US3084701A

US3084701A - Pumping mechanism and pump inlet cover for use therein

Info

Publication number: US3084701A
Application number: US108006A
Authority: US
Inventors: Albert L Hardy; Donald S Cushing; Thomas E Jenkins
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1961-05-05
Filing date: 1961-05-05
Publication date: 1963-04-09
Anticipated expiration: 1980-04-09
Also published as: CH392795A; DE1428399A1; GB987706A; NL278055A; DE1428399B2; NL134030C

Description

April 1963 A. 1.. HARDY EIAI. 3,084,701

PUMPING MECHANISM AND PUMP INLET COVER FOR USE THEREIN Filed May 5, 1961 2 Sheets-Sheet 1 FWGJ INVENTORS ALBERT L. HARDY, DONALD s. cusnms ysTHoMAs a. TENKINS ozfw THE\ R ATTORNEY April 9, 1963 A. L. HARDY ETAI. 3,

PUMPING MECHANISM AND PUMP INLET COVER FOR USE THEREIN Fil'd May 5, 1961 2 Sheets-Sheet 2 INVENTORS ALBERT L. HARDY, DONALD S. CUSHING 8 THOMAS E. :rsmuus Wfm THEIR ATTORNEY United States Patent 3,084,701 PUMPING MlEtCHANlSli i AND PUMP INLET OUVER FGR USE THEREHN Albert 11.. Hardy, Donald S. Qushing, and Thomas E.

Jenkins, Louisville, Ky, assignors to General Electric (Iompany, a corporation of New York Filed May 5, 1961, Ser. No. $,ii06 13 Claims. (Cl. 134-115) This invention relates to a pumping mechanism for liquids and more particularly to a pumping mechanism for an automatic dishwasher employing two pumps drawing liquid simultaneously from a single sump space.

Automatic dishwashers of the reaction spray type are generally designed to employ an operating cycle including a series of separate washing and rinsing operations in each of which a comparatively small amount of water is admitted to the washing compartment, circulated therein, and then discharged from the machine. The washing water generally is sprayed upon the dishes in one or more spray streams under a pressure head provided by a pumping mechanism contained in the dishwasher housing. This mechanism also effects a rapid draining of the soiled water from the dishwasher at the appropriate times in the cycle of dishwashing operation. The conjoint use of two pumps in such a pumping mechanism, however, frequently results in an inefiicient pumping operation when both pumps have their inlets connected to the same sump space in the dishwasher tub. It is a purpose of the present invention to overcome this disadvantage of automatic dishwashers through the employment of an improved pumping mechanism.

A general object of the invention is to provide a compact and efficient pumping mechanism having a plurality of commonly-driven pumps having inlets communicating with a single liquid collecting space.

Another object is to provide a novel pump inlet cover for use with a slow speed axial flow pump having a low pump inlet head.

Another object is to provide an improved dishwasher having a single sump space and with a pumping mechanism having a plurality of pumps each of which has a separated inlet communicating with that sump space.

A further object of the present invention is to design an axial flow pump with novel straining means to prevent foreign particles from entering the pump.

A further object of the present invention is to design a vane type pump with a non-clogging inlet opening which will not accept hard foreign objects but which will mulch and draw through the pump soft food waste.

A still further object of the present invention is to provide a combined axial flow pump and drain pump mechanism having a single driving means, with separating.

means between the two pumps to prevent the starvation of water and the forcing of air into the drain pump.

Further objects and advantages of the invention will become apparent as the description proceeds, and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

In accordance with one aspect of this invention there is provided a compact pumping mechanism having a combined axial flow pump and a vane type drain pump, the pumping mechanism being arranged to be positioned for example, within a sump space at the lower part of the washing compartment of a dishwashing structure. An upper pump housing encloses the axial flow pump and has an outlet which in the dishwashing application directs pumped liquid into a spray means; and a lower pump housing encloses a vane type pump which may have two outlets, one of which leads to a drain sewer and the other prising a suitable fifih ifiiil Patented Apr. 9, 1963 ice of which leads to an additional spray means. Each of the pumps has an inlet communicating with the same sump space, and interposed between the respective pump housings is a special pump inlet cover or separator which directs the flow of liquid simultaneously to the pumps as well as performing other useful functions which will be explained hereinafter.

