Double seat valve and method for cleaning a double seat valve

Abstract

The invention relates to a double seat valve, comprising a first housing part (12) which can be connected to a first fluid connection and a second housing part (14) which can be connected to a second fluid connection, between which housing parts a housing passage (16) is formed, and comprising a first closing element (18) and a second closing element (20), wherein the first closing element and the second closing element can be moved by means of a valve drive (25) coaxially along a valve axis (24) respectively between a closed position and an open position, wherein the closing elements block a flow of fluid through the housing passage in the closed position and permit a flow of fluid though the housing passage in the open position. The invention also relates to a method for cleaning a double seat valve.

Description

[0001] Double seat valve and method for cleaning a double seat valve

[0002] The invention relates to a double-seat valve comprising a first housing part connectable to a first fluid port and a second housing part connectable to a second fluid port, between which a housing passage is formed, further comprising a first closing element and a second closing element, wherein the first closing element and the second closing element are each movable coaxially along a valve axis between a closed position and an open position by means of a valve actuator, wherein the closing elements block the flow of fluid through the housing passage in their closed position and allow the flow of fluid through the housing passage in their open position, wherein the first closing element interacts sealingly with a first valve seat in the closed position and is lifted from the first valve seat in the open position.and wherein the second closing element, in the closed position, seals against a second valve seat and, in the open position, is lifted from the second valve seat, wherein the housing passage has a cylindrical inner surface, and wherein, as the first closing element moves into its open position, it is received in a recess formed in the second closing element, and the second closing element is also moved into its open position as the first closing element moves into its open position, wherein the recess is bounded by a cylindrical inner wall aligned with the cylindrical inner surface of the housing passage, and wherein the closing elements define a leakage cavity between them connected with a drain opening.and wherein the first closing element for cleaning the first valve seat and the second closing element for cleaning the second valve seat can be moved independently of one another by a partial stroke into a seat cleaning position in which a cleaning fluid can flow through a cleaning gap opened in the seat cleaning position along the valve seat to be cleaned into the leakage cavity. The invention also relates to a method for cleaning such a double-seat valve.

[0003] Double-seat valves of the type described above have two independently movable closing elements, designed, for example, as valve discs. In the closed position, the closing elements seal a housing passage connecting two fluid ports. In the open position, the closing elements release the housing passage, allowing fluid to flow. Such valves are used, for example, in hygienic applications, such as in the food industry. Between the closing elements, the valve elements define a leakage cavity, which is connected to the valve's surroundings via a drain opening. If the seal of one of the closing elements fails, fluid can enter the leakage cavity in the closed position and be detected, thus identifying the seal defect.

[0004] The leakage cavity also serves to clean the valve, particularly the valve seats of the closing elements and the seals. For this purpose, one of the closing elements, while the other closing element is in the closed position, can be moved relative to it into a seat-cleaning position. In this position, a cleaning fluid can flow into the leakage cavity through a cleaning gap formed in the seat-cleaning position. The cleaning fluid flows over the valve seat of the closing element in the seat-cleaning position and usually also over the seal of the closing element, thus cleaning the surfaces over which it flows.

[0005] Such a double-seat valve is known, for example, from WO 2013 / 113341 AL. Further such double-seat valves are known from EP 2 861 898 Bl or EP 2 167 850 B1. The cleanability of such double-seat valves is of great importance for hygienic applications. This is particularly true in the food sector. The double-seat valve described, for example, in WO 2013 / 13341 AL exhibits particularly good cleanability due to the design of the contours in the leakage cavity. The cleaning fluid flow through the cleaning gap also passes over an engagement area where the other closing element engages with its valve seat. According to the Bernoulli effect, the fluid flow creates a negative pressure at this engagement area. This prevents mixing between the leakage cavity and the respective housing chambers connected to the fluid ports.

[0006] Based on the prior art described above, the invention aims to provide a double-seat valve and a method of the type mentioned above, with which the mixing-proof cleanability of a double-seat valve of the type mentioned above can be further improved, in particular the mixing safety in the event of a sealing defect can also be increased.

[0007] The invention solves the problem through independent claims 1 and 14. Advantageous embodiments can be found in the dependent claims, the description and the figures.

