Abstract:
A diaphragm valve has a valve housing and a valve member movable relative to said housing. The valve member includes a diaphragm carrier that can be driven to execute a switchover motion having a sealing diaphragm mounted thereon, which delimits a valve chamber in which a valve seat is found. The sealing diaphragm has a sealing section opposite said valve seat belonging at least partially to a loose diaphragm section of the sealing diaphragm, which can lift from the diaphragm carrier to reduce the stress on the sealing diaphragm when said diaphragm carrier is removed from the valve seat during switching.

Description:
This application claims priority based on an International Application filed under the Patent Cooperation Treaty, PCT/EP2013/000715, filed Mar. 11, 2013, which claims priority based on German Patent Application No. DE102012005093.5, filed Mar. 14, 2012. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a diaphragm valve, having a valve housing and at least one valve member movable relative to this housing, wherein the valve member has a diaphragm carrier movable relative to the valve housing through the execution of a switchover movement and also a flexible sealing diaphragm which, together with the valve housing, bounds a valve chamber, wherein the sealing diaphragm is fixed to the valve housing under sealing at its outer edge section and has a mounting diaphragm section fastened to the diaphragm carrier with clearance from said outer edge section and accompanying the switchover movement, wherein there is mounted in the valve chamber a valve seat facing the sealing diaphragm, against which a sealing section of the sealing diaphragm at least partly supported by a base surface of the diaphragm carrier facing the valve chamber may be pressed with sealing, in order to separate from one another two fluid passages opening into the valve chamber. 
     A diaphragm valve of this type known from EP 1 722 137 A2 contains at least one valve member, mounted in a valve housing and comprising a sealing diaphragm bounding a valve chamber, and a diaphragm carrier which carries the sealing diaphragm and is designed in the manner of a plunger and may be moved linearly relative to the valve housing. The diaphragm carrier supports with its base surface an annular sealing section of the sealing diaphragm which may be brought into contact with an annular valve seat located in the valve chamber, so as to separate from one another two fluid passages opening into the valve chamber. The sealing section is part of a diaphragm section fixed to the valve member and which may be described as the mounting diaphragm section and which accompanies the switchover movement of the diaphragm carrier. At its outer edge section the sealing diaphragm is clamped with sealing to the valve housing. A disadvantage of the known diaphragm valve lies in the fact that, during switchover of the valve member, the sealing diaphragm is for a time heavily stretched and therefore subject to great stress, which may have a disadvantageous effect on its service life. 
     Known from DE 20023225 U1 is a diaphragm valve of similar design, which has two valve members, each containing a diaphragm carrier designed in the manner of a plunger, and a sealing diaphragm fastened to the diaphragm carrier and cooperating with a valve seat, wherein the sealing diaphragms may be made in one piece with a diaphragm body. 
     DE 60017310 T2 discloses a diaphragm valve with a valve housing with a diaphragm carrier carrying a sealing diaphragm and suspended from a valve housing. With its base surface the diaphragm carrier supports two sealing sections of the sealing diaphragm, each able to cooperate with a separate valve seat in order to connect with or separate from one another altogether three fluid passages opening into a valve chamber. The switching position of the valve carrier may be preset by drive means which act on the diaphragm carrier and generate its pivoting switchover movement. With this diaphragm valve too there is the problem that the flexible sealing diaphragm, especially in the diaphragm section extending between the diaphragm carrier and the fixed edge section, is heavily stretched and subject to high tensile stresses. 
     In the case of a diaphragm valve known from DE 20 2009 016 447 U1, a sealing diaphragm is fastened to a pivotable diaphragm carrier only in the area of two sealing sections, each opposite a valve seat. The problems of a sealing diaphragm which is heavily stressed on account of its being stretched also apply to this diaphragm valve. The same applies to the diaphragm valve described in DE 20 2009 000 593 U1, in which the diaphragm valve is pivotable in the manner of a rocker, in order to change the switching position of the valve. 