For a better understanding of the invention, reference may now be made to the following description and accompanying drawings in which:

FIG. 1 is a side elevation view, with parts broken away and with parts in section, of a portable automatic dishwasher incorporating the present invention;

FIG. 2 is an enlarged side elevation view, with parts broken away and with parts in section, of the pumping mechanism embodying the present invention and installed in the tub of a dishwasher;

FIG. 3 is a sectional plan view, with parts broken away, of the pump inlet cover taken on line 3-3 of FIG. 2;

FIG. 4 is a top plan view of a centrifugal drain pump taken on line 44 of FIG. 2, and

FIG. 5 is a side elevation view of the pump inlet cover.

Referring to FIG. 1 of the drawings, this invention has been shown in one form as applied to a portable automatic dishwasher comprising a tub 9 defined by

side walls

10, 11, 12 and 1G and having a bottom wall 14 sloping downwardly to form a single sump space 15 for the collection of washing liquid. This liquid is supplied to the machine by any suitable means, not shown, and which supply forms no part of the present invention. In the type of dishwasher as shown, the tub is closed at its top by a cover 16 hinged along one edge of the tub at 17 although the invention, as will be understood, is in no way limited to a dishwasher having this type of access opening. The design is of equal usefulness in such machines as the front-opening drop door type. A suitable latch means 18 may be provided at the front edge of the access cover and tub for locking the cover in closed position during the operation of the dishwasher, and a cover push plate 19 serves to assist in the opening and closing of the cover. Within the front panel 20 of the cabinet structure the controls of the machine may conveniently be mounted, and a handle 21 for moving the machine on its casters 212 may likewise be mounted on this front panel. Disposed within the tub is an upper dish rack 23 and a separate lower dish rack 24. A suitable electrical heating element 25 may also be mounted within the bot tom of the tub 9 below these racks.

Referring now to FIGS. 2 and 4, the preferred pumping mechanism of the present invention is shown as comreversible electric motor 30 having a rotor assembly and motor housing including an end bell 31. Fastened to the end bell 31 is a series of three or more clamp-down bolts '32 for securing the stationary parts of the pumping mechanism to the motor. The motor shaft 33 has rigidly attached thereto the impeller 34 of an axial flow pump rotatable on the same axis as the motor shaft and movable within an upper pump housing 35. Surrounding the motor shaft beneath the axial flow pump impeller 34 is a centrally apertured lower drain pump housing 29 having a floor portion 36, an upwardly extending wall portion 37 and a fiat peripheral rim portion 38 extending over the bosses 31 of the motor and in clamping relation thereto. A pair of drain openings (not shown) from the back Wall portion of this housing lead into

conduits

45 and 46, later to be described.

Disposed within the lower drain pump housing 29 is a centrifugal pump impeller of drawn metal shape having pumping

vanes

40 and 41 and arranged to pump efiiciently in either direction of motor rotation. This pump impeller may be atfixed directly to motor shaft 33, or to an extension of the axial flow pump impeller 34 as shown, and in any event is driven by the motor shaft as the motor rotates. Suitable liquid sealing means 43a formed as part of the drain pump impeller between the housing 29 of the centrifugal pump and the motor shaft 33 also is provided to prevent leakage from the pumping mechanism into the motor. Overlying the rim 38 of the centrifugal pump housing is a centrally apertured pump cover plate 4-2 the aperture of which not only receives the motor shaft but also provides an annular opening 4-3 of small clearance with respect to the rotating pump elements and serving as an inlet to the centrifugal pump and communicating with the sump space of the tub. This annular clearance 43 is of primary importance because it is so located and proportioned that it serves as a non-clogging inlet opening for the drain pump. -It is possible for hard foreign objects such as hair pins, broken glass, screws, coins, etc. to fall into the dishwasher tub. These destructive objects are left out of the drain pump by the small clearance opening 43 in the pump cover 42. In an automatic dishwasher it is desirable to be able to load the soiled dishes into the machine without first scraping or rinsing the food soil off. Accordingly, it is necessary that the drain pump accept large food particles such as corn kernels, potatoes, meat particles, carrots, spaghetti, etc. without plugging up the pump.

