Abstract:
The invention relates to a double-seat valve, the seats of which can be cleaned, which is improved compared to the prior art in that discharge of the seat cleaning flow into and out of the leakage cavity as much as possible without turbulence is ensured, and pressure-increasing direct action on the seat areas is reliably avoided. This is achieved among other things in that the double seat valve ( 1 ) has closing elements ( 3, 4 ) which can be transferred independently of one another by a respective partial lift gap-wide into the seat cleaning position for purposes of flushing their coaxial seat surfaces ( 2   a,    2   b ), the second closing element ( 4 ) by a second partial lift (T 2 ) which acts in the same direction as the opening motion and the first closing element ( 3 ) by a first partial lift (T 1 ) which acts in the direction opposite the opening motion travelling into its respective seat cleaning position, that the second closing element ( 4 ) in its closed position with a stop face ( 4   f ) which forms a second circumferential edge (U 2 ) with the circumferential wall ( 4   c;    4   h ) adjoins the second seat surface ( 2   b ), directly bordering the first seat surface ( 2   a ), that the circumferential wall ( 4   c ) on its end facing away from the first closing element ( 3 ) undergoes transition into a rotationally symmetrical deflection surface ( 4   d ) (starting point of the contour (K)) and this deflection surface ( 4   d ) discharges in the front face ( 4   e ) of the recess ( 4   b ) which is oriented essentially perpendicular to the longitudinal axis of the second closing element ( 4 ) (discharge point of the contour (K)), and that viewed in a vertical center section, the deflection surface ( 4   d ) has a contour (K) which runs without bends, and the direction vector at the discharge point of the deflection surface ( 4   d ) is oriented toward the center discharge bore ( 3   d;    3   d *) located in the first closing element ( 3 ) without colliding with the first closing element ( 3 ) in the area of its regions enclosing the leakage cavity ( 5 ) to form impact pressure ( FIG. 3 ).

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a double seat valve, the seats of which can be cleaned, with two serially arranged closing elements which can be moved relative to one another and which in the closed position of the double seat valve prevent overflow of fluids from one valve housing part into another, which border between themselves both in the closed and also in the open position a leakage cavity which is connected to the vicinity of the double seat valve, in the closed position the first closing element which is made as a slide piston being accommodated to form a seal in a connection opening which joins the valve housing parts to one another and in the course of its opening motion making sealing contact with a second closing element which has a second seal and which is associated with the second seat surface, and the latter closing element in the continued opening motion being likewise transferred into the open position, the first closing element in its end section having a first seal which radially seals relative to a cylindrical first seat surface which is made in the connection opening, the second closing element on its end facing the first closing element having a recess with an essentially cylindrical circumferential wall which is flush with the cylindrical first seat surface and the recess being dimensioned in such a way as to accommodate the end section and the radial first seal of the first closing element to form a seal during the opening motion before the second closing element opens. 
       PRIOR ART 
       [0002]    EP 0 039 319 B1 discloses a double seat valve of the initially described type. The second closing element in this double seat valve is made as a seat disk whose seal acts purely axially on the assigned seat (seal with pressing engagement). The double seat valve, however, is not able to have its seats cleaned so that the prior art discloses no indications of flow engineering treatment of the seat cleaning flows generated when the seat is cleaned. Cleaning of the seats can be adequately defined as gap-wide exposure of the two seat surfaces of a double seat valve, separately and independently of one another, by partial lifting of the respective closing element, as a result of which cleaning liquid flows out of the valve housing part which is associated with the closing element on the path via the exposed seat into the leakage cavity. 
         [0003]    A seat-cleanable double seat valve which allows cleaning of the respectively exposed seat by gap-wide opening of its seats is disclosed by DE 38 35 944 C2. Each of the three seals in this known double seat valve is a discrete seal, each seal having only a single function. The first seal in the first closing element is a strictly radially acting seal which slides in the first sealing surface made as a cylindrical envelope and seals there as a result of the provided pretensioning (seal with sliding engagement). The second seal in the second closing element acts on the second seat surface which is conical in shape so that the seal can act axially/radially here (seal with sliding/pressing engagement). The third seal, the so-called intermediate seal, develops its action when the first closing element in the opening lift comes into contact with the second closing element by way of this intermediate seal and, in the course of the continued opening motion, entrains the second closing element into the fully open position (seal in pressing engagement). The intermediate seal, in this case, is located in the front face which faces the leakage cavity on the second dependently driven closing element. 
         [0004]    The seat cleanable double seat valve according to DE 38 35 944 C2 has two so-called seat cleaning positions, the first seat cleaning position being produced by the first partial lift of the first closing element which acts in the opposite direction to the opening lift. In the seat cleaning position of the first closing element (relative to the position of the drawing as shown in  FIG. 3 , this is the lower closing element) the passage of a discharge bore which is connected to the first closing element and which is made as a pressure balance piston through the lower valve housing is at the same time exposed for purposes of cleaning of the assigned seal. The seat cleaning position of the second (upper) closing element is not further addressed in DE 38 35 944 C2; it takes place by the second partial lift which acts in the same direction as the opening lift. The respective amount of cleaning liquid in seat cleaning is limited by a more or less complex and often inadequate adjustment of the exposed gap between the respective seal and the associated seat surface. 
