US2396083A - Variable volute chamber centrifugal pump - Google Patents

Description

March 5, 1946. c. w. CHASE VARIABLE VOLUTE CHAMBER CENTRIFUGAL PUMP Filed May 7, 1943 35' 3g 3 jg. 35 25%? 9 6 4 2 Sheets-Sheet 1 March 5, 1946. c w, CHASE 2,396,083

ARIABLE VOLUTE CHAMBER CENTRIFUGAL PUMP Filed May 7, 1945 2 Sheets-Sheet 2 w 9; 2 l. NORMAL CAPACITY E w; a m I 3: 1 HIGH CAPACITY n- I Q I, 0 :5 m

ANGLE IN DEGREES AROUND VOLU TE CLOCKWISE FROM TONGUE BOUNDARIES OF VOLUT LOW CAPACITY OUTER EDGE OF IMPELLER [5/6'027 {ga e U/Jfys:

Patented Mar. 5,1946

s PATENT orncs VARIABLE VOLUTE CHAMBER GENTRIFUGAL rum Corson'W. Chase, Marion, Ind, assignor to Chicago Pump Company, a corporation of Dela- -ware Application May 7, 1943, Serial No. 486,012

11 Claims.

This invention relates to improvements in centrifugal pumps.

The centrifugal pumps to which thisinvention relates comprise an impeller and a volute case.

The impeller adds energy to the iiuid flowing through it and, at the discharge from the 1mpeller, the added energy is manifested in an increase in velocity and of pressure of the fluid. The volute case serves to collect the fluid as it discharges around the impeller'periphery.

In the prior art centrifugal pumps, the circular locating surfaces on the volute case and on the suction and cover plates are concentric with the axis of rotation of the impeller and, in consequence, the relationship of the volute with respect to the peripheries of the impeller shrouds is always the same, regardless of the position at which the volute case is secured to the suction and cover plates. By virtue of this construction, the volute chamber between the impeller shrouds and the volute case always has a fixed and invariable increase of radius around the volute case with respect to the peripheries of the impeller shrouds, thereby providing a fixed path of increasing radius for the now of fluid.

These prior art centrifugal pumps are generally designed to operate at a definite specific speed and for a given head and capacity. When operated according to design, the water in the volute chamber has a substantially uniform and constant pressure at all points around the volute and the pump operates with a maximum of efiiciency. In general, test results show that a prior art centrifugal pump has its maximum eiiiciency only when. operated at the designed speed and a very narrow zone of high efliciency when operated at speeds varying from the designed speed,

either above it or below it.

When the prior art pump is operated at low capacities the pressure of the water in the volute chamber is distributed unequally around the volute and, in general, increase clockwise from the tongue of the pump. At high capacities there is also an unequal static pressure distribution around the volutebut in these cases the pressures, in general, decrease clockwise from the tongue. Where the pressure within the volute chamber immediately behind the tongue or cutof! is high, the velocity of the water and the amount of water leaving the impeller decrease and, not infrequently, water actually flows back from the volute chamber into the impeller. As a rule, unequal pressures within the volute chamher during any type of operation develop nonuniform and unstable flow conditions within the.

impeller and volute chamber and, consequently, seriously impair the emciency of operation of the pump. m I

In addition to impairing the efllciency of the pump, the unequal distribution of the pressure of the water within the volute chamber imparts a radial thrust on the impeller and impeller shaft causing them and, in turn, the pump to vibrate. This radial thrust develops an inciting force on the impeller shaft which results, in some cases,

in such violent vibration as to break the shaft.

Not infrequently, the radial thrust causes the shaft to bend and bring the wearing rings into metallic rubbing contact. This results in excessive wear and increased leakage which finally necessitates costly replacements.

In accordance with the present invention I provide a centrifugal pump having its maximum efiiciency at the designed speed, as before, and a broad zone of high efiiciency at operations above and below the capacity for which the pump is designed. In the pump of the present invention the pressure or the water around the volute and the flow of the water in the volute chamber is substantially uniform and stable not only at the designed normal capacity operations, but also in a wide range of low or high capacity operations. This is accomplished by providing locating surfaces on the suction plate and cover plate which are circular, as before, but which are eccentric with respect to the axis of the impeller shaft, thereby enabling the volute case with its similar eccentric locating surface to be adjusted relative to the impeller for operations above or below the designed capacity so that substantially uniform pressures will exist around the volute during these operations. By virtue of these eccentric locating surfaces the volute case may be rotated on the suction and cover plates to vary the shape of the volute chamber for operations other than the designed optimum capacity operation to compensate for the usual pressure variations at these operations, thereby making possible the attainment of high emciencies at operations above and below the designed capacity of the pump.

