Patent Publication Number: US-11642637-B2

Title: Vane for an impeller of an agitator, impeller and agitator

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of U.S. patent application Ser. No. 15/433,383, filed Feb. 15, 2017, which claims priority to European Application No. 16158040.2, filed Mar. 1, 2016, the contents of each of which is hereby incorporated herein by reference. 
    
    
     BACKGROUND 
     Field of the Invention 
     The invention relates to a vane for an impeller of an agitator for mixing or agitating a process fluid. The invention further relates to an impeller of an agitator comprising such vanes as well as to an agitator having such an impeller. 
     Background of the Invention 
     Agitators are used in many different industrial processes for mixing or agitating a process fluid. In most applications, the process fluid is contained in a tank or a tower or another vessel and the agitator is mounted to a wall or the bottom or the cover of the vessel. Amongst the wide range of industries where agitators are used is, for example, the pulp and paper industry. Here, agitators are used for example for dilution, mixing or bleaching processes. 
     Basically an agitator comprises an impeller or propeller for agitating the fluid, a shaft which is connected at one end to the impeller and at another end to a drive unit for rotating the shaft with the impeller. The drive unit usually has a motor and a coupling for connecting the motor with the shaft, wherein the coupling comprises a belt drive or a gear box or any other suited transmission device. 
     Typically the drive unit is arranged outside of the vessel and the shaft with the impeller is located inside the vessel for agitating the process fluid. There are known both top-mounted and side-mounted agitators. Top-mounted agitators are usually mounted to the cover or the top part of the tower or the vessel with the shaft of the agitator extending vertically. Side-mounted agitators are usually mounted to a side wall of the tower or the vessel with the shaft extending horizontally. Examples for both types of agitators are those which are sold by the applicant under the brands SALOMIX™ and SCABA™. 
     SUMMARY 
     In modern industrial processes there is a demand for highly efficient mixing and agitation solutions. Especially a minimal power consumption, a reliable operation and an optimum process result are desired. In addition, it is often requested that an agitator is quite flexible with respect to its use, i.e. the agitator shall be adaptable to different processes or process conditions, for example to different or changing compositions of the respective process fluid. 
     Therefore, it is an object of the invention to propose a new vane for an impeller of an agitator for mixing or agitating a process fluid, providing a high agitating efficiency, a reliable operation and flexibility with respect to the adaption to different applications. In addition, it is an object of the invention to propose a corresponding impeller for an agitator as well as a new agitator having such an impeller. 
     The subject matter of the invention satisfying this object is characterized by the features described herein. 
     Thus, according to the invention a vane for an impeller of an agitator for mixing or agitating a process fluid is proposed, comprising a socket for mounting the vane to an impeller and a blade for mixing or agitating the process fluid, the blade being connected to the socket, the blade having a leading edge, a trailing edge, and a blade tip extending from the leading edge to the trailing edge at the end of the blade facing away from the socket, and the blade having a height and a width, wherein the height is the maximum distance of the blade tip from the socket and wherein the width is the distance of the leading edge from the trailing edge, wherein the blade has a maximum width that is at least 55 percent, preferably at least 65 percent of the height. 
     This new design of the blade, and especially the considerably large width of the blade as compared to its height, results in a very high efficiency regarding the mixing or agitating action combined with a reliable and very good result of the mixing or agitating. 
     In addition, since the vane comprises a socket for mounting the vain to an impeller, the vane according to the invention is very flexible in view of adapting the vane to different or changing conditions of the process fluid. Because the vane is designed such that it is detachable from an impeller it may be easily replaced or fixed in another orientation with respect to a hub of an impeller. 
     Especially in view of a very high efficiency for many applications such embodiments are preferred in which the maximum width is at least 70 percent, preferably at least 75 percent of the height. 
     The width of the blade typically changes from the socket in direction to the blade tip. In view of a high efficiency it is a further preferred measure, when the maximum width of the blade is located in a region between 40 percent and 70 percent of the height of the blade, preferably in a region between 50 percent and 60 percent of the height. Thus, starting at the socket and moving in direction to the blade tip the width of the blade is first increasing until it reaches the maximum width in the region. Further moving towards the blade tip the width of the blade is preferably decreasing. 