         [0005]    For the double seat valve as shown in EP 0 039 319 B1, the seal in the first closing element has a double function; on the one hand it acts as a seat seal and, on the other hand, in the course of the opening motion and in the full open position of the double seat valve, also assumes the function of an intermediate seal in the double seat valve according to DE 38 35 944 C2. 
         [0006]    A double seat valve which is limited solely to exposing the seat in the region of the associated closing element in seat cleaning and which, moreover, implements a connection of the leakage cavity to the vicinity of the double seat valve, which connection is generously dimensioned, the passage cross section of the connection corresponding roughly to the passage cross section of the greatest pipe width connected to the double seat valve, is described in company publication “Operating Instructions BAA D620-PMO.32, Double Seat Valve Type D 620 PMO” of Sümo Components GmbH, D-73469 Riesbürg. This double seat valve, due to its generous dimensioning of the connecting line between the leakage cavity and the exterior, is basically suited to preventing a pressure build-up in the leakage cavity in case of major seal defects. 
         [0007]    To limit the amount of cleaning liquid in seat cleaning, providing throttle gaps which are located, for example, on the leakage space side and which are series-connected to the respectively exposed seat is known. A double seat valve, in this connection, is described in DE 196 08 792 A1. In this double seat valve the first seat cleaning position is produced by the first partial lift which acts in the opposite direction to the opening lift. Here, a cylindrical lug located on the first closing element on the leakage space side with the assigned cylindrical first seat surface forms the first throttle gap via which the amount of cleaning liquid which has been delivered from the adjacent first valve housing part can be limited. The seat cleaning position of the second closing element takes place by the second partial lift which acts in the same direction as the opening lift, in the partially open position the cylindrical lug located on the second closing element on the leakage space side forming with the assigned part of the connection opening a second throttle gap which quantitatively limits the second seat cleaning flow produced in this seat cleaning position. Since the two closing elements and the assigned cylindrical lugs have different diameters, the associated sections of the connection opening between the two valve housing parts are likewise different in diameter so that between these two diameters a transition surface arises. 
         [0008]    This transition surface, which forms an obtuse, preferably, a right deflection angle with the section of larger diameter, results in that in the seat cleaning position of the first closing element, the first seat cleaning flow does not directly impact the second throttle gap and thus the seat region of the second closing element. Analogously, the second seat cleaning flow is prevented from acting directly on the first throttle gap and thus the seat region in the seat cleaning position of the second closing element. 
         [0009]    In the seat and closing element configuration of the double seat valve according to EP 0 039 319 B1, such a transition surface and its action mechanism as a rule are unavailable so that the currently popular demand for preventing direct action on the seat regions in the course of cleaning the seat cannot be satisfied by this known double seat valve. 
         [0010]    The requirements imposed on a seat-cleanable double seat valve in certain countries go beyond the aforementioned limitation of the amount of cleaning liquid and prevention of direct action on the seal region and are more extensive. Thus, for example, in the United States of America, it is required that for larger seal defects or even the loss of one of the two seat seals of the closing element in the closed position in the course of seat cleaning of the other closing element, no cleaning liquid may pass through via the respective seal defect or the seat region without a seat seal. Under these conditions, not only is the requirement for limiting the amount of cleaning liquid and avoiding direct admission into the seat regions in the course of seat cleaning imposed on this double seat valve, but also the requirement for discharge of the seat cleaning flow as much as possible without turbulence initially into the leakage cavity and from there into the exterior without the respectively closed seat region being exposed to a direct incident seat cleaning flow and/or its secondary flows or being acted upon in such as way as to raise the pressure. 
         [0011]    Direct action is defined as any velocity component from the respective seat cleaning flow, which component is directed perpendicular to the walls that border the seat region. Specifically, it has been shown that any direct action in this respect leads to conversion of kinetic flow energy into static pressure. Depending on the impact angle of the flow on the flow-exposed wall surface or body surface there is a branching flow with a so-called “branching flow line”, the latter dividing the flow into two halves. The branching flow line itself runs against the so-called “stagnation point” so that the velocity is equal to zero at this point. The pressure increase as a result of this velocity stopping is also called the “impact pressure”. The above described pressure-increasing mechanisms, if they become active, generate a leakage flow via the respective throttle gap and the defective seat seal or one which is completely absent. 
         [0012]    Direct impact of the seat cleaning flow on the surfaces which border the leakage cavity is therefore always counterproductive. With the exception of the double seat valve according to DE 196 08 792 A1, in the other known double seat valves described above, the first seat cleaning flow, which is generated by air striking the first closing element by the first partial lift, can more or less perpendicularly strike the front face boundary surface of the second closing element which holds the intermediate seal (DE 38 35 944 C2; double seat valve Type D 620 PMO) or the cylindrical recess (EP 0 039 319 B1). At the impact site this flow is diverted mainly toward the center of the leakage cavity. Furthermore, at the impact site a branching flow line arises whose branch facing the seat region can generate a vortex and an impact pressure there. The second seat cleaning flow which is generated by air striking the second closing element by the second partial lift more or less directly strikes the front face boundary surface of the first closing element, and, here as well, the part of the flow located between the branching flow line and the seat region can be supplied to the latter, forming impact pressure. 