     A diaphragm valve known from DE 7324333 U has a sealing diaphragm which seals a valve chamber and which is held tight by a stiffening plate. Projections extending away from the sealing diaphragm pass through the stiffening plate and rest on an actuating element mounted pivotably independent of the sealing diaphragm in a valve housing. The sealing diaphragm does not take part in the pivoting movement of the diaphragm carrier, which impairs the available valve stroke. 
     FR 2795798 A discloses a diaphragm valve with a valve member which has a pivotable diaphragm carrier and a diaphragm body fastened to the diaphragm carrier, wherein the diaphragm body forms a sealing diaphragm, fixed in the valve housing at the edge with sealing. In pivoting of the diaphragm carrier, a diaphragm section of the sealing diaphragm bordering the diaphragm carrier is subject to high tensile stress, which can impair life expectancy. 
     Further types of diaphragm valve are known from U.S. Pat. No. 6,789,781 B2, WO 2004/005778 A1, GB 596533 A, DE 102005021583 A1 and U.S. Pat. No. 7,779,867 B2. 
     SUMMARY OF THE INVENTION 
     The invention is based on the problem of creating a diaphragm valve with a sealing diaphragm which is subject to low stress in order to gain high life expectancy. 
     To solve this problem it is provided that, in conjunction with the features described above, the sealing section is at least partly a constituent of a loose diaphragm section of the sealing diaphragm which extends, without being fastened to the diaphragm carrier, from the mounting diaphragm section to the outer edge section of the sealing diaphragm fixed to the valve housing, so that it is able to lift from the base surface of the diaphragm carrier when the diaphragm carrier removes itself from the valve seat during its switchover movement. 
     In this way, to break the fluid connection of two fluid passages, a sealing section of the sealing diaphragm is also pressed with sealing, by the diaphragm carrier bearing the sealing diaphragm, against an assigned valve seat. By this means, even with high fluid pressure, undesired lifting of the sealing section from the valve seat is counteracted and high sealing quality is ensured. At the same time, the sealing diaphragm itself is subject to only minimal stretching when the sealing section is lifted from the assigned valve seat by the appropriate switchover movement of the diaphragm carrier. The reason for this is that at least a portion of the sealing section belongs to a diaphragm section of the sealing diaphragm which extends between the mounting diaphragm section and the outer edge section of the sealing diaphragm fixed to the valve housing, in a manner not fastened to the diaphragm carrier, and is therefore able to detach itself from the base surface of the diaphragm carrier when the diaphragm carrier moves away from the assigned valve seat during its switchover movement. This non-fixed diaphragm section is described as the loose diaphragm section. Whereas the sealing section therefore, for fluid-tight interaction with the valve seat, is supported physically by the diaphragm carrier, at least a portion of the sealing section has scope to lift itself from the base surface of the diaphragm carrier with which it was previously in contact, or to detach itself from this base, when the diaphragm carrier is moved, in the sense of moving away from the valve seat, for the purpose of opening a fluid connection. Here in particular a pattern of behaviour may occur which might be described as a folding back or folding away of the loose diaphragm section. At the same time, in particular a gap, expanding wedge-like towards the edge of the base, may open up between the loose diaphragm section and the diaphragm carrier. Since the sealing diaphragm is not compelled, in the sections which are able to lift from the diaphragm carrier, to accompany the switchover movement of the diaphragm carrier to the full extent, it is subject to relatively low tensile stress. This results in a high life expectancy for the diaphragm valve, combined with the opportunity to design the diaphragm valve with compact dimensions. The fact that a constituent part of the sealing diaphragm containing at least a portion of the sealing section is able to detach itself from the diaphragm carrier makes it possible to use a sealing diaphragm which, in addition to the diaphragm carrier, needs no special space for deformation in the valve housing. 
     The diaphragm valve may have only one valve member or several and in particular two valve members. In a design with several valve members, each valve member expediently includes a separate diaphragm carrier and a separate sealing diaphragm, wherein however the sealing diaphragm is a one-piece component of a uniform diaphragm carrier. 
     Advantageous developments of the invention are revealed in the dependent claims. 
