CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of international patent application no. PCT/EP2004/000987, filed Feb. 4, 2004 designating the United States of America and published in German as WO 2004/081431 on Sep. 23, 2004, the entire disclosure of which is incorporated herein by reference. Priority is claimed based on Federal Republic of Germany patent application no. DE 103 10 662.6, filed Mar. 12, 2003. 


   BACKGROUND OF THE INVENTION 
   The present invention relates to a valve, particularly for pressure exchanger installations comprising pressure exchangers with tubular chambers through which an alternating flow takes place, a rotatable closing element arranged inside a housing, the housing having a plurality of connections for connecting lines, the housing being connected to a first pipe system and in each case one end of at least one pressure exchanger, a respective other end of each pressure exchanger being connected through a valve to a second pipe system, and the closing element being provided with a motor-operated drive shaft. 
   In order to treat water, the reverse osmosis process is often used. In this process, a fluid stream to be purified is forced at high pressure through a membrane system which, in the case of large quantities of fluid, comprises a plurality of membrane modules. In such membrane modules, separation into pure water and an enriched concentrate is carried out through a membrane, since only some of a fluid to be purified can flow through a membrane. The proportion flowing through emerges as a usable proportion, as pure water or else permeate, on the other side of the membrane. The part which does not flow through leaves a membrane module as brine, a concentrate of the fluid enriched with salts and minerals, as a proportion which cannot be used and is under high pressure. This pressure is around 2 bar with a module inlet pressure of about 65 bar. 
   U.S. Pat. No. 5,306,428 discloses a reverse osmosis installation in which pressure exchangers in the form of tubular chambers are used to recover energy. By using these, the still high pressure of the high energy brine flowing out of the membrane module is transferred to a fluid still to be purified. Thus, a pump drive output which is lower by the amount of this pressure increase is required for the fluid to be introduced in order to generate the high pressure needed for the reverse osmosis process. 
   In order to control and/or switch the fluid paths of the brine into and out of the pressure exchangers, a Valve with a rotating closing element is used, in addition to other Valves. By using such a Valve, the tubular chambers of the pressure exchangers have brine emerging from the membrane modules applied to them alternately. The rotating closing element is constructed as a roll, in which connecting ducts are arranged in the manner of a three-way valve. During the changeover operations, all the flow paths are shut off completely. In order to avoid pressure surges during such changeover operations, pressure equalizing ducts are arranged within the roll. 
   Depending on the operating period of a membrane, its separation capability decreases and a fluid to be purified has to remain for a correspondingly longer time within a membrane module. For this reason, in the prior art, the changeover times of the roll are regulated using an actuating motor. However, this valve is suitable only for small reverse osmosis installations, since the flow cross sections within the valve are approximately the same size as the flow cross sections of the ducts to be filled. In large installations and the fluid columns to be displaced therein, and as a result of the forces necessitated thereby, a considerable problem of dimensioning the valve arises. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a changeover device, in particular for large reverse osmosis installations and the like, with which large flows of fluid can be distributed between different pressure exchangers in a straightforward and fault-free manner. 
   The solution to this program provides for a flow splitter provided with a plurality of transfer paths to be arranged within the housing, for openings of the transfer paths to be arranged at two axial ends and on the circumference of the flow splitter, and for a rotating, disk-like control element to be arranged in a sealing manner at each end of the flow splitter. Thus, in the case of such fluid flows which are to be controlled and which change direction periodically, a changeover with few pressure surges can be achieved. 
   Refinements of the invention provide for the end regions of the flow splitter inside the housing to be connected to the tubular chambers in which a pressure exchange is carried out with the aid of the changing fluid flows. In each case a connection for a supply of high pressure fluid and a discharge of low pressure fluid are arranged on the housing of the valve, in the circumferential region of the flow splitter and on the housing. What is known as brine under high pressure (HPB), for example, flows to the valve through the connection for a high pressure fluid. Following pressure transmission, the brine then flows in depressurized form, as what is known as low pressure brine (LPB) out of the housing through the discharge for low pressure fluid. 
   In the flow splitter there are arranged flow paths with the aid of which the flows having different pressures are distributed. In this case, within the flow splitter, two outer flow paths are connected to a high-pressure side and a central flow path, arranged between the former, is connected to a low pressure side. In order to ensure long-term operating reliability under the continuously changing pressure loadings, one or more reinforcing elements can additionally be arranged in one or more of the flow paths. This depends on the physical configuration of the flow splitter and the materials used. 