         [0013]    WO 2007/054 131 A1 and WO 2007/054 134 A1 already propose measures to ensure discharge of the seat cleaning flow into and out of the leakage cavity as much as possible without turbulence and to avoid pressure-increasing direct action on the seat surfaces. These measures, however, relate to a double seat valve with the features of DE 196 08 792 A1 which were briefly outlined above. 
         [0014]    The object of this invention is to develop a double seat valve of the initially described type such that discharge of the seat cleaning flow into and out of the leakage cavity as much as possible without turbulence is ensured and pressure-increasing direct action on the seat areas is reliably avoided. 
       SUMMARY OF THE INVENTION 
       [0015]    The object is achieved by a double seat valve with the features of claim  1 . Advantageous embodiments of the double seat valve whose seats can be cleaned according to the invention are described in the dependent claims. 
         [0016]    To achieve the object underlying the invention, the first basic inventive concept consists in feeding the seat cleaning flow which emerges from the assigned gap between the seat seal and the seat surface in the respective seat cleaning as much as possible without turbulence and barriers into the leakage cavity and from there discharging it into the exterior in the same manner. This is achieved, on the one hand, by a new flow contour which steers and guides the seat cleaning flows in the leakage cavity. This new flow contour for seat cleaning of the first closing element which lies underneath provides for the first seat cleaning flow to follow the wall shape in the region of the first seat surface without detachment. Then, in the cylindrical recess of the second closing element, which recess is flush with the cylindrical first seat surface, smooth deflection of this first seat cleaning flow takes place so that the latter can travel into a discharge bore which is located centrally in the first closing element without colliding with the regions enclosing the leakage cavity, forming impact pressure. This is achieved in that the circumferential wall of the cylindrical recess on its end facing away from the first closing element undergoes transition into a rotationally symmetrical deflection surface and this deflection surface discharges in the front face of the recess which is oriented essentially perpendicular to the longitudinal axis of the second closing element. 
         [0017]    Smooth deflection of the seat cleaning flow in the deflection surface is essential. This is achieved according to the invention in that, viewed in a vertical center section, the deflection surface runs without bends, a direction vector in the discharge point of the deflection surface under the aforementioned conditions being oriented toward the central discharge bore located in the closing element. 
         [0018]    In flow guidance of the second seat cleaning flow generated by air striking the second closing element, it is essential that this flow detaches in a defined manner on a first circumferential edge which is formed by the second seat surface and the first end section of the first seat surface and is reliably routed tangentially past the surfaces which enclose the first closing element in the region of the leakage cavity. For this purpose, between the first circumferential edge and the pertinent regions of the first closing element there is a safety distance which under all possible circumstances of production engineering prevents impact in this connection. 
         [0019]    This safety distance of the first closing element from the direction vector at the exit site of the second seat surface into the first end section of the first seat surface is advantageously dimensioned such that it is at least as large as the sum of all production tolerances of the components of the double seat valve which in the closed position of the first closing element determine its smallest axial distance to the second seat surface. 
         [0020]    A second basic inventive concept consists in shifting the end position boundary, the desirable fixed stop of the second closing element which is not or cannot be accomplished in all cases (seat disks with axially acting seal in pressing engagement or seat disks with radially/axially acting seal in sliding/pressing engagement) in its closed position to the end of the seat, directly bordering the first seat surface. This is achieved according to the invention in that the second closing element in its closed position adjoins the second seat surface with a stop face which is located on its boundary surface adjacent to the second seal radially inside. Here, the stop face with the circumferential wall forms a second circumferential edge. 
         [0021]    This measure eliminates the current gap which borders the leakage cavity between the second closing element and the valve housing, its generally being a metallic closure. At this point, in the course of seat cleaning of the closing element, cleaning liquid cannot reach the potentially defective seat seal or the seat seal which may not be entirely present any more by way of the metallically closed gap between the second closing element and the second seat surface. 
         [0022]    Until now this defined closing of this critical gap was not provided in prior art double seat valves of the initially described type. In the implementation of the second basic inventive concept it is essential that the respective stop face on the second closing element and on the valve housing tightly and directly touch at the leakage cavity, completely circumferentially, as far as this is possible for solid or metallic contact. 
         [0023]    The degrees of freedom in the configuration of the second closing element with respect to possible action mechanisms of the seat seal are not limited by the aforementioned stop face. Fundamentally, in this region there can be purely axially or radially/axially acting second seals. 
