Bi-directional centrifugal pump

[57] ABSTRACT

An impeller for a bi-directional single impeller centrifugal pump characterized by a blade configuration capable of pumping water at different capacities from a common pump cavity to either of two outlets depending upon the direction of rotation of the impeller. The capacity of the pump is generally much larger through one outlet than the other. In order to prevent unwanted discharge through the higher capacity opening when the impeller is rotating to pump through the other opening, each of the impeller blades includes a blocking segment at the discharge end of the blade which is defined by a circumferential extension of the blade having a center of curvature at essentially the axis of rotation of the impeller and extending for a distance from the blade discharge end.

Claims, 3 Drawing Figures

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PATENTED® τ«’ί

3,751.179

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3,751,179

BI-DIRECTIONAL CENTRIFUGAL PUMP

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a bi-directional centrifugal pump having a single impeller and more particularly to an improvement in an impeller for such a pump.

2. Description of the Prior Art

Bi-directional single impeller pumps are well known in the art and are advantageously employed in automatic washing machines. In such machines, especially the type commonly described as center-post agitators wherein a reversible electric motor is used which drives an agitator to provide a washing operation and, in the reverse direction, spins the tub containing the clothes at a relatively high speed to centrifuge the water therefrom, it is desirable to be able to either pump the wash water to a drain, as during the centrifuging operation, or pump the water through a recirculating line containing a lint filter, as during agitation or washing operation.

Single impeller pumps ideally lend themselves to such application as they require only one outlet from the clothes tub into the single inlet of the pump. Also, the particular discharge or outlet of the pump desired to be used is dependent on the mode of operation of the machine which in turn is directly related to the direction of rotation of the motor so that the impeller, which selectively discharges to the separate outlets, can also be directly driven by the motor.

However, such pumps to be satisfactorily useful in the above environment should satisfy, at least, the following criteria: the ability to pump sudsy water; efficient enough to completely pump-out the tub including any remaining foamy suds; sufficiently large capacity when pumping to drain so that relatively little time is required to pump-out, and a much smaller capacity for pumping in the reverse direction, to recirculate the water through the filter in a manner that can accommodate the flow.

The bi-directional single impeller pumps of the prior art generally satisfactorily accomplished all of the above objectives, however, as both outlets always remained open to the pumping chamber it was not uncommon that such pumps exhibited an undesirable characteristic of permitting a trickle of water to be pumped to the drain outlet during the recirculation mode of operation. Over the length of the wash or agitation mode, this trickle could account for a relatively large amount of water (e.g., up to 5 gallons) being lost before the wash cycle was complete and adversely affected the washing capability of the machine. It is acknowledged that proper valving of the drain line of the pump could reduce and/or eliminate such trickle but, in this highly competitive environment in which the pump was used, such solution would add an additional prohibitive expense. The present invention obviates this problem with the blade configuration of the impeller.

SUMMARY OF THE INVENTION

The impeller of the present invention is employed a bi-directional centrifugal pump and generally has an arcuate blade construction with the addition of a circumferential segment continuing from, and unitary with, the blade discharge end.

In the direction of rotation of the impeller to cause the pump to pump-out to drain, the circumferential segment trails the discharge end of the blade and has essentially no effect on the capacity of the pump. However, in the opposite direction of rotation, i.e., to recirculate the water, the circumferential segment leads the discharge end and effectively eliminates the unwanted flow through the drain outlet by: reducing the efficiency of the blades in this direction; substantially restricting the flow path of the water to the drain outlet; and, providing a surface moving generally in a direction opposite to that required by the water if it is to flow to the drain outlet. The net result is believed to be that the pressure developed in the pump adjacent the drain outlet is insufficient to overcome the above combination to produce any water flow through the drain outlet, thereby eliminating unwanted loss of water during recirculation.

