to employ the impulse wheel outside the conditions under which it h »t 
 
 ;;; nto existele. Thi. problem is specially interesting in a country 
 
 T there i^' an abundance of water power, and at a time when the 
 
 :• ". ^n water power is assuming the place of one of the most 
 
 tt nt en<.ineerinA««-''io»« °f ^l'« ^^^^^ "^'"^ "^^''' °^ ''"' »'"'" 
 ;:rr: rd tie csd.; or some experimental research on this subject 
 
 Inda^Io to discuss the question by the light of those results and from 
 
 nilinv considerations. , i .„ 
 
 Thehistoryofthe development of the impulse water wheel may 
 adv nt a-lsly be .^kotohed briefly. The first wheels of this class 
 we e s mply P-vided with flat projections on the rim of the wheel, and 
 Tiet was ar,.an.'ed to impinge normally on these flat surfaces. This 
 'Jr, .rw^Ikn^wn as th^.urdy.gurdy. Itean easily be diown lom 
 To Itieal considerations that the ideal efficiency o such a wheel is oO 
 PC but it is probable that most of those in use did not give a greater 
 efficiency than from 20 to 30 per cent. 
 
 >ig.3 
 
 The first notable improvement was that of substituting hollow cup 
 fn, the fl^U vanes, so that the jet struck the interior part of the cup and 
 'J fl cte 1 biM. a.^un until it left the vane, travelling, with r.spect 
 r^l::l:almo;;theoppo..^d..U.to^^^^^^^ 
 
 ;;-:^S"SSi:e;;::i;tticetheefficiencywasstill.r 
 from what it theoretically might be. 
 
Tho next modification wns that of so curving the surface of the eup 
 that the jet might follow tho surface with very little deviation at the 
 first point of contact. Thus some wheels arc formed with a conical 
 projection in the interior of the cup at the point where the jet strikes 
 the surface, so that the water on striking may he^'in to paiss along the 
 generating linen of the cove, and may gradually be deflected further to 
 follow the curved sides of tho interior of the Viuie. This formation is 
 illustrated iu B^. 4. The more coiimion construction is to place a 
 wedgeehapod projection across tho intirior of the cup or vane. This 
 modification was introduced about 1880. It may be .seen in the 
 bucket illustrated in fig. 2. Tho function of tho widge is twofold. 
 
 (1) To prevent the heaping of dead watei- upon the vane during its 
 passage through the are of action, or the pait of its path iu which 
 the vnno receives the jet of water. 
 
 (2) To give the diverted streams a direction of motion which will 
 finally carry them dear of the wheel. 
 
 In a bucket unprovided with any conical or wo(lt;;;-sh,iped projection, 
 there is no sudden angular deflection of the water. Some of f.hc water 
 IS heaped upon the flat suifaco upon which tiic jet is impinging, thereby 
 forming ■>, curved suifaco over which the foUowio;: water is deflected, 
 as shewn in fig. 3. With a stationary vane on which tlie stream i.s 
 continuously playing, the loss of force duo to this cause is very flight. 
 When, howcvor, the impfct is taking place intermittently on a moving 
 vare, the dead water i» discharged after very inifficicnt action at the 
 end of every Miort period of action, and the total Iosp in efreotive 
 work niity be considi rablo. This loss is reduced by placing a solid 
 prnjiction in the bucket, which takes the place of thiit formed by the 
 water and leave.- all the water free to be deflected in the most efficient 
 manner. See fig. 4. 
 
 
 Fig. 5 
 
 
 
 ^^^^^■1^ 
 
 .>^i^^ 
 
 >.••-* 
 
 ..^ 
 
 
 i^M--- 
 
 fig. 6 
 
 As regards the second function of the wedgo, it is virell known that, 
 when astroiim of water strikes normally upon a surface it is deflected 
 equally in all direction.s. This is illustrated in the wheel bucket, of 
 which two views are shown in fig. 5. The same action takes place 
 when the stream strike.'" centrally upon the apex of a cone. This is 
 undesirable in ihe ease of the vano of a water wheel, as the water which 
 is directed towards the centre of the wheel gets into position to strike 
 the back of the following vane, thus oppo,sing tho useful effect of the 
 action. When the jet stiikoj a wedgo, as in fig. li, it is cut into two 
 pcrtions, which aie diflicted away from one another in a plane per- 
 pendicular lo ihe cutting edge of the wedge. In a wheel tliis moticn 
 causes the water to be discliiirged at each side of the wheel where it is 
 fno frcni all liability to interloic with any following parts of the wheel. 
 
 Numerous modifications of the form of the curved surfaces of the 
 buckets have been brought out at difforer:t times by inventors with a 
 view of modifying the passage of tho water over the vane in .«ome part, 
 icular, but it is not necessary to describe them more particularly. 
 
 Of the impulse wheels in u,sc at the present day the best known is 
 probably the Pelton water wheel. These wheels arc made in sizes 
 varying from in. to 6 ft. in diameter, according to the head of water 
 available and the velocity required. These wheels have been applied 
 under heads ranging up to 1,700 feet and, as has bt-eri said, there is no 
 doubt that under such conditions the highest efficiency is realized. 
 On the other hand, there are said to bo instances in which Pelton 
 wheels are running with good results under heads of from 50 to 75 feet. 
 
 3 
 
c J cntalof<ued a« ,he Pelton Motor No. 3. This wl.eel is approxim! 
 
 H« J<20 pounds. Two d.vations of thin motor arc .mvc« i,. fie. 1. 
 
 Ihe tc8t« were made in the Hydraulic Laboratory of McOill 
 W.ty and abriefdesenption of ,l,„ n.chods on.pfoycd St 
 .VCD. It was .mposs.blc to make test, with heads as high as some of 
 ^.«eunerwh.ch these .notors run. The n.a.imum tad eily 
 Tel" Kv the ety supply fVom the higl, level rjrv ir, 
 
 which Kives a pressure of 125 lbs. per square in. in the laboratorv 
 
 Mht 1'! :h^' 1 7 '-'t ^°"" p'^-- -- -^'^ o^s 
 
 oy throttling the supply from the same source 
 
 of moto*!. '" 1 '' """ T "," ''''" "'■ '"'"' '"*y '"' •'^P'=«^'-'J «f 'his type 
 01 motor when use.l under ordinary heads of from 100 to 300 feeV 
 
 lu many d.stne,s these „re aslar.o heads as are com.nonly -net ^. 
 
 Also, where U .s proposed to take p.wer fron, a w.ter-works systen. th 
 
 In the present series of trials the wheel tested was small compared 
 w th n,any ,n use ; the effective work done did not in any case eL ed 
 7 horsepower. There ,s no doubt that with « machine dii.^nod n a 
 ar,er scale as w,th la,,er h.ads, the efBeieney would sho^ some in' 
 crease over the values found in the present case 
 
 The,esult. obtained in these experiments are offered as bearin-^ 
 .Inectly on the cjuesfon of the utilisation of this sy.tem for small 
 
 W n f 'f '" "'V''"""'''""" '■" ^•••"^y •"■«'' f'^il-f water. 
 
