US3260216A

US3260216A - Venturi-centrifugal pump

Info

Publication number: US3260216A
Application number: US391131A
Authority: US
Inventors: Mann John; Philip J Olmstead; Vincent D Buffone
Original assignee: Goulds Pumps Inc
Current assignee: Goulds Pumps Inc
Priority date: 1964-08-21
Filing date: 1964-08-21
Publication date: 1966-07-12
Anticipated expiration: 1983-07-12

Description

July 12, 1966 MANN ET AL 3,260,216

VENTURI-CENTRIFUGAL PUMP Filed Aug. 21, 1964 3 Sheets-Sheet 1 INVENTOR. J'oH/v MAN/v PHIL/P J- MJ AD VIA/CENT a. auFra/vs ATTO FYS July 12, 1966 Filed Aug. 21, 1964 J. MANN ET L VENTURI-CENTRIFUGAL PUMP 3 Sheets-Sheet 2 INVENTOR. JOHN MANN P/l/l/P .7. 0007540 BY VINCE/YT a EUFFdA/E '@m ATTORNEYS July 12, 1966 J. MANN ETAL 3,260,216

VENTURI-CENIRIFUGAL PUMP Filed Aug. 21, 1964 3 Sheets-Sheet 3 r- THEORETICAL MODIFIED VENTURl-CENTRIFUGAL D LOW RATIO L/d I c\ /CONVENTIONAL VENTURI- K 2 I CENTRIFUG L PUMP MODIFIED VENTURI'CEN HIGH RATIO L/d CONVENTIONAL VOLUTE'GENTRIFUGAL PUMP CAPACITY INVENTOR. Jam! All/WV PHILIP a. omsrsno BY VIA/CENT 0. El/FF'OA/E United States Patent 3,260,216 VENTURI-CENTRIFUGAL PUMP John Mann, Philip J. Olmstead, and Vincent 1). liuifone,

This invention relates to centrifugal pumps and pertains, more particularly, to certain improvements in centrifugal pumps of the venturi-centrifugal type.

Centrifugal pumps of the type utilizing a rotating impeller surrounded by and enclosed within a fixed or stationary casing member may be divided roughly into two general types; one, in which the casing forms a scroll or vo'lute chamber around the periphery of the impeller, and the other in which the casing forms an annular chamber around the periphery of the impeller and is provided with an essentially tangentially disposed diffuser passage leading from such chamber. The former of .these types will be hereinafter referred to as a volutecentrifugal pump and the latter type will be hereinafter referred to as a venturi-centrifugal pump. Both of these types of pumps are well known and conventional in the art and it is also well known in the art that the volutecentrifugal type pump produces a head-capacity performance curve which displays decreasing head as the pump is operated between shutoff" and full capacity, and

the venturi-centrifugal type pump is well known to display a head-capacity performance curve in which the head remains substantially constant throughout various rates of discharge from shutofi toward maximum capacity until substantially full capacity is reached wherein the head drops sharply and suddenly. It is further Well known that the maximum head theoretically available from centrifugal pumps generally is equal to V /g whereas, in practice, a conventional volute-centrifugal pump delivers approximately no more than half this theoretical head, that is, V /Zg. It is also well known that the venturi-centrifugal type pump is capable of supplying a maximum head somewhat greater than the maximum head attainable by a volute-centrifugal type pump so that, in effect, the head available with a venturi-centrifugal type pump may be equal to some integer K greater than unity times the maximum available head from a volute-centrifugal type pump, that is, K(V /2g).

-Howe-ver, even though the venturi-centrifugal type pump is capable of supplying a greater head than the volute-centrifugal type pump, the essentially flat perform- I ance curve of the former is a definite drawback in many fields of application and, for this reason, its use is eschewed whenever a decreasing head is required as the rate of discharge increases, as in the volute-centrifugal type pump. In accordance with the present invention, it has been found that certain modifications to conventional venturi-centrifugal type pumps are effective to provide decreasing head performance curves comparable to the types of performance curves available with conventional volute-centrifugal type pumps while still attaining the greater maximum head capacity performance of venturicentrifugal type pumps.

It is, therefore, of primary concern in connection with this invention to provide an improved form of venturi- 'centrifugal type pump which obviates the substantially constant head characteristics of a conventional venturicentrifugal type pump without sacrificing the maximum 7 head performance characteristics thereof.