     It is an additional advantageous measure in view of high efficiency, when the leading edge extends from the socket to the blade tip with a main curvature that is larger as a main curvature with which the trailing edge extends from the socket to the blade tip. The term “main curvature” can be used to indicate that the curvature both of the leading edge and of the trailing edge is not constant but changes along the respective edge. However, especially in the region where the blade has its maximum width the curvature of the leading edge and the curvature of the trailing edge may be approximated by a respective constant curvature, for example by a respective circle. The radius of the circle can be then considered as the main curvature of the respective edge. 
     According to an embodiment of the vane in accordance with the invention, the main curvature of the trailing edge has a radius that is at least 1.5 times, preferably at least 1.8 times, a radius of the main curvature of the leading edge. 
     According to a preferred embodiment of the vane, the blade is connected to the socket in a base plane and has a main axis extending perpendicular to the base plane in direction to the blade tip, wherein the blade is twisted around the main axis. 
     Preferably this twisting of the blade is realized such that the mean direction of a camber line of a profile of the blade parallel to the base plane is turning around the main axis with increasing distance from the base plane. 
     In a preferred embodiment of the vane, the mean direction of the camber line of a profile near the base plane and the mean direction of the camber line of a profile near the blade tip extend with a twist angle of at least 30° with respect to each other. 
     The twisting of the blade around the main axis is advantageous with respect to a high mixing or agitating efficiency of the vane. 
     In view of a high flexibility regarding the adaption to different applications or to changing properties of the process fluid it is a preferred measure when the socket is designed as a flange socket for flange mounting the vane to a hub. 
     In addition, according to the invention an impeller of an agitator for mixing or agitating a process fluid is proposed comprising a hub and a plurality of vanes mounted to the hub, wherein each vane is designed according to the invention and each vane is mounted to the hub by the respective socket. The impeller has a high mixing or agitating efficiency and provides reliable, very good process results. 
     Preferably each vane is adjustably mounted to the hub. By this measure the impeller may be adapted in a very easy manner to different applications or different conditions of the process fluid. 
     According to a preferred embodiment the impeller has three vanes. 
     According to yet a further aspect of the invention an agitator for mixing or agitating a process fluid is proposed comprising an impeller for agitating or mixing the process fluid, a drive unit for rotating the impeller, and a drive shaft connecting the impeller with the drive unit, wherein the impeller is designed according to the invention. This agitator ensures a high efficiency, reliable operation and very good process results in combination with a low energy consumption. In addition, the agitator may be adapted in a very easy manner to a lot of different applications. 
     According to a preferred embodiment, the agitator has a mounting flange for fastening the agitator to a wall of a vessel for the process fluid, wherein the drive shaft comprises an inner shaft and a sleeve coaxially surrounding the inner shaft and extending between the hub of the impeller and the mounting flange, wherein the sleeve is designed in such a manner that the sleeve prevents the inner shaft from a contact with the process fluid when the agitator is mounted to the wall of the vessel. By providing the drive shaft with the protecting sleeve it is possible to use a cost-efficient inner shaft wherein this inner shaft is protected against aggressive process fluids or against corrosion and/or wear by the sleeve. 
     According to an embodiment the agitator is designed for being mounted horizontally to a wall of a vessel for the process fluid. However, the agitator may also be designed for other types of mounting it to a vessel, a tower, a tank or the like. 
     Further advantageous measures and embodiments of the invention will become apparent from the description herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in more detail hereinafter with reference to the drawings. 
         FIG.  1    is a perspective view of an embodiment of an agitator according to the invention, 
         FIG.  2    is a perspective view of an embodiment of a vane according to the invention, 
         FIG.  3    is a top view of the embodiment of the vane shown in  FIG.  2   , 
         FIG.  4    is a plan view of the embodiment of the vane shown in  FIG.  2   , 
         FIG.  5    is a bottom view of the embodiment of the vane shown in  FIG.  2   , 
         FIG.  6    is a plan view similar to  FIG.  4   , illustrating the main curvatures of the leading edge and the trailing edge, respectively, 
         FIG.  7    is a profile of the blade of the vane shown in  FIG.  2    in a cross-section parallel to the base plane and near the socket of the vane, 
         FIG.  8    is a profile similar to  FIG.  7   , but near half the height of the blade, 
         FIG.  9    is a profile similar to  FIG.  7   , but near the blade tip of the blade, 
         FIG.  10    is a perspective view of an embodiment of an impeller according to the invention, and 
         FIG.  11    is a cross-sectional view of an embodiment of the shaft of the agitator shown in  FIG.  1   . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     For the sake of a better understanding, firstly the general setup of an agitator will be explained referring to  FIG.  1   .  FIG.  1    shows a perspective view of an embodiment of an agitator according to the invention which is designated in its entity with reference numeral  100 . The agitator comprises an impeller  50  having a hub  51  and three vanes  1 , each of which has a socket  2  for mounting the respective vane  1  to the hub  51  as well as a blade  3  connected to the socket  2  for agitating or mixing a process fluid. Both the impeller  50  and each vane  1  are designed as embodiments of the impeller or the vane, respectively, according to the invention, which will be explained in more detail hereinafter. 