 Wnh rca on and judgment, the general conclusions arrived at by the 
 cons.derat.on of these .esults may be extended to cases whe e h 
 machinery and the generation of power is on a larger scale 
 
 . .aLcis, and the auxiliary apparatus was fitted in aeeordaneo with 
 their instruefons The water, after passing through the valve wS 
 was used to regulate the pressure, was led along a length of 2! ch 
 p.pe straight for 8 or 10 feet before reaching the nozzle.'' A Bou don 
 gauge v^ashtted on the supply-pipe less than one foot from the mou h 
 oftlonozzle-tip. This gauge was arranged on a pres.ure-ehamber 
 enveloping the pipe and communicating with the interior throu.! a 
 series of small holes. Before being us.d the gauge was calibrated by 
 jans of a gauge tester. In the experiments the pressure in the pipe 
 of course varied slightly. The pressure was read at intervals of 0^ 
 or two minutes, and the mean value during the whole trial was accept- 
 ed as the pressure under which the flow took place. The extreme 
 variation of the prcure was about one pound pel' square ind. 
 
 Three different sized nozzle tips were supplied with the wheel 
 Ihese nozzles tapered gradually on the inside from the diameter of the 
 -pply pipe to that of the actual orifice. The outlet diameters we 
 
 .5277' 
 
 .0307' 
 
 .7532' 
 
 Sts of trials w.re n.ade using (he largest and smallest of these 
 nozz ef ps, the largest giving the more .satisfactory results 
 
 The water was discharged from the motor into a flume bone.th 
 whence it ran into measuring tanks, and all the water used was thus 
 actually measured. For the purposes of these trials two \Z 
 used, each the capacity of 1,000 gallons ; these had both bl 
 previously calibrated. '•" 
 
 The power given by the wheel was estimated by means of an absorp- 
 tion brake and » revolution counter. 
 
 The shaft was provided with an 18" diameter brake wheel of special 
 design, and ,hc , „wer was taken off this. In the earlier tria^ 1 
 brake consis-ed of one or more cords embracing a suitable arc of the 
 penph ry of t e brake wheel, and having spring balances lUt.el.d 
 U.e tight and slack ends to indicate the eoirespondin. tensions in the 
 eord. As the power varied slightly all the time, both readings w 
 
taken at intcrvalt* of one or two minutes, and the moans asod in calcul- 
 Btiug the final rcHult of the trial, Later a dircot-ruuding, 8clf-udjui4- 
 ing binko, designed by Mr. Wiibycombo, wus subi-titutcd for the cortis 
 B!id (Spring bulances with very satisfactory results. 
 
 All ordinary revolution counter was used, but arranged to bo tlirown 
 ID and out of un^'a^eucDt willi tlic .-sbaft at the beginning and end of 
 each trial. The ncceBsary readings could (bus be made at IcLsuro, 
 insuring greater accuracy. 
 
 Jn addition to the revolution counter ii tuiliuniutcr was connected 
 to the sbuft, Tbis .served u>i a guide v\liin adju!!tiiig llio load on the 
 brake wheel pievious to a trial to give a desired ,-peed of running. It 
 also served to indicate any considtrablo departure from the intended 
 speed which might take place during u tri:il, and which would vitiate 
 the accuracy oi' the ealculaleil re>ults. 
 
 Before passing to the exauiiuatioii of tiie cxpciinioiilal results of the 
 trials, it may be well to ujake a brief ibeoretical analysis ol' the subject. 
 
 The eleuieiitary theory of an inipuiso wIkiI is very simple — fo 
 tiinpie indeed that no attem])t seems to have b(en made to consider to 
 what extent known and obseivablu phenomena nay modify theoretical 
 caleulutious; but rather the elementary thenrctieal result is generally 
 taken as the last word which can be suid on the suhJLCt IVi m a theore- 
 tical jioint of view. 
 
 In the following investigation the efficiency is deiluced from a con- 
 sideration of the circumstances, as far as tiiey can bo muthcuiatically 
 expressed, under which the mechanical action takes place. 
 
 In the elemeutary theory of the impulse water wheel the assump- 
 tions generally made are sub'^tantially as Ibllows : — 
 
 1. That the jet has the theoretical velocity due to the available Lead 
 of water. 
 
 2. That the jet strikes the vane centrally and tangentially to the 
 wheel. 
 
 .S. That the jot passes over the surface of the vane without any loss 
 of relative velocity. 
 
 4. Tbat llie vane is so formed a.s to turn the stream through an 
 angle of 180° eoiniiletely back on itself. 
 
 In all these particulars lliero are some modifications which can be 
 more or less exactly stated : — 
 
 (a) The velocity of the impinging j' t is reduced in the ratio of a 
 coefficient of velocity dejending on the pipe line and nozzle. 
 
 (?y) Instead of striking the vnne tangentially, the jet generally a ,u 
 the case particularly alluded to strikes at a point nearer to the nozzle. 
 Thus suiniose a horizontal jet is applied underneath a wheel. If in 
 tig. 7 be the centre of the wheel and L its lowest point, the jet strikes at 
 J\ where L U I' makes au angle say. Of course the water begins to 
 play on the vane before it reaches P, and continues for a short Sf.ace 
 alterwards until the stream is cut otl by the next apjiioaching viinc ; 
 but P may be taken as a mean position. 
 
 Fig. 7 
 
 The wedges of the vanes then are formed noriral to the jctjat^this 
 point instead of being radial to the wheel. This iDVoives their being 
 inclined at an angle d to the radius of the wheel. 
 
 
(c) Tlio force of impact is reduced owinj; to the velocity lost by 
 the w«t«r in pawling over tlio surface ol the vane. Some previous 
 experiments on lliis subject afford data which will bo used in approxim- 
 utiiig to the loss due to tliis cause. 
 
 (d) It is Impossible, praotieally, to turn tlio water completely back 
 on itself on account of the reaction which would take effect on the back 
 of the s iccoeding vane. _ 
 
 I,,t u bo the resolved velocity of the vane at F in the direction of 
 
 iiiotiou of the jet. 
 
 I) that of the jet. 
 
 The water .-trikes the vane with relative velocity (u - «) nnd leaves 
 it with relative velocity <•„, (v - «), whore c,, is the ratio of final to ini- 
 ti'il relative velocities. 
 
 The force exerted "n tlio vano in the direction of motion of the water 
 is equivalent to the nionientiini of water dostroyo 1 per unit time, which 
 is : — 
 
 - \ (v - u) -c,civ - u) cog,! [ 
 ;!(• of deflection of the wa 
 
 (C — u) (1 — Ctf . C0S(J) 
 
 where is the iingU^ of deflection of the water 
 9 
 
 Now U =; 0/' . <l) . COS ('. 
 