In low capacity operations of the pump of the present invention, the volute chamber has the same volume as the volume of the volute chamher at the designed capacity. but the distance between the tongue and periphery of the impeller for the low capacity operation is greater than that at the designed capacity operation. For high capacity operations, the volute chamber also has the same volume as the volume of the volute chamber at the designed capacity, but the distance between the tongue and periphery of the impeller for the high capacity operation -ls less around the volute during substantially all oper-' ating conditions, inciting forces" are substantially eliminated and, consequently, bending or breaking of the shaft with their costly repairs and replacements are reduced to a minimum.

The pump of the present invention can be manufactured at no greater cost than the prior art non-variable volute chamber-type of centrifugal pump. It has many other advantages which will be apparent from the following description of the illustrative embodiments shown in the drawings, in which:

Figure 1 is a central vertical longitudinal section through a centrifugal pump embodying the present invention;

Fig. 2 is a vertical cross section thereof taken along the lines 2-2 of Fig. 1;

Fig. 3 is a diagrammatic view showing the positions of the volute case with respect to the peripheries of the impeller shrouds for the normal designed capacity operation (in solid lines), a low capacity operation (in dotted lines) and a high capacity operation (in dot-dash lines);

Fig. 4 is a diagrammatic view representing the volute chamber shapes and the relative distances between the tongue and the periphery of the impeller for the different positions of the volute shown in Fig. 3; and Fig. 5 is a comparative representation of characteristic curves of the static pressure distributions around the volute of the pump of the present invention and of a prior art pump in the three different operations represented in Fig. 3.

.Referring to the drawings, the numeral l0 designates pedestals or supports upon which the centrifugal pump is mounted, The pump itself comprises a housing l2 containing bearings l4, E5, in which an impeller shaft I1 is mounted for rotation. The shaftis adapted to be driven from I a suitable source of power such as an electric motor (not shown).

Bolted to the housing I2 is one side wall or cover plate 19 of the impeller housing. This side wall is formed with a housing 20 containing the usual packing 2| for sealing the impeller shaft. A circular ledge or locating surface 23 is machined in the forward wall 24 of the cover plate adjacent the extremity thereof. -This circular surface, which forms one seat for the end wall or volute case 25 of the impeller housing, is machined from a center off-set from the axis of the shaft so that the surface is eccentric with respect to the axis of the shaft.

Volute case 25 is bolted to the cover plate H, as at 26, and to the other side wall or suction plate 28 of the impeller housing, as at 29. The suction plate 28 is also provided with a machined circular locating surface 30, opposed to locating surface 23, of the same size and eccentricity with respect to the axis of the shaft as locating surface 23. Locating surface 30 forms the other seat for volute case 25. The undersides of the depending side portions 32 and 33 of the volute case are also machined to provide locating surfaces 34 and 35, of substantially the same size and eccentricity as locating surfaces 23 and 20, which are seated on locating surfaces 23 and 30, respectively, and which are rotatable thereon as hereinafter described.

Suction plate 28 has an opening centrally thereof as at 38 to form the inlet tothe pump. An inlet pipe (not shown) may be connected to the suction plate with the bore of the pipe disposed in coaxial alignment with aperture 38. The discharge end of the pump is formed integrally with the volute case and is shown at 39.

The impeller shaft l1 projects interiorly of the impeller housing and this end of the shaft is tapered. Impeller 40 is mounted on the tapered end of the shaft as by a hub 42 and is held in place thereon as by a bolt 43, threaded into the end of the shaft. The impeller shown herein for illustrative purposes is of the closed type having circular walls or shrouds 45, 46 and impeller blades 41. Shroud 4B is formed integrally with hub'42 andis connected to the other shroud by the impeller blades. The eye 48 of the pump is in coaxial alignment with aperture 38 in suction plate 28. The eye opens to the impeller passageway 49 within the impeller.

Wearing rings 50 and 5i are secured to the shrouds 45'and 46, respectively, intermediate the extremities thereof and these wearing rings cooperate with adjacent wearing rings 52, 53 in the suction and cover plates 28, I5, respectively, to take up any wear between these parts.

The axis of impeller 40 is coincident with the axis of impeller shaft H and hence the peripheries of shrouds 45, 46 are concentric with the axis of the shaft. Since the locating surfaces on suction plate 28, volute case 25 and cover plate l9 are eccentric with respect to the axis of the shaft, they are also eccentric with respect to the peripheries of the shrouds. The space or chamber 55 between the peripheries of the impeller shrouds (in effect the periphery of the impeller) and the volute of volute case 25 is termed the volute chamber.