     The diaphragm carrier may for example be so designed that the switchover movement is a pivoting movement. Regarded as especially expedient, however, is a design in which the switchover movement of the diaphragm carrier is a linear movement. Such a diaphragm carrier is in particular plunger-like and has an axial end face facing the sealing diaphragm and forming the base surface serving to support the sealing section. 
     Preferably the sealing diaphragm is fastened by its mounting diaphragm section in the area of the base surface of the diaphragm carrier in such a way that there is radial clearance between this mounting diaphragm section and the outline of the base surface of the diaphragm carrier. The section of the sealing diaphragm between the mounting diaphragm section and the outline of the base surface is a constituent part of the loose diaphragm section. The mounting diaphragm section is in particular located centrally in the area of the base. Especially expedient is a variant in which the mounting diaphragm section encloses the mounting diaphragm section all round in an area in front of the base. This leads in particular to an annular area of the loose diaphragm section, which is movable relative to the diaphragm carrier during the switchover movement of the diaphragm carrier, so that it is not compelled to follow the switchover movement to the diaphragm carrier to the full extent, in which it would be subject to a high tensile loading. 
     In a preferred embodiment, the valve seat of the diaphragm valve is annular and closed, so that it frames the passage opening of a fluid passage. To block this fluid passage, a similarly annular sealing section of the sealing diaphragm also fits up against the valve seat. At least one portion of this annular sealing section is in the form of a part of the loose diaphragm section, so that it can lift up from the diaphragm carrier when the latter is moved away from the valve seat to open up the fluid passage. 
     Preferably the sealing diaphragm is so designed that an annular sealing section cooperating with an annular valve seat is in its entirety a constituent part of the loose diaphragm section, so that it is able to lift as a whole from the base surface of the diaphragm carrier, when the diaphragm carrier moves away from the valve seat in the course of the switchover movement. In principle, however, a design is also possible in which the sealing section cooperating with the valve seat is partly a constituent part of the mounting diaphragm section and only partly a constituent part of the loose diaphragm section. 
     When the base surface of the diaphragm carrier is viewed in a plan view, the sealing section lies expediently completely within the outer contour of the base surface of the diaphragm carrier. 
     In a similarly advantageous embodiment of the diaphragm valve, the valve seat is web-like and extends in such a way between two opposing side wall sections of the valve chamber that it divides this valve chamber into two chamber sections lying this side and that side of the web-like valve seat. The sealing section, in this case strip-like, belongs at least partly to the loose diaphragm section. In particular a form of construction is provided in which the sealing section is formed partly by the mounting diaphragm section, so that it is able to lift only partially from the base surface of the diaphragm carrier. The sealing section expediently has two areas able to lift from the diaphragm carrier and flanking the mounting diaphragm section on opposite sides. 
     Preferably the sealing diaphragm, in the area of the mounting diaphragm section, is fastened solely in the interior of the diaphragm carrier. In particular in this connection it is advantageous if the sealing diaphragm is part of a one-piece diaphragm body, which has in the area of the mounting diaphragm section at least one and preferably exactly one mounting extension, extending from the base surface to engage in the diaphragm carrier. At the point where the mounting extension engages in the diaphragm carrier, the base surface has an opening, wherein the base surface is in particular annular and preferably circular-arc-shaped. 
     The fastening of the sealing diaphragm inside the sealing diaphragm is effected in particular solely on the basis of positive or friction locking. For example a diaphragm body may, in the course of its manufacture by injection moulding, be moulded on to the diaphragm carrier, wherein a mounting extension engaging in the diaphragm carrier is formed. It is however quite easily possible to fix the mounting diaphragm section alternatively or additionally by adhesive bonding to the diaphragm carrier, for example through an adhesive bond. 
     The sealing diaphragm is preferably so designed that it extends all round the diaphragm carrier along the outer contour of the base surface of the diaphragm carrier and has a diaphragm outer section bordering the base surface on the outside and merging into the outer edge section fixed with sealing to the valve housing. This diaphragm outer section is expediently covered at its top which faces away from the valve chamber by a support wall of the valve chamber, so that it can also withstand high fluid pressures prevailing in the valve chamber. The support wall expediently has an orifice through which the diaphragm carrier extends in a manner which allows the switchover movement, giving the advantage that the gap between the diaphragm carrier and the support wall can be kept very small. 
