Abstract:
An impeller plate of an impeller of a centrifugal pump, particularly a channel impeller pump, for pumping liquids with solid or gaseous admixtures, is provided with at least one wide vane that is displaced toward the impeller drive by a distance  D  so that the impeller chamber is enlarged by a rearward portion thereof. In addition, the impeller comprises at least one auxiliary vane having a center width at between 25%-75% of the width of the wide vane. This arrangement improves particularly the gas transporting ability of the pump.

Description:
BACKGROUND OF THE INVENTION 
     The present invention refers to a centrifugal pump for pumping liquids with solid or gaseous admixtures, more particularly a channel impeller pump, and particularly concerns the impeller and the chamber in which it rotates. 
     CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a 35 U.S.C. §§371 national phase conversion of PCT/CH2005/000337, filed Jun. 16, 2005. The PCT International Application was published in the German language. 
     In known pumps of this type, the cross-sections of the channels between the vanes of the impeller are designed so as to allow the passage of relatively large solid bodies. This implies a construction where the channel impellers generally comprise only 1 to 3 vanes. Channel impeller pumps are successfully used for pumping liquids that are charged with thick matter, sludge, slags, etc. Their ability to expel gaseous accumulations (including air), however, is limited as in other centrifugal pumps too. 
     The underlying aim of the invention is to provide a centrifugal pump whose ability to expel gaseous accumulations is significantly improved. 
     Centrifugal pumps or channel impeller pumps having satisfactory specific characteristics for solving this problem are not known to the inventor. 
     Since this class of pumps is not comparable to free-flow pumps on account of their different operating modes, measures for modifying their properties are generally not transferable from one to another. 
     A free-flow pump has an impeller chamber in which an impeller is arranged and a vortex chamber that extends in front of the impeller chamber and is not swept by the vanes. 
     The liquid enters into the vane channels axially from the front side of the impeller near the hub thereof, moves outwards on an arc of nearly 180°,and leaves the impeller again in its outer area in an axial, however opposite direction on the front side thereof. The exiting liquid sets the liquid mass in the vortex chamber into rotation by pulse transmission. As described in DE 34 08 810 C2,individual wider vanes are used in order to improve the coupling effect with the liquid mass in the vortex chamber. Due to the path that the liquid follows through the impeller, an enlargement of the vanes, which must be kept within certain limits in any case, also amounts to a lengthening of the vanes as measured along the flow path. 
     The centrifugal pump, more particularly channel impeller pump, that is known per se in the prior art, has an impeller chamber in which an impeller is arranged but, in contrast to free-flow pumps, has no vortex chamber. 
     In a known manner, the ability to expel gas inclusions with the liquid increases with the flow velocity and the flow turbulence of the medium along its way through the pump. In other words, an increase of this velocity might therefore constitute an apparent possible solution to the encountered problem. In view of the fact that solids have to be transported along with the liquid, and of the resulting constructive requirements, the approach using an increased flow velocity proves unpractical. 
     Only through numerous and varied tests was it finally discovered that the ejection of gaseous admixtures in the liquid is sensibly improved by several features. The impeller plate, which supports the vanes, is set back or rearward more than in prior art pumps and extends into a rearward impeller chamber that has a volume corresponding to the distance to the rear. The forward impeller chamber receives the front region of the impeller. Also, the objective is achieved without a reduction of the free passage, which is an indispensable general condition as it is required to pump the solids contained in the liquid. 
     On this basis, the features defined in the dependent claims represent particularly advantageous embodiments of the invention since they produced even better results with regard to the problematic gas transport and ultimately to the general efficiency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Flow phenomena, particularly those taking place in centrifugal pumps, can often only be detected empirically and are barely reproducible or comprehensible mathematically and physically. The interior of the correspondingly redesigned casing of the centrifugal pump of the invention is now comprised of a forward cavity and of a rearward cavity separated from the former by a virtual plane. The forward cavity that forms the original impeller chamber holds the forward portion(s) of the vane(s) while the impeller plate and the rear portion(s) of the vane(s) connected thereto are accommodated in the rearward cavity. It can be assumed that due to this novel arrangement of the impeller and the resulting chamber differentiation and enlargement, the centrifugal effect produced in the forward chamber extending between the liquid entrance and its exit is destroyed, i.e. the formation of a liquid ring inside which gas accumulates and which prevents a further continuous entry of the liquid to be conveyed, while a certain vortex or turbulence is formed instead. Furthermore, due to a slow flow-through velocity, it is believed that there is probably a flow breakaway on the suction side of the vanes. Finally, the pump of the invention is characterized by an even higher efficiency as compared to prior art pumps for media containing gases. 
       The results could be further improved by providing the impeller with auxiliary vanes in addition to the regular vanes. The auxiliary vanes have an axial width of about 25% to 75% of the center width of the regular vanes. Here, in fact, the liquid molecules and the solids will impinge on the leading edge(s) of the auxiliary vane(s) while it is noted that the advantage resulting from the improved gas distribution that is achieved outweighs the disadvantage incurred by the frictional forces produced by the additional friction surfaces of the auxiliary vanes by far. 
