US2190670A - Centrifugal pump - Google Patents

Description

Fe. zo, 1940. J. MANN j 2,1%670` CENTRIFUGAL PUMP Fild July 9, 1957 g sheets-sheet 1 TTURIEY- Patented ret.2o,194o A 2,190,670

UNITED STATES PATENT ori-ICE CENTEIFUGAL PUNIP John Mann, seneea Falls, N. Y., assigner te Goulds Pumps, Inc., Seneca Falls, N. Y., a corporation of New York Appueatien July s, 1931, serial Ne. 152,801

2 claims. (ci. 10s-97) My invention relates to new and useful impump, within limits, may be readily varied While provements in centrifugal pumps. still mainttaining the pump at relatively high ef- Heretofore it has been necessary for a manuciency, whereby without maintaining an abnorfacturer of pumping equipment, if he wished to mally large stock of pumps,`a wide range of operl 5 compete with his competitors in the matter of ating conditions may be met.

quick deliveries upon orders received, to maintain Another object of my invention is to provide a a large stock of -pumps on hand. Usually the centrifugal pump Which'may be readily conmanufacturer keptin stock a range of sizes of verted into a pump having different operating pump casings and an innumerable number of characteristics. l pump impellers, each having different operatingl Another object of my invention is to provide a 10 characteristics. Upon receipt of an order for a centrifugal pump so constructed and arranged pump, in accordance with certain specifications, that the fluid capacity and pressure head, of the manufacturer selected the proper size of caswhich the pump is capable, may be varied over ing and mounted therein the impeller most nearrather wide limits. l ly adapted to obtain the characteristics, as to Another object of my invention is to provide 15 fluid capacity and pressure head, required. Not means whereby the volute of the casing, into only did this compel the manufacturer to mainwhich liquid is discharged by the impeller vanes, tain a large inventory of pump casings and immay be varied in volumetric'capacityand'in cross pellers, but also, particularly in the case of pumps sectional area, particularly at the throat thereof,

for small capacities, the emciency of the average. to thereby vary the uid capacity and pressure 20v resulting pump was comparatively low because a head of the pump. pump and its impeller for the best operating char- Another object of my invention is to provide a acteristics and elciency, must be designed for small capacity relatively high pressure centrifueach other. The maintenance of a large stock of gal pump which is eiicient in operation and which, 2d pump casings and impellers is a distinct hardmay be manufactured and sold at a reasonable 25 ship on the manufacturer and is particularly neccost. essary in pumps for small capacities because My invention further contemplates the provithe customer, dueto the small size of the pump, sion of novel means for sealing the impeller drive expects shipment substantially upon receipt of shaft to protect the shaft from the-corrosive and t@ the order. abrasive action of the liquid being pumped.

In addition, centrifugal pumps, except centrif- My invention, in addition, contemplates the ugal pumps of special design, in the past have provision of means for minimizing leakage from been primarily used where a large volume of liqvthe high to the low pressure side of the' pump, uid was to be pumped at reasonably low pressures whereby to increase the emciency thereof. or where a small volume of liquid was to be Other objects and advantages of my invention 35 pumped at relatively low pressures. Where v'will be more apparent from the following dehigher pressures were desired, particularly at scription when taken inconnection with the alcsmall capacities, other types of pumps have been companying drawings, in which:

used-usually a positive displacement pump. Figure 1 is a view showing the pump and motor 40 Probably, the reason why centrifugal pumps have assembly. 40 very rarely been used for small capacities, 100 Figure 2 is a sectional view showing thepump gallons per minute or less, at relatively high prescasing, the impeller, the stuiiing box assembly sures, one hundred and fifty to two hundred and and other parts of my novel pumping unit. op iifty feet totalhead, is because the leakage fac- Figure 3 is a view taken on the line 3-3 of tor, while relatively unimportant in large capac- Figure 2.