DRAWING DESCRIPTION

FIG. 1 is a plan view of the impeller of the present invention a pump housing;

FIG. 2 is an isometric view of the impeller; and

FIG. 3 is a plan view of a blade for purposes of illustrating a vector diagram.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The impeller 10 of the present invention is shown in FIG. 1, disposed within the lower housing member 12 of a centrifugal pump 11, which is completed by a mating top housing member 13 (only a portion of which is shown) including a central inlet opening as bounded by an inlet nipple 15 to define a pump cavity or chamber 17.

The annular wall 14 of the lower housing member 12 defines two openings 16 and 18, with associated outwardly projecting nipples 20 and 22 integral with the housing and on which hoses (not shown) can be mounted for directing the water discharged from each outlet. It is noted that opening 16 is so disposed in the housing that its outermost wall 24 is substantially tangential to wall 14 whereas opening 18 is disposed somewhat inboard of a tangential position. Also, opening 18 is of a smaller diameter than opening 16. These two characteristics in conjunction with the shape of the impeller blades, which will be discussed later, and abutment members 26, 28, and 30 projecting inwardly from the annular wall generally adjacent the openings, and defining what were previously referred to as dams, determine the discharge capacity of the pump for each outlet, with the capacity to pump out to drain through opening 16 being much larger, and on the order of 20 gpm, than to recirculate through opening 18, which is on the order of 6 gpm.

The impeller 10 of the pump is characterized as a semi-enclosed impeller in that it has a single bottom wall 34 supporting a plurality of blades 36 and is open at the top adjacent the pump inlet.

Wall 34 is generally contoured so as to conform to the configuration of the pump cavity and to this end has an outer, generally planar, annular portion 38 integral with a frustro-conical inner portion 40 for receiving the bearing and sealing structure (not shown) between the pump housing and the drive shaft (also not shown) of the drive motor of the washing machine. A central hub portion 42 of the impeller comprises a sleeve-like mem

3,751,179 bcr for receiving the drive shaft and is keyed for a direct drive connection between the impeller and the motor.

The blade configuration is clearly shown in FIG. 1. Referring thereto, each blade 36 is seen to have an arcuate profile, i.e., the blade shape as viewed in a plane perpendicular to the axis of rotation, which can be divided into at least two distinguishable arcuate portions referred to hereinafter as the pumping segment 44 and the blocking segment 46.

The pumping segment 44 is similar in profile to known curved centrifugal impeller blades. The blocking segment 46, however, as distinguished from the generally outwardly radiating pumping portion, has no radial component in the arc it defines and extends only circumferentially along the outer periphery of the impeller bottom wall 34. These two separate arcuate segments are preferably integrally molded and blend together to maintain a generally smooth face 48, but with a definite knee 50 formed at their juncture.

THEORY OF OPERATION

As is well known in centrifugal pump theory, the function of the impeller is to impart velocity to the water or fluid therein and the function of the housing or pump cavity is to transform this velocity into a pressure. The theoretical absolute velocity, both direction and value, transmitted to the fluid can be determined from a representative vector diagram of the separate component velocities. Such a diagram is shown in FIG. 3, and in the ensuing discussion of theory as to why it is believed that the impeller blades function to give the improved results observed is used to illustrate these velocity components and their relationship to the shape of the blade. However, in this diagram the disclosed vectors are not to be considered as illustrating the actual value of the velocities developed by the pump.

Thus referring to the vector diagram of FIG. 3, and more specifically the diagram having symbols with a subscript 1, which designates the vectors for counterclockwise rotation of the impeller, represents the tangential speed of the exit point of the blade in a direction perpendicular to the radial line to this point dependent upon the rpm of the impeller in this direction, whereas Wj represents the relative velocity of the water with respect to the blade in a direction tangential to the curvature of the blade at its exit. The theoretical velocity is a combination of the above relative velocities and is represented in direction and amount by c_t. The above analysis is taken at the knee 50 as this is the radially outermost point of the pushing segment 44. It is seen that the blocking segment 46 is ineffective for pumping in that the tangential speed and the relative velocity of the water would be represented by equal and directly opposite vectors thereby cancelling each other so that this segment produces no velocity in the water.

