Thesis (B.S.)--University of Illinois, 1908.Typescript and ms

Kautz, William Waddell

Typescript and ms.Thesis (B.S.)--University of Illinois, 1908.Mode of access: Internet

Kautz, William Waddell.

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An investigation of a turbine centrifugal pump /

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KAUTZAn Investigation of a ilTurbine Centrifugal Pump IMechanical Engineering9 08UNJVKRSITYJT,L LIHRARYUNIVERSITY OF ILLINOISLIBRARY ItClass Book VolumeiMy 08-15MDigitized by the Internet Archivein 2013http://archive.org/details/investigationoftOOkautAN INVESTIGATION OF A TURBINECENTRIFUGAL PUMPBYWilliam Waddell KautzTHESIS FOR THE DEGREE OF BACHELOR OF SCIENCEIN MECHANICAL ENGINEERINGIN THECOLLEGE OF ENGINEERINGOF THEUNIVERSITY OF ILLINOISPRESENTED JUNE, 1908 ^^-W\6MUNIVERSITY OF ILLINOISJme 1> 190GTHIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION BYWILLIMi WADDELL KA^TZENTITLED -M INVEST KJAT ION OF A TURBINE CMTRIFUGAL PUMPIS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THEDEGREE OF Bachelor of Soience in Mechanical EngineeringApproved:HEAD OF DEPARTMENT OF Mechanical Engineering.114588' »»O1.INVESTiaATION 03? A TURBINE CE]\[TRII?UGAL PIMP.INTRODUCTION.The actual results olDtainable from centrifugal pumpsdiffer consideraul.7 from the results which should ohtain accord-ins to theory. This is due to incorrect assumptions as to flowthru the machine, and to indeterminate losses in the machine.Desisners who have overcome the difficulties have apparentlytried to keep their information to themselves for their ownpecuniary advantage. Up to the i^resent time, few of the practifcal methods of increasing centrif:ngal pump efficiency, or "better'ing their operation, have "become very widely known, and a numberof tests must he run on any design of pump in order to deter-mine its actual performance.Within the last few years, centrifugal puraps'have coneinto use for fire service, city pumping, "boiler feed, etc. Thesmall floor space they occupy is the greatest point in theirfavor, although their adaptability to pumping large quantitiesof water against a low head is no slight advantage.The object of this thesis is to investigate the opera-tion of a turbine type centrifugal pump. The pump under testin this investigation is a two stage, turbine type centrifugalprnnpvmanufactured by Henry R. Worthington Co., which is ownedhy the department of Tlieoretical and Applied Mechanics of theUniversity of Illinois.jiirETHOD OP TESTING:The test of the pump investigated was made to deter-2,mine the range of operation and the corresponding efficienciesfor the pump. For each run the speed was kept constant and thedischarge and efficiencj/' determined for varioiis ?:eads. Thepump was placed over the sump in the Hj^'draiilic Laboratory ofthe University of Illinois. For most of the runs the v/ater waspumped through 80 feet of 12 inch pipe arid discharged into aweir channel. In a few runs, liowever, the v/ater was pumpedthrough 110 feet of 8 inch pipe and discharged into a weir "box.In all runs the head was varied "by throttling the discharge valve,and the v/ater was measured over a weir, then allowed to returnto the SLimp to be used over again.APPARATUS: The pump was belt-connected to a 100horse power Ideal Engine. As stated before, the pump is a twostage centrifugal pump of the turbine type. The runners are15 inches in diameter and are made up of two circular discswith the runner blades between them, all cast in. one piece. Theguide vanes surroimd the runner and their outside diameter is28 inches. Figure 1 shows a section perpendicular to the shaftthrough the runner and guide vanen. Figure 2 is a vert ical . sec-tion througri the pump showing the path of the water from suctionto discharge pipe. Water enters the first runner at the center,leaves at the periphery, entering and passing thru the guidepassages; it flows do^Nn from the first guide passages to theinside of the second runner, and discharges from them, throughthe second guide passages into the spiral trumpet shaped casingand out at the discharge pipe. There are eigl-it vanes in eachrunner, four of them extending from the outside to the center3.