45 ity pumps, is a significant factor in reducing the Figure 4 is a partial View, similar to that of efficiency of small capacity pumps. To provide an Figure 3, showing the cover plate of the pump eiiicient small capacity centrifugal pump capable casing rotated to decrease the cross sectional area of developing relatively high pressures required a of the casing volute.

hand-tailored pump, the manufacturing expense Figure 5 is a development of the pump casing 50 of which did not admit of its being sold in comvolute. petition with other types of pumping equipment. Figure 6 is a view taken on the line 6-6 of An object of my invention is to provide a com- Figure 2 showing the manner in which the wearpact pumping unit so constructed and arranged ing rings are locked in the casing. l that the fluid capacity and pressure head of the Figure 'I is a view taken on the line 1-1 of 55 rI'he features of my invention, while/they may,

for the most part, be embodied in any type of centrifugal pump, are particularly adapted for incorporation in what is known in the art as a close coupled pump. The primary differences between a close coupled pump and other types of centrifugal pumps are that, in a close coupled pump, the motor and pump casings are, by what is known as an adapter, rigidly secured closely together and the drive shaft is common to both the motor and the pump.

As shown in Figure 1, the assembly, in which the novel featuresof my invention are incorporated, comprises a motor H having suitable pedestals l2 by which the unit may be supported on the oor or other support, an adapter I3 and a pump casing generally indicated by the numeral v H3. The adapter is provided with hand holes to enable access to the stuiiing box unit. The adapter, as shown in Figure 2, is rigidly bolted, as indicated at it, to the motor casing, and the pump casing is in turn rigidly bolted, as indicated at il, to the adapter. A third pedestal It is provided for supporting the unit on the oor or other support. Any suitable means may be provided for rigidly securing the pump and its motor to the floor, no special foundation being required with this type of pump. If desired, the pump unit may be secured in a vertical position as the unit is particularly adapted to operate in amr position.

The pump casing comprises a casing proper i9 anda cover plate 2i which may be bolted thereto as indicated at 22. The shaft 23, which is common to both the motor and pump, has a suitable bearing 2S at the pump end of the motor casing and another bearing (not shown) at the other end of the motor casing. That portion of the shaft 23 which extends beyond the motor casing H is overhung and extends through the adapter and into the pump casing i4. To the end of the shaft 23, by means of a key 2&1, is secured, against rotation with respect to the shaft, the hub 26 of arr impeller 2l. The impeller is usually made of bronze and is held in position on the shaft by means which will be later described.

The impeller comprises a web 2t, a plurality of vanes 29 cast integrally with the web 2d and a shroud 3l which may be riveted or otherwise secured to the varies, as indicated at 32. While I have shown and described the impeller as being made in separate parts and then secured together, it will be appreciated that the web,vthe blades and the shroud may be cast integrally. The main advantage of casting the web and the shroud separately is to enable the impeller to be more easily machined or filed to provide smooth water passages. Ii the impeller is rather wide, ci course, it may be more cheaply cast integral.

The shroud, as it approaches the impeller' anis, curves outward as indicated at Et to form a smooth entrance for fluid into the impeller, conimonly called the eye of the impeller. At its central portion, the shroud is anged outward, as

indicated at 3d, to provide a duid entrance or suction opening into the impeller. The suction pipe 36 is threaded, as indicated at 3i, in an opening in the cover plate 2| and is in axial alignment with the ange 3d of the impeller so that fluid being drawn through the suctionvpipe, or owing thereto vby gravity, will smoothly enter the eye o f the pump impeller. ,If desired, instead of using threaded connections between the suction pipe and the cover plate, flanged connections may be used.