[0008] For a double-seat valve of the type mentioned above, the invention solves the problem by providing that the outer circumferential surface of the first closing element is curved in an arc towards the valve axis in the direction of the leakage cavity, so that when the first closing element is moved into the seat cleaning position, the cleaning fluid follows the arcuate curvature when flowing into the leakage cavity, and in particular is guided along this arcuate curvature.The invention further solves the problem by a method for cleaning a double-seat valve according to the invention, in which the first closing element is moved into the seat cleaning position for cleaning the first valve seat and subsequently a cleaning fluid flows through the cleaning gap released in the seat cleaning position along the first valve seat into the leakage cavity, wherein the cleaning fluid is discharged via the drain opening after flowing through the leakage cavity and / or in which the second closing element is moved into the seat cleaning position for cleaning the second valve seat and subsequently a cleaning fluid flows through the cleaning gap released in the seat cleaning position along the second valve seat into the leakage cavity, wherein the cleaning fluid is discharged via the drain opening after flowing through the leakage cavity.

[0009] As previously mentioned, the double-seat valve can be used for hygienic applications, particularly in the food sector. The fluid conveyed through the double-seat valve can be a liquid, especially a food-grade liquid or, in the case of cleaning, a cleaning fluid. The double-seat valve has a valve body comprising a first and second body section and a passage between them. The first body section and the passage, and / or the second body section and the passage, can also be designed as a single unit. The first body section can be connected to the first fluid port, and the second body section can be connected to the second fluid port. The fluid ports can be integrated into the double-seat valve.Fluid can flow through the housing passage between the first and second fluid ports when both closing elements are in their open position. If at least one of the closing elements is in its closed position, fluid flow through the housing passage is blocked. The first closing element can comprise a first valve disc, and the second closing element can comprise a second valve disc. Seals are arranged on the first and second valve discs, which, in the closed position, seal against the respective valve seat of the closing element. These seals can be, in particular, fully circumferential ring seals, for example, circular ring seals. The ring seals can be molded seals, for example, having a V-shaped cross-section. The first valve seat can be formed by an inner surface of the housing passage, particularly a circular cylindrical one.The first locking element, in its closed position, can radially seal against this surface with a ring seal, particularly an annular one, arranged on the outer circumferential surface of the first locking element. Of course, an axial seal for the first locking element would also be possible.

[0010] The first and second locking elements are movable relative to each other. The second locking element can, for example, be cup-shaped. The first locking element can be piston-shaped. The second locking element forms a recess bounded by a wall section. When the first locking element is moved from its closed position to its open position, it is initially moved into the recess of the second locking element until it abuts the recess, for example, a bottom surface of the recess. The recess is bounded by a cylindrical inner wall of the wall section that is flush with the cylindrical inner surface of the housing opening. When the first locking element is in the recess, it can again radially seal against this inner wall with its ring seal, provided that the seal also enters the recess during the movement of the first locking element.As the first closing element moves into the open position, the second closing element is lifted from its valve seat and moved into the open position. The second closing element can be moved passively into the open position, in particular by the first closing element carrying the second closing element into the open position. Thus, the second closing element can be a passive closing element and the first a passive closing element. Of course, it is also conceivable that the second closing element is actively moved from its closed position to its open position.

[0011] In a manner known per se, the closing elements define a leakage cavity between them. If a defect occurs in the seal of the first or second closing element, fluid can enter the leakage cavity along the defective seal when the valve is closed. This fluid can be detected, thus identifying the seal defect. Fluid can be drained from the leakage cavity via the drain opening, particularly into the vicinity of the double-seat valve. A cleaning fluid, particularly a cleaning liquid, can also be introduced into the leakage cavity to clean the first or second valve seat and the respective seals, and possibly other surfaces over which a cleaning fluid flows. This cleaning fluid can then also flow out via the drain opening, particularly into the vicinity of the double-seat valve.For this purpose, one of the closing elements is moved slightly along the valve axis into a seat cleaning position, as described above, so that the seal of the closing element in the seat cleaning position is slightly lifted from the valve seat of the closing element. This creates a cleaning gap through which the cleaning fluid can flow into the leakage cavity. The other closing element remains in its closed position, so that, assuming the sealing function of the closing element in the closed position is correct, the introduced cleaning fluid cannot enter the other fluid port. Mixing is thus prevented. The cleaning fluid flowing into the leakage cavity passes over the valve seat of the closing element moved into the seat cleaning position and over the seal of this closing element, cleaning the corresponding surfaces.Other surfaces over which the cleaning fluid flows, in particular an engagement area of ​​the seal of the closing element in the closed position with its valve seat, are also cleaned by the cleaning fluid.