•4.and the other four extending only half way. l^e direction atentrance is practically radial, and at exit the angle is twelvedegrees off the tangent.A Crosby pressure gage was placed above t>ie piirap inthe discharge pipe at 45° to the axis of the pump, to indicatethe head at that point. A Crosby vacuurn gage placed in thesuction pipe showed the suction head. Calibration curves ofthese gages are mot shown as they were calibrated by the depart-ment and found to be correct. Two Crosby, inside spring, steamindicators were used and cards were taken simultaneously fromboth ends of the engine cylinder. The springs were calibratedand found to be sufficiently correct.The v;ater was discharged into a weir box and wasmeasured over a contracted weir. Por some of the runs an 18inch weir was used and for the remainder a 3 foot weir was used.The head on the weir was measured with a hook gage placed at theside of the box and about four feet back from the weir crest.Calibration curves for the two weirs are shown on curve sheetsI and II. By noting the head on the crest of the weir, the dis-charge ma3'- be read directly from the curves. The curves wereplotted between head and discharge, using values calculated bySmith's formula, using Smith's coefficients.OBSERVATIONS; The engine v/as started and run at slowspeed until the pump was primed, and then the speed increased un-til the desired R.P.M. was attained. The pump was primed byfilling from a standpipe in the Hydraulic Laboratory. In eachrun the speed was kept constant and the head was varied; and the5.discharge measured for each change of head. Readings of thehead on the pump, the suction lift, the speed of engine and pump,and the head on the weir, also indicator cards, were taken everyfive (5) minutes. Tl-ie head on the pvsmx) at starting, was madelow enough that the pmnp operated at less than maximum economy;four or five readings were taken with the head constant, and 'then it was increased by (10) or (20) feet, and four or fivereadings taken at that head and this repeated until the maxiraurmhead was reached.Water was pumped from the sicnp, through the twelveinch main, to the weir box and flowed over the ?/eir back intothe sump and the water level in the sump was noted as soon asthe pipes and the weir box were filled, after which it remainedconstant. Water was admitted from t?ie standpipe so that thedistance from the gage on the discharge pipe to the water msconstant at ten (10) feet. The speed of the engine and pump,were taken v/ith a Starrett speed counter and a stop watch. Speedreadings were taken on both engine and pump to determine theamount of slip in the belt. The head on the weir crest was readby means of a hook gage, tfiking a zero reading when the waterlevel was Just up to the crest, and subtracting that from thereadings when the water was flowing ^to get the actual head onthe crest.Indicator cards were talcen from both ends of the enginecylinder, by means of the two Crosby indicators, using (40) poundsprings. All readings were taken simultaneotisl^r and the headwas increased in each test until the point of maximum pump econ-omy was well passed.6.The belt was thrown off and the engine run light todetermine the friction of the engine parts at various speeds.Indicator cards were taken during this run with 20 pound springsin the indicators. A curve of friction horsepower is shownon curve sheet III.TABLES:The tables on the following pages contain the cal-culated data. On the test data sheets, column 1 is the numberof the readings col^jmn 2, the discharge gage reading; colTimn 3,the distance from the discharge gage to the sump water level;column 4, the total lift, being the sum of columns 2 and 3;colurrm 5 is the calculated discharge, in cubic feet per second;and colTimn 6, the calculated discharge in gallons per minute;column 7 is the R.P.M. of the pump; coliiran 8 is the net horsepow-er delivered to the pump, and column 9,^ the average net porsepowerdelivered to the pump at each head; colTiimn 10 is the hydrau-lic horsepower of the pump; col:imn 11, the calculated efficien-cies of the pump, and column 12, the average efficiency of thepump for each head.Table No. 8 , p. 23 , shows the revolutions of theptunp required to give certain discharges against different heads.It was calculated from the formula n ^ K V h -f- a which is ex-plained later.RESULTS Aim CONCLUSIONS:The discharge from the pumiJ, column 5, was obtainedfrom the calibration curve for the weir used, curve sheet No.Hthe discharge in gallons per minute, column 6, being calculated"by the formula;Gallons per minute =s w x Q x G x 60 (1)w, "being the pounds of water per cubic foot (.-562.5), Q, thedischarge, cubic feet per second, and G the gallons per cubicfoot (-7.48).The hydraulic horsepower of the |)ump, column 10, iscalculated from the formula:Hydraulic H.P. = Q x w x H x 60 (2)330dtrQ and w being the same as in (1) etnd H being the totalhead, column 4. The net horsepower delivered to the pump, col-vnm 8, is the indicated horsepower of the engine, less the fric-tion horsepower. The engine horsepowers are calculated fromthe formula:I. H. P. = P_J. AJT3;50bo"P being the mean effective pressure on thepiston (the averagefrom the t wo cards) pounds per square inch, L is the length ofthe stroke, in feet, A the area of the piston in square inchesand N, the number of strokes per minute (= R. P. M. x 2).The pump efficiencies are calculated from the for-mula.' Hydraul ic H. P^H.P. deliTI Fo pump.Prom the data of the tests curve sheet IV is plotted, expressingthe relation between R, P. M. and head on the pump, for variousdischarges. Curve sheet V