     The valve chamber and the sealing diaphragm closing the valve chamber have in particular a longitudinal shape with a narrow-sided rounded contour, or expediently have a round contour. In the valve chamber, the passage openings of the entering fluid passages are preferably arranged alongside one another wherein, in the case of an elongated valve chamber they are arranged consecutively at intervals, in particular in the axial direction of this valve chamber. 
     The diaphragm valve is expediently equipped with electrically actuable drive means, which serve for actuation of the valve member and which in particular facilitate the driving of the diaphragm carrier to perform its switchover movement as required, and also its holding in the respectively desired position. Such drive means preferably include at least one electromagnetic device and preferably also a return spring device which presets a desired basic position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The invention is described in detail below with the aid of the appended drawing, showing in: 
         FIG. 1  a longitudinal section through a preferred embodiment of the diaphragm valve according to the invention, and having a web-like valve seat, along section line I-I of  FIGS. 2 and 3 , and showing a closed position, 
         FIG. 2  the diaphragm valve of  FIG. 1  in a longitudinal section rotated through 90° relative to  FIG. 1 , and along section line II-II of  FIGS. 1 and 3 , 
         FIG. 3  a cross-section through the diaphragm valve according to section line III-III of  FIG. 1 , 
         FIG. 4  the diaphragm valve of  FIGS. 1 to 3  in an open position and in a longitudinal sectional view corresponding to  FIG. 1  along section line IV-IV of  FIG. 5 , 
         FIG. 5  the diaphragm valve adopting the open position in a longitudinal section according to section line V-V of  FIG. 4 , 
         FIG. 6  the longitudinal section illustrated in  FIG. 5 , with an isometric perspective, 
         FIG. 7  a further embodiment of the diaphragm valve according to the invention, with an annular valve seat, wherein a closed position is shown in a longitudinal section according to section line VII-VII of  FIGS. 8 and 9 , 
         FIG. 8  the diaphragm valve of  FIG. 7  in a longitudinal section rotated through 90°, according to section line VIII-VIII of  FIGS. 7 and 9 , 
         FIG. 9  a cross-section through the diaphragm valve of  FIGS. 7 and 8  according to section line IX-IX of  FIG. 7 , 
         FIG. 10  the diaphragm valve of  FIGS. 7 to 9  in an open position and in a longitudinal section corresponding to  FIG. 7  according to section line X-X of  FIG. 11 , 
         FIG. 11  the diaphragm valve of  FIGS. 7 to 10  in a longitudinal section according to section line XI-XI, illustrating by dot-dash lines a preferred embodiment of electrically actuable drive means for the valve member, and 
         FIG. 12  a further embodiment of the diaphragm valve according to the invention, with two annular valve seats, in a sectional view analogous to  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The diaphragm valve designated in its totality by reference number  1  has in all embodiments a valve housing  2  and a valve member  3  mounted in and movable relative to the valve housing  2 . In addition, the diaphragm valve  1  is equipped with electrically actuable drive means  4 , preferably accommodated in the interior of the valve housing  2  and through which the valve member  3  may be switched between two possible switching positions.  FIGS. 1 and 2  together with  7  and  8  show in each case a first switching position, which involves a closed position.  FIGS. 4 to 6  plus  10  and  11  show in each case a second switching position, involving by way of example an open position. 
     The valve member  3  is preferably designed as a composite element, comprised of a diaphragm body  5  and at least one diaphragm carrier  6  carrying the diaphragm body  5 . These components are fastened together in a manner to be explained below. Whereas the diaphragm carrier  6  is made of a stiff material, for example of a rigid plastic material or of metal, the diaphragm body  5  is made of a flexible and preferably rubber-elastic material. Preferably the diaphragm body  5  is an elastomer body. 