A filter screen might be used to keep out the hard particles but the soft food particles would tend to plug the screen. This problem has been solved by using a smooth rotating member (the shaft of the pump) in close proximity with the sharp edge of the opening 43 in the pump cover 42. Soft foods are then agitated and mulched until they reach a size capable of passing through the opening 43, but hard foreign objects cannot pass this opening.

Considering now FIG. 1, during rotation of the motor shaft in a first direction the above-described drain pump 2? upon receiving liquid through its inlet opening 43 pumps the same into a conduit 45 and upon rotation of the shaft in a second direction pumps the liquid into a drain conduit 46. This may be accomplished in accordance with the teachings of U.S. Patent No. 2,946,986 to Sholtes et al. which is assigned to the same assignee as is the present invention. This patent teaches a design using a fixed diverter member having a fioor portion conforming to the shape of the fioor 36 of the lower pump housing, a back wall supporting portion 47 conforming to the shape or" the back wall of that housing, and more importantly a pair of

barrier portions

48 and 49 spaced from each other and extending generally tangentially toward the central hub portion of the drain pump impeller but below the turning movement of the

pump vanes

46 and 41, as best seen in FIGS. 2 and 4.

Liquid pumped into conduit 4-5 serves a washing purpose and passes through a riser conduit 54) into a rotatable spray means 51 mounted to spray downwardly upon the dishes in the upper rack 23, as best described and claimed in the copending application of Russell M. Sasnett, Serial No. 853,894, filed November 18, 1959, and assigned to the same assignee as is the present invention. Likewise, liquid pumped upwardly by the axial flow pump impeller 34 serves a washing purpose as may best be noted from the construction of the upper pump housing 35. This pump housing may include a tubular central body portion 52 terminating at a lower edge 53 and having a plurality of peripherally spaced mounting

feet

54, 55, and 56 extending downwardly and outwardly of the central body portion. At its top edge the body portion 52 is reduced in diameter and is recessed to provide a circular seat 57 on which a hollow spray arm 58, as seen in FIG. 1. is arranged to rotate under the reaction propulsion force furnished by the stream of pumped liquid. A series of radially spaced internal arch-like webs, one of which is seen at 59, support a stationary upturned bell shaped central boss 69 having a bolt 61 passing therethrough. A

flanged nut 64 having an enlarged cylindrical portion is threaded over the bolt. The flange of the nut with a fiber washer underneath overlies the top surface of the spray arm, while the cylindrical portion fits into a clos fitting opening in the arm and serves as the rotating hearing for the spray arm 58. This bolts also serves to secure to the boss 6% a downwardly mounted stationary diffuser member 62 having radially spaced curved vanes 63 disposed adjacent the discharge end of the vanes of the impeller 34 of the axial flow pump. This diffuser is important to the design of the axial flow pump impeller 34 in that it takes the swirling water from the impeller 34 and straightens it out to an axial flow for supplying the high velocity wash water to the reaction spray system. An apertured disc or reinforcing plate 66 is fastened within the spray arm so that a vertical supplemental spray tube 65 communicating with the interior of the spray arm 53 may be held in place by fastening screw means 67. It should be noted that the upturned bell-shaped boss 60 serves as a flow diverter to direct most of the water received from the axial flow pump away from vertical spray tube 65 and sidewise into the interior of the rotating spray arm 58.

