US 3395649 A
Description (OCR text may contain errors)
Aug. 6, 1968 J. P. MARISCHEN IMPELLER CONSTRUCTION Filed Sept. 27, 1966 K 4 B C W M u 0 0,0 4 n 2 v z n 7 3 7 2 r a n w 2 2: 7 Z 2 5 :2 7 w 7- L NEE, Q 9, 2 5 E: 25 Q drwr/far /i7r Q Warr'sciew 3,395,649 IMPELLER CONSTRUCTION John P. Marischen, Elm Grove, Wis, assiguor to Ampco Metal, Inc., Milwaukee, Wis, a corporation of Wisconsin Filed Sept. 27, 1966, Ser. No. 582,335 6 Claims. (Cl. 103-103) ABSTRACT OF THE DISCLOSURE The invention relates to a modified close-type impeller for a centrifugal pump. The impeller includes a central hub having an inlet to receive the liquid being pumped and a pair of shrouds extend radially outward in spaced relation from the hub. Located between the shrouds are a series of blades and both the front and rear shrouds are i falloped or recessed along the pressure face of each ade.
This invention relates to a pump and more particularly to an impeller construction for a centrifugal pump.
There are two types of commonly used impellers for centrifugal pumps. The first is what is usually referred to as an enclosed type impeller which includes a pair of generally circular plates extending outward from the central hub, and a series of blades or vanes are located between the plates and extend from the hub to the periphery of the plates. The other type of commonly used impeller is an open type in which the front and back plates are eliminated and both sides of the blades are exposed. In some instances a semi-open type of impeller construction is used which includes only one plate so that the blades are exposed on only one side.
With the use of an open type of impeller it is necessary to maintain a close axial running tolerance between the blades and the pump casing. When pumping abrasive or corrosive material the close running tolerances tend to produce excessive wear of the blades during operation. On the other hand an enclosed type impeller eliminates the need for a close running tolerance between the impeller and the pump casing. However, a wear ring is normally used with an enclosed type impeller and a close radial running tolerance is provided between the hub of the impeller and the wear ring. With the use of an enclosed type impeller, a low pressure chamber is located inwardly of the wear ring and balance holes are provided in the blades of the impeller and establish communication between the low pressure chamber and the suction side of the pump. The close radial running tolerance between the wear ring and the impeller hub is necessary in order to provide a pressure differential and reduce axial thrust. A bypass may be provided so that the liquid being pumped will flow through the stuffing box or seal to the low pressure chamber and then through the balancing hole to the suction side of the pump. While the closed type of impeller reduces the close running tolerances between the impeller blades and the casing, a radial running tolerance is nevertheless necessary between the impeller hub and the wear ring. As an added problem, a negative pressure is sometimes developed at the suction side or inlet to the pump and this negative pressure acts through the balancing hole to cause air to be drawn through the stufimg box so that the packing tends to operate dry. In the ideal situation, the pressure of the liquid in the low pressure chamber should be slightly higher than atmospheric so that there is a limited flow of the liquid outwardly through the packing to the atmosphere.
The present invention is directed to an improved impeller construction for a centrifugal pump which provides greater pumping efficiency and eliminates the necessity of close axial and radial running tolerances between the 3,395,649 Patented Aug. 6, 1968 impeller and the stationary elements of the pump. More specifically, the impeller includes a central hub having an inlet to receive the liquid being pumped and a pair of plates extend radially outwardly in spaced relation from the hub. Extending between the plates are a series of blades or vanes and both the front and back plates are scalloped or recessed along the leading edge of each blade so that the impeller has a generally starfish-shape. During the pumping operation, the recessed portions of the front and back plates provide areas of low pressure near the hub of the impeller. A pumping action takes place in the axial space between impeller and casing so that the main flow is outward, i.e., in the direction of low to high pressure areas. This pumping action reduces the amount of recirculation for a given radial running tolerance. In conventional enclosed impeller pumps, flow in the axial impeller-casing clearance is inward, and equal to the amount of the recirculation.
A close running tolerance between the impeller and the casing, as in a conventional open impeller, is not required, and by eliminating the rear wearing rings, balancing holes, and the balancing chamber of the conventional closed impeller, areas of possible entrapments of solids are correspondingly eliminated, thereby facilitating cleaning of the pump.
The impeller design of this invention reduces axial thrust without reversing it by reducing pressure at the stufiing box or mechanical seal. This reduced pressure will not be negative with respect to atmospheric pressure so as to lose lubrication, draw in air, or invite cavitation.
As there is a relatively small pressure drop across the suction side, radial running clearance, the amount of recirculation which effects head and efiiciency loss is not critically related to the magnitude of the clearance. Thus, clearances up to /8" can be employed at the suction side of a 2 /2 inch pump, instead of a few thousandths of an inch as in the conventional pump.