     Inside the valve housing  2  is a hollow space forming a valve chamber  7 . The valve chamber  7  is bounded on one side by the valve housing  2  and on the other side by a diaphragm-like part of the diaphragm body  5  designated as the sealing diaphragm  8 . 
     The valve housing  2  defines a base surface  12  bounding the valve chamber  7  at the bottom. The base surface  12  is preferably part of a first housing section  13  of the valve housing  2 . 
     The sealing diaphragm  8  extends in two dimensions, extending at an upper side beyond the base surface  12 . With an outer edge section  14  defining the outer contour of the sealing diaphragm  8 , the sealing diaphragm  8  is so fixed to the valve housing  2 , with sealing, that together with the base surface  12  it bounds the sealed valve chamber  7  from the surrounding area. 
     The fluid-tight fixing of the outer edge section  14  is expediently realised by the firm clamping of this outer edge section  14  between the first housing section  13  and a second housing section  15  of the valve housing  2 . At the outer edge section  14 , the sealing diaphragm  8  has expediently in this connection a mounting bead  21  determining the outer contour of the sealing diaphragm  8 . This engages in annular slots formed on the facing surfaces of the first and second housing sections  13 ,  15 . 
     The direction in which the sealing diaphragm  8  lies opposite the base surface  12  is described below as the vertical direction  16 . At right-angles to the vertical direction  16 , the valve chamber  7  has a main axis  17  and a lateral axis  18  at right-angles to the former. In the embodiment of  FIGS. 7 to 11 , the valve chamber  7  has preferably an elongated shape, with the main axis  17  forming the longitudinal axis. In the area of the narrow sides, the valve chamber  7  is here in particular rounded.  FIGS. 1 to 6  show that the valve chamber may also have a different outline. In this embodiment the valve chamber  7 , viewed in the vertical direction  16 , has a circular outline. The specified outlines apply equally to the respectively assigned sealing diaphragm  8 , wherein the outline of the sealing diaphragm  8  is determined in particular by the course of the outer edge section  14 . 
     To the side, each valve chamber  7  is bounded by a side wall  22  determining the outline referred to above, which extends upwards above a bottom  23  of the valve chamber  7  facing the sealing diaphragm  8  and formed on the base surface  12 . The diaphragm body  5  has a mounting extension  24 , preferably formed in one piece with the sealing diaphragm  8 , and extending away in the vertical direction  16  towards the diaphragm carrier  6 . The diaphragm body  5  is fastened to the diaphragm carrier  6  by means of this mounting extension  24 . In the embodiment of  FIGS. 1 to 6 , the mounting extension  24  is provided in the central section of the sealing diaphragm  8 . Varying from this, in the embodiment of  FIGS. 7 to 11 , it is mounted off-centre on the sealing diaphragm  8  in the axial direction of the main axis  17 . 
     The diaphragm carrier  6  is mounted on the side of the sealing diaphragm  8  opposite the base surface  12  in the vertical direction  16 . The sealing diaphragm  8  therefore lies between the valve chamber  7  and the diaphragm carrier  6  in the vertical direction  16 . 
     In all embodiments, the diaphragm carrier  6  is mounted with linear movement capability relative to the valve housing  2 . The movement which may be executed by the diaphragm carrier  6  is subsequently described as the switchover movement  26 , because it acts directly on the switching position of the valve member  3 . The switchover movement  26  is preferably a linear movement, running in the case of the embodiments in the vertical direction  16 . Accordingly the diaphragm carrier  6  may be moved to and fro in the vertical direction  16  during execution of a linear switchover movement  26 . In this connection, depending on the direction of movement, the diaphragm carrier  6  moves towards or away from the base surface  12 . 
     A section of the sealing diaphragm  8  accompanies the switchover movement  26  of the diaphragm carrier  6  without restriction. This involves a diaphragm section of the sealing diaphragm  8  described hereafter as the mounting diaphragm section  36 , via which the sealing diaphragm  8  is fastened to the diaphragm carrier  6 . 
