Bulletin No. 185 June, 1940

The Homemade Centrifugal PumpBy

O. W. MONSON

Irrigation Engineer

MONTANA EXTENSION SERVICE

BOZEMAN, MONTANA

INTRODUCTION

The need for low cost pumping equipment during the recentdrouth and depression prompted investigations at the Montana Ag­ricultural Experiment Station which led to the design of the home­made centrifugal pump described in the following pages. Althoughadapted to homemade construction, this pump will deliver a largevolume of water sufficfent for irrigation, for lifts up to 20 feet.To be assured of satisfactory operation, care must be exercisedin following the instructions for building the pump, because itis designed according to basic principles governing centrifugalpumps in general.

In design it is of the vertical type, since it is driven by avertical shaft, on the lower end of which is the impeller and onthe upper end a belt pulley or other driving mechanism. Theconstruction may be of either wood or metal, the latter beingthe more durable although more difficuJt to construct. Woodenconstruction has been found to give good'results, when new, butdifficulties frequently arise in preventing leakage after the firstseason's use.

When metal construction is decided upon, old oil drums fr0mwhich the ends have been removed may be used for the "riser"or discharge well. Frame work and mountings may be madefrom old car frames, or from angle iron taken from old abandonedfarm machinery. Drive shaft, pulley and bearings may also besalvaged from old farm machinery.

A homemade pump of wooden construction is shown infigure 1.

Montana Extension Service in Agriculture and llome Economics, J. G. Taylor director.Mon~n,; State College and Umted States Depar·tment of AgrlcultUl'" cooperating,

DIstrIbuted in furthel'ance of the Acta of Congress. May 8 and June SO 1914 '6·1\1~ 8-40 • •

The Homemade Centrifugal PumpBy

O. W. MONSON

Irrigation Engineer

General Instructions

The construction of the homemade centrifugal pump iscomparatively simple when once the principle of its operationis clearly understood. A mechanic or farmer attempting to buildthis pump should have clearly in mind, therefore, the relation~

ship of the various parts to each other and to the operation ofthe pump. At each step in its construction he should be able tovisualize how the whole assembly fits together and how it willoperate when completed. In order to form such a mental picture,a careful study of figures 1, 2 and 3 and the key to figures 2 and 3will be very helpul. This may be considered the first step in theconstruction of the pump.

The next step is to obtain the necessary parts and materialsand prepare them for assembling. A list of materials necessaryfor a 14-by-7 pump of wooden construction is given below. Someof these-the drive shaft, the hub, the thrust bearing, and thebrake drums-may be salvaged from an old car or truck; others,such as the pulleys and the plain bearings, from an old thresheror other piece of machinery, while the lumber for the box andthe impeller blades and the linseed oil and paint may be purchasedat a lumber yard and the bolts and nails from any hardwaredealer.

Bill of Materials for 14-by-7 Homemade Centrifugal Pump, Double

Intake Type

1 auto or truck drive shaft1 thrust bearing to fit shaft1 rear hub reamed to fit shaft3 brake drums 14" in diameter, one to fit hub1 pulley2 babbitted bearings

4 MONTANA EXTENSION SERVICE

Lumber and angle iron (clear fir or yellow pine lumber, gradeB finish) :

2 pc. l//x10//x10' for intake plates .2 pc. 2//x4//x2' for intake plate supports and frame for base1 pc. 2//x4//x7' for intake plate supports and frame for base2 pc. 2//x2/1x40/l angle iron for intake plate supports and

frame for base12 pc. 2//x4/1 by length of pump plus 3 ft., for corner uprights

4 pc. 2/1x4//x31J2' for framing at pulley2 pc. 2/1x4//x2' for framing at pulley1 pc. 2/1x10/lx6' for base1 pc. 4/1x6//x2' for base

14 bd. ft. l//x6// vertical grain fir flooring per foot of box1 pc. 1/1x4/1x8' oak for twelve 1/1x4" hardwood impeller blades

Bolts and washers:6 size %/lx9//

26 size%/lx6//

Tie rods for box:4 size %//x46/14 size %/lx291;2/14 size %/lx251;2/1 for every foot of lift

Paint: Enough boiled linseed oil and asphalt paint to give pumpat least two coats of each.