     The hub  51  of the impeller  50  is connected to an end of a drive shaft  60 . The other end of the drive shaft  60  is operatively connected to a drive unit  70  for rotating the drive shaft  60  and the impeller  50  connected therewith around an axis A. The drive unit  70  comprises a motor  71 , for example an electric motor  71 , and a coupling  72  for operatively connecting the motor  71  with the drive shaft  60 . 
     The coupling  72  shown in  FIG.  1    has a belt drive for connecting the motor  71  to the drive shaft  60 . It goes without saying that the invention is not restricted to such a belt drive. The drive unit  70  of an agitator  100  according to the invention may also be designed with any other coupling  72  between the motor  71  and the drive shaft  60  known in the art, for example with a gear box or any other suited transmission device. In addition, the relative arrangement of the motor  71 , the coupling  72  and the drive shaft  60  shown in  FIG.  1    shall be understood exemplary. There are many other arrangements known in the art that are also suited for the agitator according to the invention. 
     The embodiment of the agitator  100  shown in  FIG.  1    is designed as a side-mounted agitator and designed for being mounted horizontally to a wall of a vessel, a tank, a tower, a container or any other receptacle, i.e. the drive shaft  60  is extending horizontally in the usual orientation of use of the agitator  100 . Although this is a preferred embodiment for the agitator  100  according to the invention, the invention is not restricted to side-mounted or horizontal agitators. An agitator according to the invention may also be designed for example as a top-mounted or vertical agitator, i.e. with the drive shaft extending vertically in the usual orientation of use. 
     The side-mounted agitator  100  shown in  FIG.  1    has a mounting flange  80  for fastening the agitator to a wall of a vessel, tank, tower or the like. The mounting flange  80  surrounds the drive shaft  60  concentrically and comprises several bores for receiving screws or bolts for fastening the agitator  100  to the wall. When the agitator  100  is mounted to the wall, the mounting flange  80 , the impeller  50  and the part of the shaft drive  60  between the mounting flange  80  and the impeller  50  are located within the vessel, the tank, the tower or the like containing the process fluid to be agitated or mixed by the impeller  50 . Further details of the agitator  100  such as seals and bearings are well known to the skilled person and therefore will not be described in more detail. 
     Turning now to the vane  1 , an embodiment of a vane  1  according to the invention will be explained referring to  FIG.  2   - FIG.  5   .  FIG.  2    shows an overall perspective view of an embodiment of the vane  1  according to the invention.  FIG.  3    is a top view of this embodiment of the vane  1 ,  FIG.  4    a plan view of a suction side of the vane and  FIG.  5    is a bottom view of the vane  1 . 
     The vane  1  comprises the socket  2  for mounting the vane  1  to an impeller and the blade  3  for mixing or agitating a process fluid. The blade  3  is connected to the socket  2 , for example by welding or by any other suited process. Of course, the blade  3  and the socket  2  may also be manufactured as a single piece, i.e. the blade  3  may be formed integrally with the socket  2  as a single piece. 
     The socket  2  is disc shaped in the form of a cylinder with a plane lower surface  22  and a plane upper surface  21  to which the blade  3  is connected. The upper surface  21  to which the blade  3  is joined defines a base plane  4 , i.e. the base plane  4  is that plane that comprises the upper surface  21 . The center of the upper surface  21  is denoted with C. 
     The blade  3  is extending in a direction perpendicular to the base plane  4  and has a leading edge  31 , a trailing edge  32  and a blade tip  33  extending from the leading edge  31  to the trailing edge  32  at the end of the blade  3  that faces away from the socket  2 . The blade  3  has two surfaces each extending from the leading edge  31  to the trailing edge  32 , namely a pressure side  34  and a suction side  35  (see  FIG.  4   ). 