In general, the capacity of the axial flow pump, which furnishes liquid for the spraying upwardly over the dishes on both of

racks

23 and 24, is much greater than the capacity of the above-described centrifugal drain pump 29, and a large inlet to the axial flow pump is required. it has been found, however, that the rotation of the axial fiow pump impeller in its upward pumping direction tends to starve the drain pump of liquid, and the rotation of the axial flow pump impeller in the reverse direction, i.e., in a downwardly pumping direction, tends to force air into the inlet of the drain pump. in addition, the use of the axial flow pump with a low pump inlet head presents problems of vortex effects in the liquid flow from the sump space 15 into the pump and necessitates some special provision for establishing a steady pump how without large surges as when the dishwasher is operated with a comparatively small total water fill of between seventeen and twenty-two pints of water. Moreover, malfunctioning of the pumping and spraying elements due to the presence of foreign objects or large food particles or the like must be avoided.

The present invention provides a solution to these problems by including in the pumping mechanism between the axial flow pump and the drain pump a fixed flowdirecting pump inlet cover 68, one suitable form of which is shown in FIG. 5. This cover fits around the pump impeller 34- and may include an uppermost rim portion 70 merging with the impeller with a circular concave body portion 71 extending from that upper rim 70 to a lower generally circular larger diameter outer periphery 72 of the cover. Extending downwardly and interiorly of the rim portion 70 is a truncated conical Wall portion or bushing 73 closely embracing the conical shaft of the impeller 34 of the axial flow pump and having a closefitting but free running lip '74 in engagement with the impeller to prevent bypassing of air and liquid. Adjacent the outer periphery 72 of the cover is a plurality of vertically extending arcuately arranged grid-

like wall portions

75, 76 and 77 (FIGS. 3 and 5) projecting upwardly from the lower periphery 72 of the body portion and being arranged outside the pump housing 35 to leave an open inlet space 78 (FIG. 2) between the grid-like wall portions and the lower edge 53 of the upper pump housing 35. A plurality of vertical, radially spaced bafiie or web portions '79 along the circular concave surface of the body portion of the cover connect the upper rim 70 to the

wall portions

75, 76 and 77 and serve to reinforce the cover as well as to straighten the flow of liquid along that concave surface while improving the performance or output of the pump by preventing vortex effects of the liquid at the inlet to the axial flow pump impeller. Intermediate the adjacent grid-like wall portions, recesses or

slots

80, 81 and %2 (FIG. 3) are provided for reception of the respective mounting

legs

54, 55 and 56 of the upper pump housing 35. Thus, with the described pump inlet cover held in place by these legs and with these legs secured by bolts 32 to the end bell 31 of the motor housing and with the entire pumping assembly clamped in sealed relation to the lower wall 14 of the tub, as by the split clamping ring 83 seen in FIG. 2, a firm stationary mounting of the pump inlet cover for the axial flow pump, is obtained. Moreover, the fastening of the pump housing directly and rigidly to the end bell of the motor housing ensures accurate concentricity of the pump elements with respect to the motor which permits smaller manufacturing tolerances, improved efficiency, longer life expectancy of the rotating parts, and a less severe shaft sealing problem.

The

recesses

80, 81 and 82 of the grid-like wall portions thus described are provided with depending feet having hold-down seats or ledges on their upper surfaces, one of which is seen at 84 in FIG. 5, and against which an inner ledge on the corresponding mounting leg 56 of the upper pump housing abuts. Projecting downwardly from these seats are

short pegs

85, 86 adapted in turn to bear against the upper surface of the pump cover plate 42 for the drain pump 29 and to maintain that cover in properly centered position. A suitable gasket 9% underlies the periphery of the pump cover 42 to prevent the leakage of liquid therefrom. The grid-like wall portions, moreover, are formed with a plurality of individual struts or posts spaced from each other at a suitable distance as shown at 87, S8 and 89 to afford comparatively free flow of liquid and soft food therebetween, but to intercept large size hard objects which may enter the tub inadvertently.