The cover plate 2i has an inwardly directed flange 38 which is preferably formed on the arc of a circle and which extends substantially three fourths of the distance around the cover plate, as shown in Figure 3. This ange is of such width that, when the pump is assembled, its edge butts against the wall 39 of the casing proper I9. The impeller 2l is concentric with and somewhat smaller in diameter than the flange 38 to provide clearance di around the impeller. The internal bore of the casing proper i9 and the flange 38 are concentric except that the casing wall, beginning at the point t2, merges -into what is known in the art as a casing volute 60. The volute portion of the casing is in open communication with the impeller, extends from the point 42 and gradually increases invwidth and depth to the point t. The volute may be either rounded in cross section or substantially square as shown at d5 in Figure 2. The function of the casing volute is to convert the velocity head of the liquid, imparted to it by the impeller, into pressure head. From the point i3 the volute merges smoothly into a discharge opening it formed in the casing proper i9. The point of merger of the volute with the discharge outlet is known as the throat of the volute or the point of cut water. The discharge opening el@ is substantially circular in cross section, the cross sectional area gradually increasing toward the outlet. In the discharge opening, in any suitable manner, is secured a discharge pipe d.

In my close coupled pump, the discharge pipe et may be located in any one of four positions. Two of the positions are indicated in Figure 3, one in solid lines and the other in dotted lines.

This may be accomplished by shifting the entire u pump casing ifi with respect to the adapter i3 and bolting the pump casing to the adapter in the desired location by means of bolts one of which is indicated at ll. The fact that the entire pump casing may be shifted to dierent discharge positions is of particular advantage in enabling the discharge pipe to be secured to the discharge opening of the pump conveniently and with as few bends in the discharge pipe as need be.

`The capacity of a pump and the pressure of liquid which it is capable of developing are known in the art as the characteristics of a pump. When the capacities and heads of which the pump is capable are plotted on graph paper, there is obtained what is known as a pump head-capacity characteristic curve. One of the features of my l invention is the means by which the pump oi 3 my invention may be converted, without substituting any new parts or modifying any cf the parts of the pump, into a pump having diierent '57d operating characteristics or rather a pump for' `as pump characteristic curves.

the cover plate to the casing proper in the desired location by means of the bolts, indicated at 22.

Shifting the cover plate in av clockwise direction, as viewed in Figure 3, moves the flange 38 so as to decrease the area of the throat of the volute or the maximum cross sectional area of the volute 48 an'd, of course, its volumetric capacity. A position to which the flange 38 may be shifted has been shown in Figure 4. From that figure, it will be apparent that the area at 48, the throat of the volute or the point of cut-water, is less than the area at 43 of Figure 3, the point of cut-water with the iiange in its normal position. It will further be apparent from Figures 3, 4 and 5, the latter of which is a development of the volute, that "the area at the throat of the volute, by properly positioning the flange 38, may be made any desired amount. The discharge of water from the pump may even be entirely cut oif by shifting the flange 38 in a clockwise direction so that the point 38 of the ange is shifted to or beyond the point 42 of Figure 3.

The practical effect of decreasing the throat area of the volute may be made clear from Figure 10 whichy shows what have been described above y We will assume that curve A is the head capacity curve of the pump described above and shown in the draw,- ings with the flange 38 in the position shown in Figure 2; that is, with the throat area at its maximum. The pump casing and impeller are designed to obtain maximum pump efliciency with maximum volute throat area. Curve B, we will asvalve or, in other words, varying the pump discharge pipe opening and by proper measurements, well known in the art, determining various headcapacity points and brake horsepower points which areplotted on graph` paper. After suiiicient points have been plotted, curve A, representing the head-capacity characteristic curve, and curve C, representing the brake horsepower, are drawn. From these two curves, the efficiency of the pump may be calculated for any condition by formulae, not necessary to be set forth herein.

Considering curve A, any condition along line A may be obtained by regulating or throttling the discharge valve, indicated at 49. For example, by properly regulating the discharge valve, the

' pump may be set to deliver forty-eight gallons per minute against a total head (static head plus friction) of seventy feet. This condition is shown at point D on curve A. Under/these conditions, the eiiiciency of the pump and the brake horsepower required to drive the pump, found on curves B and C directly below point D, will be respectively approximately 52% and 1.6 horsepower. I

In the centrifugal pumps of the prior art, if conditions of head and capacity were specied by the customer not found on curve A, another pump would have to be used-one having different operating characteristics, although there are several ways, not necessary to be described herein, of changing, within limits, the characteristics of a given pump.