         [0024]    It has furthermore been found to be favorable with respect to avoiding any formation of impact pressure if the first circumferential edge formed by the second seat surface and the end section of the first seat surface is rounded with the smallest possible second corner rounding. Ideally, a sharp-edge execution could be provided here, which, however, for reasons of production engineering and practical reasons (endangerment of the first seal) is not feasible. 
         [0025]    To achieve a smooth transition of the radial first seal from the cylindrical first seat surface into the cylindrical circumferential wall of the recess in the second closing element it is furthermore proposed that the cylindrical circumferential wall ends in the second inlet slope and the latter with the stop face forms the second circumferential edge. 
         [0026]    In order to prevent formation of impact pressure when the first seat cleaning flow enters the deflection surface in the second closing element, another proposal calls for the second circumferential edge formed by the stop face and the circumferential wall or the second inlet slope to be rounded with the smallest possible first corner rounding. A sharp-edged transition in this region is not favorable either here for reasons of production engineering and practical reasons, a relatively great radius of curvature is counterproductive and leads to unwanted formation of impact pressure. 
         [0027]    In order to prevent the first seat cleaning flow after leaving the deflection surface from flowing against the front face of the recess to form impact pressure, it is furthermore provided that the deflection surface undercuts the front face by the axial undercutting distance. In this way the contour of the deflection surface in the region of its discharge point can be pitched by a second deflection angle relative to the front face of the cylindrical recess such that the first seat cleaning flow is easily deflected in the direction to the second closing element and then can follow the wall shape of the bordering front face of the cylindrical recess for purposes of its cleaning. It has been found to be advantageous if the second deflection angle is made in the range of 5 to 20 degrees, preferably with 15 degrees. 
         [0028]    A flow result that is satisfactory in the same way is achieved according to another proposal by the contour being composed of a sequence of curved segments which on their respective transition sites each have a common tangent. Another embodiment calls for the contour to consist of a single section of continuously altered curvatures. Finally, it is also proposed that the contour is formed from a single section with a constant curvature. 
         [0029]    In order to ensure discharge of the cleaning liquid without problems or disruption under all pressure and velocity conditions, it is provided that the discharge bore connects the leakage cavity to the vicinity of the double seat valve by way of several connecting bores which are distributed over the periphery, and that the front-face boundary of the first closing element which faces the leakage cavity has a chamfer which declines toward the discharge bore and which is circumferential on all sides. 
         [0030]    In order to prevent the formation of vortices and impact pressure not only in the region of the above described seats surfaces of the double seat valve, it is advantageous if any internals and barriers in the remaining leakage cavity, as much as this is structurally possible, are omitted. In this respect, therefore, another proposal calls for the discharge bore to connect the leakage cavity to the vicinity of the double seat valve, and for the front-side boundary of the first closing element which faces the leakage cavity to have a chamfer which declines circumferentially on all sides toward the discharge bore. In this version a first shifting rod which is connected to the first closing element concentrically penetrates a second shifting rod which is made as a hollow rod and which is connected to the second closing element, continues floating through the discharge bore and is tightly connected on the end of the first closing element facing away from the second closing element to the first closing element via at least one essentially radially oriented traverse. In this way, the struts and other connecting means which are otherwise conventional in the region of the leakage cavity are avoided and shifted to the end which is relatively far away from the leakage cavity, where they can no longer have disruptive effects on flow guidance. 
         [0031]    The aforementioned chamfer of the front face of the first closing element which is facing the leakage cavity is advantageously made as the envelope of a cone which is inclined relative to the base surface of the cone in the range of 10 to 20 degrees, preferably 15 degrees. 
         [0032]    In this context, it is furthermore proposed that there are three traverses which are arranged distributed uniformly over the circumference securely on a section of the shifting rod, and which are tightly connected each radially outside to the circumferential ring and that the section of the shifting rod, the crosspieces and the ring form an integral welding part. 
         [0033]    Here, it is furthermore advantageous if the welding part on the outside via the ring adjoins a pressure balance piston which borders the section of the discharge bore away from the leakage cavity, and on the inside adjoins the first shifting rod by way of a section of the shifting rod and if the ring in its inside diameter is enlarged relative to the diameter of the discharge bore with the interposition of a conically widening transition region such that the inside passage of the discharge bore is not narrowed by the traverses. 
         [0034]    A second embodiment which relates to the second seat surface calls for the second seat surface to be made conical and to be tilted relative to the cylindrical recess by the seat angle, and for the second seal to seal axially/radially relative to the second seat surface in sliding/pressing engagement, the stop face adjoining the second seat surface according to the invention. The seat angle is made here in the range between 25 and 35 degrees, preferably with 30 degrees. 
         [0035]    According to another configuration, it is proposed that the second seat surface is perpendicular to the longitudinal axis of the double seat valve, and that the second seal surface seals axially relative to the second seat surface in pressing engagement, here, the stop face also adjoining the second seat surface according to the invention. 
         [0036]    Such solutions are possible with the advantages of an axially/ radially or a purely axially acting seal and a correspondingly interacting seat disk when the second seal is on the one hand made ductile and on the other can also undergo a change of shape with constant volume within the scope of its embedding such that the fixed contact of the second closing element with its stop face against the second seat surface, which contact is provided according to the invention, is ensured under all conditions, the fixed contact generally being a metallic contact. 
