Abstract:
The invention relates to an apparatus for sealing a pump chamber of a rotary lobe pump vis-a-vis a fluid-free region of the rotary lobe pump, in particular in the region of a shaft duct, wherein the apparatus has two or more sealing elements, which can be disposed adjacent to a front side of a rotary piston disposed on a shaft in the pump chamber of the rotary lobe pump in such a way that a labyrinth gap extends between the sealing elements, said labyrinth gap being arranged in a radial direction relative to the shaft and in an axial direction in order to extend the seal land. According to the invention, the seal land is larger in a radial direction relative to the shaft than the seal land in an axial direction relative to the shaft.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. national phase of International Application No. PCT/EP2012/058783 filed on May 11, 2012, which application claims priority to German Patent Application No. 20 2011 100 622.4 filed on May 12, 2011, the contents of both of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to an apparatus for sealing a pump chamber of a rotary lobe pump vis-a-vis a fluid-free region of the rotary lobe pump, in particular in the region of a shaft duct, wherein the apparatus has two or more sealing elements, which can be disposed adjacent to a front side of a rotary piston disposed on a shaft in the pump chamber of the rotary lobe pump in such a way that a labyrinth gap extends between the sealing elements, said labyrinth gap being arranged in a radial direction relative to the shaft and in an axial direction in order to extend the seal land. 
     The invention further relates to a rotary lobe pump for conveying fluids, in particular liquids containing solids, having a housing with a pump chamber and at least one pair of interlocking rotary pistons disposed inside the pump chamber, which are each mounted on a shaft, wherein the shaft extends out of the pump chamber into a fluid-free region of the rotary lobe pump. 
     Within the context of this description, axial is understood to be the orientation in the direction of the rotational axis of the piston or pistons respectively, which is also the shaft axis. 
     BACKGROUND OF THE INVENTION 
     In order to protect the functionality of known rotary lobe pumps, it is necessary to isolate fluid-free regions of the rotary lobe pump, for example areas containing gearing or bearings, from the fluid-conducting pump chamber by means of sealants. Otherwise, the penetration of liquids containing solids into the gear mechanism leads to severe signs of wear to the point of the failure of the gear mechanism after even a short period of time. In addition, the shaft and the shaft bearings must be protected against contamination by the liquid being conveyed. The region of the shaft duct from the fluid-conducting pump chamber to the fluid-free region of the pump requires special attention. 
     Known sealing apparatuses and known rotary lobe pumps provide for the use of sealing labyrinths in this context, which, as a contactless sealing element, make fluid transport from one side of the seal to the other side of the seal more difficult by extending the seal land, and on this basis, achieve a certain sealing action. The known sealing devices in the rotary lobe pumps do not function in a manner that is fully satisfactory, however. In the region of the base circle diameter of the rotary pistons in known rotary lobe pumps, a short-circuit current of fluid (leakage flow) from the discharge side to the suction side of the rotary lobe pump occurs at the front sides of the rotary pistons. This creates undesired piston-side wear in connection with the fiber materials being conveyed. 
     SUMMARY OF THE INVENTION 
     The object of the invention was therefore to specify an apparatus for sealing a rotary lobe pump, in particular in the region of the shaft duct, which mitigates the aforementioned disadvantages as much as possible and, where possible, contributes to an improved pump performance. 
     The invention achieves this underlying object with an apparatus of the aforementioned type, in which the seal land is larger in a radial direction relative to the shaft than the seal land in an axial direction relative to the shaft. Here, the invention makes use of the knowledge that the sealing action is significantly increased by the fact that the ability of a fluid containing solids to flow through the labyrinth gap decreases when the larger size of the component of the seal land in a radial direction in relation to the directional component of the seal land in an axial direction is more pronounced. This is achieved by the fact that, due to the rotation of individual or all sealing elements with the shaft, fluid located in the labyrinth gap is also involved in this rotation. A centrifugal acceleration thereby acts on the fluid, which increases the flow resistance of the fluid in relation to the radial motion component thereof. This effect becomes more pronounced the greater the ratio of fluids moved in a radial direction through the labyrinth gap in proportion to fluids moved in an axial direction. 
     Surprisingly, it has been found that the formation of a seal land that is larger in a radial direction relative to the shaft than the seal land in an axial direction relative to the shaft contributes to the sealing apparatus having an overall much more compact design in relation to the shaft length than in the case of the formation of the seal land that is larger in an axial direction. For this purpose, it is especially advantageous when the ratio by which the seal land in a radial direction is larger than the seal land in an axial direction falls in a range of 1 to 15. It is especially preferred that this ratio fall in a range of 5 to 10. 