 £0 being the angulnr velocity of the wheel. 
 If the line of the jot cuts OL in A^, and OX be cilled «, 
 
 ON 
 
 UP 
 
 .: OP 
 
 = cos 
 
 cos (' 
 
 — '— W . COS fl 
 COS '' 
 
 ... F ^ "!; (i. _ ,„) (1 _ c„ COS ,1) 
 The niciment of this lorco about the centre of the wheel is 
 
 Fz 
 
 (y — ifo) (1 — Q- cos >>) 
 
 whieli is constant. 
 Tlie work done per si cond is 
 F zw 
 
 = !!L^«' (,- = «•) (1 
 
 ■ C,r cos f) 
 
 The energy available per second is mh, 
 h being the available head of water. The efficiency thoreforc is 
 
 y'^ 
 
 (v— cfo) (1 — '■„cos.O. 
 
 If iY be the number ol' revolutions per minute 
 N (o 
 
 lit) 
 
 2 TT A' 
 
 00 y/i 
 
 •Ztt 
 
 (.- 
 
 -A' = ^ 
 
 GO -^ ^ 
 
 c„ cos ,1) (I). 
 
 In calculating llic value of u lo be inserted in tliis cxpre.ssion It must 
 be remembered that tlio velocity of the issuing jet is less than that 
 llieoretically eue to the head. 
 
 In practice there will be a reduetic n of velocity due to two causes : 
 
 (1) IJesistaneoof pipe lino. 
 
 (2) Loss in disehiii'gc iroiu the nozzle. 
 If i be the length of pipe, 
 
 d the diameter, 
 
 6 
 
the velocity lost by 
 lie. Some prcviouu 
 )o used in approxim- 
 
 ter completely b»clc 
 ko effect on the baolc 
 
 '^ in the direction of 
 
 ty (u - u) nnd leaves 
 B ratio of final to inl- 
 
 f motion of the water 
 per unit time, which 
 
 e oiUed », 
 
 ,lie wheel is 
 
 iDcy therefore is 
 
 1 — c„ cos ,() (I). 
 
 tliis expression it must 
 g jet is less than that 
 
 ty Juc to two causes i 
 
 The lots A, due to pipe rriolion is calculable by the well-known fbr* 
 niula 
 
 Ai 
 
 
 V being the velocity of the water in the pipe and/ the coefficient of 
 frieliona! resistance of pipen. 
 
 If ill a be the areas uf the pipe and noitlc respectively, 
 
 ■' d Ax' 'iij • 
 Other losNcs due to bendx, cto,, can be considered included in a co- 
 efficient A', which would have to he derived from consideration of the 
 special circ'unistaneus iu every case. TItIh would uiuko liie total loss of 
 head in the pipe lino 
 
 
 2g 
 
 The remainder of the available head is spent in producing the velo- 
 city 11, and part Ih absorbed in the resistance of the nozzle, if the noz- 
 zle offered no resistance the veloeity would bo increased in the ratio of 
 1 : Ci- , and therefore tlie velocity equivalent to the remaining head is 
 
 V 
 
 The energy remaining is therefore 
 v' 
 Co' ~g 
 
 = (l 
 
 *v[i2 
 
 '. h = hi ■^ hi + - .7, ~ 
 
 ' 'ig 
 
 Numerical values inserted in this formula will give 
 /i^n.Ofi + .026— " ., + K) 
 
 r (1.06 + .026— "! 
 a A I 
 
 -g 
 
 The results given by this formula would only .■ipproxiniate more or 
 less closely to the actual stale of affairs, wiiieh would best be determin- 
 ed by actual ineasurenient of the pressure cldso to the nozzle by means 
 of a gauge, when the conditions of flow are those actually occurring in 
 practice. 
 
 In the trials un<lor discussion the heads given arc those measured 
 close to tlio point of di>cliarg.', so tliat no loss due to the pipe line need 
 be considered. Tlie only loss of velocity is that which occurs in the 
 discharge from the iic'/.zlc, and the value of v therefore is calculated 
 from the Ibnuula 
 
 V = c, ^2'gil 
 
 where c,, is the eoeffieient of veloeity for the nozzle used. 
 
 In the ntzzles used in the experiuicnls Hie stream issued from a paral- 
 lel throat, and coiisi;qucntly tlicre would be no appreciable contrac- 
 tion of tlio jet. On this consideration it is reasonable to attribute all 
 the defieil iu discharge to the loss in velocity or 
 e,. = '-',, . 
 
 The co-efficients of discharge were deterniiiiod foi these nozzles for 
 heads up to 20 feet, ab.ivo whicli point the variation becomes very 
 slight. The results obtained therefore give an approximation to the 
 true velocity of tlie jet. 
 
 In addition to tlieso determinations tlie coefficient of discharge 
 was calculated from the data afforded by each of the trials. These co- 
 efficients agreed very clcsely with those obtained directly in the case of 
 the .5 in. nozzle. The mean values were .972 and .980 respectively. 
 
 The discrepancy is not surprising when it is considered that in the 
 former ease the outflow was from the end of a long pipe, while in the 
 latter it was from a largo body of water at rest. 
 
 7 
 
The diirrupanoy in nioro markod in the otpe of tho noiilo ^" dia- 
 nu'tur, wliorc the two vnluen iio .OO'.I nnJ .976. It in (iuirf;cHtcil that 
 tliii* (lifltTcnou iH (luti to tho l»ct that tlie interior of tl>in noitle wii* 
 ciivireil with iiiftiit tliu tltno ol' iti> bi^in^ unuil in tho water wlio'l, 
 hh it had hocn in placi' t'nr mnnt' time. Tho f0fttini( of oxido on tlio 
 interior would diniinixh tho actual ar<M of outlet, »o thut tho coefficient 
 would appear to bo Huiikller than it actuidly wiis. In addition to t)ii^ 
 there cm ho no douht that ihu rou^h xurt'iico of the oxido would 
 diniinixh the vuloeily of ihi^ i ultiowiiiu wi\ior ; this may bo piirtly tho 
 renxou why tlii^ irluln with the J" uoizio nIiow n (lui'llor e£Baicnoy thon 
 thoMo iniido with till' j'" nnz/.ie. 
 
 If thix (Xp'itnation in correct, it would point to tho desirahil'ty of 
 h.ivinj^ tiio interior .-urlHO'H of the tio»/.le-li|'« clean and froo from rmt. 
 To iieeonipli^h this, It wniihl prnbiihly hi' worth while to liavu ih tacli- 
 iihle III zzh'-iipH niiide or hriisM er .'•ouio other nietiil not k> liable to bo 
 iiuted upon a* iron in tho presence of uioi.'turo. It would iilso bo ad- 
 vtHiiblu for the ii-er to porindicnlly tako out and eloiin ths noiils tip, 
 0'<poeially if iiiaile of c',i.-.t nr \vi'oii;;hi iron. 
 