My invention involves varying the characteristics of a pump by changing the throat area of the volute. This is accomplished in the pump of my invention, as stated above, by shifting the position of the point 38' of the ange 38. The effect of this may be made more clear from a consideration of Figure 10. We will assume that E. IF and G are the head-capacity, emciency and brake horsepower curves, respectively, of the pump described above with the fiange 38 in the position shown 1n Figure 4, in which position the volute throat area is considerably less than when the flange is in the position shown in Figure 2. By throttling the pump with the flange in the position shown in Figure 4, any condition of head-capacity can be obtained along the curve E. For example, let us assume that, instead of the conditions 48 gallons per minute at 70 feet total head given above, a customer had desired a pump capable of delivering 16 gallons per minute at a total head of 'Z0 feet. This rcondition appears on the curveE at the point H. Reading below the point H on the curves F and G, it is found that the brake horsepower required to drive the pump is approximately .9 horsepower and the efliciency of the pump is approximately 32%.

It will now be appreciated that, with the same casing and impeller, by shifting the flange 38 to the proper position, various characteristic curves similar to curve E may be obtained. This eliminates the necessity of maintaining a large stock of pump casings and impellers on hand. With a limited number of pumps in stock, a wide krange of operating characteristics may be obtained. Moreover, it is possible by my invention to make the volute throat exceedingly small in area, without the necessity of attempting to cast volutes with small throat areas which is impractical. In practice, casingsl with small volute throat areas cannot be cast and must be machined.

One of the most important factors adversely aiecting the efliciency of a centrifugal pump is the leakage of liquid which occurs from the high pressure side of the impeller to the low pressure side thereof; that is, between the impeller flange 34 and the casing from the space 5I surrounding the impeller to the suction inlet. The energy applied to this leakage liquid is wasted.4 To minimize this leakage and to prevent casing wear, it is customary to employ what are known in the art as casing wearing rings. These casing wearing rings are usually tted to and rigidly held in the casing and the impeller rotates with respect to them.

In my pump construction, to limit the amount of leakage, I employ a wearing ring 52 of novel design. Pump wearing rings are usually made of bronze, although other materials can and have been employed. The wearing ring 52 is generally L-shaped in cross section, as shown in Figure 2,

comprising a sleeve portion 53 and a portion 54 extending at right angles thereto. The sleeve portion is made relatively long, as at a given pressure, the leakage is substantially inversely proportional to the length of the wearing ring; That is, with a given clearance between the wearing ring and the flange of the impeller and a given flange diameter, the leakage from the high to the low pressure side of the impeller is decreased upon increasing the length of the running t between the sleeve and the impeller ange.

In most wearing ring constructions, it is necessary to provide an appreciable diametral clearance between the sleeve and the impeller flange, of the order of ten to twenty thousandths of an times, slightly off center.

'portance because the leakage is but a small percentage of the volume of liquid pumped. However, because, other factors being the same, the amount of leakage is substantially proportional to the pressure and substantially independent of the volume of the liquid being pumped, the leakage factor is very important in small capacity pumps. A leakage of ten gallons per minute is relatively unimportant in a'pump having a capacity of4 a thousand gallons per minute, but a leakage of ten gallons per minute in a pump having a capacity of forty gallons per minute means a loss of pump emciency from this source alone of twenty-ve per cent.

In accordance with my invention, the diametral clearance between the sleeve 53 and the flange 34 is made approximately ve thousandths of an inch which appreciably decreases the leakage from the high pressure to the low pressure side as, in general, the leakage is proportional to the area of the annular opening between the sleevev and the flange of the impeller. Moreover, the shaft diameter and the weight of the impeller are selected and matched so that the maximum deflection of the shaft will not exceed one thousandth of an inch which is insulilcient to cause the shaft to whip or rotate off center. Further,

I provide additional diametral clearance between from the high pressure side of the impeller tothe low pressure side thereof between the wearing ring and the casing, the wearing ring is u free to be pressed against the casing by the pressure of liquid in the discharge chamber 5I.

` Figure 11.