     In a preferred embodiment, the orientation of the labyrinth gap is selected in such a way that the labyrinth gap has one or more gap sections that extend axially relative to the shaft, and one or more gap sections that extend radially relative to the shaft. This allows a stepped or meandering gap pattern to be achieved, wherein the bends also contribute to an increase in the flow resistance. In alternative embodiments, the labyrinth gap does not extend in a strictly axial or radial direction, but rather extends partially or completely at an angle between 0° and 90° relative to the shaft axis (when the apparatus is in an assembled state). In such an embodiment, the labyrinth gap presents itself at least in sections as a conical recess between the sealing elements. 
     It is especially preferred, however, that the labyrinth gap be formed having gap sections that extend radially and axially in alternation, since in this way, economical heating during manufacturing can be advantageously combined with a space-saving design. 
     According to another preferred embodiment of the apparatus according to the invention, at least one first sealing element can be fastened to a front side of the rotary piston by means of a form-locking or force-locking fastener, and at least one second sealing element can be fastened to the housing of the rotary lobe pump by means of a form-locking or force-locking fastener. The first sealing element is hereby formed as a co-rotating component, while the second sealing element is formed as a stationary component. In this way, the labyrinth gap or part of the labyrinth gap that extends between the first and second sealing element is bordered on one side by a rotating component and on the other side by a stationary component, through which fluid located in the gap is sheared, which leads to a further increase in the flow resistance and the sealing action. In addition, the fasteners make it possible to remove or exchange individual sealing elements. In the event of wear, the sealing elements can be exchanged for maintenance and repair purposes. In addition, an apparatus according to this embodiment having attachable sealing elements and in combination with the compact design according to the invention in terms of the axial installation space can be retrofitted in the case of conventional rotary lobe pumps without requiring that special modifications be made to the housing and/or pump chamber of the rotary lobe pumps. 
     A further advantage in connection with the labyrinth gap that extends between the sealing elements is seen in the fact that wear only occurs in the replaceable sealing elements and not on the piston surface or end face respectively, as in conventional rotary lobe pumps. 
     According to a preferred embodiment, the first sealing element is formed as an annular disk and has an outer diameter, which extends beyond the base circle of the rotary piston. The outer diameter of the first sealing element, which is formed as an annular disk, preferably delimits the start of the labyrinth gap on the piston side. The labyrinth gap thus starts in the region of the base circle diameter of the rotary piston or even further out. 
     According to another preferred embodiment, the first sealing element has a projection on the front side in an axial direction relative to the shaft, which is disposed against a shaft seal as a support. Alternatively, instead of the projection, the apparatus has a third sealing element, which is formed as a spacer ring, and which is disposed against the shaft seal as a support. It is especially preferred that the labyrinth gap extend from radially outside of the base circle diameter of the rotary piston from the front side of the rotary piston in the direction of the shaft seal, wherein the labyrinth gap extends radially in the direction of the shaft. A reduction in the flow wear to the sealing components and to the rotary piston, in particular in the region of the base circle, is achieved by means of this seal land (path through the labyrinth gap), since as compared to the path that the fluid could take without the labyrinth gap by means of the short-circuit flow from the discharge side to the suction side, the seal land is extended. 
     A further advantage provided by the design of the seal land according to the invention can be seen in the fact that a drop in pressure is created from the start of the labyrinth gap on the piston side to the end of the labyrinth gap on the shaft seal side by means of the essentially radial sealing labyrinth according to the invention. The pressure applied to the shaft seal is thus reduced in comparison with conventional arrangements, which increases the service life of the shaft seal. This functional principle can be applied to most shaft seals, in particular to cartridge seals. 
     According to another preferred embodiment, the second sealing element is formed as an outer protective plate and can be fastened to a wall of the pumping chamber of the rotary lobe pump. 
     It is also preferable that the second sealing element have a recess, the contour of which corresponds to the first sealing element in such a way that the first sealing element can be partially or fully disposed within the recess. A labyrinth gap is created when the first sealing element extends partially or completely within the second sealing element or the recess thereof respectively, and a labyrinth gap is provided, the shape of which is a function of the profiling and contour of the first sealing element and the second sealing element. 
     It is also preferable that the apparatus according to the present invention have a fourth sealing element, which is formed as an inner protective plate and can be fastened to a wall of the pump chamber of the rotary lobe pump adjacent to the first sealing element in such a way that a radial gap section extends between the first sealing element and the fourth sealing element. 
     In addition, it is preferred that the fourth sealing element have an outer diameter, which is larger than the outer diameter of the recess of the second sealing element. It is especially preferable that the fourth sealing element can be positioned overlapping the second sealing element. In this way, the labyrinth gap is closed to the outside on one side, and the fourth sealing element can still be attached to the housing of the rotary lobe pump, for example by means of the second sealing element by means of clamps. 
     In a further preferred embodiment of the invention, the first sealing element and/or the second sealing element and/or the third sealing element and/or the fourth sealing element is or are respectively formed rotationally symmetrical and can be coaxially disposed with respect to each other and with respect to the shaft. Installation, removal and production of the sealing elements are hereby made possible with higher precision at reasonable production costs. 