 Willi a iliiiy nozzle there is a direet losH of cfficirnoy corrcipondin^ 
 to wl-atover loss of velocity i.-t eiiusod by iho ri>uj;h «urlaci! of the 
 iiii'zzio, .More Ihitn thin, tluru i.s a iliniiiiutiuu in tlio area of tho outlet^ 
 iind tl (fore in the di'chiirp', with the result that tho power developed 
 by llie uiotnr fulls olf. This may bieouic a serious consiileriition if the 
 iiiiitiir is not uiueh more tlmn eipial ti the deiuaniN UHu:illy made upon 
 if. 
 
 The particular valne.s will now be insrrtcd in llio expression for the 
 cffieienc^y. 
 
 I'ressures = 75 and 1(10 1Ih. per sq. in. 
 
 Co'TeHponding heads := 175 iind -',i',) It. 
 
 V = 103,1 and lllt.ii It. per wo. 
 z — .(ItH! I't. 
 6 = 170° 
 ens 8 = -.!t<'-48 
 
 'Ihe value of (•„ can be dedni'ed, ns montinnod previously, from an 
 
 exprr,<sion derived from a sericH of experimint.s on vaues of tliis 
 
 de>orlption, 
 
 in .^1 
 r = = .0206 - i 
 
 where I" is b ss of veloeity, I), the menu velocity of Mio wa'er, <« tho 
 .sectional area of the jet :iiid .1 the wettdl urea of tho viine, 
 e„. = 1 - r approxi mutely. 
 
 A 
 
 'Ihe ratio - is about (i.O 
 
 = .17G 
 
 I 
 
 The (luantilv expre.ssed by i'„ here is the mean velccity with whieli 
 the wuter passes over the surface of a bucket and may bo taken as 
 
 {.-^J-') 
 
 in expression (I), 
 
 8ub.stitutinj.; values for the diU'ercnt eonilitions under which the 
 wl'.cel is run, the following table of values of c,^ can be deduced : — 
 
 TABLK T. 
 
 iV 
 
 h = 175 ft. 
 
 h =235 
 
 300 
 
 .953 
 
 .955 
 
 400 
 
 .9.52 
 
 .954 
 
 500 
 
 .9.50 
 
 .963 
 
 600 
 
 .948 
 
 .952 
 
 700 
 
 .940 
 
 .951 
 
 800 
 
 .911 
 
 .949 
 
 900 
 
 .941 
 
 .947 
 
 1000 
 
 .937 
 
 .945 
 
f tho noiilo J " dla- 
 
 It iit iiue(;oHtcil that 
 
 )r of tliii noule wiit 
 
 in Ihti water wlieel, 
 
 \rm of nxido on tlic 
 
 10 llint thocooffioiont 
 
 In addition to ttiin 
 
 iif tlie oxido would 
 
 is may b" (mrtly tlu^ 
 
 uii'ilor t'ffioicnay tlion 
 
 .0 tlio dp»iral)il'ty of 
 I and I'rco Ironi mit. 
 wliilu to liavu (litftoii- 
 liii not H) liable to bo 
 It would uIhc) bo ail- 
 I eluiin tba noxilc tip, 
 
 icicncy corrcfpondinn 
 r^uuli surliioi! (if tbi! 
 tlio iiica of tho (iutli't_ 
 itlho power devi'lopi'd 
 iia cnnsidoriitiiin it' tliu 
 ds uHuiilly uiiiilo upon 
 
 tlio expression for tlio 
 
 SCO. 
 
 d prcvioni-ly, froin an 
 ts on vaues of tliin 
 
 f (if Mio wa'er, <« tho 
 if tho viiue. 
 
 u\ V'lioity with which 
 I may bo taken as 
 
 ions under which tho 
 can bo dccluocd : — 
 
 h = 235 ft. 
 
 .9.-.5 
 .954 
 .!if):J 
 .952 
 .951 
 .949 
 .947 
 .945 
 
 Thew values load to value* of the factor (l-«. coi 8) u gi»«n iu 
 tho following tabic ;— 
 
 TAHLK H. 
 
 N 
 
 h = i ■ '> !<.. j 
 
 h » 2a5 r». 
 
 300 
 
 l.i):w 
 
 1.940 
 
 400 
 
 1.9:!H 
 
 i.njo 
 
 mm 
 
 l.li.iG 
 
 1. !»;!•) 
 
 liOII 
 
 i.!);u 
 
 1.!);JH 
 
 700 
 
 I.!);i2 
 
 l.!):i7 
 
 KtiO 
 
 I.D.'IO 
 
 i,9;i6 
 
 1)01) 
 
 1,927 
 
 i.9:t;t 
 
 10(10 
 
 • 
 
 l.i)23 
 
 1.P31 
 
 Tho following values are thus olituinod for tho tlicorotioal efflci ncy 
 of the wlu^ol with a J in. diiim. nozzlo ;— 
 
 
 TABLH III. 
 
 
 « 
 
 JV 
 
 h = 175 It. 
 
 h --^ 236 ft. 
 
 
 301) 
 
 59.3 
 
 tl.O 
 
 
 400 
 
 72.3 
 
 0! T 
 
 
 500 
 
 81.8 
 
 75.3 
 
 
 600 
 
 88.0 
 
 83 ■: 
 
 
 too 
 
 90.9 
 
 88 5 
 
 
 800 
 
 90.3 
 
 91.0 
 
 
 900 
 
 8>;.ti 
 
 91.2 
 
 
 1000 
 
 79.4 
 
 88.8 
 
 _ 
 
 
 max.91.1(r. 738 
 
 max. 91.5 8.^)7 
 
 
 Tho differeueenbttwecn theflo calculated values and the actual values 
 obtained aic exhibited in Table IV. These result.^ are illustrated 
 graphically in ligurea llJ luid 17. 
 
 TADLH IV. 
 
 ===== 
 
 iV 
 
 h 
 
 = 175 ft 
 
 . 
 
 b 
 
 = 235 It 
 
 
 
 UATIIKM 
 
 ACTUAL 
 
 DU'F. 
 
 MATH EM 
 
 ACTUAL 
 
 DIFK. 
 
 300 
 
 5i) •' 
 
 
 
 63.0 
 
 
 
 400 
 
 72... 
 