T increase .the effect of this pressure, the portion 54 of the wearing ring is provided with an annular sealing surface 62, as more clearly shown in This annular sealing surface is of small' area. By reason of the pressure existing in the chamber I, when the pump is operating, the wearing ring is pressed toward the left, as viewed in Figure 2, so' that the annular sealing surface 62 is pressed into sealing engagement i with the interior of the cover plate. The pressure between the sealing surfaces vwill be the pressure Aof the liquid being pumped multiplied by the effective area of thewearing ring exposed to discharge pressureA less the pressure on the suction side of the wearing ring times the effective area of the wearing ring exposed to suction pressure divided by the area of the annular sealing ring.

Of particular importance in the construction of my novel wearing ring is the fact that the wearing ring is free to oat and will normally remain concentric with the shaft sleeve, the additional clearance at 6I being available to permit the wearing ring to adjust itself to compensate for any I charge chamber 5I aiaaevo eccentricity of the mating parts, such as between the impeller flange St and the bore of the casing, and maintain a uniform clearance between the impeller flange 3% and the bore of lthe wearing ring 52. While, in general, I am aware that the use of floating wearing rings has been considered before, I am aware of no wearing ring in 4which the importance of the clearances, above specified is recognized and in which the seal between the casing and the wearing ring is accompished in the manner above described. Particularly, I am aware of no wearing ring in which the ring is locked in the casing to prevent its rotation with the pump impeller. In the floating Wearing rings with which I am familiar, the wearing ring'is' free to rotate with the impeller and is likely to jam against the casing or impeller. In my construction, as shown more clearly in Figure 6, I provide on the wearing ring a lug 63 which registers with a notch 64 in the casing to prevent the wearing ring from rotating with the impeller and yet permit the ring to oat freely.

In Figure 11, which is an enlarged View of a portion of the impeller and wearing ring of Figure 2, I haveI shown the wearing ring in engagement with a shoulder 61 on the impeller, a possible position of the wearing ring when the pump is not primed and there is no pressure difference between the discharge chamber 5| and the suction side of the impeller. With the wearing ring in this position, an annular throttling space or port 6B is provided between the wearing ring and the bore of the -casing through which leakage from the chamber 5i to the suction side of the impeller may freely occur.

With the wearing ring in the position shown in Figure 1l, when the pump is primed and develops discharge pressure, the capacity of the pump is sumciently large that the leakage through the annular space 68 is not sufficient to drop the pressure in the chamber 5l appreciably. 'I'he leakage is a'so insufilcient to build up any appreciable pressure in the suction chamber of the pump. Consequently, there is an unbalanced pressure area on the two sides of the wearing ring. That is, that portion of the area. of the wearing ring represented by the difference in diameters K and L does not have equal pressures on opposite sides thereof for the reason that the pressure in chamber 5I is greater than the pressure in the suction chsimber. Consequently, as the pressure in vchamber 5I builds up, the wearing ring will move to the left, as viewed in Figure 1 1. The annular sealing surface 62 will then engage the casing and cut olf the leakage through the throttling port 68. It is important that theparts be so constructed and arranged that the wearing ring cannot move sufliciently far to the right, as viewed in Figure 1l, to permit open access between the disand the suction chamber. That is, the wearing ring at the limit of its possible movement to the right should be approximately in theposition shown in Figure 11,-with respect to the bore of the casing, so that ya small annular throttling space 68 is provided.

In my close coupled pump, I have also provided novel means whereby the same pump casing may be employed with shafts of various diameters. In the usual centrifugal pump construction, the stuffing box, indicated by the numeral 69, is made integral with the casing and since the internal diameter-.of the stuffing box is xed, only one diameter of shaft may be used with each pump casing. In my construction.

the shaft.

13, usually of bronze, of somewhatv smaller diam' eter than the diameter of the stuffing box bore. A plurality of rings of packing are inserted in the annular space between the internal bore of the stuffing box andthe shaft sleeve.