Therefore, analysis of the above vector diagram shows that the theoretical outward velocity C! is the same velocity that would be shown in a similar vector analysis of the previous blade, and that during pumpout, the blocking segment 46 does not theoretically affect the ability of the impeller to pump.

Still referring to FIG. 3 but more specifically to the vector diagram with subscripts 2 which again represents velocity components, but in this instance in the clockwise direction of rotation of the impeller which is the direction it rotates for recirculation, u_t again repre sents the tangential speed of the outermost point of the pumping segment of the blade and w₂ the relative velocity of the water with respect to the blade. From these two components the theoretical velocity is shown as c₂. However, it is seen that, in this instance, the direction of c₂ is into the blocking segment 46 of the blade. Thus, in order to change the direction of the water to flow around the blocking segment, c₂ must be separated into a component c_2T tangential to the blocking segment and a component c_2R radial to the blocking segment. Thus, c_2T represents the available theoretical velocity to be changed to pressure with the difference between c₂ and c_2T representing the loss in velocity caused by the blocking segment. Therefore, in the clockwise direction, the blocking segment in fact lessens the efficiency of the pumping blade by a definite amount. (For a more detailed review of the theory of a centrifugal pump see Pump Handbook, Volney C. Finch, 1948, pps. 37—41.)

It is also noted (see FIG. 1) that whereas the blocking segment 46 trails the pumping segment 44 when the impeller is rotated counterclockwise, i.e., for pump-out, and does not interfere with the pumped fluid’s access to discharge opening 16, the blocking segment 46 leads the pumping segment when the impeller is rotated clockwise for recirculation. As it leads the pumping segment it has the effect, in cooperation with dam 26, of blocking flow around the blade 36 once the blocking segment 46 becomes adjacent to the dam 26, until the pumping segment 44 becomes adjacent the dam. Also the blocking segment 44 has the effect of progressively narrowing the available passageway (from an opening having a width -a- to an opening of width -b-) for the pumped fluid to be accessible to the opening 16, as the blocking segment moves by the opening 16. And, the later point in time when the blocking segment has completely moved by the dam 26 for the opening 16 to be generally accessible, the direction that the pumping segment of the blade is directing the water is generally opposite to that required for any flow into opening 16.

Thus it is seen that whereas the blocking segment had no theoretical effect on the capability of the pump to pump to the discharge opening 16 in counterclockwise direction, it has great effect in reducing the ability of the pump to discharge water through this opening 16 when rotating clockwise. This is the desirable feature of the blocking segment 46 in that it eliminates loss of water during recirculation.

WORKING EMBODIMENT

The impeller of the preferred embodiment shows six blades equally placed on the generally annular planar portion 38 of the impeller bottom wall having an inner diameter of approximately one and one-half inches and an outer diameter of about 3.8 inches. The blades are generally of constant height of 0.73 inches above the bottom wall. The arcuate blade is preferably formed as a combination of three separate arcs with the inlet of the blade defined by an arc having a 0.625 inch radius blending into an arc having a 1 inch radius to form the pumping segment 44 of the blade.

The blocking segment 46 is formed by a radius equal to and on the same center as the outer radius of the impeller bottom and continuing from the termination of the pumping segment (knee 50) for at least one-half inch. It is felt that it is important that the blocking segment 46 of the blade has a center of curvature at essen

3,751,179 tially the center of rotation of the impeller, as this configuration, as previously stated in reference to the vector diagrams, develops no pumping pressure and therefore is singularly applicable as a blocking member to eliminate unwanted discharge through the relatively large pump-out opening 16 when the pump is pumping to recirculation.

It has been found that the above described impeller, when used in the described housing and operating under substantially the same conditions as the previously utilized pumps, has a greater ability to pump-out the foamy suds (i.e., removes it from the tube in less time) than these previous pumps, and thus offers an added inherent advantage.