shows the relation between R.P.M.and discharge; curve sheet VT, the relation between R.P.M. and8efficiency and curve sheet VII shows the relation hetweon dis-charge and effioienc}^, for various heads. From a stud^r of theresults it is evident that there is a fairly wide range of dis-charge for any head without much variation in efficienc3r, andobviously the pump may operate with the sane econora^r under dif-ferent heads. It is also evident that at any discharge the headma3'- be varied considerably'- without a great change in efficiencybut the best efficiencies are obtained at high heads. The rea-sons for this appear when the variations in the term a_ are notedin the formula n = KThe maximum speed for the engine was 300 R.P.H., itbeing equipped with an inertia governor, which prevented ex-ceeding that speed; this would run the pump at 1300 R.P.M. , buta run could not be made with pump speed exceeding 1200 R.P.M.,on account of belt slippage.Variation of the engine indicated horsepower is per-haps mostly due to the poor quality of steam obtainable, butno doubt the average of the several cards, for each reading atconstant speed and constant head, represent a true average. Thefriction horsepower curve is subject to a small error, althoughrepeated trials were made to get it, and considerable care wasused in taking data for it.The losses entering into the pump operation due tovarious causes, are: (a) a loss due to Journal friction of ro-tating parts, (b) a loss due to friction of the water in thesuction pipe, (c) internal friction of the pump, due to frictionof the water over the rotating parts of the pump; and (d), im-9.pact losses, due to impact on the runner vanes. The velocity*'head [V-t^) in the suction piDe requires energy'' and that velocity2 ghead counts as a loss against the pump. The friction is perhapsexcessive through the small section in the runner, where thewater enters, since the velocity must "be necessarily high, whenlarge volumes of water are discharging. There will "be a loss,due to eddien, if trie water has much of a velocity of whirl,at entrance to the runner.TT-ie Worthington Company rate this pump at 450 gallonsper minute against a 135 foot head, nmning 1500 R.P.M., thisrequiring ahout 32 H.P. This given as pump efficiencj?- of ahout(48) per cent. Much "better economy was obtained at lower speedsand higher heads, as is seen from the data, and it is probablethat if a speed of 1500 R.P.M. could have been reached, the pumpwould have operated at economy, better than fifty (50) per cent,and against heads above two hundred (200) feet.A close approximation to t}ie actual loss in the machinecan be arrived at by means of the following analysis:(a) Velocity head in suction pipe~ hs ^ Vi^ , where v^ is the velocity in the suc-2gtion pipe, calcula. ted from the discharge and area of cross-section: (_j2 ) .(b) Loss at entrance to suction pipe =s .93 vf- andthis loss may be taken as v-j ^ , since there is a foot valveSg"on the suction pipe.(c) The friction loss may be calculated from the generalformula for friction in iron pipes, which is:10.dl 2 g(d) The velocity head in the discharge pipe r Yl^, -v?.^ >2 gwhere V2 is the velocity in the discharge pipe, calculated froma2.(e) Another loss of head occurring is what might "betermed the "machine loss", which is that due to friction, impact,etc. inside the casing. The R.P.M. required to give a certaindischarge is given approximately/ hy the following equation:n = K /h + a,where "n" is the R.P.M. of the pump, "h" is the total head,represented by the sum of the gage reading and the distancefrom the gage to the sump water level, "k" and "a" are constantsdetermined as follows: from the data in the tahles value's of"a" are determined, for different discharges, using a constantvalue of K for all discharges, which gives a constant value of"a" for the different speeds and heads for any discharge. Inorder to get at the "machine loss" in the pump, calculationsare made of the other losses, and their sura subtracted from "a"in the above formula, this difference being the machine loss,for the discharge considered. •The machine loss iij then:\ 2 E di 2g^2g/Taking account of all th^^e losses, that is, taking the headpumped against in the formula for efficiency, as the sum ofand a , the efficiency is seen to be approximately^ 81*^11.,..The 19ff not yet accounted for isj owrnal and "belt friction, charged to the pimp..BIBLIOGRAPHY.Reference has "been made to the following:Centrifugal pumps, TurlDines and Water Motors, "byCharles H. Innes, M. A.Proceedings of the Institiuition of Civil Engineers,of London, 1878, col. 53, p. 249.Treatise on Hydraulics. By Wm. C. 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An investigation of a turbine centrifugal pump

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An investigation of a turbine centrifugal pump

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