       Three preferred exemplary embodiments of the invention will be described in more detail hereinafter with reference to the drawing. Schematically, 
         FIG. 1  shows a sectional view of a first embodiment of the channel impeller, or centrifugal pump of the invention, 
         FIG. 2  shows a sectional view of a second embodiment of this pump, 
         FIG. 3  shows a perspective view of a variant of an impeller having three auxiliary vanes intended for the second embodiment, and 
         FIG. 4  shows a sectional view of a third embodiment of the pump. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     As shown in  FIG. 1 , an impeller  10  is enclosed in a casing  1  having a liquid entrance  2  and exit  3 , i.e. an intake and an outlet opening. Impeller  10  is fastened to a shaft  60  that is drivable by a non-represented motor. Casing  1 , impeller  10 , and shaft  60  have a common symmetry axis  1 A. The interior  6  of casing  1  is comprised of a forward cavity  5 A comprising a collecting chamber  4  that extends in the form of an annular space or spiral, and a rearward cavity  5 B separated therefrom by a virtual plane {T} . This plane {T} approximately coincides with the (non-referenced) plane that contains the (also non-referenced) generating line of opening  3  and extends orthogonally to symmetry axis  1 A. 
     Impeller  10  comprises an impeller plate  11  carrying preferably curved vanes  15  whose number is determined according to the size of the solids, and having a forward  12  and a rearward surface  13 . Generally, as mentioned above, one to three vanes are provided (see also  FIG. 3 ). Forward portion  15 F and rearward portion  15 R of vane(s)  15  extend in forward chamber portion  5 A and in rearward chamber portion  5 B of casing  1 , respectively. Forward edge  16  of vane  15  may move in immediate proximity past the inner surface  7  of casing wall portion  7 A extending around the inlet. Due to this proximity, a certain sealing effect is achieved as the distance between the mentioned surface and the mentioned forward edge is of the order of tenths of millimeters and generally smaller than 0.5 mm. Peripheral edge  17  of forward portion  15 F of vanes  15  may pass near liquid exit  3 . A rotation-symmetrical casing surface  8 ,  8 A of casing  1 , which surface is defined depending on the particular construction of the pump, encompasses impeller plate  11  in a preferably tight manner (i.e. in the order of some millimeters), i.e. the peripheral surface  14  thereof and the peripheral edges  17  of vanes  15 , respectively of rearward portions  15 R of these vanes, which in the example are flush with that surface. In the embodiment illustrated in  FIG. 1 , surface of revolution  8  extending around impeller plate  11  is cylindrical, whereas surface of revolution  8 A is e.g. cylindrical (in  FIG. 1 , this contour is merely symbolized by a dotted line) or conical with a cone angle of 2γ, the angle γ preferably being ≦ (smaller than or equal to) 20°. The choice of the impeller construction, more particularly of peripheral edges  17  and of peripheral surface  14 , is determined in view of the specific rotation speed n q  in a manner known to those skilled in the art. 
     In the conventional centrifugal or channel impeller pumps, the impeller plate is arranged such that its front surface is located at least approximately in the virtual plane {T} while the vanes extend entirely in the impeller chamber that is situated in front of this plane {T}. Now, in contrast to these pumps of the prior art, surface  12  of impeller plate  11  is rearwardly displaced, i.e. toward the drive, by a distance D while the vanes are enlarged by this distance (portion  15 R of the vanes) and the original impeller chamber  5 A is enlarged by an additional impeller chamber portion  5 B having a volume that corresponds to the distance D. The tests have shown that the distance D should be comprised within a range of 25% to 75% of the total axial direction width of vanes  15 , preferably approx. 50% of the mentioned total width. 
     Rearward surface  13  of impeller plate  11  may be located in immediate proximity of surface  9  of rear wall  9 A of casing  1 . According to a variant, however, a larger distance may be left between surfaces  13 ,  9  in order to make room for ridges  18  (on surface  13 ) or  19  (on surface  9 ) provided on one and/or the other of these surfaces. Ridges  18  that are known in the art per se may be curved radially or e.g. similarly to vanes  15  (see  FIG. 3 , reference numeral  23 ). Ridges  19  that are not known in the art, in contrast, preferably extend radially and fulfill the function of a swirl brake, prevent a centrifuge effect, and thus ensure a better gas flow. 
     In  FIG. 2 , a second embodiment is illustrated which, in comparison to the first or basic embodiment described above, comprises the same casing  1  but has an impeller  20  that is driven via shaft  60  and whose impeller plate  21  is provided with a vane system  25 . On one hand, this vane system consists of at least one vane  25 L that is identical to vane  15  or at least similar in width and whose forward edge  26 A is arranged to move in immediate proximity past inner surface  7  of forward wall portion  7 A of casing  1 , and on the other hand, additionally of at least one narrower, preferably curved auxiliary vane  25 S that extends at least partially in the rearward impeller chamber  5 B. This means that forward edge  26 B of this auxiliary vane  25 S may be located in virtual plane {T} or in a plane that is situated in immediate proximity to this plane {T}. The latter may be flat and parallel or inclined with respect to plane {T}, or curved. In other words, edges  26 B may be orthogonal to symmetry axis  1 A or may have another shape and may e.g. rise outwardly or inwardly (by way of illustration, dotted line  26 C shows a possible tapering shape of the forward edge of auxiliary vanes  25 S). 