   The flow splitter can be an integral constituent part of the housing. It has been shown to be advantageous if the flow splitter is constructed as a housing insert. In this way, housing fabrication is simplified and the number of sealing points located on the housing can be reduced. It has likewise proven to be advantageous with regard to the closing behavior if the flow splitter is constructed as a ceramic or a ceramic-coated component. 
   The control elements are advantageously constructed in the form of a rotating rotary slide, which means that secure management of the sealing functions is possible, in addition to simple production. Therefore, a previously known closing element is replaced by control elements which act as temporary closing elements only during their rotational movement. The control elements alternately control the flow through the overflow paths of the flow splitter, which means that secure and efficient flow changeover is ensured. Furthermore, the control elements are provided with control openings located opposite one another in pairs, which means that a flow of a large amount is achieved in a small space. 
   Using an embodiment in which the control openings of a control element are arranged to be offset by at most 90° from one another in each case in relation to the control openings of the other control element, alternating changeover of the flow direction to the tubular chambers connected to the housing is carried out in an extremely simple way during a rotational movement of the control elements. 
   Since the control elements are subjected to alternating loading in operation, they are provided with reinforcements on the side facing away from the flow splitter. It is likewise possible. to provide the control elements with reinforcements on their circumference. These may be additional material masses, built-in components, supporting elements, tensioning elements and the like. This depends on the materials used. 
   In order to reduce the forces between flow splitter and control element, one or more depressions are arranged on the ends of the flow splitter in order to form narrow bearing surfaces. This measure avoids contact over the entire area, by which higher frictional forces are caused. Instead, the formation of narrow contact surfaces is thus possible, which also permit improved sealing at the same time. 
   In order to separate different pressure regions in the chambers located in the housing, seals bear on the control elements on the side facing away from the flow splitter. These can be of a sliding ring seal design. Apart from the ability to be produced easily, the advantage of the. known secure sealing action is therefore provided. In addition, the shaft is arranged in a region of the housing which is shielded by the seals and is connected to the low pressure side LPB. As a result, a passage of the shaft through the housing wall to the outside advantageously only has to be sealed by a conventional shaft seal designed for low pressure. This entails less effort than sealing off such a shaft passageway with respect to the high pressure side HPB. And, within the Valve, as a result no additional seals are required for the passage of a shaft. 
   Further refinements provide for a shaft driving the control elements to pass through the flow splitter and for the control elements to be connected in a force-transmitting manner to the shaft. This simplifies the mounting and the driving of the control elements. The control elements are constructed as ceramic or coated components, which provide high resistance to wear and attack by the fluid flows to be controlled. 
   Mounting and maintenance are made considerably easier if flow splitter, shaft and control elements are all constructed as a housing insert. Thus, serviceability can be ensured in an extremely short time. And, as a result of the arrangement of sealing zones arranged on the circumference of the flow splitter between inlet and outlet, overflow between these two zones is avoided. 
   In order to achieve a gentle changeover, the tubular chambers of the pressure converter are connected to one another briefly by the position and the size of the control openings during a movement of the rotary slide. The position and the size of the control openings on the control elements constructed as rotary slides permits a flow changeover which is free of pressure surges, since a simultaneous connection to a supply of high pressure fluid is thereby always ensured. Closing a control opening of a connected tubular chamber is at the same time connected with opening of another previously closed control opening of a further tubular chamber and vice versa. Because of the enlarged control openings and because of their position on the control element, an overlap with the flow openings arranged fixedly in the flow splitter is achieved. Such an overlap in this case has a beneficial effect on the changeover and the behavior of the flowing fluid columns affected thereby. 
   Depending on the flow rate of the pressure converter, the position of the control openings is changed at a continuous and/or discontinuous speed. The degree to which the tubular chambers are filled can therefore be influenced. The use of a discontinuous speed permits a longer residence time of the flow openings over the control openings, utilizing the full opening cross section. The discontinuous movement achieves greater channel filling in a shorter time and thus a maximum possible flow rate. This can be done with the aid of an appropriately designed drive motor. When a conventional rotary drive with continuous movement of the control elements is used, the same device can also be used for small installations, since a smaller flow rate is switched therewith. Conversely, with a discontinuous movement of the control elements, at a given flow rate the overall volume of the device can be reduced. With the aid of adjustable switching times of the control elements, the volume throughput can be influenced as a function of the pressure differences present. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in further detail hereinafter with reference to illustrative preferred embodiments shown in the accompanying drawing figures, in which: 
       FIGS. 1   a  and  1   b  are sectional views of the Valve, offset through 90°, in a first operating state, in each case in the plane of the inlets and outlets; 
       FIGS. 2   a  and  2   b  are sectional views of the Valve, offset through 90°, in a second operating state, the control elements in each case being illustrated rotated through 90° with respect to  FIGS. 1   a  and  1   b;    
       FIG. 3   a  is a perspective view of the flow splitter; 
       FIG. 3   b  is a perspective view of the flow splitter in which one quarter of the flow splitter has been cut away in order to make the flow paths visible; 
       FIG. 4   a  is a perspective view of the flow splitter in the assembly with the two control elements in a first operating state, with the upper part having been cut away in order to clarify the flow direction; and 
       FIG. 4   b  is a perspective view of the flow splitter in the assembly with the two control elements in a second operating state, the control elements being illustrated rotated through 90° in each case with respect to  FIG. 4   a.    