As is usual in centrifugal pumps, a pipe connection 14 is provided connected between the discharge chamber of the pump and a metal ring 'I5 encircling the shaft and located in the bore of the stufng box. Sufficient pressure is applied on the packing rings to enable a slight leakage of uid to take place through the stuffing box in a direction to the right, as viewed in Figure 2, to prevent air from entering the pump. A bronze casing wearing ring 16 of the ordinary type, fixed in a bore in the stuiiing box and with respect to which the hub of the impeller is rotatable may be provided, although it will be appreciated that a casing wearing ring of the type described above may be substituted if desired.

Upon reference again to Figures 3, 4 and 10, it will be appreciated that with the flange 38 in the position sho-wn in Figure 3 with the discharge valve 49 set to obtain 48 gallons per vminute at a total of 70 feet, the motor horsepower required by the pump will be approximately 1.6 horsepower, which, in standard motors, would require the use of a two horsepower 'motor unless an overloaded 1.5 horsepower motor 'in accordance with the horsepower of the motor with which it is to be used.y A two horsepower motor naturally requires a larger diameter shaft than a one horsepower motor. In order that the same pump casing may be used with a range of sizes of motors, it is therefore necessary that the pump casing be adapted by the means described above, or equivalent thereof, so that stuffing boxes having various 4bore diameters may be used interchangeably with the same pump casing.

In lthe stuffing box construction described above, the packing is retained in positionl by a 4packing gland 11 which, as is quite common practice, is made in two complementary parts secured together by bolts 78. Upon removal of the bolts 18, the packing gland may be readily removed fromthe shaft. A solid type packing gland may be substituted, if desired, for the split and bolted type shown herein. Adjustable nut and bolt assemblies T8, extending between the stuiing box and the packinggland, may be screwed up so that the part 8| which fits into the bore of the stuffing box may be pressed tightly against the packing. A bronze water singer 88, rigidly secured to the shaft by a set screw, prevents water from creeping along the shaftinto the mo- Icor bearings.

In the close coupled pump of my construction, I have provided novel means for retaining the impeller on the shaft and, at the same time,

preventing access of the liquid being pumped to This construction is more clearly shown in Figure 8. 'I'he shaft sleeve 13 is coniined against movement along the shaft in a direction to the right, as viewed in Figure 2, by butting it against a shoulder 82 on the shaft. The other end of the shaft sleeve which, as is the usual practice, is made of bronze, has a ta- "pered countersunk portion, as indicated at 83,

so as to provide an annularv bearing surface 84 cf restricted area which is ground and finished.

A threaded bore 88 is provided in the end of the shaft along the axis thereof into which is threaded a socket head tap bolt 81 which has l washer which engages the hubr of the impeller.v

The washer does not engage the shaft at any point.

In practice, particularly insmallpumps with which we are primarily concerned, since access to the bolt must be had through the eye or suction opening of the impeller, the size of the bolt is, Within rather small limits, fixed by the diameter of the impeller suction opening. Moreover, the diameter of the shaft in small pumps does not permit the use of a large diameter bolt and further, as isA apparent upon consideration of Figure 2, a bolt with, a large diameter head restricts thefree flow of `water through the impeller. With these considerations, limiting the size of the bolt, in mind, the bolt head and the diameter of the bolt at the root of the thread (the dimension N) are made as large as possible. Then, to obtain the maximum sealing pressure between the annular sealing surface 9| of the washer 88 and the hub and between the annular sealing surface 84 of the sleeve 13 and the hub, the areas of the sealing surfaces 9| and 84 are made equal to the area of the bolttfat the root of the thread.