 58.4 
 
 13.9 
 
 65.7 
 
 52.. 5 
 
 i3.2 
 
 500 
 
 81.8 
 
 64.8 
 
 17.0 
 
 75. S 
 
 59.3 
 
 16.5 
 
 COO 
 
 88.0 
 
 08. 2 
 
 19.8 
 
 83.4 
 
 (15.0 
 
 18.4 
 
 700 
 
 90.0 
 
 69.2 
 
 £1.7 
 
 88.5 
 
 69.5 
 
 19.0 
 
 800 
 
 90.3 
 
 66.2 
 
 21.1 
 
 91.0 
 
 70.0 
 
 21.0 
 
 900 
 
 S(i . (5 
 
 
 
 91.2 
 
 66.2 
 
 25.0 
 
 1(00 
 
 79 4 
 
 
 
 «8.8 
 
 
 
 m 
 
 From thin last table it is apparent that there \x .'till a waste of from 
 15 to 25 per cut. of the orijiinal ener;;y of tho wi.ter which ha.s not 
 been accounted for. Tho lofs due to friction of bearings would bo 
 small in a simple ni.iehine of this sort, and the ^re.'iter part of tho 15 to 
 25 per cent, loss must be due to .=ouie departure in [.raetiee of tho phe- 
 nomena of action from tlinoc assumed. 
 
 It is su'jj^esled that tin; loss arises wholly or in pait from tho im- 
 pcrlect action of the vanes or buckets in tnrninj; biiek the water. 
 
 It will be remenibereil that one of the functions of tlie wedge was 
 described to be to cause tho water to be discharged to the side of tho 
 whed. A litilo consideration, however, will show that during a part of 
 tho period of action tlu wcdi^c does not perform this function. 
 
 9 
 
r<( « 
 
 When tlic vane begins to intercept the jet, a.s in fig. 8, it is the outer 
 lip or scoop whicli first comes in contact witii tlic jet. Tiie small 
 amount of water which strikes the blunt cd^c of this outer lip is 
 scattereJ, and thus only f;ives up a proportiim of its enerjiy to the 
 wheel. More th:iu this, it probiibly causes considerable di:turbancc and 
 consequent lo.ss of energy in the re.~t of the streiUii. 
 
 Fjg.S 
 
 As the vime pasfcs further into the path of the jet, as represented in 
 fig. 9, the water strikes on the interior curved surface of the outside 
 scoop portion of the bucket on each side of the outer end of tlie wedge. 
 The curve of the bucket jit this point is such that the water is mainly 
 deflected in an in-vard and backward curve in ..iic plane of the vhcel, 
 so that it (merges from the vniie surface in a plane taugentiul to the 
 wheel rim ; it proceeds in the same ilireclion until it strikes the back 
 of the following vane, proiiucing upon it a Un-Cf of impact opposite to 
 the diiiction of motion of the wheel. 
 
 tig 10 
 
 A-^ ihe wheel moves in»o such po^ilinn ihat the jet jilays upon the 
 central portion of the wedge, the stream is deliecleil to eaeh side in a 
 plane parallel to the axis of the wheel ; and it is then and only then 
 that the conditions of action assumed are approximately fi', lied. This 
 position is shown in tig. 10. 
 
 It mav be estimated that the a^'tion of the water is not what it is 
 assumed to bo while the ''ane moves over from 1-5 to 13 of the total 
 a'O of a' inn. During this interval tho action of the water is more or 
 less inellicient. 
 
 10 
 
rig.;,). 
 
 ■as in fig. 8, it is the outer 
 atii tlic jet. The small 
 ;cl^c of this outer lip is 
 ■tiim of its ciier}!y to the 
 siilcrablo disturbance and 
 
 / 
 
 ' the jet, as represented in 
 
 .d surface of the outside 
 
 111.' outer end of the wcdf^e. 
 
 that the water is mainly 
 
 ill „;it' plane of the vhcel, 
 
 a plane laugentiul to the 
 
 until it stiikes the back 
 
 jrcc of i 111 I act opposite to 
 
 ill tlic ji:t play.~ upi>ii the 
 Ji'linctrd to eacli side in a 
 it is then and only then 
 iroxiinately l\\ lied. This 
 
 le water is not what it is 
 om 1-5 to 13 of the total 
 ou of the water is more or 
 
 I 
 
 i 
 
 It will be noticed ihi.*; the dificit of the actual from tho calculated 
 efficiency increases steadily as the speed in increased. It is suggested 
 thut this may be attributed to two causes. 
 
 (1) The best ctTect of the ini|iiift occurs when the sharp edge of the 
 wedge is perpendicular to tlio line of the impinging jet. This condi- 
 tion only occurs at one point in the are of action. At all other points 
 the po.'ition of the edge of the wedge dopnrts more or less from the per- 
 pendicular position, as in fig. 1!, and the defltotiou docs not take place 
 in the manner assuiiiel with the! coiLstfjuenco that tho efficiency of the 
 impact is more or less impaired. The hif.i;h(r the speed of tl'-e whetl 
 the greater is the arc of action, and (onseijueutly the greater will be 
 the departure of the cutting edge of the wedge from perpendicularity 
 to tho line of the jet. This would mean that the los.s of efficiency of 
 the impact is less when the arc of action is smaller, or tho speed 
 small, and that the Ioks of efficiency inoieases as tho arc of action 
 increases or as the speed is increased. 
 
 (2) It was piinted out how the action of the outer lip or scoop at 
 the beginning of the arc of action tended to impair the efficiency of the 
 wheel. It will be seen that if the iirc of action is large enough the 
 same effect will take place at the end of the arc of action, as well as at 
 the beginning. If, therefore, the speed is increased to such an extent 
 as to allow this to occur, there will be a further cause of loss of cffi- 
 cieney at high speeds. 
 
 It is estimated that tlic efficiency would not .suflFer diminution from 
 this latter cause until the velocity reaches a value of 800 revolutions 
 per minute with the 175 foot head or a value of 000 revolutions per 
 minute with the 235 ft. head. It will be noticed on reference to table 
 IV^ that the discrepaiicj. between the theoretical and actual efficiencies 
 shows a marked increase for those respective speeds. 
 
 In addition to the trials quoted and compared with the theoretical 
 rcsiilts, trials were also made with the small ^ inch nozzle. Complete 
 tables of all the results obtained are givon. 
 
 J.— NOZZLE .5277" DIAMETER. 
 ((() Pressure 50 lbs. per sq. inch. 
 Equivalent head = 115 feet. 
 Discharge =: 45 galls, per second. 
 
 Speed. 
 
 Horse Tower. 
 
 Efficiency. 
 
 252 
 
 .79 
 
 50.7 
 
 322 
 
 .76 
 
 48.5 
 
 308 
 
 .9H 
 
 59.1 
 
 4110 
 
 .80 
 
 57.0 
 
 4(17 
 
 .PA 
 
 53.5 
 
 4.3S 
 
 .87 
 
 66.7 
 
 450 
 
 .94 
 
 59.9 
 
 4Vt7 
 
 .90 
 
 02.8 
 
 50(i 
 
 .94 
 
 00.4 
 
 54 .T 
 
 .95 
 
 00.0 
 
 551 
 
 .95 
 
 61.0 
 
 505 
 
 .84 
 
 .^.5.7 
 
 585 
 
 .70 
 
 47.3 
 
 588 
 
 .v">3 
 
 52.0 
 
 025 
 
 .91 
 
 55.7 
 
 038 
 
 .91 
 
 58.3 
 
 005 
 
 .83 
 
 52 " 
 
 u 
 
(h) Pressure 75 lbs, per sq inch. 
 Equivalent .Uead = 175 feet. 
 Diselmrge = S3 j,'ii11b. per niin. 
 