     The distance D between forward surface  22  of impeller plate  21  and forward edge  26 B, which corresponds to the axial direction width (or center width, determined on half of the radius of the impeller plate approximately) of auxiliary vanes  25 S, should be comprised within a range of 25% to 75% of the total width Bg of wide vanes  25 L, preferably 50% of that total width, so that vanes  25 S essentially extend in rearward impeller chamber  5 B only. 
     As shown in a perspective view in  FIG. 3 , impeller  20  of this second embodiment may preferably comprise three wide vanes  25 L and three narrower auxiliary vanes  25 S, auxiliary vanes  25 S being each arranged between two respective vanes  25 L. 
     Peripheral surface  24  of impeller plate  21 , peripheral edges  27 L of wide vanes  25 L, and peripheral edges  27 S of narrower auxiliary vanes  25 S are located on the same non-represented cylindrical or conical or otherwise shaped rotation-symmetrical circumferential surface and are closely encompassed by the rotation-symmetrical casing surface  8 ,  8 A of casing  1  in a similar manner as described in the first embodiment. 
     Here also (i.e. similarly as in the first embodiment), rearward surface  23  of impeller plate  21  may be located in immediate proximity of surface  9  of rear wall  9 A of casing  1 , or according to a variant, a larger distance may be provided between these surfaces  23 ,  9  in order to leave enough space for arranging preferably radially extending ridges  28  (on surface  23 ) or ridges  29  (on surface  9 ) on one and/or the other of these surfaces. 
     In the third embodiment illustrated in  FIG. 4 , an impeller  30  having an axis  100 A and being connected to shaft  60  is enclosed in a casing  100  having a liquid entrance  102  and exit  103 . Casing  100  is similar to casing  1  and includes a forward chamber  105 A surrounded by a collecting chamber  104  that is similarly shaped as collecting chamber  4  and a rearward chamber  105 B separated therefrom by a virtual plane {T}. 
     Impeller  30 , which is set back by the distance D, has a vane system  35  connected to impeller plate  31  that is comprised of at least one wide vane  35 L and at least one narrow auxiliary vane  35 S, and preferably, as mentioned with reference to the second embodiment, of three of each. Auxiliary vanes  35 S may be similarly shaped as auxiliary vanes  25 S, only a forward edge  36 B being illustrated here. 
     Auxiliary vanes  35 S and impeller plate  31  are encompassed by an outer ring  34 . Inner surface  34 B of ring  34  may be conically shaped with a cone angle of 2γ (where γ is preferably ≦20°). Impeller plate  31 , ring  34  and auxiliary vanes  35 S connected thereto extend within impeller chamber  105 B. Peripheral edges  37 L, which are movable past liquid exit  103  in relative proximity thereto, may be parallel or inclined with respect to symmetry axis  100 A or may be differently shaped. 
     Forward edges  36 A of wide vanes  35 L are covered by a cover disk  40 . The latter is rotatably supported in a ring  110  that is press-fitted in a sealing gap  111  near entrance  102  of casing  100 . Forward surface  41  of cover disk  40  may move in immediate proximity past surface  107  of wall portion  107 A. This cover disk, known in the art per se, is often provided for reasons of stability or in pumps having a low specific rotation speed n q . 
     Similarly as in the first embodiment, rearward surface  33  of impeller plate  31  may be located in immediate proximity of surface  109  of rear wall  109 A of casing  100 , or according to a variant, a larger distance may be provided between these surfaces  33 ,  109  in order to leave enough space for arranging preferably radially extending ridges  38  (on surface  33 ) or ridges  39  (on surface  109 ) on one and/or the other of these surfaces. 
     Furthermore, impeller plate  31  may be provided with at least one hole  45 . According to the example, three or six bores  45  with axes  45 A are arranged between vanes  35 L and auxiliary vanes  35 S and are correspondingly dimensioned. Axes  45 A extend in parallel to axis  101 A at a distance R. The measurement of radius R is preferably chosen such as to be comprised in an interval between half and two thirds of the circumferential radius of the impeller plate approximately. It has been found that these holes  45  sensibly improve the efficiency of the outward gas discharge. 
     It is understood that further preferred embodiments can be realized in which features of the described embodiments are combined. In particular, it is possible to provide impellers  11  and  21  according to the first and the second embodiment with individual or even all additional features of impeller  30  described with reference to  FIG. 4 , i.e. outer ring  34 , bores  45 , cover disk  40 , or with further features within the knowledge of those skilled in the art. 
     From the foregoing description, further modifications and variations are apparent to those skilled in the art without leaving the protective scope of the invention as defined by the claims.