More specifically, it is an object of this invention to of pump; the modification relating to the provision of a first section or portion of the passageway which extends essentially tangentially 'from the annular chamber and Which is of uniform cross sectional area throughout and in which the length of this portion is related in a particular manner to the cross sectional area thereof.

A further object of this invention resides in the provision of an improved venturi-centrifugal type pump in accordance with the preceding object wherein the axial center line of the stated first portion of the passageway bears a particular relationship to a line tangent to the impeller and parallel to such center line.

A further object of this invention resides in the provision of a modified form of venturi-centrifugal type pump which incorporates a discharge-diffuser passageway extending essentially tangentially from the annular chamber surrounding the impeller and including a first section of uniform cross section leading into a divergent, increasing cross sectional diffuser portion and wherein a recirculation passageway extends from adjacent the juncture between the first and second portions to the aforesaid annular chamber essentially tangentially thereof.

Other objects and advantages of the invention will appear from the description hereinbelow and the accompanying drawing wherein:

FIG. 1 is an axial section taken through a pump constructed in accordance with the present invention;

FIG. 2 is a transverse sectional view taken substantially along the plane of section line 2--2 in FIG. 1 and showing details of the discharge-diffuser passageway and the recirculation passageway; and

FIG. 3 is a composite graph illustrating the headcapacity performance curves of various conventional types of centrifugal pumps as compared-with pumps constructed in accordance with the present invention and also showing the theoretical maximum performance curve.

With reference now more particularly to FIG. 1, the reference character 10 therein indicates in general the stationary casing assembly provided for the pump, the interior of the casing being hollow for enclosing the impeller assembly indicated generally by the reference character 12. The impeller 12 is rotatable within the casing 10, being fixed to a suitable drive shaft 14 journalled in the casing. The casing is provided with an inlet passageway 16 flanged as at 18 for coupling purposes and the central or hub portion of the impeller 12 is provided with an inlet eye 20 in registry with the inlet passageway 16. The impeller 12 may be of entirely conventional construction and in the instance shown is of the fully shrouded type, that is the impeller is provided witha plurality of passageways 22 extending along radial planes and which passageways are open at their inner ends with the inlet eye opening and are open at their outer or peripheral ends with an annular chamber 24 defined bepartially shrouded type as by omitting the shroud wall portion 36 shown in FIG. 1.

With reference now more particularly to FIG. 2, the characteristics of the discharge-diffuser passageway will be seen. In this figure, it will be noted that internal wall portions of the casing 10 as indicated by the reference character 36 define a discharge passageway 38 which is of uniform cross section throughout itslength and which is disposed essentially tangent to the annular chamber 24 formed between the casing 10 and the periphcry of the impeller 12. By essentially tangent is meant that the passageway should merge smoothly with the inner wall 26 of the casing 10 and should as nearly as possible establish a point of tangency therewith, as at 39 in FIG. 2. The portion 38 of the discharge-diffuser passageway is preferably of circular cross section and has a diameter not greater than the total axial width of the impeller 12 at the periphery thereof and is, preferably, of a diameter commensurate with the axial dimension of the passageways 22 of the impeller 12. For optimum performance, as will hereinafter be more particularly described, the length of the uniform cross sectional area portion 38 of the passageway is from about 5 to about 7 times the diameter thereof, such lengths being measured between the

points

40 and 42 in FIG. 2.

'The diffuser portion of the passageway is formed by internal wall portions 44 of the casing 10 and these wall portions are tapered to provide a frusto-conical diffuser passageway 46 forming a coaxial extension of the passageway 38. At or near the juncture between the two

passageway portions

38 and 46 the casing 10 is provided with further internal wall portions 48 defining a recirculation passageway 50 which extends from such point adjacent the juncture between the

passageways

38 and 46 to the chamber 24, essentially tangent to the latter, substantially as is shown. The taper of the internal wall portions 44 is optimally between about 5 to about 7 degrees total included angle.