In the prior art centrifugal pumps the distance between the tongue or cut-off and the impeller periphery remains constant at every position of volute case 25 on the locating surfaces and for all conditions of operation and because of this the shape of the volute chamber remains constant in all positions of the volute case and, consequently, the static pressure of the liquid around the volute and throughout the impeller during different conditions of operation vary widely, being fairly uniform only during the designed or normal capacity operation. At low and high capacity operations the static pressure distributions around the volute are very wide. This is evident from the-characteristic curves 60, GI and 62, shown in Fig. 5, of the static pressure distributions around the volute of a prior art pump at normal, low and high capacity operations, respectively. I

The lack of uniformity of static pressure around the volute at low and high capacity operations gives rise to unbalanced resultant radial forces which causes large impeller shaft deflections. This results in metallic contact, excessive wear, particularly of the wearing rings, and ultimate increased leakage. breaking of the shaft.

In the centrifugal pump of the present invention the distance between the tongue or cut-off At times it has resulted inaseaoss static pressure distributions around the voiute are substantially uniform during these operations. This is evident from the characteristic curves 64 and 65, Fig. 5, of the static pressure distributions around the voiute of the pump of the present invention at low and high capacity operations, I

- respectively. The characteristic static pressure distribution curves of the pump of the present invention for the designed normal capacity operation are substantially the same as those for a corresponding operation of the prior art pumps and for this reason characteristic curve 80 is used to represent also the static pressure distribution around the voiute of the pump of the present invention for the designed normal capacity. It is manifest from the foregoing that the shape of the voiute chamber which will provide substantially uniform pressure conditions within the chamber at any given operation of the pump may be determined readily byexperimentation.

It will be noted from Fig. 3 that in each position of the volute case with respect to' the periphery of impeller 40 the shape of voiute chamber 55 progressively changes from the tongue or cutoff 56 of the pump, formed in voiute case 25 adjacent the mouth 51 of the discharge end 39 of the voiute chamber, to the mouth. 'When voiute case 25 is positioned for a low capacity operation (the dotted line position) or for a high capacity operation (the dot-dash position) the total volume of the voiute chambers at these positions is the same as the total volume of the voiute chamber 7 formed by the volute case when it is positioned capacity operation the distance between the cutof! and the impeller periphery is greater than that for the designed normal capacity. In the area immediately behind the cut-off the velocity is decreased, thereby raising the pressure. The adjusted voiute path appears to decrease the velocity of the liquid in the area between approximately 30 and 240 and that resultsin a greater conversion of velocity energy to static energy and, consequently, an increase in pressure in this area. In the area between approzdmately 240? and 360 the pressure of the liquid is, in general, lowered. The foregoing is apparent from a comparison of curves ii and 64.

From a consideration of-curves 60, 6e and 65 it is manifest that by a simple adjustment of the position of the voiute case around the eccentric locating surfaces of the pump of 'the present invention it is possible to provide substantially uniform static pressure distributions around the voiute for normal capacity operations as well as for low and high capacity operations. In consequence there are no substantially unbalanced radial forces on the impeller during any of these operations and the pump operates with a minimum of vibration and with no breakdown of the shaft due to fatigue resulting from continued severe shaft deflections. Due to the substantial uniformity of static pressure distri butions around the voiute during low and high capacity operations, the efficiency of the pump during these operations is high although not as high as when the pump is operated at the designed normal capacity. The broad' zone of high eiflciency at varying operations possible with the pump 'of the present invention gives this pump a versatility and usefulness not heretofore attained with the prior art centrifugal pumps.

for the normal designed capacity operation (the solid line position); however, as is evident from Fig. 4, the relative shapes of these chambers are different in the different positions. The differences in the shapes of the chambers for each type of operation is due to the eccentricity of the locating surfaces with respect to the periphery of impeller 60, about which volute case 25 is rotated in bringing it to the best position for maximum efliciency in the type of operation to be carried out.

His evident from Figs. 3 and 4 that when voiute case 25 is positioned for a high capacity operation the distance between the tongue or cut-off and the impeller is less than that for the designed normal operation. In the area immediately behind the cut-ofi, the pressure is raised, contrast curves 62 and of Fig. 5. The reason for this appears to be that there is a lesser escape of water from this area into the discharge opening than there is in the prior art pumps because of the smaller distance between the cut-off and the impeller. The adjusted voiute path in my pump in the high capacity position of the voiute case appears toincrease the velocity of the liquid behind the cut-off and that results in a lesser con- When the voiute case is positioned for a low Once the voiute case is adjusted for the particular operation desired the impeller functions in a conventional manner.