 Speed. 
 
 Horse Power. 
 
 Efficiency. 
 
 346 
 
 1.3S 
 
 49.8 
 
 409 
 
 1.52 
 
 .')4.9 
 
 477 
 
 1.(18 
 
 60.7 
 
 6L'3 
 
 1.68 
 
 61.4 
 
 S82 
 
 1.80 
 
 64.7 
 
 694 
 
 1.79 
 
 6r5.8 
 
 682 
 
 1.75 
 
 64 4 
 
 632 
 
 1.76 
 
 63.1 
 
 672 
 
 1.78 
 
 64.1 
 
 677 
 
 1.56 
 
 55.3 
 
 726 
 
 1 . 63 
 
 58.3 
 
 726 
 
 1.65 
 
 59.6 
 
 737 
 
 1.61 
 
 59.7 
 
 768 
 
 1 . 55 
 
 55.1 
 
 779 
 
 1.57 
 
 57.0 
 
 847 
 
 I.IO 
 
 51.2 
 
 879 
 
 1.31 
 
 47.7 
 
 ((•) Pressure 100 lbs. per ,s((. iucii. 
 Equiviilent bead = 235 ft. 
 Dischinge = 63 galls, per minute. 
 
 Speed. 
 
 Horse Power. 
 
 Efficiency, 
 
 276 
 
 1.70 
 
 37.9 
 
 306 
 
 1.85 
 
 41.2 
 
 346 
 
 1.98 
 
 44.4 
 
 387 
 
 1.90 
 
 44.5 
 
 469 
 
 2/J2 
 
 49.7 
 
 470 
 
 2.36 
 
 52.8 
 
 641 
 
 2.52 
 
 56.0 
 
 605 
 
 2.67 
 
 60.0 
 
 644 
 
 2.80 
 
 63.2 
 
 698 
 
 2.76 
 
 64.0 
 
 760 
 
 2.96 
 
 65.0 
 
 834 
 
 2.6,1 
 
 59.5 
 
 858 
 
 2.78 
 
 61.8 
 
 914 
 
 2.76 
 
 58.6 
 
 939 
 
 2.76 
 
 57.9 
 
 >?) Pres.sur(> = 125 Ib.s. per sq, inch. 
 Equiviiient bead = 290 ft. 
 Discbarge =: 70 galls, per minute. 
 
 1 ' —~^ =- — =. 
 
 Speed, 
 
 Morse Power. 
 
 Efficiency, 
 
 
 494 
 
 3.25 
 
 52.0 
 
 
 636 
 
 3.3:! 
 
 53.6 
 
 
 592 
 
 3.50 
 
 57,5 
 
 
 664 
 
 3,7:t 
 
 62.1 
 
 
 702 
 
 3.83 
 
 63.3 
 
 
 766 
 
 4,ai 
 
 65.2 
 
 
 813 
 
 3.8il 
 
 62,8 
 
 
 867 
 
 3.93 
 
 6 1 , 8 
 
 
 918 
 
 3.95 
 
 61.0 
 
 12 
 
nch. 
 
 
 feet. 
 
 
 r 
 
 niin. 
 
 
 
 Efficiency. 
 
 ! 
 
 49.8 
 
 
 
 M.O 
 
 
 
 60.7 
 
 
 
 01.4 
 
 
 
 64.7 
 
 
 
 6r5.8 
 
 
 
 64 4 
 
 
 
 03.1 
 
 
 
 04.1 
 
 
 
 55.3 
 
 
 
 58.3 
 
 
 
 59.0 
 
 
 
 59.7 
 
 
 
 55.1 
 
 
 
 57.0 
 
 
 
 51.2 
 
 
 
 47.7 
 
 
 
 (. iucli. 
 
 
 ') (t. 
 
 
 per uinute. 
 
 
 Efficiency. 
 
 
 
 ;;7.9 
 
 
 
 41.2 
 
 
 
 44.4 
 
 
 
 44.5 
 
 
 
 49.7 
 
 
 
 52.8 
 
 
 
 56.0 
 
 
 
 00.0 
 
 
 
 03.2 
 
 
 
 64.0 
 
 
 
 05.0 
 
 
 
 59.5 
 
 
 
 61.8 
 
 
 
 58.6 
 
 ' 
 
 57.9 
 
 s(|, iuc 
 
 1, 
 
 ft. 
 
 
 r minute. 
 
 
 
 Efficitucy. 
 
 
 
 52.0 
 
 
 
 53.0 
 
 
 
 57 . 5 
 
 
 
 02.1 
 
 
 
 03.3 
 
 
 
 65.2 
 
 
 
 Oil.S 
 
 
 
 61.8 
 
 
 
 64.0 
 
 II.— NOZZLE -7632" DIAMETER. 
 
 (a) Pressure 75 lbs. per eq. iiich. 
 Equivalent Head =: 175 I'eet. 
 Dischar^ie = 120 j^alla. per minute. 
 
 Speed. 
 
 Horse Power. 
 
 Efficiency. 
 
 402 
 
 3.08 
 
 58.5 
 
 501 
 
 4.10 
 
 65.0 
 
 618 
 
 4.34 
 
 68.8 
 
 675 
 
 4.34 
 
 68.9 
 
 750 
 
 4.33 
 
 68.7 
 
 770 
 
 4.30 
 
 67.7 
 
 (i) Pressure 100 lbs. pel' pq. inob. 
 Equivalent Head = 235 feet. 
 Discbargc = 138 galls, per minute. 
 
 Speed. 
 
 Horse Power. 
 
 Efficiency. 
 
 370 
 
 4.82 
 
 49 4 
 
 371 
 
 4.80 
 
 50.0 
 
 475 
 
 5.07 
 
 .^8.4 
 
 515 
 
 5.95 
 
 60 7 
 
 588 
 
 0.20 
 
 63.9 
 
 6,"i4 
 
 6 . 60 
 
 07.8 
 
 698 
 
 6.66 
 
 68.6 
 
 756 
 
 6.88 
 
 70.8 
 
 815 
 
 6.72 
 
 69.3 
 
 911 
 
 0.35 
 
 65.6 
 
 The resultb given in tbo foregoins; table.s aro represented grapbiciily 
 in figures 12-17. 
 
 In connection witb the above re.juhs it is interesting and important 
 to notice that tlie highest actual efficiency iippears at a speed vfhicli is 
 about -9 of that which theoretically should give tlic maximum effici- 
 ency. 
 