' As will now be apparent, the comparatively large inlet to the axial fiow pump impeller 34, through both the space '78 and through the fence-

like wall portions

75, 76 and 77, communicates with the sump space 15; and at the same time the annular opening 43 below the body portion of the axial flow pump inlet cover 68 that Serves the drain pump communicates with the same sump space. As the motor turns in a first direction (counterclockwise) to cause the axial flow pump impeller 34 to draw liquid through its inlet, such liquid is trapped between the vertical stationary baffies 79, and the radial movement thereof is converted into a steady flow generally axially of the axial flow pump. At the same time, the concave surface of the inlet member directs the flow of the incoming liquid from anupper level of the sump space, and the lower portion of that same inlet member is so positioned that the flow of incoming liquid to the drain pump may take place from the lowermost level of the sump space. The liquid passing under the inlet cover 68 and into the drain pump thus submerges that pump and the pumping action of the larger axial flow pump therefore is unable to starve the smaller drain pump. As the motor turns in its second direction (clockwise), the axial flow pump may draw in air from the spray arm 58 and tube 65. and discharge the same laterally through space 78 or through the fence-like wall portions of the cover, but due to the presence of the concave upper portion of the cover 68 such air is directed away from the inlet 43 of the drain pump and will not interfere with the functioning of the drain pump during its draining action.

Having described above a novel pump mechanism with regards to the details of a preferred embodiment, it will readily be apparent to those skilled in this art that the pump inlet cover of this invention can be used alone with the axial flow pump without the incorporation of the lower drain pump. A reversible drive motor has been described, but a motor having but one direction of rotation could be used if a diverter valve were used with the two outlets of the drain pump to control the flow of liquid therethrough. In the drawing, the drain pump is illustrated as a centrifugal type pump but other vane type pumps could also be used to advantage here.

The production model of this invention handles a water load of between seventeen and twenty-two pints of water at a pumping rate in the washing direction of fifty-eight gallons per minute with a one-third horsepower motor at a load of seven hundred watts and a speed of 3450 r.p.m.

While we have shown and described particular embodiments of the invention, we do not desire the invention to be limited to the particular constructions disclosed, but rather we intend by the appended claims to cover all modifications within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In a dishwasher having a washing tube with a sump space for collecting washing liquid, a pumping mechanism including an axial flow pump having an inlet communicating with said space, a vane pump positioned below said axial flow pump and having an inlet communicating with said space, means for driving said pumps, an

upper pump housing enclosing said axial flow pump and having an outlet, a lower pump housing enclosing said vane pump and having an outlet, and a flow-directing pump inlet cover interposed between the respective housings of said pumps, said cover having an upper portion arranged to direct liquid from an upper level of said space into the inlet of said axial fiow pump, and said cover having a lower portion arranged for flow of liquid thereunder from a lower level of said space into said vane pump thereby to relieve said vane pump from liquid starving as liquid is simultaneously supplied from said sump space to each of said pumps.

2. Apparatus as defined in claim 1 wherein said upper portion of said cover is concave and includes substantially vertical baffles projecting radially of the axis of said axial flow pump, said baiiies being spaced from each other and positioned to prevent swirling of liquid entering said axial flow pump.

3. Apparatus as defined in claim 1 wherein said lower portion of said cover includes mounting feet radially spaced from each other and held in stationary position by said upper pump housing, the spaces between said feet' serving to communicate the inlet of said vane pump with said sump space.

4. A flow-directing cover for the inlet of an axial flow pump comprising a generally annular shaped member having a central aperture for receiving the shaft of said pump and defining an inner rim of said cover, a concave body portion extending from said rim to the periphery of said member, an apertured wall portion generally parallel to the axis of said aperture and projecting from said body portion on its concave side adjacent the periphery of said member, and baffles spaced from each other and extending radially along said concave body portion between said rim and said wall portion whereby liquid flowing through said Wall portion for entrapment of objects carried by said liquid may pass across said concave surface between said baffles and may be changed in direction from a flow generally spirally of said pump shart to a flow generally parallel to said pump shaft.