         [0037]    In the above described first embodiment of the double seat valve according to the invention, the amount of cleaning liquid in seat cleaning is conventionally limited by adjusting the gap between the respective seat seal and the associated seat surface. 
         [0038]    This invention within the scope of a second embodiment calls for limiting the amount of cleaning liquid in seat cleaning by means of a conventional throttle gap. For this purpose, it is provided that the end section provided on the first closing element on the leakage cavity side is made in the form of a cylindrical lug which with the first seat surface forms an annular first throttle gap. The second closing element, relative to its second seal, radially outside has a cylindrical circumferential contour, the latter forming an annular second throttle gap with an annular cylindrical recess in the connection opening on the side of the second closing element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]    Embodiments of the proposed seat cleanable double seat valve according to the invention are shown in the drawings and are described below according to structure and function. 
           [0040]      FIG. 1  shows in a longitudinal and vertical center section the seat-cleanable double seat valve according to the invention in a first embodiment, the closed position being shown, 
           [0041]      FIG. 1   a  shows in a longitudinal and vertical center section the double seat valve as shown in  FIG. 1 , its being in its open position, 
           [0042]      FIG. 2  shows in a longitudinal and vertical center section the double seat valve according to the invention in a second embodiment, the double seat valve being in its closed position and there being a limitation of the amount of cleaning liquid in both seat cleaning positions at this point by means of a throttle gap; 
           [0043]      FIG. 2   a  shows in a longitudinal and vertical center section the double seat valve shown in  FIG. 2  in its open position, 
           [0044]      FIG. 3  shows in a longitudinal section and extract an enlargement of the seat region of the double seat valve as shown in  FIGS. 1 to 2   a ; 
           [0045]      FIG. 4  shows schematically and enlarged the contour of the seat region for the first closing element and the bordering second seat surface for a double seat valve as shown in  FIGS. 1 to 3 ; 
           [0046]      FIG. 5   a  shows in a perspective an integral welding part consisting of three traverses which tightly connect the section of the shifting rod to a ring, for connecting the first valve rod to a pressure balance piston which is located on the end of the first closing element away from the leakage cavity, and 
           [0047]      FIG. 5   b  shows in a vertical center section a composite construction of a first closing element and indirectly bordering pressure balance piston, welding part and first valve rod. 
       
    
    
     DETAILED DESCRIPTION 
       [0048]    The double seat valve  1  according to the invention ( FIGS. 1 and 1   a ) in a first embodiment consists essentially of a valve housing  10  with a first and a second valve housing part  1   a  and  1   b,  two closing elements  3  and  4  which can move independently of one another with associated shifting rods  3   a  and  4   a,  and a seat ring  2  which produces a connection between the valve housing parts  1   a,    1   b  by way of an inside connection opening  2   c.    
         [0049]    The first closing element  3  (active closing element) which is made as a slide piston in the closed position of the double seat valve  1  is held to form a seal in the first seat surface  2   a  which is formed by the connection opening  2   c  and which is made as a cylindrical seat surface. For this purpose, in the slide piston  3 , there is a first seal  6  which interacts with the first seat surface  2   a  exclusively by radial pretensioning (radial seal with sliding engagement). The second closing element  4 , which is made as a seat disk, in the closed position of the double seat valve  1  interacts with a second seat surface  2   b  which is made perpendicular to the longitudinal axis of the double seat valve  1  on the top of the seat ring  2 . Sealing takes place by way of a second seal  7  which seals axially relative to the second seat surface  2   b  in pressing engagement (seal with pressing engagement). 
         [0050]    The two closing elements  3 ,  4  both in the illustrated closed as well as open position between themselves form a leakage cavity  5  which is connected to the vicinity of the double seat valve  1  by way of a discharge bore  3   d  which centrally penetrates a connecting part  3   b  which is connected to the first closing element  3  and a pressure balance piston  3   c  which continues on the connecting part. 
         [0051]    Conventionally, the first shifting rod  3   a  in the region of the first closing element  3  is securely connected to the latter by way of several webs which penetrate the discharge bore  3   d  in a star shape and in the radial direction. In the present case, these webs are formed between connecting bores  3   d * ( FIG. 3 ) which penetrate the closing element  3  distributed over the circumference and connect the discharge bore  3   d  to the leakage cavity  5 . Since these webs between the connecting bores  3   d * can have adverse reactive effects on the flow conditions and the flow pattern in the leakage cavity  5 , in the double seat valve  1  according to the invention it is preferably provided that these mechanically necessary connecting sites in the form of three traverses  3   e  which are located distributed uniformly over the circumference are shifted a distance away from the leakage cavity  5 , preferably towards the end of the pressure balance piston  3   c  facing away from the first closing element  3  ( FIGS. 1 ,  1   a ). The fixed connection to the piston takes place by way of a circumferential ring  3   g  to which the traverses  3   e  are securely connected radially on the outside. Advantageously, the traverses  3   e,  the ring  3   g,  and shifting rod section  3   a  are combined in an integral welding part  30  ( FIGS. 5   a ,  1 ). 