In general, it may be stated that my invention contemplates the provision of adjustable means for varyinggthe shape of the voiute chamber for operations of the pump above and below the designed optimum capacity operation to compensate for the usual pressure variations at these operations; that is, by simple adjustment ofthe "means to provide the best shape of the voiute chamber for a given operation, be it the designed optimum capacity operation or operations above and below it, the pressure at all points in the voiute chamber may be adjusted to substantially the mean pressure. I have described herein the locating rings and the formation thereof eccentric to the axis of the impeller shaft as the priferred embodiment of an adjustable means" in accordance with the present invention.- It is to be understood, however, that the present invention is not to be limited to the described embodiment since it contemplates other means of adjustment to compensate for pressure variations at operations above and below the designed optimum capacity operation; for instance, the bolt holes through which bolts 26 and 29 pass may be designed to allow for relative adjustment of the voiute case to .vary the shape of-the voiute chamber. a

While my invention has been described in connection with the pump shown in the drawings it is, of course, to be understood that my invention is not to be limited to this particular pump since the principle of my invention is applicable to all centrifugal pumps of the character illus- "fl by the pump disclosed in the dral shown since these maybe varied largely without departing from the scope ofmy invention.

I- claim:

i. A centrifugal pump comprising an impeller, a rotatable impeller shaft and an impeller housing, said housing comprising a side wall having an inlet communicating with the eye-of said impeller, a second side wall with a locating bear.-

ing for the shaft fixed thereto and an end wall in the form of a volute case having a discharge; opening for the fluid expelled by the impeller, said volute case being rotatably mounted on a circular locating surface on each of said sidev walls and said locating surfaces being eccentric with respect to the axis of the shaft. a 1

escapes eccentric locating surfaces on said side walls in either direction from said fixed position for op erations other than said maximum emciency operation.

4'. A centrifugal pump comprising an impeller, a rotatable impeller shaft and an impeller housing, the axis of said impeller being coincident with the axis of said shaft and the periphery of said impeller beingconcentric with said shaft-axis, said housing comprising a side wall having an inlet communicating with the eye of the impeller,

2. A centrifugal pump comprising an impeller,

a rotatableimpeller-shaft and an impeller housing. the axis of said'impellerbeing coincident with the axis of. said shaft and the periphery of said impeller being concentric with said shaft axis, .said housing comprising a side wall having an inlet communicating with the eye of the impeller, a second sidewall and an end wall in the form of a volute case having a discharge opening for the fluid expelled by the impeller, said volute case having a pair of circular locating surfaces each being in engagement with'a circular locating surface on each of said side walls and being rotatable on said second-named locating surfaces, said locatixig surfaces being eccentric with respect to the periphery of the impeller and fixed relative thereto, a tongue adjacent the discharge opening and spaced from the periphery of the impeller, the volute of said volute case forming with the periphery of the impeller a volute chamber having an increasing radius around the volute with respect to the periphery of the impeller from said tongue, the distance between the tongue and the periphery of the impeller and the said increasing radius being fixed at any one position of the volute case on the locatingsurfaces, and said distance and said increasing radius'being alterable by'movement of the volute case over the eccentric locating sur-- a second side wall and an end wall in the form of a volute case having a discharge opening for the fluid expelled by the impeller, said volute case having a pair of circular locating surfaces each being in engagement with a circular locating surface on each of said side walls and being rotatable on said second-named locating surfaces,

said locating surfaces being eccentric with respect to the periphery of the impeller and fixed relative thereto, a tongue adjacent the discharge opening and spaced from the periphery of the impeller, the volute of said volute case forming with the periphery of the impeller a volute chamber having an increasing radius around the volute with respect to the periphery of the impeller from said tongue, the distance between the tongue and the periphery of the. impeller being fixed for a designed normal capacity operatlon by fixingthe volute case on the eccentric surfaces on said side walls at a fixed position and being alterable by movement of the volute case over the eccentric locating surfaces for other operations, above and below the designed operation, the volute case being movable in one direction from said fixed position for operations below the designed peration to increase the distance between the tongue and the periphery of the impeller from that of the designed operation and being movable in the other direction from said fixed position for operations above the designed operation to decrease the distance between thetongue and periphery of the impeller from that of the designed operation.