5. A cover as defined in claim 4 including a hollow bushing portion for surrounding said shaft, said bushing portion terminating at one end at said inner rim and having a sealing member adjacent its other end for contact with said shaft.

6. In a dishwasher having a washing tub with a sump space for collecting washing liquid, a pumping mechanism comprising a reversible motor having a shaft arranged to rotate in a first direction and in a second di rection, an axial flow pump driven by said shaft and having an inlet communicating with said space, a centrifugal pump driven by said shaft and positioned below said axial flow pump and having an inlet communicating with said space, an upper pump housing enclosing said axial flow pump and having an outlet, :1 lower pump housing enclosing said centrifugal pump and having a first outlet discharging into said tub and a second outlet discharging from said tub, and a flow-directing pump cover interposed between the respective housings of said pumps, said cover having a concave upper portion arranged to direct liquid from an upper level of said space into the inlet of said axial flow pump when said shaft is rotating in said first direction and to direct air pumped by said axial flow pump when said shaft is rotating in said second direction away from the inlet to said centrifugal pump, said cover having a lower portion arranged for flow of liquid thereunder from a lower level of said space into the inlet of said centrifugal pump when said shaft is rotating in either direction.

7. A washing compartment having a sump in the bottom thereof, an opening in the bottom of the sump, a pumping mechanism supported in the said opening, said pumping mechanism including a single driv motor, a vertical shaft driven by the motor, an axial flow pump supported within the sump and having an impeller mounted on the top end of the motor shaft, a vane pump located beneath the sump for use in draining the sump, the vane pump also having an impeller driven by the said motor shaft, and a pump inlet cover surrounding the motor shaft and fixed in position slightly above the bottom of the sump, the inlet for the axial fiow pump being above the pump inlet cover while the inlet for the vane pump is below the said inlet cover, a supplementary Washing system within the compartment, the vane pump having two separately controlled outlets, a first outlet connected with the supplementary washing system and a second outlet for draining the sump of liquid, so that during one operation of the pumping mechanism the axial flow pump recirculates liquid within the compartment While the vane pump delivers liquid through its first outlet only to the supplementary washing system, the second operation of the pumping mechanism preventing said axial flow pump from recirculating liquid within said compartment and causing the vane pump to deliver liquidthrough its second outlet for draining the sump completely.

8. A Washing compartment as recited in claim 7 wherein the single drive motor is a reversible motor which turns in one direction for the first-mentioned operation of the pumping mechanism and in the opposite direction for the second-mentioned or draining operation of the pumping mechanism.

9. A washing compartment as recited in claim 7 wherein the top surface of the said pump inlet cover is a circular concave surface which is directed horizontally inwardly into the axial fiow pump and then upwardly so that the liquid will be guided in its fiow 'therethrough, and a series of vertical radially spaced baflles rising from the top surface of the said cover for straightening out the flow of liquid and prevent swirling as it enters the axial flow pump.

10. A washing compartment as recited in claim 9 wherein the top surface of the pump inlet cover also includes a grid-like member adjacent the periphery of said cover for screening large foreign objects from entering the axial flow pump.

11. A Washing compartment as recited in claim 7 wherein the inlet for the vane pump is an annular opening having a slight clearance from the drive shaft of the motor so that large hard objects may not pass through the opening but soft food soil will accumulate in the vicinity of the opening during the draining operation, the soft food being agitated by the rotation of the drive shaft for mulching the food until the food is drawn through the opening and driven from the vane pump.