     It shall be understood that the terms “leading edge”, “trailing edge”, “pressure side”, “suction side” and the like respectively refer to the operational state, when the vane  1  is mounted to the impeller  50  of the agitator  100 . 
     The blade  3  extends along a main axis M, which is that axis perpendicular to the base plane  4  on which the center C of the upper surface  21  is located. 
     The blade  3  has a height H (see  FIG.  4   ) which is the maximum distance of the blade tip  33  from the upper surface  21  of the socket  2 , i.e. the maximum perpendicular distance of the blade tip  33  from the base plane  4 . The blade  3  has a width W, defined as the shortest distance of the leading edge  31  from the trailing edge  32  measured in a direction perpendicular to the main axis M. Thus, the width W at a given distance D from the base plane  4  is measured in a plan view of the suction side  35  (or the pressure side  34 ) as the length of a straight line parallel to the base plane  4 , which connects a point L on the leading edge  31  with a point T on the trailing edge  32 , whereas the points L and T have the same perpendicular distance D from the base plane  4 . 
     In the top view shown in  FIG.  3    the width W of the blade  3  at a given distance D from the base plane  4  is the shortest distance of the leading edge  31  from the trailing edge  32  measured in a direction parallel to the base plane  4  and perpendicular to the main axis M. 
     As can be best seen in  FIG.  4   , starting from the upper surface  21  of the socket  2  the width W of the blade  3  is first increasing with increasing distance D from the base plane  4 , reaches a maximum width WM and then decreases with further increasing distance D towards the blade tip  33 . 
     According to the invention the maximum width WM of the blade  3  is at least 55 percent and preferably at least 65 percent of the height H of the blade  3 . The optimum value for the maximum width WM depends on the respective application as well as on the absolute value of the height H of the blade  3 . For many embodiments of the blade  3  it is even preferred when the maximum width WM is at least 70 percent and preferably at least 75 percent of the height H. 
     In the embodiment shown in  FIG.  4    the maximum width WM of the blade  3  is approximately 80% of the height H of the blade. 
     The considerable maximum width WM of the blade  3  as compared to its height H ensures a high efficiency as well as reliable operation and very good process results when the blade  3  is used in an agitator  100 . 
     Preferably, the maximum width WM of the blade  3  is located at a distance DM from the base plane  4  that is between 40 percent and 70 percent of the height H of the blade  3 . This region of 40% to 70% of the height H is in  FIG.  4    delimitated by the lines L 1  and L 2 . For most applications it is preferred when the maximum width WM is located at a distance DM from the base plane  4  which is between 50% and 60% of the height H of the blade  3 , i.e. the maximum width WM is preferably located in the upper half of the blade  3  (relating to the representation in  FIG.  4   ). The height H of the blade  3  shown in  FIG.  4    is for example approximately 340 mm and the maximum width WM is located approximately at 57% of the height H. 
     A further preferred measure is the embodiment of the leading edge  31  and the trailing edge  32  as seen in the plan view of  FIG.  4   . In this projection into a plane perpendicular to the base plane  4  the blade  3  has a generally biconvex shape—apart from the very small region immediately adjacent to the upper surface  21  of the socket  2 . This means, both the leading edge  31  and the trailing edge  32  are outwardly cambered, i.e. both edges  31  and  32  are convex essentially over their entire length. 
     For the sake of clearness it shall be mentioned that the terms “convex” and “concave” are used with their common meaning, i.e. a surface of a body is called concave, if the surface is curved inwardly with respect to the body and a surface is called convex, if the surface is curved outwardly with respect to the body. 