Referring now to FIG. 3, the curve A shown therein represents the theoretical maximum attainable with a centrifugal pump and is not, of course, achieved in practice. The maximum head available with this theoretical pump is equal to V /g, as shown and, in comparison therewith, the curve B indicates a conventional volutecentrifugal type pump having an approximate maximum head performance characteristic of V 2g with the head decreasing with increasing rate of discharge toward maximum capacity of the pump. The curve C, on the other hand, represents the head-capacity performance curve achieved with a conventional venturi-centrifugal type pump and, from this curve, it will be clear that the head is substantially constant throughout the operating range of, the pump from shutoff to maximum capacity except at or near maximum capacity, the head drops sharply. Thus, the venturi-centrifugal type pump provides performance characteristics similar to the theoretical performance available from a centrifugal pump while achieving a maximum head which is greater than that available with a conventional volute-centrifugal type pump.

The curves D and E, on the other hand, represent performance curves attainable with a pump constructed in accordance with the principles of the present invention. These two curves illustrate that in accord with the present invention, a decreasing head is achieved as the pump is operated from shutoff towards its maximum flow capacity to produce performance curves similar to the curves attainable with a conventional volute-centrifugal type pump (curve B) but while attaining substantially greater maximum head performance. For comparison purposes in regard to this aspect of the present invention, it might be mentioned that a pump of the type disclosed herein having an impeller diameter of 11% inches will develop a head equivalent to that which would normally require a 13 inch diameter impeller in a conventional volutecentrifugal type pump.

Curves D and E also show the effect of varying the ratio between the length and diameter of the passageway portion 38. Thus, curve D shows a ratio L/ d at or near the lower limit of 5/ 1 whereas the curve B shows an L/ d ratio at or near the maximum of 7/ 1. For ratios of L/d significantly less than the lower limit of 5/ 1, the headcapacity performance curve sharply degrades toward the type of performance curve inherent with a conventional venturi-centr-ifugal pump (curve C); and if the upper lim- A it of 7/ 1 is significantly exceeded, the head will drop too sharply with increasing flow.

In addition to the aforesaid relationships between the length and diameter of the passageway portion 38, it has been found that the performance characteristics of the pump are enhanced if the axial center line 52 of the discharge-diffuser passageway is located such that a line 54 tangent to the tips of the impeller vanes 30, 32 (it being appreciated that on fully shrouded impellers, the shrouds may extend beyond the vane tips) and parallel to such center line 52 lies radially inwardly from such axial center line 52 but within the confines of the

passageways

38 and 46. Optimally, the line 54 lies radially offset inwardly from the center line 52 by an amount approximately equal to d/ 4 where d is the diameter of the passageway 38. Furthermore, the recirculation passageway 50 has been found to be essential to prevent 'droop of the head-capacity performance curve at or near shutoff conditions so that, if the pump is to be operated within this region and no droop can tolerated, the recirculation passageway 50, disposed as described hereinabove and as shown in the drawing in FIG. 2 is an essential feature.

It is to be understood that certain changes and modifications as illustrated and described may be made without departing from the spirit of the invention or the scope of the following claims.

We claim:

1. A centrifugal pump assembly comprising, in combination,

a casing defining a circular chamber,

an impeller rotatably mounted in said casing concentrically within said chamber and having a peripheral portion spaced radially inwardly of said casing,

said casing having a discharge passage extending substantially tangentially of said chamber, said discharge passage having a first portion of uniform cross section extending directly from and intersecting with said chamber and a second portion forming a diffuser of increasing cross section from said first portion,

said first portion of the discharge passage having a length/diameter ratio within the range of from 5/1 to 7/ 1 and the diameter of said first portion of the discharge passage being not greater than the axial width of said impeller at said peripheral portion thereof. 2. In a centrifugal pump assembly, in combination, an impeller comprising a body having a circular peripheral edge and .a plurality of radial vanes extending to said peripheral edge, 1 a casing rotata bly supporting said impeller in enclosing relation thereto and having .an internal wall lying concentric with and spaced radially outwardly from said peripheral edge of the impeller to define an annular chamber between said impeller and said internal wall of the casing, said casing also having a discharge passage of uniform cross section leading from said annular chamber and a diffuser passage extending from said discharge passage and increasing in cross section therefrom in which the axial center line of the discharge passage is parallel to and lies between parallel lines tangential to said impeller and said internal wall respectively, said discharge passage having a predetermined length and a predetermined diameter in which the length is of a magnitude several times the diameter.

3. In the assembly as defined in claim 2 wherein said discharge passage has a length/diameter ratio within the range of 5/1 to 7/1.