[0012] According to the invention, the outer circumferential surface of the first closing element has an arcuate curvature in the direction of the leakage cavity. The cleaning fluid entering through the regularly narrow cleaning gap is partially deflected away from the cylindrical inner surface of the housing passage and thus also from the engagement area between the second closing element and the second valve seat by the arcuately curved outer circumferential surface of the first closing element. In this process, the cleaning fluid is guided by the curvature as it enters the leakage cavity. This can also lead to a division or fanning out of the cleaning fluid flow in the direction of the valve axis. Therefore, according to the invention, a flow contour is provided on the side of the first closing element following the flow direction of the introduced cleaning fluid of the ring seal of the first closing element, which in longitudinal section points towards the valve axis.The stroke axis of the double-seat valve points away from the cylindrical inner surface of the housing passage and consequently also away from the cylindrical inner wall of the recess, which is aligned with it. It should be noted that the aforementioned effect of the arc-shaped curvature, namely the guiding of incoming fluid, occurs not only in the seat cleaning position of the first closing element, but also in the event of a defect in the ring seal of the first closing element and the resulting ingress of fluid into the leakage cavity in the closed position of the first closing element. According to the invention, it was found that a portion of the fluid or cleaning fluid entering the leakage cavity adheres to the arc-shaped flow contour and is thereby deflected away from the engagement area of ​​the second closing element and second valve seat, which is particularly critical with regard to mixing-proof cleaning.This reduces the fluid volume at this engagement point. While guiding the flow along the curvature may lead to a decrease in the fluid flow velocity, fluid stagnation near the inlet between the second closing element and the second valve seat is reduced and ideally prevented. The effect of stagnation or pressure field on the critical engagement point is thus reliably avoided, ensuring a particularly dependable and sufficient vacuum in this area. The leakage cavity is typically at atmospheric pressure, while the fluid connections are usually at least atmospheric pressure or higher. A vacuum is generated in the engagement area relative to the pressure acting in the leakage cavity, which is generally atmospheric pressure. The pressure at the fluid connections is often higher than in the leakage cavity.The lowest pressure in the arrangement is therefore generally found at the aforementioned engagement area. The cleanability of the double-seat valve according to the invention is further improved, and the mixing safety is further increased, both during cleaning and in the event of a seal defect.

[0013] The arcuate curvature of the outer circumferential surface can extend to an end face of the first closing element that defines the leakage cavity. Furthermore, it is possible for the arcuate curvature to extend to a receiving opening in the outer circumferential surface that accommodates the ring seal. It is also possible for a section, for example cylindrical, to be located between the end face and the curvature and / or between the curvature and the receiving opening. The ring seal can be held clamped in the receiving opening. The receiving opening can, for example, be formed by an annular groove in the outer circumferential surface. The inventive effect of the arcuate curvature is particularly pronounced in the aforementioned embodiments, since the curvature extends over a particularly large area.In a further embodiment, the cylindrical inner wall of the second locking element can transition into an annular end face on its side facing the first locking element in the closed position, and an edge between the cylindrical inner wall and the end face can be chamfered. The chamfer can form a conically circumferential surface. The annular end face of the second locking element can be circular. The chamfer is a circumferential chamfer over the edge between the cylindrical inner wall and the end face. It is possible that the chamfer has no curvature in the direction of the valve axis.