     As can be best seen in  FIG.  4    the main curvature of the leading edge  31  is larger than the main curvature of the trailing edge  32 , that is the leading edge  31  is stronger curved than the trailing edge  32 . To explain the meaning of the term ‘main curvature’ reference is made to  FIG.  6    showing a plan view of the blade  3  similar to  FIG.  4   . Although the curvature both of the leading edge  31  and of the trailing edge  32  does not change its respective algebraic sign, the curvatures are not constant over the entire length of the respective edge  31 ,  32 . However, it is possible to approximate the curvature of the leading edge  31  by a circle RL having the radius R 1  whereupon R 1  is chosen as the maximum value of the radius of a circle that still fits the curvature of the leading edge. In the same manner the curvature of the trailing edge  32  is approximated by a circle RT having the radius R 2 . The respective radius R 1  or R 2  is then considered as the main curvature of the leading edge  31  or the trailing edge  32 , respectively. The smaller the radius R 1 , R 2  is, the stronger is the curvature of the respective edge  31 ,  32 . The preferred ratio between the main curvature R 1  of the leading edge  31  and the main curvature R 2  of the trailing edge  32  is such that the main curvature R 2  of the trailing edge  32  is at least 1.5 times and preferably at least 1.8 times the main curvature R 1  of the leading edge  31 . In the embodiment shown in  FIG.  4    or  FIG.  6    the ratio R 2 /R 1  is approximately 1.8. The radius R 1  of the main curvature of the leading edge  31  is approximately 140 mm. 
     As can be best seen in  FIG.  3    the blade  3  is twisted around the main axis M. This twisting of the blade  3  may be described by a camber line of different profiles of the blade  3 . Each profile is a cross-section through the blade  3  in a plane parallel to the base plane  4 , i.e. perpendicular to the main axis M.  FIG.  7 - 9    show three different profiles taken at different distances D from the base plane  4 .  FIG.  7    shows the profile of the blade  3  very close to the base plane  4  in a distance D which is less than 1% of the height H.  FIG.  8    shows the profile of the blade  3  at a distance D that is approximately half of the height H and  FIG.  9    shows the profile of the blade  3  near the blade tip  33  at a distance D of approximately 90% of the height H. Each profile is laterally delimited by a first border line  6  and a second border line  7 . 
     In  FIG.  7    and in  FIG.  8    the camber line  5  of the respective profile is shown. The camber line  5  is the center line of the profile having at each point the same distance from both border lines  6 ,  7 . As indicated in  FIG.  7    and in  FIG.  8    the camber line  5  may be determined by inscribing circles into the profile, each circle touching both the first and the second border line  6 ,  7 . The camber line  5  is then obtained by connecting the centers of the circles. 
     As can be seen by comparing especially  FIG.  7    and  FIG.  8    the camber line  5  is turning counterclockwise around the main axis M with increasing distance D from the base plane  4 , which demonstrates the twisting of the blade  3  around the main axis M. 
     As can be also seen in  FIG.  7    and  FIG.  8    the camber line  5  is not a straight line but curved. At least for some profiles the camber line  5  changes the algebraic sign of its curvature, i.e. the camber line  5  comprises a part with positive curvature and a part with negative curvature. 
     For quantifying the twisting of the blade  3  around the main axis M the mean direction of the respective camber line  5  may be considered. The mean direction of the camber line  5  means that direction in which the camber line  5  is mainly extending. The mean direction may be determined for example by approximating the respective camber line  5  by a straight line. 
       FIG.  9    shows the mean direction of the camber line  5  of two different profiles. The mean direction of the camber line  5  (first camber line  5 ′) of the profile shown in  FIG.  7    is denoted with K 1  and the main direction of the camber line  5  of the profile shown in  FIG.  9    is denoted with K 2 . That is, main direction K 1  belongs to the profile adjacent to the socket  2  ( FIG.  7   ) and the main direction K 2  belongs to the profile near the blade tip  33 . The main directions K 1  and K 2  delimit a twist angle α, describing the twisting of the blade around the main axis M. The twist angle α is determined in the base plane  4 , i.e. the main directions K 1  and K 2  are projected on the base plane  4 . 
     Preferably, the twist angle α between the mean direction K 1  of the camber line in a profile near the base plane  4  ( FIG.  7   ) and the main direction K 2  of the camber line  5  (second camber line  5 ″) in a profile near the blade tip  33  is at least 30°. In the embodiment of the vane  1  shown in  FIG.  9    the twist angle α is approximately 40°. 
     Viewed in a direction perpendicular to the main axis M of the blade  3 , the pressure side  34  (see for example  FIG.  2    or  FIG.  8   ) of the blade  3  comprises both convex and concave regions. In a middle region around the main axis M the pressure side  34  is convex. Moving towards the leading edge  31  the pressure side  34  becomes concave and moving from the middle region towards the trailing edge  32  the pressure side becomes concave, too, such that the overall shape of the pressure side  34  is concave with a convex region in the middle. As to the suction side  35  the dominating curvature of the suction side  35  is convex. In the region between the leading edge  31  and the main axis M the suction side  35  is convex. In the region between the main axis M and the trailing edge  32  the suction side  35  becomes slightly concave, wherein ‘slightly’ means that the dominant curvature of the suction side  35  remains convex. 