     The invention achieves this object with a rotary lobe pump of the aforementioned kind, wherein the rotary lobe pump has an apparatus for sealing the pump chamber in accordance with the preferred embodiments described above. 
     The pump chamber is sealed vis-a-vis the fluid-free region by the apparatus. The rotary lobe pump is preferably further developed in that the labyrinth gap extends from the front side of the rotary piston in the region of the base circle diameter of the rotary piston out to a shaft seal in the region of the shaft diameter. 
     According to another preferred embodiment of the rotary lobe pump, the shaft seal is formed as a cartridge seal. 
     In regard to further advantages of the rotary lobe pump according to the invention, reference is made to the above statements regarding the sealing apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in greater detail below on the basis of preferred embodiments and with reference to the attached drawings. The figures show the following: 
         FIG. 1  a schematic side view through a rotary lobe pump according to the present invention; 
         FIG. 2  a first cross-sectional view of the rotary lobe pump from  FIG. 1  along the line A-A; 
         FIG. 3  an enlarged detail of the illustration in  FIG. 2 ; 
         FIG. 4  a detailed view of the apparatus according to the invention according to a second preferred embodiment; and 
         FIG. 5  a detailed view of the apparatus according to the invention according to a third preferred embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  first shows the basic structure of a rotary lobe pump. A rotary lobe pump  1  having a housing  3  is shown. A pump chamber is provided within the housing  3 , within which pump chamber two interlocking rotary pistons  5  are disposed. In each case, a rotary piston  5  has a base circle diameter  9  and a crown circle diameter  7 . A section on the crown circle of one of the rotary pistons  5  revolves on a respective section of the base circle of the other rotary piston  5  in a manner that is generally known. In so doing, the rotary pistons  5  each form a cavity between a wall of the pump chamber and the rotary piston  5 , within which the fluid is conveyed. The rotary pistons  5  are each housed on a shaft  11 . A plurality of sealing elements is provided on a front side of each of the rotary pistons  5 . According to  FIG. 1 , each of these are a first sealing element  13 , which is formed as a co-rotating protective plate ring and can be fastened to each rotary piston  5  by means of a force-locking fastener, in the present example, clamping bolts  15 . The first sealing element  13  is housed in a respective recess  17 . The recess  17  is provided in a second sealing element  19 . In the embodiment according to  FIG. 1 , two recesses  17  are provided in a single second sealing element  19  to house a first sealing element  13  for the respective rotary piston  5 . Alternatively, two separate second sealing elements  19  may be provided in the housing  3  of the rotary lobe pump  1 . The assembly of only a second sealing element  19 , which at the same time houses both first sealing elements  13 , has proven to be advantageous. In this exemplary embodiment, the second sealing element  19  is formed as an outer protective plate and can be connected by means of a force-locking fastener  21 , in the present example likewise connecting bolts, to the housing  3  in a reversibly detachable manner. 
     In addition, a third sealing element  23  can be disposed on each shaft  11 . According to the present exemplary embodiment, the third sealing element  23  is formed as a spacer ring. 
       FIG. 2  shows a cross-sectional view along the line A-A in  FIG. 1 . The rotary lobe pump  1  shown in  FIGS. 1 and 2  has an apparatus  10  according to the invention for the sealing of the pump chamber of the rotary lobe pump  1  against the leakage of fluid from the pump chamber. Within the housing  3 , the first sealing element  13  is fastened to a front side of the rotary piston  5  by means of the fasteners  15  on the rotary piston  5 . The first sealing element  13  according to  FIGS. 1 and 2  is formed as an annular disk, the thickness of which in an axial direction is to be understood in relation to the axis of rotation  2  of the shaft and as essentially equal to the thickness of the second sealing element  19 . The second sealing element  19  is connected to the housing  3  in a stationary manner. The recess  17 , within which the first sealing element  13  is housed, has a diameter, which is slightly larger than the outer diameter of the first sealing element  13 , so that a gap or annular gap is formed, which extends axially in the present exemplary embodiment between the first sealing element  13  and the second sealing element  19  in in an assembled arrangement. 
     In addition to the first sealing element  13  and the second sealing element  19  as well as the third sealing element  23 , a fourth sealing element  25  is provided. The fourth sealing element  25  is formed as an inner protective plate and is connected to the housing  3  and the second sealing element  19  in a stationary manner. In alternative embodiments, the fourth sealing element is either formed as a body having two recesses  27  analogous to the second sealing element  19 , or as a rotationally symmetrical body, for example in the form of an annular disk having only recess  27  in each case. The recess  27  is adapted to house the third sealing element  23 . The diameter of the recess  27  is slightly larger than the outer diameter of the third sealing element  23 , so that in an assembled arrangement, an annular gap extending in an axial direction extends between the fourth sealing element  25  and the third sealing element  23 . 