[0014] According to the aforementioned further development of the second closing element, the edge between the annular end face, which in particular includes the ring seal of the second closing element, and the cylindrical inner wall, which serves as a seat for the ring seal of the first closing element in the recessed state, has a chamfer. It was found according to the invention that the chamfer has an advantageous effect on the flow pattern of fluid during cleaning of the double-seat valve or in the event of a seal defect, particularly in conjunction with the arcuate flow contour of the first closing element according to the invention. The chamfer thus creates a space that can be briefly surrounded by fluid during a switching operation of the double-seat valve, which is then discharged via the leakage cavity during this brief moment. This process is also referred to as switching leakage.The aim in designing a double-seat valve is to minimize switching leakage. The chamfer provided in the aforementioned design, extending towards the ring seal of the second closing element, promotes the generation of a favorable vacuum in the engagement area between the second closing element and the second valve seat. Simultaneously, the chamfer, particularly its axial extension across the double-seat valve, shifts the design-related stagnation point, as described above, away from the critical engagement area between the second closing element and the second valve seat, towards the transition of the chamfer to the cylindrical inner wall of the second closing element. This further improves the necessary vacuum generation in the critical engagement area.The aforementioned advantages of the chamfer thus have a particularly beneficial effect on the cleanability and mixing safety of the double seat valve according to the invention in combination with the arc-shaped curved flow contour of the first closing element, by achieving the necessary negative pressure with simultaneously reduced switching leakage.

[0015] As previously explained, a ring seal can be arranged on the annular end face of the second closing element, with which the second closing element, in the closed position, seals against a seat surface of the housing passage that forms the second valve seat. The ring seal can itself be an annular ring seal.

[0016] In a further embodiment, the chamfer can have an angle relative to the valve axis of between 2° and 15°, preferably between 3° and 8°, and more preferably 5°. According to the invention, a positive correlation was observed between increasing chamfer height in the axial direction of the double-seat valve and the arcuate flow contour according to the invention. In principle, it therefore appears desirable to design the chamfer to be high in the axial direction and, if necessary, also to provide it with a large depth perpendicular to the valve axis in order to achieve a particularly pronounced negative pressure and to make the flow contour according to the invention particularly effective through the described shift in the stagnation point. On the other hand, such a chamfer design undesirably increases the switching leakage. According to the invention, it was found that the chamfer angle ranges described above are particularly preferred in order to minimize the switching leakage.With these angle ranges, it is possible to select the chamfer depth in a direction perpendicular to the valve axis in such a way that switching leakage is minimized, resulting in a correspondingly advantageous chamfer height due to the specified angle values.

[0017] Valve actuators can be designed in various ways. For example, they can be pneumatic, hydraulic, or electric.

[0018] The first closing element can comprise a first valve disc arranged on a first valve stem that is movable along the valve axis by the valve actuator. Similarly, the wider closing element can comprise a second valve disc arranged on a second valve stem that is movable along the valve axis by the valve actuator. The first valve stem can be designed as an axially movable hollow stem in which the second valve stem is axially movably mounted. Alternatively, the second valve stem can also be designed as an axially movable hollow stem in which the first valve stem is axially movably mounted.

[0019] The double-seat valve according to the invention can further comprise a cleaning fluid supply configured to allow a cleaning fluid to flow through the cleaning gap, which is released in the seat cleaning position, along the valve seat to be cleaned and into the leakage cavity. The cleaning fluid supply can include a cleaning fluid reservoir. The cleaning fluid can be a cleaning liquid, as explained above.

[0020] An embodiment of the invention is explained in more detail below with reference to the figures. They schematically show:

[0021] Figure 1 shows a double-seat valve according to the invention in a partially longitudinally sectioned side view, Figure 2 shows a partially enlarged view of the double-seat valve shown in Figure 1, and

[0022] Figure 3 shows a representation corresponding to Figure 2 in the seat cleaning position of the first locking element.

[0023] Unless otherwise stated, the same reference symbols in the figures denote the same objects.

[0024] The double-seat valve according to the invention comprises a valve housing 10 with a first housing part 12 and a second housing part 14, between which a housing passage 16 is formed. The first housing part 12 can be connected to a first fluid port and the second housing part 14 to a second fluid port. The double-seat valve further comprises a first closing element 18 and a second closing element 20, which are shown in their closed positions in Figures 1 and 2. The first closing element 18 is designed as a valve disc, which is arranged on a first valve stem 22. By means of a valve actuator 25, which can be, for example, a pneumatic, hydraulic, or electric actuator, the first valve stem 22 and with it the first closing element 18 can be moved along the valve axis 24.The second closing element 20 is also designed as a valve disc and is arranged on a second valve stem 26, which is designed as a hollow stem. The first valve stem 22 is guided axially within the second valve stem 26. By means of the valve actuator 25, the second valve stem 26 and with it the second closing element 20 can also be moved in the axial direction.