Contruction of Impeller

In building the pump, the box and the impeller are assembledseparately, and then the impeller is installed in the box. It isnot important which is built first, although the description ofthe impeller assembly is given first. .Figure 3, showing thevarious parts of the impeller and the impeller assembly, will befound helpful in connection with figures 1 and 2.

The first step is to fit the hub, H, to the shaft, S. Do notpin them together, however, as the exact point on the shaft canbest be determined after the lower bearing, a, and the lowerintake plate, G, are in place. A %-inch hole for the pin maybe drilled through the hub and the hole through the shaft leftto be drilled later when its location has been determined.

Next, prepare the center disk, A, by cutting the flange fromone of the brake drums (see figure 3). This can be done best ona lathe but it can also be cut off with a hack saw and filed orground down smoothly. After the flange has been removed andthe edge finished smoothly, the plate, A, can be bolted to thehub, H.

HOMEMADE CENTRIFUGAL PUMP

HOMEMADECENTRIFUGAL

PUMPDOl/,ble Impeller Model

Pulley mayacfjusted to anyconvenient Height ..

Height of' pumpmay be varied tosuit cONditions upfo 20 reet lirf

5

Figure I.-Isometric view of double intake homemade centrifug'al pump.

6 MONTANA EXTENSION SERVICE

Then cut off the flange from the other two brake drums tomake the plates Band B l . On these two drums leave about %inch of the flange to provide clearance for the heads of the boltsthat hold the impeller blades in place.

When the flange has been removed from Band B I> cut outthe center equal to one-half of the diameter.

The six holes in plates A, B, and B l , for the bolts which areto hold the impeller blades in place are drilled in a circle, halfwaybetween the intake opening and the outside of the disk, and arespaced equal distances apart.

The impeller blades, D, may be sawed from hardwood boardof the proper width and thickness (see figure 4). The specialpattern for laying out the blades should be drawn on a piece ofcardboard and cut out. When the blades have been cut out, theyshould be smoothed down with a wood rasp and with sandpaperuntil as smooth as possible. After the hole for the bolt, % inchin diameter, has been bored in the center of each blade, the bladesshould be soaked in hot linseed oil and may then be bolted in placeas shown in figure 3. Note that the position of the blades is suchthat the impeller will operate in a clockwise direction.

The blades may be made of metal, providing foundry facil­ities and metal are available so that castings can be accuratelymade. In some cases the blades have been shaped from bar ironand welded to the center plate and to the shrouds.

This assembly of blades and disks attached to the hub is thenfree to slide on the shaft so as to be accurately located beforebeing pinned to the shaft.

The thrust bearing, C, should next be fitted to the lower endof the shaft and a washer, E, cut to fit over the top of it andaround the shaft to hold in the grease. The bearing is then fitteainto a bearing block (figure 2), and bolted down to the block soas to be held firmly. This block forms part of the base on whichthe pump rests.

Construction of the Box

The box is built from dressed and matched clear fir lumberSma~l pump~ for li~ts up to 10 feet can be made from 1- by 6-inchvertIcal gram floormg, but the larger units for higher lifts shouldbe made from, 2-inch material. The lumber should be given twocoats of hot hnseed oil before the box is nailed together.

. The box. consists of two parts: the impeller chamber, whichIS the. extenSIon at the ~ottom into which the impeller is set, andthe dIscharge well, whIch connects with. the impeller chamberat the bottom and conveys the water up to the point of discharge.

HOMEMADE CENTRIFUGAL PUMP

HOMEMAOE CENTRIFUGAL PUMP

0008L£ INTAKE

DlSCHARG,-.J.u..JoJ.f-f.!-I-

$ ---j--H-"11

~=E~~~~.~r-=---v3~9EA -+-f!I--L.D-t-H--t---tl'-U-.I:::f.I!H~--~

Ga.c--I---f-____..C--I--f--

SECTION VIEW OFIMPELLER BOX

TEf?LINE

7

Figure 2.-Sectional view of double intake homemade cenb'ifugal pump.