         [0052]    The second closing element  4  on its end facing the first closing element  3  has a recess  4   b  with an essentially cylindrical circumferential wall  4   c  which is flush with the cylindrical first seat surface  2   a  ( FIGS. 1 to 3 ). This circumferential wall  4   c  is dimensioned such that during the opening motion it accommodates the end section  3 * and the radial first seal  6  of the first closing element  3 , forming a seal, before the second closing element  4  opens. 
         [0053]    The circumferential wall  4   c  of the cylindrical recess  4   b  in the second closing element  4  on its end facing away from the first closing element  3  undergoes transition into a rotationally symmetrical deflection surface  4   d  (starting point of the contour (K)) ( FIGS. 3 ,  1 ), and this deflection surface  4   d  discharges in the front face  4   e  of the recess  4   b  which is oriented essentially perpendicular to the longitudinal axis of the second closing element  4  with a second deflection angle β. A second circumferential edge U 2 , which is formed by the circumferential wall  4   c  and a closing element-side stop face  4   f,  in the closed position of the second closing element  4  directly borders the first seat surface  2   a.  Viewed in a vertical center section, the deflection surface  4   d  has a contour K which runs without bends, a first section K 1  of the contour K which borders the circumferential wall  4   c  continuing over other sections K 2  and K 3  ( FIG. 3 ) and the direction vector at the end point of the last section K 3  or Kn being oriented toward the discharge bore  3   d  which is located centrally in the first closing element  3  or toward the connecting bores  3   d * without colliding with the first closing element  3  in the area of its regions enclosing the leakage cavity  5 . 
         [0054]    So that a first seat cleaning flow R 1  which is routed via the gap between the first seal  6  and the first seat surface  2   a  after the first partial lift T 1  of the first closing element  3  which is oriented downward relative to the position in the figure can be routed along the front face  4   e  of the recess  4   b  as tangentially as possible, without taking effect to form stagnation pressure ( FIG. 3 ), the deflection surface  4   d  undercuts the front face  4   e  by an axial undercut distance y. A front-side boundary of the first closing element  3  facing the leakage cavity  5  has an axial safety distance x from the direction vector at the exit site of the second seat surface  2   b  into a first end section  2   g  which is made on the first seat surface  2   a,  the exit site being made in the form of a first circumferential edge U 1 . 
         [0055]    In the open position of the double seat valve ( FIG. 1   a ), when a full opening lift H has been accomplished, it becomes clear that the first seal  6  which acts radially on the circumferential wall  4   c  of the recess  4   b  provides for reliable sealing of the two closing elements  3 ,  4  between the valve housing parts  1   a,    1   b  which are connected to one another by way of the connection opening  2   c  on the one hand and the leakage cavity  5  on the other. 
         [0056]      FIGS. 1 and 3  illustrate that the cylindrical circumferential wall  4   c  on its end facing the first closing element  3  begins with a second inlet slope  4   h  which is made preferably with a chamfer angle λ in the range from 5 to 15 degrees and here, in turn, preferably with 15 degrees and that the circumferential wall  4   c  on its other end undergoes transition into the first section K 1 . The latter is angled radially to the outside at a first deflection angle ε relative to the circumferential wall  4   c,  this first deflection angle ε being less than 15 degrees. 
         [0057]      FIG. 3  furthermore illustrates that in the closed position of the double seat valve  1  the first and the second circumferential edge U 1 , U 2  end congruently at the leakage cavity  5 . Here, the first end section  2   g  can be made as a conical section (first inlet slope) with exclusively curved or curved and straight contour elements, which is joined to the seat surface  2   a  by the radius of curvature r 2  (see also  FIGS. 4 and 1   a ) and opens toward the second closing element  4 . The first end section  2   g  is tilted by an angle of pitch δ against the first seat surface  2   a.  The angle of pitch δ is made in the range of 0 to 15 degrees, preferably in the range of 5 to 15 degrees and here, in turn, preferably with δ=15 degrees. 
         [0058]    Further optimization of the first end section  2   g  in the form of a further improved inlet slope is characterized as shown in  FIG. 4  in that the first end section  2   g  is formed by two envelopes of a cone which undergo transition into one another rounded with the radius of curvature r 2 , a second envelope of a cone  2   g . 2  which is joined directly to the first seat surface  2   a  being tilted by a second angle of pitch δ 2  against the first seat surface  2   a  and the other (the first) envelope of a cone  2   g . 1  being tilted by a first angle of pitch δ 1  against the first seat surface  2   a.  The first angle of pitch δ 1  is made in the range of 7.5 to 15 degrees, preferably with δ 1 =15 degrees, and the second angle of pitch is made in the range of 5 to 10 degrees, preferably with δ 2 =7.5 degrees. 
