US3659955A

US3659955A - Device for automatically stopping delivery of liquid by a centrifugal pump during reverse operation thereof

Info

Publication number: US3659955A
Application number: US841299A
Authority: US
Inventors: Siegfried Schonwald
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1968-07-13
Filing date: 1969-07-14
Publication date: 1972-05-02
Anticipated expiration: 1989-05-02
Also published as: CH492880A; GB1217460A; SE354689B; NL6909152A; FR2014590A1; DE1703815B2; DE1703815A1; GB1213448A; CH503907A

Abstract

Device for automatically stopping delivery of liquid by a centrifugal pump operating in reverse running condition through the introduction of air into the pump chamber of the pump includes means defining a bore formed in the housing of the pump for connecting the pump chamber to atmosphere, and means cooperating with the bore-defining means for adjusting the pressure in the pump chamber to positive pressure in forward running condition of the pump rotor and to negative pressure in reverse running condition thereof whereby in the latter condition air is sucked from the atmosphere into the pump chamber to stop delivery of liquid by the pump.

Description

United States Patent Schiinwald [54] DEVICE FOR AUTOMATICALLY STOPPING DELIVERY OF LIQUID BY A CENTRIFUGAL PUMP DURING REVERSE OPERATION THEREOF [72] Inventor: Siegfried Schiinwald, Bad Neustadt, Saale,

Germany [73] Assignee: Siemens Aktiengesellschaft, Berlin, Germany [22] Filed: July 14,1969

[21] App1.No.: 841,299

[451 May 2,1972

Primary Examiner-Henry F. Raduazo Attorney-Curt M. Avery, Arthur E. Wilfond, Herbert L. Lerner and Daniel J. Tick 5 7] ABSTRACT Device for automatically stopping delivery of liquid by a centrifugal pump operating in reverse running condition through the introduction of air into the pump chamber of the pump includes means defining a bore formed in the housing of the pump for connecting the pump chamber to atmosphere, and means cooperating with the bore-defining means for adjusting the pressure in the pump chamber to positive pressure in forward running condition of the pump rotor and to negative pressure in reverse running condition thereof whereby in the latter condition air is sucked from the atmosphere into the pump chamber to stop delivery of liquid by the pump.

12 Claims, 6 Drawing Figures DEVICE FOR AUTOMATICALLY STOPPING DELIVERY OF LIQUID BY A CENTRIFUGAL PUMP DURING REVERSE OPERATION THEREOF My invention relates to device for automatically stopping delivery of liquid by a radial centrifugal pump having a spiral housing, during reverse operation of the pump, by introducing air into the pump chamber.

A centrifugal pump of radial construction delivers liquid, during reverse rotation of the pump rotor, in the same flowthrough direction as during nonnal or forward rotation of the pump rotor, although with markedly reduced pumping power. This delivery of liquid during reverse operation of the pump must be stopped if, for example, a second pump assembly operates from the same drive shaft as the first-mentioned pump and is dependent on rotary direction, as is, for example, the case with circulating and draining or discharge pumps of dishwashing machines, A further requirement is that the delivery of liquid should stop from the very instant that the pump is switched from forward to reverse operation so that as little liquid as possible leaves the pump at the pressure side thereof.

The delivery of a centrifugal pump having suction tubes to which liquid, such as, water, runs, can be stopped by partly filling the rotor chamber thereof with air. Since the liquid, such as water, present in the pump chamber forms a circulating ring due to centrifugal action, the air tends to keep to the inner rotor space. Consequently, only a relatively small pressure increase is possible from the rotor inner diameter to the rotor outer diameter; the liquid (water) flowing to the suction tubes cannot penetrate into the rotor chamber.