KEY TO FIGURES 2 AND 3

A, center impeller disk; Band B, outside disks, 2 required; C, thrustbearing; D, impeller blades, set of 12; E, grease retainer, made of old rubberBelt; F, spiral; G, lower intake plate; H, hub; I, upper intake plate; J, steadybearing for shaft over 4 feet long; K, wooden blocks to hold spiral, F, in place;1, 2, 3 and 4, clearance at quarter points.

8 MONTANA EXTENSION SERVICE

First, cut the upright corner pieces, UI3 they constitute theframework of the pump. They may be cut a good deal longerthan the intended lift of the pump, making it possible to increasethe lift at some future time and also allow a submergence of about12 inches of the impeller. In figure 1, showing how the box isbuilt, the corner uprights are cut flush at the top. Undoubtedlythis adds to its appearance, but leaving a little extra length on

IMPELLeR ASSEMBLY

PULLEY

BRAKE DRUMBEFORE CUTTINGFOR A, ~ AND B'

12 BLADES-D

PARTS OF IMPELLER ASSEMBLED IMPELLER

Figure 3.-Impeller assembly of double intake homemade centrifugal pump.

HOMEMADE CENTRIFUGAL PUMP 9

them would add to the convenience of adjusting for any additionallift that might be required later on.

Figure 1 shows the details of corner construction and howthe sides at the bottom are extended to form the impeller chamberat one side of the discharge well.

The flooring or other materials from which the sides arebuilt must be cut carefully so that the boards are all of the rightlength and the ends are perfectly square so as to form a water­tight corner.

The inside dimensions of the impeller chamber should be atleast 5 inches greater than the diameter of the impeller, to allowsufficient clearance. The discharge well for a 14-by-7 pumpshould be 19 inches square, inside dimensions.

The impeller chamber should be made deep enough to allowthe top and bottom inlet plates, I and G, to fit between the sideswith the impeller in place. It is not necessary to rip a board tomake it to an exact depth, however. If the sides extend abovethe top intake plate, I, an inch or two, it will do no harm. as theentire impeller chamber must be submerged at least 12 incheswhen pumping. .

After completion of the box, the intake plates, I and G, shouldbe made to fit snugly inside it. The plates are made from two

. thicknesses of 1-inch lumber nailed crosswise of each other tohelp overcome the warping that would result if a single thicknesswere used. The intake hole should be cut on a 45-degree angle.rrhese holes are slightly off center to allow for the volute or spiralin the impeller chamber and care must be used so that they willbe "centered" with respect to the impeller. The impeller is setto allow lh-inch clearance between it and the spiral at position 1,figure 2. This clearance is increased by 1 inch for each ofthe quarter points 2, 3, and 4. This represents the minimum forpoints 2, 3, and 4. A half-inch more at each of these three pointswill increase the efficiency of the pump.

The Spiral

Before the impeller is put in place, a spiral, F, is built intothe impeller chamber (see figure 2). This spiral is made from16-gage galvanized sheet metal held in place by two smallbolts at each of the quarter points, and three triangular blocks,K, are put in the corners to brace it firmly.

Pump Assembly

The lower intake plate, G, may be loosely fastened into posi­tion before the assembled impeller is put in place. The positionof the plate is about 12 inches· above the base. This allows 2

10 MONTANA EXTENSION SERVICE

inches for the extra thickness of the bearing block, 5 inches for!the thrust bearing, C, and about 5 inches of throat clearancebetween the top of the bearing, C, and the intake plate, G.

The hub may now be pinned to the shaft and the intake plate,G, be adjusted so as to provide %-inch clearance between thelower impeller plate, Bt, and the intake plate, G, after which itmay be permanently fastened into position and supported by2-by-4 girders or 2-by-2 angle irons as shown in figure 2.

Next, slip the upper intake plate, I, over the shaft and adjustit in position,. allowing Va-inch clearance between it and the topof the impeller. Two short 2-by-4 blocks above the intake plate, I,will hold it securely in place (see figure 2).

BLADE DIMENSIONS FOR VARIOUS SIZ£ PUMPS

ROTOR B AD£ SIZESD/a ot

~;,..z:'* L.e"!l m TllIckne"liotor l- T

8 4 Jl fi-fO 5 Ji- .L

8

/2 0 4.3- .li.4 32

13 of 51 if14 7 sf I,,~

IS 7f sf l,f16 8 of- If

Figure 4.-Pattern and sizes of impeller blades.