 
 
 
 
 Fig 12 
 
 
 
 
 ''■ « 
 
 
 
 
 t 
 
 ! 
 
 1 ■ - 
 1 
 
 
 
 
 
 
 
 OlAGlAh 
 
 « or [iricitflCY 
 
 
 ■ : 
 
 M 
 
 
 
 
 
 Hoiltt • S27f'4m 
 Uttd - hi fin 
 
 1 
 
 
 h 
 
 
 
 
 
 
 
 
 
 
 
 o 
 
 • 
 
 k 
 
 
 
 
 •• 
 
 
 
 
 » 
 
 
 
 
 
 
 
 
 
 
 
 
 
 R t « I. w 1 lort s f t <« M > N u r c 
 
 
 
 
 
 F.fl 
 
 15 
 
 
 
 
 w W 
 
 
 
 
 
 1 
 
 
 
 h 
 
 
 
 
 
 Oi«M>M or [r 
 
 iCtChcv 
 
 . y 
 
 « 
 
 " 10 
 
 
 
 
 
 *jj* - nn-dam . 
 
 mt . Hi Hfi. 
 
 r 10 
 
 
 
 s^ 
 
 ^-4- 
 
 •s^ 
 
 
 
 t 
 
 
 ^ 
 
 y 
 
 
 o 
 
 ^v. 
 
 N 
 
 
 
 
 
 
 
 
 
 
 r' 
 
 
 
 
 
 
 
 
 '■ 
 
 
 31 
 
 ID M 
 
 V i W T 
 
 ONI 
 
 no M 
 
 « M 
 
 » . « 
 
 »^ ' 
 
 13 
 

 
 
 
 '11 
 
 14 
 
 
 
 
 
 
 
 
 
 1 
 
 
 
 
 
 Dl« 
 
 MAM Of tfflCIt 
 
 NCV 
 
 
 
 
 
 
 
 
 
 Sv ' ■■ 
 
 zutfi 
 
 
 
 
 , 
 
 
 
 
 
 ^■^ 
 
 
 
 
 
 
 
 
 
 ^ 
 
 ^ 
 
 
 
 
 ^ 
 
 
 
 y° 
 
 ^<i 
 
 
 
 
 
 
 
 «^ 
 
 
 ■"1 
 
 
 
 
 
 *iyoittiio«» »t» M'NoTi 
 
 
 
 
 
 "! 
 
 15 
 
 
 
 
 
 
 
 I 
 
 ( 
 
 1 1 
 
 
 
 s 
 
 
 \ \ ^- 1 , 
 
 Diagram or tfrtctCNCt j | 
 
 
 
 c 
 
 
 
 »lil .noM 
 
 
 
 
 
 
 a '" 
 
 
 
 
 
 _^ 
 
 
 
 
 •<« 
 
 
 c 
 
 
 
 1 
 
 ^ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 rig. 16 
 
 J 
 
 ' 
 
 — r 1 1 
 
 OiMRAM OF Erriciinn 
 
 rSt*^ 
 
 
 
 
 ■ M 
 
 
 -, Hon' ' '" 
 
 It. rat «•■ - 
 . ITS 1^ ll- 
 
 -Ji'"' 
 
 
 ■^..^ 
 
 ■••-.. 
 
 ■I 
 
 
 i 
 
 / 
 
 
 
 
 
 
 „ IK 
 
 
 / 
 
 / 
 
 1 
 
 
 "•^s, 
 
 
 
 
 *• / 
 
 
 r 
 
 
 
 
 
 rig. 17 
 
 Of AontM or Cffien NCY ^ 
 
 
 tn*^ 
 
 ^ 
 
 I 4fl0 WO 100 ^ w» o< 
 
 u 
 
A most important differcDce between av impulse watpr ^h^i a 
 
 l^oragivenarea of outlet the horso-pawer of the issuing stream 
 vanes as A3 To illustrate tins the horse-power of,. ,tr. • . 
 
 TABLE V. 
 
 Head. 
 
 KM) 
 200 
 800 
 400 
 500 
 GOO 
 700 
 800 
 900 
 1000 
 1100 
 1200 
 1300 
 1400 
 1500 
 1600 
 1700 
 1800 
 1900 
 2000 
 
 Horse power. 
 
 4.96 
 14.02 
 25.75 
 3.4.65 
 55.41 
 ■ 72.84 
 91.79 
 112.15 
 1.J3.S2 
 156.73 
 180.82 
 20(;.03 
 
 2;d2.;{i 
 
 259.63 
 287.04 
 317.21 
 
 347.40 
 378.50 
 410.48 
 443.31 
 
 Jots to give 
 1000 H.-P. 
 
 202 
 
 72 
 
 39 
 
 26 
 
 18 
 
 14 
 
 U 
 
 9 
 
 8 
 
 7 
 
 6 
 
 5 
 
 5 
 
 4 
 
 4 
 
 3 
 3 
 
 n 
 
 In order to develop cousidcrablo power wifl, .. „ 
 head usiog an i.npui.se wheel, one ofZ ^hiZ IZ^T""' ^T" 
 the urea of the no.zle ..nd eon.ser,uently thlt T ' '"' ^""^ ^ '^"''^r 
 -de very ..r^e, whieh is only praiieable t^^ 1 .£ :r;^'""^'^ 
 te number of nozzles and wheels „,ust be n>ul iS Tr \r 
 of i.npul,se wheels under small heid, in.^ , "" "'' 
 
 ".aehinery for the power obtained. " ^'"''' ''"'«"'^' "^ 
 
 On the other hand, the in.pulse wheel has many points in !f ^ P 
 Ch,et a,no„, wineh i> ,t. simphcity of eonstvuetin,' E ^^ ^Z' 
 . "■'''^;'?'."'^"''^''.'»P^/'"'' '" «««« of maintenance "' 
 
 are si.np.e, bein, meroi;those on th^ho L IT^ a" n sj " "'"^^ 
 as to be easily ,ot. at wl,e„ neee.ssary to nn ke 1' '" 'T.'"" 
 
 ments. Th.re are no bearings running under vat^ ZZ "\ '■'''• 
 are not subjeet .0 any other ...etioo than U t W e , r l"?^" 
 of the water on the wheel ; no diffiedty is ok. w U e " • '"'"'' 
 
 that of balaneing the statie pressure of the woo '""r ''' '" 
 beeomes such an important Jobien. whe ant «■! , '"' ^'"""' 
 
 The impure wheel has no water-ti-^lul n"' , '''' ^'""^ "^'^•'' 
 
 Bnre to be n.aintained among the w^ii Ipln ''Z " "I "•'"'''"" 
 does not eontain any parts whieh are likri; ^vork 1 7 ' '"7 "f" 
 become deranged and so lead to trouble. " °""'^"''-^« 
 
 15 
 
Another good feature ia the absence of pas-ages in the working parto 
 of the tuotor, whicli would bo liiiblo to become choked bj debris carried 
 through by the water. Onoo through the oriBco the water has a per- 
 fectly clear and open course until it falls into the tail-race. 
 