This operating condition of the pump is known as snapping-off." The problem that is thus presented is to bring the pump to a rapid snapping-off" condition during reverse operation thereof even when the suction tube is full, yet not prevent this effect from occuring when the pump is in forward operation,

ln this regard, it has become known to insert into the liquid flow a dynamic pressure or backpressure tube which is connected to the outer air. During reverse rotation of the pump rotor, air is sucked from the outside into the pump housing through this tube by a sort of jet pump action, and the delivery of liquid is thereby stopped; during forward rotation of the rotor, the liquid accumulates at the tube so that a small portion thereof can leave the pump chamber. Such an arrangement is disadvantageous however, inasmuch as the liquid flow is disturbed by the dynamic pressure tube under certain conditions during forward rotation of the pump rotor; and because there is constant danger of obstruction of the quite narrow dynamic pressure tube by dirt which is present in the liquid i.e., water, as for example in the case of circulating pumps. Furthermore, due consideration must be given to the fact that the dynamic pressure tube is relatively costly.

lt is accordingly an object of my invention to provide device for automatically stopping delivery of liquid by a centrifugal pump during reverse operation of the latter which avoids the disadvantages of the heretofore known devices for effecting this purpose. More specifically, objects of my invention are to provide such device which will not disturb liquid flow during forward rotation of the pump rotor, which will not present any danger of obstruction, and which will moreover be relatively inexpensive.

With the foregoing and other objects in view, I provide, according to my invention, device for automatically stopping delivery of liquid by a centrifugal pump during reverse operation thereof by introducing air into the pump chamber of the pump, comprising means defining a bore formed in the housing of the pump for connecting the pump chamber of the pump to atmosphere, and means cooperating with the boredefining means for adjusting the pressure in the pump chamber to positive pressure in forward running condition of the pump rotor and to negative pressure in reverse running condition thereof, whereby in the latter condition air is sucked from the atmosphere into the pump chamber to stop delivery of liquid.

In accordance with another feature of my invention, the bore is formed in a surface of the pump housing that is sub jected to flow dependent upon rotational direction, and a bulge is provided upstream of the bore in the reverse rotating direction of the pump rotor. In the forward running condition of the rotor, the liquid flow adjacent the surface of the pump housing is blocked by and accumulates at the bulge so that a positive pressure is produced at the bore opening in the pump chamber. In the reverse running condition of the rotor, the liquid flow adjacent the surface of the pump housing is accelerated as it flows over the bulge so that a negative pressure is produced at the bore opening in the pump chamber.

In accordance with a further feature of the invention, the bulge extends partly around the bore.

At locations at which a bulge projecu'ng out of the housing wall would have a disturbing efiect, such as for example in the space between the housing wall and the pump rotor, the flow device comprising the bulge and the bore-defining means are recessed in the housing wall. Thus, two pockets are machined or otherwise formed in the housing wall, a bulge being left between the pockets. The bore is located at an end of one of the pockets adjacent the flow-engaging surface of the bulge, which has a steep construction, The surface of the bulge facing away from the bore slopes upwardly from the other pocket. The side surfaces of the pockets, in accordance with another feature of the invention, have an upwardly opening funnel shape so as to be able to capture as much liquid as possible.

In accordance with additional features of my invention, the bore-defining means extend transversely to the rotational plane of the pump rotor and are located within the confines of an angle located between the minimum of the local meridian velocity as the leading limiting edge thereof in the rotational sense of the rotor in the reverse running condition thereof and the maximum of the local meridian velocity as the trailing limiting edge thereof. In other words, the bore is located in a region of the space occupied by the rotor wherein, in the reverse running condition of the centrifugal pump, the lowest pressure from the inner to the outer diameter of the rotor occurs. This region is characterized by a minimum of the local meridian velocity as a forward or leading limit in the rotational direction of the rotor in the reverse running condition thereof and a maximum of the local meridian velocity as a rear or trailing limit. This region corresponds substantially to the confines of the angle respectively 15 forward of to 35 behind the tongue point or the narrowest cross section between the housing wall and the rotor or the location of the smallest angle between the housing wall and the radius vector to the housing wall.