     The fourth sealing element  25  has an outer diameter, which exceeds the diameter of the recess  17  of the second sealing element  19  in the embodiment shown, so that the fourth sealing element  25  and the second sealing element are disposed so that they overlap and are fastened to the housing  3 . This makes it possible to adjust a distance between the first sealing element  13  and the fourth sealing element  25  in an axial direction. The result of this distance is a circumferential gap extending in a radial direction, which merges radially outward into the axial gap between the first sealing element  13  and the second sealing element  19 , and which merges radially inward into the axial gap between the fourth sealing element  25  and the third sealing element  23 . In regard to the profile of the gap, reference is made to the Figures below. 
     The third sealing element  23  is supported against a shaft seal  29 , which is disposed between the housing  3  and the shaft  11 . Furthermore, a bearing  31  is provided on the shaft  11 , which is either introduced directly in the housing  3  by the outer ring thereof, or alternatively by means of a cup mount (not shown). According to  FIG. 2 , the bearing  31 , the shaft seal  29 , and the third sealing element  23  are secured by means of a shaft nut  33  due to the position of a fitting key  35 . Alternatively, it is possible to secure these relative to a shaft shoulder or the like. The shaft nut  33  is disposed on a shaft end  37  of the shaft  11 . 
       FIG. 3  shows an enlarged view of the profile of the labyrinth gap according to the invention. Different sections of the labyrinth gap extend between the first sealing element  13  and the second sealing element  19 , between the first sealing element  13  and the third sealing element  23 , and between the first sealing element  13  and the fourth sealing element  25 . A first gap section  39  is formed between the first sealing element  13  and the second sealing element  19 . This gap section  39 , which essentially takes an axial course, merges into an essentially radial gap section  41  between the first sealing element and the fourth sealing element  25 . The seal land from the entrance into the gap section  41  to the exit from the gap section  41  in a radial direction is larger than the seal land through which the fluid must pass when passing through the axial gap section  39  and a gap section  43  in an axial direction between third sealing element  23  and the fourth sealing element  41 . The profile of the radial gap section  43  begins radially outward in the region of the base circle diameter relative to the shaft  11 , especially preferably radially outward therefrom, and ends in a radial direction closer in the direction of the shaft  11  on the side of the shaft seal  19 . 
       FIG. 4  shows an alternative embodiment of the apparatus  10  according to the invention in  FIGS. 1 to 3  in an assembly with a rotary lobe pump  1  according to the invention. The apparatus  10   I  shown in  FIG. 4  has a second sealing element  19  and a fourth sealing element  25  along the lines of the embodiment in  FIGS. 1 to 3 . In contrast to the embodiment according to  FIGS. 1 to 3 , the first sealing element and the third sealing element are designed as a single first sealing element  13   I . A projection is formed radially inward, relative to the shaft  11 , in the direction of the shaft seal  29  on the side of the first sealing element  13   I  adjacent to the labyrinth gap. Consequently, both the radial gap section  41  and the inner axial gap section  43  are formed between the first sealing element  13   I  and the fourth sealing element  25 . Strictly speaking, the fourth sealing element  25  according to this exemplary embodiment could be designated as the third sealing element, because the apparatus  10   II  only has three sealing elements. For reasons of clarity, however, this designation is retained. 
       FIG. 5  shows a third embodiment of the apparatus  10   II  according to the invention, installed in a housing  3  of the rotary lobe pump  1  according to the invention. Like the embodiments in the preceding Figures, the apparatus  10   II  has a second sealing element  19 . A first sealing element  13   II  is housed within the recess  17  of the second sealing element  19 , thereby forming a gap section  39  of the labyrinth gap extending essentially axially between the second sealing element  19  and the first sealing element  13   II . The gap section  41  of the labyrinth gap extending essentially radially is formed between the first sealing element  13   II  and the wall  45  of the shaft seal  29 . The shaft seal  29  is thus optionally formed as a “fourth” sealing element  25   I . 
     According to this exemplary embodiment, the first sealing element  13   II  is formed having a projection  51 , which extends into the inside of the shaft seal  29 . The first sealing element  13   II  is preferably formed as an integral element of a cartridge seal or the like. According to this embodiment, the first sealing element  13   II  is partially integrated in the shaft seal  29  and, together with the shaft seal  29 , is optionally exchangeable. In analogous terms, the shaft seal  29  is optionally integrated into the apparatus  10   II . In this way, the apparatus  10   II  can be retrofitted in rotary lobe pumps  1  of all design sizes by exchanging the shaft seals previously installed therein and replacing these with the shown solution according to  FIG. 5 . The seal land, which the labyrinth gap forms according to this embodiment, consists of an axial section, the gap section  39 , and a radial section, the gap section  41 .