[0025] The piston-shaped first closing element 18 is received in the housing passage 16 in the closed position of the double-seat valve shown in Figures 1 and 2. In this position, the first closing element 18, with a ring seal 28 arranged in a receiving opening on an outer circumferential surface of the first closing element 18, abuts radially against a cylindrical inner surface 30 of the housing passage 16, which forms a first valve seat. The cup-shaped second closing element 20 has a cylindrical inner wall 32 that is flush with the cylindrical inner surface 30 and transitions into an annular end face 34 on its side facing the first closing element 18 in the closed position.A ring seal 36 is arranged in a receiving opening on the annular end face 34. In the closed position, the second closing element 20 seals against this ring seal and rests against a seat surface 38 of the housing passage 16, forming a second valve seat, as can be seen particularly in the enlarged views of Figures 2 and 3. In their closed position, the first closing element 18 and the second closing element 20 block the housing passage 16 against the flow of fluid between the first housing part 12 and the second housing part 14, and thus between the first fluid port and the second fluid port.

[0026] To move into its open position, the first closing element 18 is moved upwards by the valve actuator 25 over the first valve stem 22 in Figure 1, whereby the first closing element 18 is received in a recess 40 bounded by the cylindrical inner surface 32 of the second closing element 20. At the end of this receiving movement, the upper surface of the first closing element 18 abuts the bottom surface 42 of the recess 40. During a further upward movement of the first closing element 18, it carries the second closing element 20 in Figure 1 upwards with it, so that this second closing element 20 is also moved into its open position. In the process, the seals 28 and 36 are lifted from their respective valve seats.In the open position of the first and second closing elements 18, 20, the housing passage 16 is open for fluid flow between the first housing part 12 and the second housing part 14, and thus between the first fluid port and the second fluid port. The first closing element 18 and the second closing element 20 also define a leakage cavity 44 between them, which is connected to the environment of the double-seat valve via a drain opening (not shown). If a seal defect occurs in one of the closing elements 18, 20, and fluid passes through the contact point between the respective seal and the respective valve seat in the closed position, this fluid can be detected in the leakage cavity 44 and, if applicable, in the drain opening. This function and this design of the double-seat valve are known per se.

[0027] With reference to the enlarged views in Figures 2 and 3, the inventive design of the flow-guiding contours, particularly in the area of ​​the leakage cavity 44, will be explained in more detail. Figures 2 and 3 show an enlarged view of the section shown at X in Figure 1.

[0028] While Figure 2 shows the closed position of the closing elements 18, 20, as also shown in Figure 1, Figure 3 shows the state in which the first closing element 18 has been moved into its seat cleaning position by a partial stroke. As explained, the first closing element 18 and the second closing element 20 can be moved independently of each other in the direction of the valve axis 24. In particular, the closing elements 18, 20 can be moved independently of each other by a partial stroke along the valve axis 24 into a seat cleaning position for cleaning their respective valve seats. In this position, a cleaning fluid can flow through a cleaning gap opened in the seat cleaning position along the valve seat to be cleaned into the leakage cavity 44.Figure 3 illustrates this for the first locking element 18, which, to move into the seat cleaning position, was moved slightly downwards compared to the closed position shown in Figure 1, i.e., in the opposite direction to the movement into the open position. The second locking element 20 can be moved slightly in the same direction to move into the seat cleaning position as to move into the open position, i.e., upwards in Figure 1.

[0029] Figure 3 shows that the ring seal 28 has been lifted downwards from the cylindrical inner surface 30 of the housing passage 16, which forms the first valve seat, into an area where the cylindrical inner surface 30 of the housing passage 16 has a recess 46. A narrow cleaning gap 48 is formed between the outer circumferential surface of the first closing element 18 and the cylindrical inner surface 30 of the housing passage 16, which forms the valve seat. A cleaning fluid can flow from the chamber 50 along the recess 46 into the leakage cavity 44 through this gap. The surfaces over which the cleaning fluid flows, which may in particular be a cleaning liquid, including the ring seal 28 and the first valve seat, are cleaned in this process.