     Common to all the embodiments is that the sealing diaphragm  8 , in the area of the mounting diaphragm section  36 , is fastened solely inside the diaphragm carrier  6 . For this purpose the mounting extension  24  is provided directly on the mounting diaphragm section  36  and engages, from the side of a base surface  38  of the diaphragm carrier  6  facing the sealing diaphragm  8 , in a mounting recess  43  of the diaphragm carrier  6  which is open towards the base surface  38 . The base surface  38  is preferably flat and extends in particular at right-angles to the vertical direction  16  and/or the direction of the switchover movement  26 . 
     The mounting extension  24  is so fixed in the mounting recess  43  that it directly accompanies the linear switchover movement  26  of the diaphragm carrier  6 . This also applies, consequently, for the mounting diaphragm section  36  mounted directly on the mounting extension  24  and lying outside the mounting recess  43 . In both embodiments the mounting diaphragm section  36  is assigned to the central section of the base surface  38 . 
     The sealing diaphragm  8  is expediently held to the diaphragm carrier  6  solely in the area of the mounting diaphragm section  36 . Expressed more precisely, the final connection results from the interaction between the inner periphery of the mounting recess  43  and the mounting extension  24  dipping into the mounting recess  43 . Between these two components there is in the embodiments an adhesive-bonded connection, obtained by means of an adhesive which is not visible in the drawing. Additionally or alternatively, however, a friction-locked connection is also possible. Moreover the mounting recess  43  may also be so contoured that it additionally or alternatively makes a positive-locking connection in the vertical direction  16  with the mounting extension  24 . The latter may be obtained for example by providing the mounting recess  43  with at least one constriction which engages or presses into a constricted or wasted circumferential section of the mounting extension  24  in a direction radial to the vertical direction  16 . 
     Several fluid passages  45  which pass through the valve housing  2  open out into the valve chamber  7 . In the embodiments of  FIGS. 1 to 11  there are altogether two fluid passages, since the diaphragm valve  1  is used here as a shut-off valve with a 2/2 valve function. If a diaphragm valve  1  with greater valve functionality is to be realised, for example with a 3/2 valve function, then at least three and preferably exactly three fluid passages lead into the valve chamber  7 . This applies to the embodiment of  FIG. 12 . 
     In the embodiments, two fluid passages  45  may also be described below, for better distinction, as the first and second fluid passage  45   a ,  45   b . Both fluid passages  45   a ,  45   b  expediently pass through the base surface  12  and open out at the bottom  23  into the valve chamber  7 , each with a passage opening  46 . For better distinction, here too the passage openings  46  may be designated as first and second passage openings  46   a ,  46   b.    
     In the embodiments of  FIGS. 1 to 11 , depending on the switching position of the valve member  3 , the two fluid passages  45   a ,  45   b  may either be separated by the diaphragm valve  1  with fluid-tightness from one another, or else have a fluidic connection with one another through the valve chamber  7 . The latter occurs in the open position of the valve member  3  referred to earlier. To break the fluid connection, the valve member  3  is shifted into the closed position. 
     In order to exercise this valve functionality, the valve member  3  cooperates with a valve seat  47  mounted immovably relative to the valve housing  2 . The illustrated diaphragm valves  1  differ from one another in the structure of their valve seat  47 . The valve seat  47  according to the embodiment of  FIGS. 1 to 6  is web-like in form and may therefore also be described below as the web-like valve seat  47   a . Each valve seat  47  of the embodiment of  FIGS. 7  to  11  and  FIG. 12  is annular and closed and may therefore be described below as the annular valve seat  47   b.    
     The web-like valve seat  47   a  extends in the valve chamber  7  transversely to the vertical direction  16  between opposite side wall sections  22   a ,  22   b , in particular diametrical, of the side wall  22 . In this way the valve chamber  7  is divided by the valve seat  47   a  into two chamber sections  52   a ,  52   b , in which is to be found one of the two passage openings  46   a ,  46   b . Preferably the valve seat  47   a  has a linear longitudinal extent, which may be well seen in  FIG. 5 . 