   


   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   A Valve  1  is shown in section in  FIG. 1   a . The housing  2  has two connections  3 ,  4  through which a connection to the tube chambers (not shown) of a pressure exchanger system is made. An alternating exchange of a fluid which flows in under high pressure and flows back at lower pressure is effected via the connections  3 ,  4 . Arrows  5 ,  6  show the respectively prevailing flow directions. The distance between the connections  3 ,  4  is chosen in accordance with the distance between tubular chambers to be connected thereto. This integration of the connections  3 ,  4  into the housing  2  avoids unnecessary additional sealing points. 
   Arranged inside the housing  2  is a flow splitter  7  which, in the illustrative embodiment shown, is configured as a separate insert. It can equally well be configured as a single-piece component with the housing  2 . The flow splitter  7 , formed as an insert here, is sealed off with respect to the housing  2  with the aid of seals  8 . In the region of the circumference of the flow splitter  7  there is arranged a chamber  9 , which is used to discharge a depressurized fluid. In each case a control element  12 ,  13  bears in a sealing manner on the ends  10 ,  11  and is set rotating with the aid of a shaft  14  driven by a motor, not illustrated. The force is transmitted between shaft  14  and the control elements  12 ,  13  by means of bearing elements  15 . These can be configured as polygons or force-Valve and form-Valve in another way. The shaft  14  is mounted in the interior of the housing  2  at one end and, on the opposite side, is mounted and sealed off in a cover  16  which closes the housing  2 . 
   The rotating control elements  12 ,  13 , which are configured in the manner of rotary slides here, have reinforcements  12 . 1  to  13 . 2 . These reinforcements improve the alternating bending loading of the control elements  12 ,  13  during the changeover operation. Depending on the materials used, that is to say metal or ceramic or combinations thereof, these reinforcements can be formed as accumulations of material, plates, rings, struts or the like. 
   In the illustration of  FIG. 1 , a fluid under high pressure, for example a high pressure brine (HPB), flows from two T-shaped flow paths  17 ,  18  through control openings  19 ,  20  arranged opposite one another in pairs and belonging to the control element  13  into an end region  21  of the housing  2  and from there, via the connection  4 , to a tubular chamber. At the same instant, a fluid under a low pressure, for example a low pressure brine LPB, flows through the connection  3  from a tubular chamber into the end region  22  of the housing  2 . 
   Seals  23  bearing on each control element  12 ,  13  prevent fluid exchange with other housing regions. The seals  23  are constructed in the manner of a sliding ring seal, held in the housing  2  so as to be secured against rotation, and bear in a sealing manner on the control elements  12 ,  13  under the pressure of springs  24 . 
     FIG. 1   b  corresponds to the illustrative embodiment of  FIG. 1   a  in terms of the instantaneous position of the control elements in relation to the flow splitter. However, a section rotated through 90° is shown in  FIG. 1   b . It reveals that, of the control element  12 , the control openings  25 ,  26  arranged in pairs are connected in a fluid-carrying manner to a flow path  27  which is arranged in the center of the flow splitter  7 . The central flow path  27 , designed for an outward flow of a low pressure fluid (LPB) is arranged between the two flow paths  17 ,  18  designed for a high pressure fluid (HPB). In order to manage the alternatingly occurring forces securely, a reinforcing element  29  of a transverse rib type is arranged in the flow path  27 . This ensures a beneficial flow of force within the flow splitter  7 . 
   A low pressure fluid supplied through the connection  3  into the housing  2  flows via the control opening  25 ,  26  into the flow path  27  and from there flows out of the housing as low pressure fluid via an opening  28  in the flow splitter  7  and an outlet  30 . Arranged opposite the outlet  30  on the housing  2  is a connection  31  for the supply of high-pressure fluid HPB to the housing  2 . With the aid of the chamber  32  arranged on the circumference of the flow splitter  7 , the high pressure fluid is conducted to the two T-shaped flow paths  17  and  18 . With the aid of the low pressure chamber  9  arranged opposite, the low pressure fluid is discharged from the housing  2  via the outlet  30 . 