' 5. Acentrifugal pump comprising an impeller, a rotatable impeller shaft and an impeller housing, said housing comprising a side wall having an inlet communicating with the eye of said impeller, a second side wall with a locating bearing for the shaft fixed thereto and an .end wall in the formof a volute case having a discharge opening for the fluid expelled by the impeller, said volute case being rotatably mounted on a circular locating surface in said housing and said locating axis, said housing comprising a side wall having an inlet communicating with the eye of the impeller, a second side wall and an end wall in the form of a volute case having a discharge opening nor the fluid expelled by the impeller, said volute case having a pair of circular locating surfaces each being in engagement with a circular locating surface on each of said side walls and being rotatable on said second-named locating surfaces, said locating surfaces being eccentric with respect to the periphery of the impeller and fixed relative thereto, a tongue adjacent the discharge opening and spaced from the periphery of the impeller, the volute of said volute case forming with the periphery of the impeller a volute chamber having an increasing radius around the volute with respect to the periphery of the impeller from said tongue, the distance between the tongue and the periphery of the impeller and the said increasing radius being fixed for a maximum efliciency operation and. being alterable by movement of the volute case over the surface being eccentric with respect to the axis of the shaft.

6. A centrifugal pump comprising an impeller, .a rotatable impeller shaft and an impeller hous ing which defines with the periphery of the impeller a volute chamber which has a fixed shape for a designed capacity operation, said housing comprising a pair of side walls and an end wall in the form of a volute case a circular locating surface on one of said side walls, said locating surface being eccentric with respect to the axis of the shaft and fixed relative thereto, and said volute case being rotatably mounted on said'locating surface whereby upon rotation of said volute case the shape of said chamber is varied throughout the area thereof for operations other than the designed capacity operation.

7. A centrifugal pump comprising an impeller, a rotatable impeller shaft and an impeller housing which defines with the p riphery of the impeller a volute chamber which has a fixed shape for a designed capacity operation, said housing comprising a pair of side walls and an end wall in the form of a volute case, a circular locating surface on each of said side walls, said locating surfaces being eccentric with respect to the axis of the shaft and fixed relative thereto, and said volute case being rotatably mounted on said locating surfaces whereby upon rotation of said volute case the shape of said chamber is varied throughout the area thereof for operations other than the designed capacity operation.

8. A centrifugal pump comprising an impeller, a rotatable impeller shaft and an impeller housing which defines with the periphery of the impeller a volute chamber which has a fixed shape for a designed capacity operation, said housing comprising a pair of side walls and an end wall in the form of a volute case, a circular locating sur- ,face on one of said side walls, said locating surface being eccentric with respect to the axis of the shaft and fixed relative thereto, and said volute case being mounted on said locating surface whereby upon relative rotation of said volute case and said locating surface the shape of said chamber is varied throughout the area thereof for operations other than the designed capacity operation. 9. A centrifugal pump comprising an impeller, a rotatable impeller shaft and an impeller housing which defines with peller-a volute chamber which has a fixed shape for a designed 'capacity operation, said. housing comprising a pair of side walls and an end wall in the form of a volute case, a circular locating surface on each of said side walls, said locating surfaces being eccentric with respect to the axis of the shaft and fixed relative thereto, and said volute case being mounted on said locating surfaces whereby upon relative rotation of said volute case and said locating surfaces the shape of said chamber is varied throughout the area thereof for operations other than the designed capacity operation. 7

the periphery of the im- 10. A centrifugal pump comprising an impeller, a rotatable impeller shaft and an impeller housing which defines with the periphery of the impeller avolute chamber which has a fixed shape for a designed capacity operation, said housing comprising a pair of side walls and an end wall in 'the form of a volute case, one of said side walls having an inlet. communicating with the eye of the impeller and the end wall having a discharge opening for fiuid expelled by the impeller, a circular locating surface on at least the other of said side walls, said locating surface being eccentric with respect to the axis of the shaft and fixed relative thereto, and said volute case being mounted on said locating surface whereby upon relative rotation of said volute case and said locating surface the shape of said chamber is varied throughout the area thereof for operations other than the designed capacity operation.

11. A centrifugal pump comprising an impeller, a rotatable impeller shaft and an impeller housing which defines with the periphery of the impeller a volute chamber which has a fixed shape for a designed capacity operation, said housing comprising a pair of side walls and an end wall in the form of a volute case, one of said side walls having an inlet communicating with ,the

eye of the impeller and the end wall having a discharge opening, for fluid expelled by the impeller, a circular locating surface on each of said side walls, said locating surfaces being eccentric with respect to the axis of the shaft and fixed relative thereto, and said volute case .being mounted on said locating surface whereby upon relative rotation of said volute case and said locating surfaces the shape of said chamber is varied throughout the area thereof for operations other than the designed capacity operation.

CORSON W. CHASE.

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