12. A washing compartment having a sump in the bottom thereof, an opening in the bottom of the sump, a pumping mechanism supported Within the sump above the opening and having an inlet adjacent the said opening, means located below the washing compartment for driving the pumping mechanism, said means including a vertical shaft extending through the sump opening and having an impeller of an axial flow pump on the top end thereof, a pump housing surrounding the impeller, a pump inlet cover supported in the pump inlet and fixed in position with respect to the pump housing, the pump inlet extending substantially completely around the pump housing, the inlet cover having a circular concave upper surface for directing liquid radially into the pump housing and then axially to the pump impeller, vertically-extending radiallyspaced baffles rising from the concave surface to straighten out the flow of liquid as it is drawn into the impeller, a filtering wall means arranged on the periphery of the pump inlet cover between the cover and the pump housing to govern the particle size of foreign matter entrained in the liquid that will pass through the pump, and pump inlet cover closely embracing the pump impeller to prevent air and liquid passing therebetween.

13. A Washing compartment as recited in claim 12 wherein the filtering wall means comprises a series of vertical posts arranged around the periphery of the pump inlet cover, and the center of the cover is in the shape of a hollow inverted truncated cone, the pump impeller having a lower converging shank for close-fitting engagement with the hollow cone of the pump cover to prevent air and liquid passing therebetween.

References Qited in the file of this patent UNITED STATES PATENTS 1,637,376 Gibney Aug. 2, 1927 1,817,328 Weimers Aug. 4, 1931 1,942,452 Rogers Jan. 9, 1934 2,023,107 Stoddard Dec. 3, 1935 2,054,797 Franklin Sept. 22, 1936 2,250,314 Rocke July 22, 1941 2,257,436 Walker Sept. 30, 1941v 2,305,136 Campbell Dec. 15, 1942 2,729,219 Smith Jan. 3, 1956 2,946,286 Sholtes et al July 26, 1960 2,959,179 Sasnett et al Nov. 8, 1960 FOREIGN PATENTS 649,783 Great Britain Jan. 31, 1951

Claims

7. A WASHING COMPARTMENT HAVING A SUMP IN THE BOTTOM THEREOF, AN OPENING IN THE BOTTOM OF THE SUMP, A PUMPING MECHANISM SUPPORTED IN THE SAID OPENING, SAID PUMPING MECHANISM INCLUDING A SINGLE DRIVE MOTOR, A VERTICAL SHAFT DRIVEN BY THE MOTOR, AN AXIAL FLOW PUMP SUPPORTED WITHIN THE SUMP AND HAVING AN IMPELLER MOUNTED ON THE TOP END OF THE MOTOR SHAFT, A VANE PUMP LOCATED BENEATH THE SUMP FOR USE IN DRAINING THE SUMP, THE VANE PUMP ALSO HAVING AN IMPELLER DRIVEN BY THE SAID MOTOR SHAFT, AND A PUMP INLET COVER SURROUNDING THE MOTOR SHAFT AND FIXED IN POSITION SLIGHTLY ABOVE THE BOTTOM OF THE SUMP, THE INLET FOR THE AXIAL FLOW PUMP BEING ABOVE THE PUMP INLET COVER WHILE THE INLET FOR THE VANE PUMP IS BELOW THE SAID INLET COVER, A SUPPLEMENTARY WASHING SYSTEM WITHIN THE COMPARTMENT, THE VANE PUMP HAVING TWO SEPARATELY CONTROLLED OUTLETS, A FIRST OUTLET CONNECTED WITH THE SUPPLEMENTARY WASHING SYSTEM AND A SECOND OUTLET FOR DRAINING THE SUMP OF LIQUID, SO THAT DURING ONE OPERATION OF THE PUMPING MECHANISM THE AXIAL FLOW PUMP RECIRCULATES LIQUID WITHIN THE COMPARTMENT WHILE THE VANE PUMP DELIVERS LIQUID THROUGH ITS FIRST OUTLET ONLY TO THE SUPPLEMENTARY WASHING SYSTEM, THE SECOND OPERATION OF THE PUMPING MECHANISM PREVENTING SAID AXIAL FLOW PUMP FROM RECIRCULATING LIQUID WITHIN SAID COMPARTMENT AND CAUSING THE VANE PUMP TO DELIVER LIQUID THROUGH ITS SECOND OUTLET FOR DRAINING THE SUMP COMPLETELY.