         [0059]    Furthermore, it is shown in  FIGS. 1 to 3  that the front face of the first closing element  3  toward the discharge bore  3   d  is provided with a declining conical chamfer  3   f,  the latter preferably being made as the envelope of a cone and being inclined by an angle of inclination ζ relative to the base of the cone. This angle of inclination ζ is preferably made in the range of 10 to 20 degrees and here again preferably with ζ=15 degrees. 
         [0060]    The first seat cleaning flow R 1  which emerges after completion of the first partial lift T 1  from the gap between the first seal  6  and the first seat surface  2   a  ( FIG. 3 ) in the course of seat cleaning of the first closing element  3  first flows vertically along the first seat surface  2   a,  without detaching follows the shape of the end section  3 * made as a first inlet slope  2   g  or as envelopes of a cone  2   g . 2 ,  2   g . 1  ( FIG. 4 ), bridges the inlet slope  4   h,  follows the circumferential wall  4   c  and the adjoining first section K 1  which is angled at the second deflection angle ε and without impact enters into the further shape of the deflection surface  4   d  with its following sections K 2  and K 3 , is diverted there according to the contour K, leaves the third and last section K 3  (K 3 =Kn) with the second deflection angle β, is largely tangentially deposited on the front face  4   e  and ultimately travels into the region of the discharge bore  3   d  and the connecting bores  3   d *. So that the first seat cleaning flow R 1  cannot form an impact pressure on the second circumferential edge U 2 , the latter in the closed position of the second closing element  4  directly borders the first end section  2   g  and is rounded with the smallest possible first corner rounding r 1 . 
         [0061]      FIG. 3  details, in particular, the contour K which runs without bends. The first section K 1  and the third and last section K 3  (K 3 =Kn) which discharge from the front face  4   e  are each made straight and these sections K 1  and K 3  are connected to one another by way of a second section K 2  which rounds the latter tangentially with a deflection radius as large as possible. 
         [0062]    A further configuration of the deflection surface  4   d  calls for the contour K to consist of a sequence of curved sections K 1  to Kn (e.g., arc of a circle, ellipses, parabolas, hyperbolas) which at their respective transition sites each have a common tangent. According to another configuration, the contour K is formed from a single section of continuously altered curvature (e.g., spirals or another curve shape which can be described as mathematically closed). The contour K according to another proposal is made with a single section with a constant curvature (e.g., a single arc of a circle with the required tangential entry and exit at the first deflection angle ε and the second deflection angle β. 
         [0063]    In the double seat valve  1  according to the invention in the first embodiment the second seat surface  2   b  is arranged perpendicular to the longitudinal axis of the double seat valve ( FIGS. 1 and 1   a ,  3 ), the second seal  7  located in the second closing element  4  sealing axially relative to this second seat surface  2   b  in pressing engagement. This solution is possible when the axially acting second seal  7  is ductile and a change of shape of constant volume is possible such that the first stop position of the second closing element  4  is ensured over the closing element-side chamfer surface  4   f  in the region of the second seat surface  2   b  which emerges in the first seat surface  2   a.  The front face of the second closing element  4  which encloses the second seal  7  radially outside recedes a distance to ensure the above described defined fixed stop position by the stop face  4   f  in the axial direction ( FIG. 3 ). 
         [0064]    The second seat surface  2   b  can also be made conical, the second seal  7  sealing axially/radially relative to the second seat surface  2   b  in sliding/pressing engagement. 
         [0065]    Seat cleaning of the second closing element  4  takes place ( FIG. 3 ) by the latter being struck by air by the second partial lift gap-wide from its associated second seat surface  2   b  and cleaning liquid in the form of a second seat cleaning flow R 2  being routed from the bordering first valve housing part  1   b  via the exposed second seat surface  2   b  into the leakage cavity  5 . To ensure that the second seat cleaning flow R 2  is not diverted prematurely in the direction of the first closing element  3 , the first circumferential edge U 1  formed by the second seat surface  2   b  and the first end section  2   g  is rounded with the smallest possible second corner round r 3  ( FIG. 4 ), as a result of which a defined flow detachment site forms at this location. This measure ensures that the second seat cleaning flow R 2  is not directed at the seat region of the first seal  6 . 
         [0066]    The first closing element  3  in seat cleaning of the second closing element  4  is axially positioned such that the second seat cleaning flow R 2  can flow unobstructed beyond the first closing element  3 . Depending on the given pressure conditions and under the influence of gravity in the arrangement of the double seat valve  1  as shown in the drawings, the liquid jet runs slightly parabolically so that the front face of the first closing element  3  with its chamfer  3   f  is overflowed tangentially; this is desirable for reasons of cleaning. Thus flow guidance and positioning of the first closing element  3  even achieve suction of the seat region of the first seal  6  so that even with loss or significant damage of the first seal  6 , cleaning liquid R 2  cannot enter the adjacent first valve housing part  1   a.    