 It is an easy matter in designing an impulse motor to arrange the 
 diameter of the wheel so as to give a desired speed of rotation under an 
 available head with the most efficient results. Small departures from 
 this speed do not nffeot the efficiency to any g-oat oxUnt, as may bo 
 judged from nn examination of the tabulated results. The follow! ng 
 table is compiled to show the percentage loss of output of work due to 
 a subsequent departure from the pfC-arriingcd speed. This is illus- 
 trated graphioallj in fig. 18. 
 
 TABLE Vr. 
 
 Percentage. 
 Increase or Decrease of 
 speed. 
 
 5 
 
 10 
 1.5 
 20 
 25 
 
 Percentage, 
 Drcrease of output of 
 work. 
 
 
 
 
 
 ng. Ill 
 
 
 
 1! 
 
 
 
 
 ^ 
 
 ^v. 
 
 VI 
 
 m • 
 M 
 
 VAf 
 Comspm^ 
 
 fATioN or wouh 
 lins fo vifiatwn from 3 
 Mairflium tWanK". 
 
 f>nl' 
 
 
 
 
 1 
 .... 1 
 
 Peffccnr^ot . VAUiAfiON, Of intn^ '' 
 
 An important point in determining the practical usefulness of water 
 motors is their adaptiib ility to be run with a fair degree of efficiency 
 under a fraction of the full load. This state of things is generally 
 liable to occur either intonnitfently as whore a number of Toads are 
 being continually put on and off the meclianism driven by the motor ; 
 or periodically as where for portions of a day or week or year the 
 work required from the motor is heavier than at otiier times. 
 
 Three methods will be mentioned which are employed to vary the 
 output of work from the wheel. 
 
 It was mentioned that throe nozzle tips of different sizes were sup- 
 plied with the wheel with which the fest.s were made. By changing these 
 the quantity of water discharged under a given pressure can bo varied 
 as t;.e area of the orifice. The power of the jet will consequently 
 vary in the same ratio ; and so any cliango of load which can be anti- 
 cipated and will last for a considerable period can bo provided for. 
 
 The changing of the nozzle tips need not be a very difficult opera- 
 tion. It it, however, a very incDuvenieiit plan to have to resort to 
 regulate the output of power from the wheel. 
 
 These wheels are sometimes built with several nozzles placed at 
 intervals round the periphery of the wheel. When this is the case tho 
 power can be reduced by shutting off the stream from one or more of 
 the nozzles. 
 
 The third method is to employ a value or gate in the supply pipe 
 which can be shut off to any desired extent by hand or by some auto- 
 matic regulating machinery. This method is almost always necessarily 
 employed in addition to those aforementioned. It will he noticed that 
 the etlect of the value to reduce l.lic power is reached by throttling the 
 water as it passes the gate, thus reducing tho pressure of the water as it 
 reaches the orifice and consequently reducing also the discharge. It 
 
 It) 
 
effect ■■„,';? !•'" """'""" ''^ "" ''•'^«^'""' "-ithout u,,:ful 
 
 ' '.", "' ■ '•"•^'^'"nco of tho partially closed valvo 
 
 Ad Id™ of the actual efficiency ivached cm 1,h ., : l c 
 s dfiMtinn «c.i o . 'V "'"'"i-u ciii lie <',iiiie(l from a con- 
 
 avail 1 e'Z if"" ::'"'' "" '^^' ^"^ '"^'^" ^'^ ">« '-^' P--- 
 When the presure i nT T ""' ""^ '•"='' ''^■•^"■■''''« ?'■«-"••«''« 
 
 he product of M 'J available work nm^t be eun.idered to be 
 
 Prnn • > '°'''* ""y throttling took place. 
 
 in e ;rii';r tl •' "'■'• "' "r-'^ ""-• =""°"'"^ «'-•'' 'J"- obtained 
 in every ;; '^ I?:'':"^^' ''--"^idorin. the energy available 
 gi-s result a low ' '° "P^-reon^:, lb. per square in., 
 
 Frcssuie. 
 
 125 
 
 Kill 
 75 
 
 .1(1 
 
 TAiiLt; vir. 
 
 I^ad. 
 
 This 
 
 '■< IS illustiatrd ill (iir. I!) 
 
 Kull 
 .7,5 
 
 .ir 
 
 ^g. 11 
 
 i^fficiency, 
 
 65% 
 
 50% 
 
 3;{% 
 
 »hout 18% 
 
 Besides the fact that a lar-o anioimf „P 
 throttling in the nine ., |„rt|!. T, "'^ ""'=^ "* ^^"«'«'l i" the 
 
 l"aJ exi^s in the 't t " "^ lossof ofEcionoy under a light 
 
 n.vorabl. condit , r;X :a;d v''|: -1^"?'^ ^^""''^'"^ -^«'- "»■ 
 to keep the velocity co,:;::; ' ^^r^ "^l^^, " f«"- ^''^^--ble 
 -.ann that ifthe niotor is .ic;i.n,ed t I; ''""'^ '""^ ^'"■^- '^'"'^ 
 under full pressure, it will evec?. ^ i '"°-^' ^■*^"''''" ^P^'^^^ 
 
 p.-evious tables if there is a 7 • S^ "' """ '"'"^^"^'^ ''^ >'- 
 
 tho uiuto,.. ^ 'OEs.de.able vanatton in the load put on 
 
 In the prccediuir reinaiks an uttonint V 
 
 discuss the aethn of iu.p„,se w. e '7 r" *"''"''-' '" ''^'-^"ibe and 
 
 wheel „n which the e.f^ n C ^^ ""' ""-.■'"'■^i-'a-iy of the 
 
 tion of cffieiency has 1^;, i , t ' "" V^ "■''''' ""' ' "'" "lUcs- 
 
 ;^..s and disadLtages eon;;;;t;n;; ht :::;■ i::' rrr- 
 
 heen pomtal out. It is honed tl,„, .i, ■''-^"'''"' '"'^■'' 
 
 -,^'- i-r.sting and l^XZ^^!:: "'"^ ""^ ^"^""- ^^ "^"' 
 i he writir wishos to I'enrno- l.; • j i. > 
 
 l-ki.ide.-op,.,.ationinaZ:.tu':^:?'" " ''''"'■ ^"^''^ ^'^ 
 /br cariyuig out the experi.nJ; ^a^ , « '' U;' '"'" "7 '"'""^ 
 Mr. Withvconibe for useful advice a7,l Universuy, and al-o to 
 
 l-.tical details connec,e;w;;!:i:;Lr'^''" "'•' ^''^'''-^ '"' 
 
 Juiany 
 
 17