[0030] Figures 2 and 3 further show that the outer circumferential surface of the first closing element 18 has a flow contour 52 curved in an arc towards the valve axis 24 in the direction of the leakage cavity 44, which can extend to an end face 54 of the first closing element 18 that bounds the leakage cavity 44. On the opposite side, the curved flow contour 52 can extend essentially to the receiving opening for the ring seal 28. However, a cylindrical surface section can also be provided between the arc-shaped curvature and the receiving opening, as in the example shown. The cleaning fluid flowing in through the cleaning gap 48 is guided along the curved flow contour 52, and in particular divided, as illustrated by arrows 56 in Figure 3.In particular, at least part of the cleaning fluid flow is deflected away from the cylindrical inner surface 30 of the housing passage 16 and thus also from the inner circumferential wall 32 of the second closing element 20 located above it.

[0031] In Figures 2 and 3, reference numeral 58 illustrates the contact area between the annular end face 34 with the ring seal 36 of the second closing element 20 and the seat surface 38 of the housing passage 16, which forms the second valve seat. This contact area 58 is particularly critical for preventing mixing between the fluid ports of the double-seat valve. The relatively narrow cleaning gap 48 constricts the flow path of the cleaning fluid, thereby accelerating the flow. The cleaning fluid flow also passes over the contact area 58, creating a negative pressure on the minimal gap between the annular end face 34 of the second closing element 20 and the seat surface 38 of the housing passage 16, which forms the valve seat. This negative pressure prevents cleaning fluid from entering the gap and contaminating the second valve seat.By guiding the cleaning fluid flow along the arc-shaped flow contour 52, the cleaning fluid flows to the contact area 58 in a reduced quantity, thus preventing undesirable stagnation of the cleaning fluid in this area. Such stagnation would reduce the negative pressure acting in the contact area 58. The same effect can be advantageously used in the event of a defect in the sealing action of the first closing element 18 by the ring seal 28.

[0032] An additional improvement in the mixing-proof cleaning is achieved by providing a chamfer 60 to an edge between the cylindrical inner wall 32 and the end face 34 of the second closing element 20. In the example shown, the chamfer 60 is formed at an angle of 5° to the valve axis 24 and to the cylindrical inner wall 32. As explained above, this further improves the flow conditions, particularly with regard to good cleanability and high mixing resistance. Of course, other chamfer angles relative to the valve axis 24 and to the cylindrical inner wall 32 are also possible.

[0033] Reference sign

[0034] 10 Valve housings

[0035] 12 first housing part

[0036] 14 second housing part

[0037] 16 Housing passage

[0038] 18 first locking element

[0039] 20 second locking element

[0040] 22 first valve shaft

[0041] 24 valve axis

[0042] 25 Valve Actuator

[0043] 26 second valve shaft

[0044] 28 ring seal

[0045] 30 interior surface

[0046] 32 Interior wall

[0047] 34 Front surface

[0048] 36 ring seal

[0049] 38 Seating area

[0050] 40 Exclusion

[0051] 42 floor area

[0052] 44 Leakage cavity

[0053] 46 In-depth study

[0054] 48 cleaning gap

[0055] 50 Room

[0056] 52 Flow contour

[0057] 54 Front surface

[0058] 56 arrows

[0059] 58 Contact area

[0060] 60 phase

Claims

Claims 1. Double seat valve, • comprising a first housing part (12) connectable to a first fluid connection and a second housing part (14) connectable to a second fluid connection, between which a housing passage (16) is formed, • further comprising a first closing element (18) and a second closing element (20), wherein the first closing element (18) and the second closing element (20) are each movable coaxially along a valve axis (24) between a closed position and an open position by means of a valve actuator (25), wherein the closing elements (18, 20) block a flow of fluid through the housing passage (16) in their closed position and allow a flow of fluid through the housing passage (16) in their open position, • wherein the first closing element (18) in the closed position interacts sealingly with a first valve seat and in the open position is lifted from the first valve seat, and wherein the second closing element (20) in the closed position interacts sealingly with a second valve seat and in the open position is lifted from the second valve seat, • wherein the housing passage (16) has a cylindrical inner surface (30), wherein the first locking element (18) is received in a recess (40) formed in the second locking element (20) as it moves into its open position, and the second locking element (20) is also moved into its open position as the first locking element (18) moves into its open position, wherein the recess (40) is formed by a cylindrical inner surface (30) of the The housing passage (16) is limited by the aligned cylindrical inner wall (32), • wherein the closing elements (18, 20) define between them a leakage cavity (44) connected with a drain opening, and wherein the first closing element (18) for cleaning the first valve seat and the second closing element (20) for cleaning the second valve seat can be moved independently of each other by a partial stroke into a seat cleaning position in which a cleaning fluid can flow through a cleaning gap (48) released in the seat cleaning position along the valve seat to be cleaned into the leakage cavity (44), characterized in that the outer circumferential surface of the first closing element (18) is curved (52) in the direction of the leakage cavity (44) towards the valve axis (24), so that when the first closing element (18) is moved into the seat cleaning position, the cleaning fluid follows the arcuate curvature (52) when flowing into the leakage cavity (44).