When the bolt is tightened upv by a man, in the ordinary manner, so that the bolt is loaded within the elastic limit` of the material of the bolt, the pressure applied on the bolt is trans-.- mitted to the sealing surfaces 9| and 84. This places the maximum pressure possible at the seal points without destroying the surface contacts between the sealing surfacesand the hub. It will be appreciated that if the areas 9| and 84 are made larger than the area of the'bolt at the root of the thread. the pressure at the sealing surfaces will not be the maximum amount possible. If the areas 9| and 84 are made smaller p than the bolt area at the root of the thread, then the pressure applied on the sealing surfaces may be suiciently great to destroy the surface contacts at the sealing surfaces. When the sealing surfaces are loaded just within their elastic limit, the whole area of the machined surfaces at the sealing points will be in contact because any slight unevenness of the surfaces will be crushed out for the reason that the areas of these uneven surfaces will be less than the area of the bolt at the root of the thread and the sealing surfaces will imbed themselves slightly into the hub of the impeller. V The seal thus provided effectively prevents the liquid being pumped from gaining access to the shaft and is capable of withstanding a pressure of approximately 300 pounds per. square inch, a pressure far above the pressure which the seals may be called upon to withstand. The shaft seal described eliminates the use of troublesome packing. A copper seaiing ring d3 is interposed between the head o! the tap bolt 81 and the washer 89 which eiectively prevents leakage along the threads of the bolt. If desired, the bolt and washer may be made integral. Aiso if desired, instead of using a tap bolt threaded into a threaded bore in the shaft, as shown herein, the end of the shaft may project slightly beyond the hub of the impeller.. The projecting end may then be threaded to receive a nut and there may be interposed between the nut and the hub of the impeller a washer having a sealing surface engaging the hub of the impeller.

The hub of the impeller of the pump thus far described is provided with openings 95 spaced around the hub so that the pressure on both sides of the hub will be the same and the impeller will, therefore, be hydraulicallyl balanced since the pressure in the discharge chamber on opposite sides of the impeller are the same. In Figure 9 I have shown how the shaft seal above described may be applied to an impeller in which the apertures through the huh of the impeller are omitted and the impeller is, therefore, not hydraulically balanced. The construction is the' same as that described above, differing therefrom only in the omission of the apertures and in the omission of an impeller wearing ring corresponding to the wearing ring 1E of the structure shown in Figurez.

It will be appreciated that I have provided e. novel centrifugal pump of the close coupled type which is efiicient in operation, in which a novei means of sealing the drive shaft is employed and in which the characteristics of the pumpl may be readily varied to suit the conditions required, It will further be` apparent that features of my invention may be readily incorporated in other types oi centrifugal pumps and that various modications may be made in the structure shown and described without departing from the spirit of my invention.

i claim:

1. In a pump of the class described, the combination of a casing having a bore dening a peripheral hangs, a discharge outlet from said casing, a volute formed in said ange and can-l nected to the discharge outlet. a rotatable impeller having a suction inlet adjacent its center, operable in said casing and discharging liquid peripherally into said volute, a cover plate having a suction inlet in registry with the suction inlet of said impeller, said cover plate having its periphery secured to the casing flange, a ange integral with said cover plate and extending only part way around the cover plate, said ange forming a shroud around the impeller and in-l sertable in said bore, with the vangeless portion of said cover plate normally in registry with said volute portion of4 the casing so that liquid may freely discharge from the impeller into said volute portion of the casing, said cover plate being shiftable with respect to the casing so as to change the position of the ange on the cover plate with respect to the casing volute and thereby vary the characteristics of the pump.

2. In a pump ofy the class described, the combination of a casing having an open side and having a discharge opening, a portion of the casing adjacent said discharge opening forming a ilxed cut-o, a volute extending substantially from said cut-on part way around the inner periphery of the casing and discharging into the discharge opening, a rotatable impeller having a suction inlet adjacent its center operable in said casing and discharging liquid peripherally into said volute, a cover plate removably secured to said casing adapted to close the open side of the casing and having a suction inlet in registry with the suction inlet or said impelier, a fiange integral with and extending inward from said cover plate and forming a shroud around the impeler, said ange extending oniy part way around the cover plate to denne flange ends, the space between the ends of the 'frange ming open and one end o the hangs normally lying adjacent the xed cut-od with the opening nor-1 mally in registry with said volute whereby liquid may freely discharge from said mpeller into said volute, said cover plate being shiftable with respect to the casing to shift the end of the ange

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