The shaft should now be lined up, the pulley put on, and thebearings secured. Considerable care is needed in doing this toprevent the impeller from wearing unevenly or binding on theintake plates.

After the whole pump is assembled, the tie rods of B/a-inchmild steel are put in and tightened so as to make the box water­tight and brace it rigidly. The lo""er tie rods should be not morethan 12 inches apart and the spacing gradually increased to 2 feetat the top.

The last step in the construction is to apply two coats ofwater-proof paint to the entire pump both inside and out.

HOMEMADE CENTRIFUGAL PUMP 11

Installation and Care

Becaus~ of its construction, the home-made centrifugal pumpis necessarIly rather cumbersome. It is therefore advisable touse considerable care in selecting a site for its installation, and toprotect the pump from disturbance hy floating timber and highwater.

A screen of heavy chicken wire should be placed around thepump, well up above the waterline, to prevent entrance of sticks,blocks of wood, stones, rags or other objects that would be likelyto damage the pump if drawn into the impeller. At the end ofthe season the pump should be lifted out of the sump or pit andplaced on a couple of logs or a trestle so that any necessaryrepairs can be made. When dry it should be swept or brushedclean and given another coat of waterproof paint. That this isa homemade 'pump is no reason why it should not be given goodcare. A little care does not add greatly to the expense but willadd materially to the life and usefulness of the pump.

Figure 5.-A homemade pump of metal construction.

Metal construction is obviously more durable than wood,but is adaptable to homemade construction only wnen the farmeror mechanic has had welding experience and has welding equip­ment available. A first-class example of such construction isshown in figure 5.

The riser or discharge pipe of this pump was made fromfour 50-gallon oil drums from which the ends had been removed.These barrels were welded together to form a large pipe. Theframework was made of channel iron from an old car chassisThe impeller was welded together with the blades made from

12 MONTANA EXTENSION SERVICE

cast aluminum. The drive is through the rear axle and differ­ential, making is possible for the pulley to be mounted in a hori­zontal position.

It is possible to drive the. pump directly from a car motorby using the asembly as shown in figure 6. This picture showsan old Dodge car being used to drive a homemade pump by directdrive.

Figure 6.-Homemade pump driven from a Dodge car by direct drive.

A few examples of the performance of this homemade pumpare given in table 1. They show the performance at speeds ofoperation varying from about 400 to 600 revolutions per minute.The tests are divided into five sets of three each. The first setgives the results obtained when the pump was operated at a speedof 395 revolutions per minute, the second at about 450 revolutionsper minute, the third from 490 to 493 revolutions per minute, thefourth from 530 to 550 revolutions per minute, and the fifth from591 to 603 revolutions per minute. The first line of each set givesthe maximum capacity for that particular speed; the second line,

HOMEMADE CENTRIFUGAL PUMP 13

the maximum efficiency2; and the third line, the highest practicallift in feet for each speed.

For example, at 395 revolutions per minute the maximumdischarge of 3.98 cubic feet per second was obtained when thelift was 5.61 feet, with an efficiency of 42.9 per cent. At a slightlyhigher lift, 6.89 feet, the efficiency was increased to 50.1 percent but the discharge dropped to 3.75 second-feet. The highestpractical lift at this speed was 8.57 feet. At 591 revolutions perminute the pump developed a maximum capacity of 6.25 cubicfeet per second, or 2800 gallons per minute, at a lift of 8.37 feet,with an efficiency of 28.6 per cent. The best efficiency at thisspeed was 32.4 per cent, which was at a lift of 10.5 feet with adischarge of 5.47 cubic feet per second, and the highest practicallift was 16.65 feet, at which the capacity was 2.73 cubic feet persecond and the efficiency was 27.3 per cent.