2. Double seat valve according to claim 1, characterized in that the first valve seat is formed by the cylindrical inner surface (30) of the housing passage, against which the first closing element (18) in its closed position abuts a sealing ring seal (28) arranged on an outer circumferential surface of the first closing element (18).

3. Double seat valve according to one of the preceding claims, characterized in that the first closing element (18) when it is received in the recess with the ring seal (28) abuts the cylindrical inner wall (32) of the recess (40) in a sealing manner.

4. Double seat valve according to one of the preceding claims, characterized in that the arc-shaped curvature (52) of the outer circumferential surface extends to an end face (54) of the first closing element (18) that limits the leakage cavity (44).

5. Double seat valve according to one of the preceding claims, characterized in that the arcuate curvature (52) of the outer circumferential surface extends to a receiving opening of the outer circumferential surface receiving the ring seal (28) or that a cylindrical section is provided between the arcuate curvature (52) of the outer circumferential surface and a receiving opening of the outer circumferential surface receiving the ring seal (28).

6. Double seat valve according to one of the preceding claims, characterized in that the cylindrical inner wall (32) of the second closing element (20) transitions into an annular end face (34) on its side facing the first closing element (18) in the closed position, and that an edge between the cylindrical inner wall (32) and the end face (34) is provided with a chamfer (60).

7. Double seat valve according to claim 4, characterized in that the chamfer (60) forms a conically circumferential surface.

8. Double seat valve according to one of claims 6 or 7, characterized in that a ring seal (36) is arranged on the annular end face (34) of the second closing element (20), with which the second closing element (20) in the closed position abuts a seat surface (38) of the housing passage (16) forming the second valve seat.

9. Double seat valve according to one of claims 6 to 8, characterized in that the chamfer (60) has an angle relative to the valve axis (24) of between 2° and 15°, preferably between 3° and 8°, more preferably of 5°.

10. Double seat valve according to one of the preceding claims, characterized in that the valve actuator (25) comprises a pneumatic actuator, a hydraulic actuator or an electric actuator.

11. Double seat valve according to one of the preceding claims, characterized in that the first closing element (18) comprises a first valve disc (18) arranged on a first valve stem (22) movable along the valve axis (24) by the valve actuator (25), and that the second closing element (20) comprises a second valve disc (20) arranged on a second valve stem (26) movable along the valve axis (24) by the valve actuator (25).

12. Double seat valve according to claim 11, characterized in that the first valve stem (22) is designed as an axially movable hollow stem in which the second valve stem (26) is axially movably received, or that the second valve stem (26) is designed as an axially movable hollow stem in which the first valve stem (22) is axially movably received.

13. Double seat valve according to one of the preceding claims, characterized in that it further comprises a cleaning fluid supply which is configured to allow a cleaning fluid to flow through the cleaning gap (48) released in the seat cleaning position along the valve seat to be cleaned into the leakage cavity (44).

4. A method for cleaning a double-seat valve according to one of the preceding claims, wherein the first closing element (18) is moved into the seat cleaning position for cleaning the first valve seat and a cleaning fluid is subsequently introduced through the cleaning gap (48) released in the seat cleaning position along the first valve seat into the leakage cavity (44), wherein the cleaning fluid is discharged via the drain opening after passing through the leakage cavity (44) and / or wherein the second closing element (20) is moved into the seat cleaning position for cleaning the second valve seat and a cleaning fluid is subsequently introduced through the cleaning gap (48) released in the seat cleaning position along the second valve seat into the leakage cavity (44), wherein the cleaning fluid is discharged via the drain opening after passing through the leakage cavity (44).

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