A centrifugal pump of radial construction with a rotor and spiral housing is conventionallydesigned so that above the rotor space, relative to the rotor, a symmetrical source or intake flow of liquid occurs i.e., the flow velocities or accelerations in concentric or coaxial circles in the rotor space are constant. In reverse running condition of the pump, the flow pattern over the rotor assumes a completely different, nonsymmetrical shape due to superimposition of two flow fields, Also, in reverse rotating condition of the rotor, there is present a source or intake flow symmetrical to the rotor yet having a reduced source magnitude. This flow is superimposed by a second velocity field oscillating relative to the rotor due to the guidance of liquid in the spiral housing. This superimposed velocity, however, in the end region of the narrowing spiral and as a result of the mass moment of inertion is directed inwardly a short distance after the tongue point and outwardly in the remaining part thereof. The meridian velocity of the entire flow is accordingly a minimum for example, in the immediate vicinity of the tongue. The meridian velocity increases to a maximum behind the tongue in the vicinity of the pressure tube extension and until entering the spiral. In this region of radially outwardly directed acceleration, the pressure gradient is a minimum i.e., the pressure at farther radially outward locations of the housing is only slightly greater or even lower than in the suction opening of the pump. If, for example, the bore were provided at that location, negative pressure would occur in the reverse running condition of the pump and air would be sucked into the pump chamber so that the pump would then snapoff. In forward running condition of the pump, by contrast, the normal positive pressure corresponding to the centrifugal field prevails at this bore so that liquid is delivered through this bore and no air at all is aspirated.

The pressure reduction adjusted between the minimum and the maximum of the meridian velocity for reverse rotational direction of the rotor can be increased if the intermediate region is shortened in the rotational direction, and a greater radial acceleration is thereby produced. In this regard, according to my invention, the narrowing spiral is sharply inwardly bent at the tongue. The minimum of the meridian velocity is thereby lowered more deeply and is displaced toward the pressure tube extension. To intensify the pressure increase or decrease, the bore in the pump housing is additionally surrounded by flow guides open to the main liquid flow, in accordance with another feature of my invention. Thus, for example, the bore in the housing wall is provided with the aforementioned bulge at one side thereof which, in another embodiment of the invention, partly surrounds the bore so as to increase the blocking of the liquid and thereby the positive pressure at the bore in the forward running condition of the pump.

The aforedescribed flow device including the bore-defining means for admitting air to the pump chamber is not limited only to the aforedescribed region of alternating pressure but rather can actually be applied to all surfaces of the pump housing subjected to flow dependent upon rotational direction. Especially advantageous is, of course, the effect at a location at which the pressure, in the reverse running condition of the pump, is in any case already lower than in the forward running condition of the pump. Such a region is found, as aforementioned, transversely to the plane of rotation of the rotor in vicinity of the pressure tube extension at the spiral.

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in device for automatically stopping delivery of liquid by a centrifugal pump during reverse operation thereof, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a partly diagrammatic plan view of the pump of my invention with the housing cover thereof removed;

FIG. 2 is a plan view of the housing cover removed from the housing of FIG. 1;

FIGS. 3a and 3b are a top plan view and a longitudinal sectional view, respectively, of one embodiment of the flow guiding device of my invention wherein the bulge and bore thereof are recessed in the housing wall of the pump; and

FIGS. 4a and 4b are a top plan view and a longitudinal sectional view, respectively of another embodiment of FIGS. 3a and 3b wherein the bulge projects from the housing wall of the pump.

Referring now to the drawings and first particularly to FIGS. 1 and 2 thereof, there is shown a centrifugal pump having a rotor l which, in forward rotating condition thereof, rotates in the direction of the arrow 20, and liquid, such as water, is flung centrifugally outwardly from the suction opening 3 into the channel 4 widening outwardly spirally between the rotor l and the housing wall 13, and is discharged from the pump through the pressure tubes 5.

Even in the reverse running condition of the rotor l in direction of the arrow 2b, liquid continues to be delivered although in much-reduced quantity. In order to stop this delivery of liquid, a bore 7 is formed in the pump housing cover 6, and can be connected by a tube to the inner chamber of a dishwashing machine, for example.