     Preferably, the socket  2  of the vane  1  is designed as a flange socket for flange mounting the vane  1  to the hub  51  of the impeller  50  (see  FIG.  10   ) in an adjustable manner, i.e. the relative orientation of the vane  1  with respect to the hub  51  is adjustable. 
     Referring to  FIG.  5    showing a bottom view of the vane  1  the socket  2  comprises a plurality, here four, arcuate oblong holes  23  arranged adjacent to the circumferential rim of the disk shaped socket  2 . The oblong holes  23  are positioned pairwise diametrically opposing. Two of the oblong holes  23  are located in front of the pressure side  34  of the blade  3  and two of the oblong holes  23  are located in front of the suction side  35  of the blade  3 . Each oblong hole  23  may receive a screw  8  (see  FIG.  10   ) for fasting the vane  1  to the hub  51  of the impeller  50 . Due to the arcuate shape of the oblong holes  23  the orientation of the respective vane  1  with respect to the hub  51  may be adjusted. In order to fix the vane  1  in the desired orientation the lower surface  22  of the socket  2  comprises a plurality of blind bores  24  arranged adjacent to the circumferential rim of the disk shaped socket  2  wherein all blind bores  24  have the same distance from the center of the lower surface  22  of the socket  2 . The hub  51  of the impeller  50  comprises one positioning pin (not shown) for each vane  1 . Upon mounting of the vane  1  to the hub  51  the positioning pin engages one of the blind bores  24 , thus fixing the desired orientation of the vane  1 . 
       FIG.  10    shows a perspective view of an embodiment of the impeller  50  according to the invention. The impeller  50  comprises the hub  51  and three identical vanes  1  flange mounted to the hub  51  and fastened by the screws  8 . Each of the three vanes  1  is designed as explained hereinbefore. The vanes  1  are arranged equally spaced around the circumference of the hub  51 . The hub  51  comprises three planar mounting faces  52  having essentially the same shape and the same dimensions as the lower surface  22  of the socket  2 . In the illustration of  FIG.  10    the three mounting faces  52  are covered by the sockets  2  of the vanes  1 . Each mounting face  52  is arranged parallel to the axis A around which the impeller  50  rotates. 
     Depending on the specific application the number of vanes  1  of the impeller  50  may be different from three. In other embodiments of the impeller according to the invention the impeller may for example comprise four vanes. 
     As already explained hereinbefore with reference to  FIG.  1    showing an embodiment of the agitator  100  according to the invention the impeller  50  is mounted to one end of the drive shaft  60  of the agitator  100 . 
       FIG.  11    shows a preferred embodiment of the drive shaft  60  of the agitator  100  in a cross-sectional view.  FIG.  11    only shows the part of the drive shaft  60  between the mounting flange  80  and the impeller  50 . The drive shaft  60  comprises an inner shaft  61  extending in the direction of the axis A and a sleeve  62  coaxially surrounding the inner shaft  61  and extending between the impeller  50  and the mounting flange  80 . Adjacent to the mounting flange  80  the sleeve  62  is connected to another sleeve which is fixed with respect to the inner shaft  61 , for example by a shrink fit. The sleeve  62  is connected both to the sleeve adjacent to the mounting flange  80  and to the impeller  50  in a sealing manner, such that the process fluid cannot enter the sleeve  62 . Thus, the sleeve  62  protects the inner shaft  61  against any contact by the process fluid. Such a contact could cause corrosion or other kinds of degradation of the inner shaft  61 . Protecting the inner shaft  61  with the sleeve  62  has the advantage that the inner shaft  61  and the sleeve  62  may be manufactured with different, usually metallic, materials, wherein only the sleeve  62  has to be resistant against corrosion or other degradations caused by the process fluid. It is a further advantage that in case of a degradation of the sleeve  62  only the sleeve  62  has to be replaced and the inner shaft may  61  still be used. 
     Of course in other embodiments the drive shaft  60  may be designed as a bare shaft without the sleeve  62 .