The impeller design of the invention also provides substantial casting advantages over the conventional enclosed type impeller. With the conventional enclosed type impeller a high cleaning cost is encountered present design utilizing the scalloped or recessed front and rear plates, the cleaning cost is substantially reduced. Moreover, the conventional enclosed type impeller provides high scrappage due to core breakage in casting. With the present design, the recessed or scalloped areas in the front and back plates provide areas where gases can vent through, and areas for core prints supporting the internal core, thus resulting in less scrappage and better casting efliciency.
The impeller of the invention can be used for pumping any type of liquid normally used with a centrifugal pump and is particularly effective for pumping abrasive or corrosive materials or materials which contain solid particles such as in the food processing industry.
Other objects or advantages will appear in the course of the following description.
In the drawings:
FIGURE 1 is a longitudinal section of a centrifugal pump incorporating the impeller design of the invention;
FIG. 2 is a plan view of the impeller with parts broken away in section; and
FIG. 3 is a section taken along line 33 of FIG. 2.
The drawings illustrate a centrifugal pump 1 including a casing 2 having a liquid inlet 3. Casing 2 is provided with a flange 4 which is secured to the flange 5 of an adapter or pedestal 6 by a series of bolts 7.
The pump is driven by a motor 8 secured to adapter 6 and the motor drive shaft 9 carries an impeller 10 which is located within casing 2 and is secured to the end of the shaft 9 by a nut 11.
To minimize the flow of fluid outwardly along the drive shaft 9, a packing 12 is located within a recess in the inner surface of a rear cover plate 13 and the packing 12 is maintained Within the recess by a gland 14. In addition, a slinger 15 is secured to the shaft between the gland 14 and motor 8 and during operation of the shaft the slinger serves to throw any particles outwardly by centrifugal action which may be moving along the motor shaft.
According to the invention the impeller includes on outer section 16 and an inner section 17 which are connected together by a series of curved blades 18. Lo cated centrally of the outer section 16 is an inlet opening 19 which is positioned in alignment with the inlet 3 of casing 2.
Inner section 17 of impeller 10 includes a central hub 22 defining a central opening 23 which receives the reduced-diameter section 24 of drive shaft 9. Hub 22 is keyed to shaft section 24 so that the impeller 10 will rotate in accordance with shaft rotation. The outer end of shaft section 24 is tapped and receives a stud 25, and nut 11 is engaged with stud 25 and serves to retain the impeller 10 on the shaft.
The outer portion 26 of each blade 18 is arranged generally normal to the axis of the impeller, while the inner portion 27 of each blade extends from the outer portion 26 to the inlet 19 and is twisted in the form of a Francis impeller.
According to the invention, the impeller sections 16 and 17 are provided with recesses 28 which are located between the blades 18. As best shown in FIG. 2, the edge 29 bordering each recess 28 coincides with the leading edge of the corresponding blade 18, and the bottom of each recess 28, indicated by 30, is located at the junction between the outer portion 26 and inner portion 27 of the blade. The edges 31 bordering recesses 28 extend generally parallel to the next succeeding blade or vane 18, in the direction of impeller rotation, and the edges 31 are spaced rearwardly in the direction of impeller rotation from the next succeeding blade, as shown in FIG. 2.
The rear surface or face 32 of the inner impeller section 17 of impeller 10 is spaced from the adjacent surface 33 of cover plate 13 to provide a clearance 34 therebetween. Similarly the annular surface 35 of hub 22 is spaced from the inner surface 36 of the cover plate 13 to provide a clearance 37 which communicates with the clearance 34. Clearance 37 also communicates with the recess in cover plate 13 which contains the packing 12.
During rotation of the impeller a low pressure area is produced within the clearance 34 adjacent the hub 22 due to the recesses or scallops 28 between the adjacent blades. Although the pressure increases in clearance 34 from surface 35 towards the outer diameter of the impeller, the flow in this clearance 34 is outward, i.e., from low to high pressure, which is a pumping action. This is in contrast to the conventional enclosed impeller which produces 'an inward flow of liquid within the clearance between the back side of the impeller and the cover plate. As the low pressure areas are developed within the clearance 34 adjacent the hub, and as this low pressure is above atmospheric, a small leakage flow of liquid is pro duced outwardly through the clearance 37 and packing 12, resulting in the packing being continuously impregnated with the pumped liquid. In contrast to the con ventional enclosed type impeller which includes balancing holes, it is not possible to obtain a negative pressure within the clearance 34 with the present impeller design. This insures that the low pressure areas in the clearance 34 will always be above atmospheric so that the liquid flow through the packing 12 will be outward and air will not be drawn through the packing.
As previously mentioned, the conventional enclosed type impeller employs a rear wearing ring which is in close running proximity with the impeller hub to provide a low pressure area adjacent the hub. The present impeller design eliminates the need of the rear wearing ring and also eliminates the need of the balancing chamber and balancing holes. The conventional balancing chamber provides an area where particles or foreign matter can accumulate, and by eliminating the balancing chamber the possibility of accumulation of foreign matter is minimized.