     In the embodiment of  FIGS. 7 to 11 , only the first passage opening  46   a  is framed by an annular valve seat  47   b , which is preferably raised in the manner of a collar at the bottom  23 , extending upwards from that point in the vertical direction  16  towards the sealing diaphragm  8 . 
     In all embodiments the sealing diaphragm  8  extends over the valve seat  47 . At the same time it has, in a section opposite the valve seat  47  in the vertical direction  16  a sealing section  53 , which is provided before the base surface  38  in the vertical direction  16  and which, in execution of the switchover movement  26  and depending on the direction of movement, may be pressed by the diaphragm carrier  6  on to the assigned valve seat  47  with a fluid-tight seal, or else lifted from the valve seat  47 . In the closed position of the valve member  3 , the sealing section  53  fits up with sealing against the assigned valve seat  47 , while in the open position of the valve member  3  it is lifted from this valve seat  47 . 
     The sealing section  53  is that portion of the sealing diaphragm  8  which may be brought into contact with the assigned valve seat  47 . Its shape therefore corresponds to that of the valve seat  47 . Accordingly, the sealing section  53  of  FIGS. 1 to 6  has a strip-like sealing section  53   a , and in the embodiments of  FIGS. 7 to 12  it has an annular sealing section  53   b . Each sealing section  53  lies opposite the valve seat  47  in the vertical direction vertical direction  16 . 
     In the embodiment of  FIGS. 7 to 11 , the annular valve seat  47   b  lies expediently wholly within the outer contour  54  of the base surface  38  of the diaphragm carrier  6  facing the sealing diaphragm  8 . In both embodiments this base surface is formed by an axially oriented end face of the diaphragm carrier  6 , which is preferably plunger-like in form. Even with a web-like valve seat  47   a  it is according to  FIGS. 1 to 6  advantageous if the web-like valve seat  47   a  is covered at least approximately over its whole length by the base surface  38  of the diaphragm carrier  6 . 
     The outer edge section  14  fixed to the valve housing  2  and the mounting diaphragm section  36  of the sealing diaphragm  8  are arranged transversely to the vertical direction  16 , with clearance from one another. Preferably the outer edge section  14  encloses the mounting diaphragm section  36  all round in the manner of an enclosed frame. 
     The sealing diaphragm  8  also has a special diaphragm section, described below as the loose diaphragm section  55 . This loose diaphragm section  55  extends between the mounting diaphragm section  36  and the outer edge section  14 ; it is not fastened to the diaphragm carrier  6 —except via the mounting diaphragm section  36 —and is loosely mounted in front of the base surface  38 . The sole connection between the sealing diaphragm  8  and the diaphragm carrier  6  effecting any fixing is therefore provided by the mounting diaphragm section  36 . While this mounting diaphragm section  36  directly accompanies the switchover movement of the diaphragm carrier  6 , the loose diaphragm section  55  is able to lift up from the base surface  38  when the diaphragm carrier  6  moves from the closed position into the open position, at the same time moving away from the valve seat  47 . The sealing section  53  belongs at least in part to the loose diaphragm section  55 . Therefore the sealing section  53  may also be lifted at least partially from the base surface  38  in the direction of the switchover movement  26 . For the part of the sealing section  53  belonging to the loose diaphragm section  55 , also described below as the unfixed part  32  of the sealing section  53 , it therefore applies that, in the closed position of the valve member  3  it is supported by the base surface  38  of the diaphragm carrier  6  and is pressed against the valve seat  47 , while in the open position of the valve member  3  it is lifted not only from the valve seat  47  but also in an advantageous manner from the base surface  38  of the diaphragm carrier  6 . 
     In  FIGS. 3 and 9 , the portion of the loose diaphragm section  55  lying within the contour  54  of the base surface  38  is made recognizable by dot-dash shading  50 . It is mounted in front of the base surface  38  in the vertical direction  16  and frames the mounting diaphragm section  36 , preferably coaxially. Here it may also be easily recognized that the mounting diaphragm section  36  is arranged expediently all-round with radial clearance from the outer contour  54  of the base surface  38 . 