The optimum location of the bore is dependent in a known manner upon the construction of the pump. lts exact position is variable for example, in accordance with the amount of bend in the point of the tongue 8 forming part of the pump housing.

In FIG. 1 there is shown in single-line hatching a region 9 of the pump substantially wherein a bore will produce the desired effect for a centrifugal pump of the illustrated type. This region 9 is radially inwardly limited by the fact that negative pressure prevails at this inner limit both in the forward as well as the reverse operating conditions of the rotor 1, while the region 9 is limited radially outwardly by the fact that no adequate pressure reduction is realized any longer at this outer limit in the reverse operating condition of the rotor.

If the radius between the rotor axis and the hook-shaped inwardly bent point of the tongue 8 is taken as a reference line, the bore 7, in the structure of the embodiment shown in FIG. 1, is located on a radius angularly displaced 25 from the reference radius in the reverse running direction of the rotor l, and actually still within the confines of the space occupied by the rotor 1.

To increase the positive pressure and to reduce the negative pressure at the bore 7, additional flow guides are provided as shown in FIGS. 30, 3b and 4a, 4b.

In FIGS. 3a and 3b there is shown one embodiment of the flow guide according to my invention wherein two pockets [0 and 11 are machined or otherwise formed in the inner surface of the cover 6 of the pump housing, a bulge 12 being left between the two pockets. A bore 7 is located at one end of the pocket 11 adjacent the flow-engaging surface of the bulge 12, which has a steep construction. The surface of the bulge 12 facing away from the bore 7 extends upwardly at an inclination from the other pocket 10. The side surfaces of the

pockets

10 and 11 are funnel-shaped and open upwardly as viewed in FIG. 3b so as to capture as much of the liquid in the pump, as possible. As seen in FIG. 3b, both the bulge l2 and the bore 12 are thus recessed in the housing cover 6.

Under certain conditions, the aforedescribed flow device can be dispensed with, in fact when the bore is formed in a recess which has inclined side surfaces in the reverse running direction of the rotor. The bore and the non-illustrated tube connected thereto are thereby prevented from filiing with spray water in the reverse running condition of the pump.

In the embodiment of the flow device shown in FIGS. 40 and 4b there is provided a bore 7 formed in the housing cover 6. In front of the bore 7, as viewed in the forward running condition of the rotor represented by the arrow 30 there is provided a bulge 22 which partly surrounds the bore 7. In the forward running direction shown by the arrow 30, the liquid flow adjacent the surface of the housing wall and cover accumulates at the bulge 22 so that a positive pressure is produced at the bore 7. Consequently, in the forward running direction of the rotor, only water is delivered but no air is aspirated into the pump. In the reverse running condition of the rotor represented by the arrow 3b, the liquid flow adjacent the housing wall and cover is accelerated as it flows over the bulge 22 so that a negative pressure is produced at the bore 1 through which air is sucked into the pump from the outer atmosphere. The pump accordingly snaps off" and the delivery is immediately and abruptly interrupted.

It must again be emphasized that for the aforedescribed pump, the regions at which the bore may be located approximately coincide. By suitable selection of the shape of the pump housing, it is possible however to spread out these regions i.e., to locate the bore at nearly any desired position of the periphery thereof, for example at a location at which the radius vector r forms the smallest angle a with the tangent to the wall of the housing, as shown in FIG. 1, or where the channel 4 is at its narrowest.

I claim:

1. Device for automatically stopping delivery of liquid by a centrifugal pump having a spiral housing provided with a transverse side wall and a rotor with an open blading rotatably mounted therein and operating in reverse running condition through the introduction of air into the pump chamber of the pump comprising a tongue formed on the spiral housing and projecting adjacent the periphery of the rotor, means defining a bore formed in the side wall of the housing of the pump for connecting the pump to atmosphere, said means having an abrupt projecting surface engageable by the liquid in forward running condition of the pump and a smooth inclined surface, located opposite said abrupt projecting surface, and engageable by the liquid in reverse running condition of the pump, said bore extending transversely to the rotational plane of the pump rotor and communicating with the open blading of said pump rotor, said bore being located within the peripheral area covered by the rotor blading and said location being within the confines of an angle forward of to 35 behind said tongue in the forward running condition of the pump.