Construction difficulties in the laboratory setup made it im­practicable to compare the performance of the pump at the vari­ous speeds for a constant lift. This accounts for the fact that the

TABLE 1.-PERFORMANOE OF DOUBLE INTAKE HOMEMADE OENTRIFUGALPUMP, 141!x71! IMPELLER. 4/f BLADES

Speed Discharge

Revolutions Gallons Cu. ft. Horse-Total liit. pcr per per power Efficiency

feet minute minute second required per cent

6.61 396 1790 3.98 5.9 42.96.89 896 1686 8.75 6.8 50.18.57 395 896 1.99 4.9 39.6

6.68 461 2052 4.51 8.8 40.78.77 452 1610 3.36 7.9 42.4

10.85 451 910 2.08 6.8 36.8

7.16 490 2200 4.90 11.4 34.910.78 493 1560 3.47 10.8 39.111.90 498 1150 2.56 10.0 84.6

7.28 530 2580 5.76 16.6 80.210.80 637 2160 4.78 15.3 36.514.66 650 1290 2.98 14.1 33.6

8.37 691 2800 6.25 20.7 28.610.50 591 2465 6.47 20.1 32.416.65 603 1225 2.73 18.9 27.3

The theoretical H. P. per foot sec. foot is .113.

2The efficiency of a pump is the ratio which the power equivalent of thewater lifted bears to the power required to lift it. For example, referring totable 1, an efficiency of 42.9 per cent was observed when 3.98 cubic feet persecond was delivered against a head of 5.61 feet. This represents 1395 foot­pounds per second, or 2.54 horsepower. It required 5.9 horsepower to oper~tethe pump, and therefore the efficiency was 2.54 divided by 5.9, or .429, WhIChis 42.9 per cent. A ,high efficiency; indicates a low power. ~equir~m~nt inproportion to the amount of water dIscharged, and a low eff1clency mdIcatesa high power requirement in proportion to the amount of water discharged.

14 MONTANA EXTENSION SERVICE

lift as well as the discharge increased with an increase in speed.If a test could have been made at a lift of 5.91 feet with a speedof 600 revolutions per minute, the results obtained indicate thatthe discharge would have been more than 6.25 cubic feet persecond. However, it is also probable that the efficiency wouldhave been less than 28.6 per cent. .

In general it was found, as wm be seen from table 1, that thedischarge of the pump may be increased by increasing the speedbut that this has an inverse effect on the efficiency of operation.In other words, it is desirable from the standpoint of economy ofoperaton to build the pump large enough to deliver the desiredamount of water when operated at the lowest speed which thelift will permit. The data in table 1 represent the perfonnanceof a 14-by-7 pump with twelve 4-inch blades.

Varying the Capacity by Changing the Diameter'

The capacity of the homemade centrifugal pump depends,among other things, upon the diameter of the impeller. The testsmade thus far to determine the effect of diameter upon capacitydo not cover a wide range of sizes; in fact, only 14- and 16-inchimpellers have been tested. However, the results of these testsshowed that the capacity of the 16-inch impeller was nearly twiceas much as that of the 14-inch at speeds of 450', 500, and 550 revo­tions per minute. The efficiency of the 14-inch pump was thegreater of the two, however. In testing the effect of diameteron capacity, both impellers were equipped with 3-inch blades andthe tests were made under lifts of 8 and 10 feet. The resultsobserved are given in table 2. The choice of the proper diameteris important in building the homemade centrifugal pump becausein this way the capacity is increased without increasing the speedof operation, which would reduce its efficiency.

Effect of Width of Impeller Blades on Capacity

To determine the effect of blade width on the capacity ofthe homemade pump, tests were made with 2-inch, 3-inch, and4-in blades on a 14-by-7 impeller of the double intake type',The results of these tests showed that the capacity of the pump,especially at high speeds, depends a great deal on the width of the~mpeller blades At 400 revolutions per minute the capacity wasmcreased from 1.5 cubic feet per second with 2-inch blades to 2.75

"The 14- and 16-inch impellers tested to determine the effect of diameteron the capacity were of the single intake type, over which the double intake!Dodel represents. a great improvement. It is believed that a correspondingmcrease III the dIameter of the double intake pump would affect the capacityto about the same amount as was observed with the models tested.

'For more complete discussion of these facts see Appendix, figures 19, 20and 21, and .tables 8, 9 and 10 of Bul. 324, Mont. Agr. Expt. Sta.