         [0067]    The leakage space-side end of the gap between the second closing element  4  and the associated second seat surface  2   b  is, for the most part, sealed tight by the above described fixed stop position of the second closing element  4  with its stop face  4   f  on the second seat surface  2   b  (as far as this is generally possible in solid against solid contact, preferably metal against metal). Cleaning liquid of the first seat cleaning flow R 1  can no longer enter the gap between the second closing element  4  and the associated second seat surface  2   b  and thus the region of the second seal  7 . Even for a potentially seriously damaged or potentially completely removed second seal  7  therefore there is no longer any passage for cleaning liquid R 1 . 
         [0068]    A second embodiment of the double seat valve  1  according to the invention is shown in  FIG. 2  (closed position) and  FIG. 2   a  (open position). The end section  3 * provided on the first closing element  3  on the leakage space side is made in the form of a cylindrical first lug which with the associated section of the first seat surface  2   a  forms an annular first throttle gap D 1  (see also  FIG. 3 ). This first throttle gap D 1  takes effect when the first closing element  3  is pushed down by the first partial lift T 1  within the cylindrical first seat surface  2   a  so far that the first seal  6  detaches from the latter and the first seat cleaning flow R 1  is routed out of the first valve housing part  1   a  and is fed into the leakage cavity  5 . 
         [0069]    The second closing element  4 , relative to its second seal  7 , radially outside has a cylindrical circumferential contour  4 *, formed by the cylindrical external shape of the second closing element  4  which, with an annular cylindrical recess  2   d  in the connection opening  2   c  on the side of the second closing element  4 , forms an annular second throttle gap D 2  ( FIG. 3 ). This second throttle gap D 2  takes effect when the second closing element  4  is raised by the second partial lift T 2  off the second seat surface  2   b  so that the second seat cleaning flow R 2  is routed out of the second valve housing part  1   b  and fed into the leakage cavity  5 . 
         [0070]      FIG. 5   a  shows the integral welding part  30  which is formed from the shifting rod section  3   a *, the three traverses  3   e,  and the ring  3   g.  The three traverses  3   e  which are arranged uniformly distributed over the circumference of the shifting rod section  3   a * are connected securely to it. They are each connected radially outside likewise securely to the circumferential ring  3   g.  The welding part  30  on the outside is welded by way of the ring  3   g  to the pressure balance piston  3   c  (see  FIG. 5   b ) which borders the section of the discharge bore  3   d  away from the leakage cavity and inside to the first shifting rod  3   a  by way of the shifting rod section  3   a *. Here, the ring  3   g  in its inside diameter is enlarged relative to the diameter of the discharge bore  3   d  with the interposition of a conically widening transition region such that the inside passage of the discharge bore  3   d  is not narrowed by the traverses  3   e.    
       REFERENCE NUMBER LIST OF THE ABBREVIATIONS USED 
       [0000]    
       
           1  double seat valve 
           10  valve housing 
           1   a  first valve housing part 
           1   b  second valve housing part 
           2  seat ring 
           2   a  first seat surface (cylindrical seat surface) 
           2   b  second seat surface (axial; axial/radial) 
           2   c  connection opening 
           2   d  annular recess 
           2   g  first end section (first inlet slope) 
           2   g . 1  first envelope of a cone 
           2   g . 2  second envelope of a cone 
           3  first closing element (slide piston) 
           3 * end section (first cylindrical lug) 
           3   a  first shifting rod 
           3   b  connecting part 
           3   c  pressure balance piston 
           3   d  discharge bore 
           3   d * connecting bore 
           3   f  chamfer 
           30  welding part 
           3   a * shifting rod section 
           3   e  traverse 
           3   g  ring 
           4  second closing element 
           4 * cylindrical circumferential contour 
           4   a  second shifting rod 
           4   b  recess 
           4   c  circumferential wall 
           4   d  deflection surface 
           4   e  front face 
           4   f  stop face (closing element-side) 
           4   h  second inlet slope 
           5  leakage cavity 
           6  first seal (radial) 
           7  second seal (axial; radial; axial/radial) 
         r 1  first corner rounding (second closing element  4 ) 
         r 2  radius of curvature (first inlet slope  2   g;    2   g . 1 ;  2   g . 2 ) 
         r 3  second corner rounding (housing-side; seat ring  2 ) 
         x axial safety distance 
         y axial undercutting distance 
         β second deflection angle 
         δ angle of pitch (of first inlet slope  2   g ) 
         δ 1  first angle of pitch (first conical section  2   g . 1 ) 
         δ 2  second angle of pitch (second conical section  2   g . 2 ) 
         ε first deflection angle 
         ζ angle of inclination 
         λ chamfer angle (of second inlet slope  4   h ) 
         D 1  first throttle gap 
         D 2  second throttle gap 
         H complete opening lift (completely open position) 
         K contour of deflection surface  4   b    
         K 1  first section (first straight line) 
         K 2  second section (curved contour) 
         K 3  third section (second straight line) 
         Kn last section 
         R 1  first seat cleaning flow 
         R 2  second seat cleaning flow 
         T 1  first partial lift (first partially open position/first seat cleaning position 
         T 2  second partial lift (second partially open position/second seat cleaning position 
         U 1  first circumferential edge 
         U 2  second circumferential edge