2. Device according to claim 1 including means cooperating with said bore-defining means for adjusting the pressure in the pump chamber to positive pressure in forward running condition of the pump rotor and to negative pressure in reverse running condition thereof whereby in the latter condition air is sucked from the atmosphere into the pump chamber to stop delivery of liquid by the pump.

3. Device according to claim 2 wherein said pressure adjusting means comprises a bulge located in fluid flow stream of the pump upstream of said bore in the reverse running condition of the pump.

4. Device according to claim 3 wherein said bulge partly surrounds said bore.

5. Device according to claim 3 wherein two pockets are fonned in the surface of the pump housing, located between said pockets.

6. Device according to claim 5, wherein said bore is recessed in one of said pockets adjacent said bulge, the side of said bulge facing said bore having a steep liquid-engaging surface, and the side of said bulge facing away from said bore extending outwardly at an inclination from the other of said pockets.

7. Device according to claim 6 wherein said pockets have side walls opening outwardly in the shape of a funnel.

8. Device according to claim 7 wherein said bore is located in a recess formed in the side wall of the pump housing, said recess having inclined wall surfaces extending in the reverse running direction of the pump rotor.

9. Device according to claim 1 wherein the spiral pump housing is formed with a tongue disposed adjacent the periphery of the pump rotor, said bore being located on a radius of the rotor displaced substantially through an angle of 25 from a radius of the rotor passing through the tip of said tongue as viewed in reverse running direction of the rotor.

10. Device according to claim 9 wherein the spiral housing has a construction wherein an angle a between a tangent to the spiral of the housing and a radius r located at the vicinity of said tongue is smaller than at the remaining periphery of said spiral.

11. Device according to claim 9 wherein the tip of said tongue has a hook-like radially inward bend.

12. Device according to claim 1 wherein the bore formed in said pump housing is surrounded by flow guide means open in direction toward oncoming main liquid flow, said flow guide means, in forward running condition of said rotor, being adapted to produce positive pressure at said bore and, in reverse running condition of said rotor, to produce negative pressure at said bore.

said bulge being i t i k lOlDJl 056i

Claims

1. Device for automatically stopping delivery of liquid by a centrifugal pump having a spiral housing provided with a transverse side wall and a rotor with an open blading rotatably mounted therein and operating in reverse running condition through the introduction of air into the pump chamber of the pump comprising a tongue formed on the spiral housing and projecting adjacent the periphery of the rotor, means defining a bore formed in the side wall of the housing of the pump for connecting the pump to atmosphere, said means having an abrupt projecting surface engageable by the liquid in forward running condition of the pump and a smooth inclined surface, located opposite said abrupt projecting surface, and engageable by the liquid in reverse running condition of the pump, said bore extending transversely to the rotational plane of the pump rotor and communicating with the open blading of said pump rotor, said bore being located within the peripheral area covered by the rotor blading and said location being within the confines of an angle 15* forward of to 35* behind said tongue in the forward running condition of the pump.

4. Device according to claim 3 wherein said bulge partly surrounds said bore.

5. Device according to claim 3 wherein two pockets are formed in the surface of the pump housing, said bulge being located between said pockets.

9. Device according to claim 1 wherein the spiral pump housing is formed with a tongue disposed adjacent the periphery of the pump rotor, said bore being located on a radius of the rotor displaced substantially through an angle of 25* from a radius of the rotor passing through the tip of said tongue as viewed in reverse running direction of the rotor.

10. Device according to claim 9 wherein the spiral housing has a construction wherein an angle Alpha between a tangent to the spiral of the housing and a radius r located at the vicinity of said tongue is smaller than at the remaining periphery of said spiral.