The present impeller design also reduces thrust without reversing it. Due to the fact that a greater surface area of the inner section 17 is exposed to the pressure of the liquid being pumped than that of the outer section 16 an outward thrust is normally developed on the impeller, and the thrust is generally equal to the area between A and B, as shown in FIG. 1, multiplied by the average pressure between A and B. With the present pump design using the recesses 28 the pressure at B on the backside of the impeller is reduced over a conventional closed type impeller, thereby reducing the average pressure between A and B over the conventional design and this results in a reduction in the amount of thrust developed by the present impeller design.
As an added advantage, the pump of the invention eliminates the need for a close radial running tolerance between the front wearing ring 38 and the surface 39 of the impeller. The running clearance between the rear wearing ring 38 and surface 39 is not as critical in the present pump design because the pressure along the front side of the impeller is reduced due to the recesses 28 in the outer impeller section 16. As the pressure at B is substantially reduced over the pressure at C, a larger clearance can be employed between the wear ring 38 and the surface 39 and this again simplifies the machining and serves to increase the life of service of the pump.
Due to the recesses or cutouts 28 in both of the impeller sections 16 and 17, the casting procedures for making the impeller are simplified. A considerable portion of the overall cost of casting the conventional enclosed type impeller results from the difficulty in cleaning out the core from the inside of the casting and smoothing of the internal metal surfaces. With the recesses 28 the removal of the core is facilitated, resulting in a cost savings in the overall casting procedure. Moreover, the present design minimizes scrappage due to core breakage and this again reduces the overall cost of the impeller.
The present impeller can be used for pumping any type of liquid that lends itself to centrifugal pumps and is particularly adaptable for pumping materials containing solid particles, or abrasive or corrosive materials.
Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.
1. An impeller for a centrifugal pump comprising a hub having a central inlet to receive a liquid to be pumped, a first member extending radially outward from the hub, a second member extending radially outward from the hub in spaced relation to the first member, and a series of blades extending between said first and second member, the peripheral edge of both the first and second members being provided with recesses which extend between adjacent blades, each recess including a first edge portion coinciding with pressure face of the blade and each recess including a bottom edge portion disposed adjacent the hub and each recess including a second edge portion coinciding with and spaced to the rear of, in the direction of impeller rotation, the suction face of the next adjacent blade.
2. The structure of claim 1 in which the recesses in the first and second members are substantially identical in shape.
3. The structure of claim 1, in which each blade includes an outer section and an inner section extending from said outer section to a location adjacent the hub, said bottom edge portion of each recess being located adjacent the junction of said outer and inner sections of the blade, said outer sections being disposed generally normal to said members and said inner sections being twisted with respect to said outer sections.
4. The impeller of claim 1 in which the blades are curved in a trailing direction, away from the direction of rotation of the impeller, and the first edge portion of each recess is flush with the pressure face of the corresponding blade.
5. An impeller for a centrifugal pump comprising a hub having a central inlet to receive a liquid to be pumped, a series of vanes extending outwardly in a radial direction from the hub, and a pair of flanges extending rearwardly, with respect to the direction of impeller rotation, from the side edges of each vane, the flanges on each vane being spaced apart and extending generally normal to the axis of said hub, the outer peripheral portions of the flanges of each vane terminating in spaced relation to the next succeeding vane.
6. A pump comprising casing means having a liquid inlet and a liquid outlet and defining an impeller chamber, a rotatable shaft extending within the impeller chamber, and an impeller secured to the shaft and located within the chamber, said impeller including a central hub having a liquid inlet communicating with the inlet of said casing means, said impeller having an inner radially extending section located adjacent a first wall of said casing means and an outer radially extending section located adjacent a second wall of said casing means, said impeller also in cluding a series of blades extending between said first and second sections, the peripheral edge of both the first and second sections being provided with recesses extending between adjacent blades, each recess including a trailing edge portion coinciding with the pressure face of a blade and including a bottom edge-portion disposed adjacent the hub, and each recess including a leading edge portion coinciding with, and spaced to the rear, in the direction of impeller rotation, of the suction face of the next adjacent blade, said inner section and said first wall being spaced apart to provide a radially extending clearance therebetween, said clearance being of a substantially uniform width throughout its radial length and extending in a single plane, said recesses providing areas of low pressure in the portion of said clearance adjacent the hub to provide a flow of liquid within the clearance from the hub toward the outer periphery of the blades.
References Cited UNITED STATES PATENTS HENRY F. RADUAZO, Primary Examiner.
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,395,649 August 6, 1968 John P. Merischen It is certified that error appears in the above identified patent and that said' Letters Patent are hereby corrected as shown below:
Column 2, line 42, after "encountered" insert due to the difficulty in cleaning out the core same line 42, before "present" insert With the Column 4, line 65, before "pressure" insert the Signed and sealed this 3rd day of February 1970.
Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR.
Attesting Officer Commissioner of Patents