4. A centrifugal pump assembly comprising, in combination,

a circular impeller having a central inlet portion, and

provided with vanes extending radially from said inlet portion,

a casing assembly supporting said impeller for rotation about an axis normal to and passing through the center of the impeller, said casing assembly having internal wall portions defining an inlet pass-age leading to said inlet portion of the chamber and defining an annular discharge chamber surrounding said im peller, said casing assembly also having internal wall portions defining (a) a discharge passage of uniform circular cross section extending essentially tangendaily from said annular discharge chamber and (b) an energy conversion passage of frusto-conical shape forming a coaxial extension of said circular discharge passage, the ratio of the length to the diameter of said discharge passage being in the range of 5/ 1 to 7 1.

5. The assembly as defined in claim 4 wherein said impeller and said discharge passage are positioned such that a line tangent to said impeller and parallel to the axis of said discharge passage is spaced radially inwardly from such axis by an amount approximately equal to d/ 4 where d is the diameter of said discharge passage.

6. The assembly as defined in claim 5 wherein said casing is further provided with internal wall portions defining a recirculation passage essentially tangent to said annular discharge chamber and intersecting said discharge passage substantially at the juncture thereof with said energy conversion passage.

7. The assembly as defined in claim 4 wherein said casing is further provided with internal wall portions defining a recirculation passage essentially tangent to said annular discharge chamber and intersecting said discharge passage substantially at the juncture thereof with said energy conversion passage.

8. A centrifugal pump assembly comprising, in combination,

a casing defining a circular chamber,

an impeller rotatably mounted in said casing concentrically Within said chamber and 'having a peripheral portion spaced radially inwardly of said casing,

said casing having a discharge passage extending substantially tangentially of said chamber, said discharge passage having a first portion of uni-form circular cross section extending directly from and intersecting with said chamber and a second portion of frustoconical shape forming a dilfuser of increasing cross section from said first portion, said first portion of the discharge pas-sage having a length which is several times the diametrical dimension of said first portion. 9. A centrifugal pump assembly of the type including a casing having a hollow interior defining a circular chamber and provided with an inlet passage, an impeller rotatably supported in said casing in alignment with said inlet passage and provided with radial vanes for accelerating fluid in outwardly spreading relation from said inlet passage, and said casing having a frusto-conical diffuser passage communicating with and having an axis whose extension is essentially tangent to said impeller, the improvement consisting of:

said casing having wall portions defining a discharge passage of uniform circular cross section intersecting said circular chamber and extending substantially tangentially therefrom to said diffuser passage, said discharge passage being of a length which is at least about five times its diameter.

References Cited by the Examiner UNITED STATES PATENTS 776, 835 12/1904 Goth 103-103 1,439,365 12/ 192-2 Hazell 103-103 1,914,919 6/1933 Heermans 103-403 1,988,875 1/1935 Salorio 103103 2,190,670 2/1940 Mann 103103 3,162,135 1 2/1964 Nichols etal 103103 3,205,828 9/1965 Rupp 103103 FOREIGN PATENTS 472,357 9/1937 Great Britain.

MARK NEWMAN, Primary Examiner.

HENRY F. RADUAZO, Examiner.

Claims

1. A CENTRIFUGAL PUMP ASSEMBLY COMPRISING, IN COMBINATION, A CASING DEFINING A CIRCULAR CHAMBER AN IMPELLER ROTATABLY MOUNTED IN SAID CASING CONCENTRICALLY WITHIN SAID CHAMBER AND HAVING A PERIPHERAL PORTION SPACED RADIALLY INWARDLY OF SAID CASING, SAID CASING HAVING A DISCHARGE PASSAGE EXTENDING SUBSTANTIALLY TANGENTIALLY OF SAID CHAMBER, SAID DISCHARGE PASSAGE HAVING A FIRST PORTION OF UNIFORM CROSS SECTION EXTENDING DIRECTLY FROM AND INTERSECTING WITH SAID CHAMBER AND A SECOND PORTION FORMING A DIFFUSER OF INCREASING CROSS SECTION FROM SAID FIRST PORTION, SAID FIRST PORTION OF THE DISCHARGE PASSAGE HAVING A LENGTH/DIAMETEER RATIO WITHIN THE RANGE OF FROM 5/1 OF 7/1 AND THE DIAMETER OF SAID FIRST PORTION OF THE DISCHARGE PASSAGE BEING NOT GREATER THAN THE AXIAL WIDTH OF SAID IMPELLER AT SAID PERIPHERAL PORTION THEREOF.