HOMEMADE CENTRIFUGAL PUMP 15

TABLE 2.-EFFECT OF DIAMETER OF IMPELLER ON CAPACITY OF HOMEMADECENTRIFUGAL PUMP

Capacity of pump, gallons per minute

Size 1411x7 II impeller,

311 blades

Size 1611x81J impeller,

311 bla.desSpeed ofimpellet

t.p.ro.

460600650

8-foot lift

78510101390

10-foot lift

6701146

8-foot lift

162020702470

10-foob lift

116616802070

cubic feet per second with 4-inch blades, an increase of 50 per cent.At 600 revolutions per minute the capacity was increased from3.25 cubic feet per second with 2-inch blades to 6.25 cubic feet persecond with 4-inch blades, an increase of nearly 100 per cent (seetable 3). These results were obtained when lifts of 8, 10, or 12feet were compared.

It was also found that changing from a 3-inch to a 4-inchblade resulted in a greater increase in capacity than was obtainedby changing from a 2-inch to a 3-inch blade, especially at speedsgreater than 500 revolutions per minute. Briefly the capacityvaries almost in direct proportion to the width of blades up to4 inches for the 14"-by-7" size. A larger diameter will permitwider blades.

TABLE 3.-EFFEOT OF BLADE WIDTH ON DISCHARGE OF DOUBLE INTAKEHOMEMADE CENTRIFUGAL PUMP, 1411x711 IMPELLER

Discharge-cubic feet per secondSpeed,

8·foot lift 10-foot lift 12-foot liftrevolutions 2-in. 3-in. 4-in. 2-ln. 3-in. 4-in. 2-in. 3-in. 4-in.per minute blade blnde bl..de blade blade blade bInde blads blade

400 1.60 2.00 2.76460 2.67 8.26 3.70 1.80 1.66 2.60600 3.20 3.60 4.76 2.76 2.96 3.76 2.00 2.00 2.60660 3.25 3.76 6.56 2.76 3.16 4.80 2.20 2.60 4.15eoo 3.26 3.86 6.26 2.90 3.30 5.66 2.60 2.70 4.85

The limit in blade width has not been determined, but testsindicate that when the discharge of the pump reaches a pointwhere intake velocity exceeds 12 feet per second, the efficiencydrops very rapidly.

Table 4 will be found helpful in determining what size tobuild for various lifts, depending upon the amount of waterneeded. The values given in the table represent the best efficiency,The discharge at any given lift may be increased by increasingthe speed, but this will generally result in lower efficiency.Usually the best results are obtained if provision is made forthe desired capacity by choosing the proper diameter of impellerwith the appropriate width of blades.

TABLE 4.-CAPACITY*, SPEED, AND HORSEPOWER FOR BEST OPERATION UNDER VARIOUS LIFTS.

f-'0>

Impeller SUPS

~

Total Diameter 8 inches. Diameter 10 inches Diameter 12 inches Diameter 1G inches 0Intake 4 inches Intake 5 inches Intake 6 inches Intake 8 inches Z

>-3lift,

CapacityISpeed IHorsepower capaCity/ Speed jHorsepower CapacityI Speed IHorsepower CapacityISpeed IHorsepower >Z

feet c. f. s. RP.M. I reqnired c. f. s. RP.M. I required c. f. s. IR.P.M. required c. f. s. R.P.M. I required >tz:j

6 .92 650 .70 .98 500 1.10 2.15 450 2.00 - - - >4>-3

8 .58 700 .70 1.20 600 2.10 1.79 500 2.80 - - - tz:jZ

3.20rn

10 1.04 850 2.23 750 5.60 2.78 600 6.00 2.62 400 5.30 ....0

12 - - - 2.23 800 6.50 2.88 650 7.30 3.20 450 9.20 Zrn

14 - - - 2.25 850 7.70 3.00 700 9.20 5.27 550 19.50 tz:j~

16 - - - - - - 8.18 750 11.80 4.50 550 18.60 <:....(')

18 - - - - - - 3.48 800 14.90 5.10 600 24.00 tz:j

20 - - - - - - 4.51 900 18.20 5.50 650 30.00

·Oapacity of any size may be increased at any lift by increasing speed, although usually at a reduction in efficiency.