     FIGS. 2   a  and  2   b  show the same sections through the Valve as  FIGS. 1   a  and  1   b , but in a second operating state. In this case, the control elements  12  and  13  have been rotated onward through 90° in each case via the shaft  14  and the bearing elements  15 . The fluid (HPB) flowing into the flow paths  17 ,  18  through the high pressure connection  31  and the chamber  32  is now deflected via the control openings  25 ,  26  into the chamber  22 , from where it passes via the connection  3  to a tubular chamber (not shown). At the same time, low pressure fluid (LPB) flows via the connection  4  from a second tubular chamber into the chamber  21 , through the control openings  19 ,  20  into the central flow path  27  in the flow splitter  7  and from there out of the Valve via the opening  28 , the chamber  9  and the connection  30 . By further rotation of the parts  12 ,  13 ,  14  and  15  through 90°, the first operating state, illustrated in  FIGS. 1   a  and  1   b , is then reached again. 
     FIG. 3   a  shows a perspective view of the flow splitter  7  with a central flow path  27 , and  FIG. 3   b  shows, by means of a partial section in the flow splitter  7 , the position of the outer flow paths  17  and  18  still located therein. In the central flow path  27  there is a reinforcing element  29 , in which there is an opening for the shaft  14  to extend through. Furthermore, a plurality of depressions  33  are made in the end  11  of the flow splitter  7 , which means that narrow bearing surfaces  34  are formed on the end face  11 . This reduces the frictional forces between the parts sliding on one another and at the same time improves the sealing action. The T-shaped course of the flow paths  17 ,  18  ensures in the simplest way that an alternating outflow of a high pressure fluid into the respectively connected tubular chamber becomes possible as a result of the control openings  19 ,  20 ;  25 ,  26  sliding alternately past. A fluid flows out of the central flow path  27  to the outside via an opening  28  and via the outlet  30  from the housing  2 . 
     FIGS. 4   a  and  4   b  show a perspective arrangement of the functional parts in the form of the flow splitter  7 , the control elements  12 ,  13 , the shaft,  14  and the bearing elements  15  of the Valve  1 , in each case in partial section. Here,  FIG. 4   a  shows the first operating state and  FIG. 4   b  the second operating state with the parts  12 ,  13 ,  14  and  15  rotated through 90° in each case with respect to the flow splitter  7 . In  FIG. 4   a  it becomes clear how, in a first operating state, the high pressure fluid HPB flows through the flow paths  17 ,  18  and the control openings  19 ,  20  to the side at the front in this view. At the same time, on the other side or, here, the rear side, the path via the central flow path  27  to the opening  28  is free via the flow openings  25 ,  26  arranged in pairs, the latter being hidden. 
   In the second operating state, shown in  FIG. 4   b , the relationships in the converse state are illustrated. For this purpose, the control elements  12 ,  13  are shown as having been rotated through 90° with respect to the flow splitter  7  with the aid of the shaft  14  and the bearing elements  15 . In this view of the drawing, a high pressure fluid (HPB) flows rearward via the flow openings  25 ,  26  of the control element  12 . At the same time, via the flow openings  19 ,  20  likewise arranged in pairs ( 19  has been cut away by the partial sectional illustration), a depressurized low pressure fluid LPB passes from the front side of the view of the drawing into the central flow path  27  and flows out of the Valve from there via the opening  28 . 
   By means of this solution having the control elements  12 ,  13  arranged on both sides of a flow splitter  7 , an extremely compact changeover Valve with high operational reliability is provided. At the same time, the number of sealing points and pipeline connections needed for such a Valve could be reduced to a minimum. 
   The foregoing description and examples have been set forth merely to illustrate the invention and are not intended to be limiting. Since modifications of the described embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed broadly to include all variations within the scope of the appended claims and equivalents thereof.
A valve for switching fluid paths, particularly for pressure exchanger installations with tubular chambers through which fluid flows in an alternating manner, including a rotatable closing element ( 12, 13) provided with a motorized drive shaft ( 14) and arranged inside a housing ( 2) having a plurality of connections ( 3, 4) for connecting lines leading to a pipe system and to a respective end of at least one pressure exchanger. Another end of each pressure exchanger is connected through a valve arrangement to a second pipe system. A splitter ( 7) provided with a plurality of overflow paths ( 17, 18, 27) is arranged inside the housing ( 2); mouths of the overflow paths are located on two axial end faces ( 10, 11) and on the circumference of the splitter ( 7), and a rotatable, disk-shaped control element ( 12, 13) is arranged in a sealing manner at each end face of the splitter ( 7).