     When the loose diaphragm section  55  lifts from the diaphragm carrier  6 , this expediently results in a roughly wedge-shaped widening gap  34  between these two components, from the mounting extension  24  towards the contour  54 , and very clearly visible in  FIGS. 4 to 6, 10 and 11 . 
     Due to the fact that the sealing diaphragm  8  is not fastened to the diaphragm carrier  6 , except at the mounting diaphragm section  36 , the sections of the sealing diaphragm  8  adjoining the mounting diaphragm section  36 , in particular the loose diaphragm section  55 , are not compelled to accompany the switchover movement  26  of the diaphragm carrier  6  to the full extent, which reduces the tensile loading of the sealing diaphragm  8  and has a positive effect on life expectancy. 
     The diaphragm valve  1  may be so designed that only a portion of the sealing section  53  forms part of the loose diaphragm section  55 . By way of example, this applies to the embodiment of  FIGS. 1 to 6 . The sealing section  53   a , here strip-like in form, extends in part over the mounting diaphragm section  36  and in part over the loose diaphragm section  55 . Accordingly the sealing section  53  has a fixed part  33  formed by the mounting diaphragm section  36  and at least one unfixed part  32  formed by the loose diaphragm section  55 . In the embodiment, in which the strip-like sealing section  53   a  extends diametrically beyond the base surface  38 , consequently only the two unfixed parts  32  of the sealing section  53  are able to fold back from the diaphragm carrier  6  during the switchover movement  26 . 
     The diaphragm valve  1  may also be so designed that the sealing section  53  in its totality is a part of the loose diaphragm section  55 . This is the case in the embodiments of  FIGS. 7 to 12 . The sealing section  53 ,  53   b , here annular in form, extends with lateral clearance and in particular with radial clearance from the mounting diaphragm section  36  around this mounting diaphragm section  36 , so that it is able to lift completely from the base surface  38  of the diaphragm carrier  6  when the latter moves away from the annular valve seat  47   b  in the course of its switchover movement  26 . 
     The loose diaphragm section  55  expediently includes a diaphragm outer section  56  which, viewed in the vertical direction  16 , frames the outer contour  54  of the base surface  38  all round and merges into the outer edge section  14 . The embodiments of  FIGS. 7 to 12  show such a design. Since this diaphragm outer section  56  is not covered by the diaphragm carrier  6 , it receives no support from the diaphragm carrier  6  against the fluid pressure prevailing in the valve chamber  7 . So that equally the diaphragm outer section  56  is subject to no overloading even at high fluid pressures, it is expediently covered on its upper side facing away from the valve chamber  7  by a support wall  48  of the valve housing  2  which provides a supporting effect relative to the diaphragm outer section  56 . The support wall  48  is preferably a part of the second housing section  15 . It extends from the outer side facing the outer edge section  14  over the sealing diaphragm  8  and preferably as far as the immediate vicinity of the diaphragm carrier  6 , which expediently passes through a wall opening  44  in the support wall  48  with linear sliding capability. 
     The axial support of the diaphragm outer section  56  is possible without impairing the functioning of the valve member  3 , since the sealing diaphragm  8  has in the area of the loose diaphragm section  55  the necessary freedom of movement to ensure the lifting movement of the diaphragm carrier  6  including the assigned sealing section  53 . 
     The diaphragm valve  1  may also be so designed that the part of the sealing diaphragm  8  reaching as far as the outer contour  54  immediately adjoins the outer edge section  14  fixed to the valve housing  2 . This applies to the embodiment of  FIGS. 1 to 6 . Here the diaphragm carrier  6  covers with its base surface  38  the entire cross-sectional surface of the valve chamber  7 . 
     On account of the scope for the loose diaphragm section  55  to lift from the diaphragm carrier  6  or to fold back or away from the diaphragm carrier  6 , there is the advantageous option of producing the sealing diaphragm  8  with a flat structure with no outward bulges. The best example of this is the design of  FIGS. 1 to 6 , in which the sealing diaphragm  8 , apart from the mounting bead  21 , has a flat shape with substantially constant wall thickness. Equally the sealing diaphragm  8 , in particular in the area of the outer contour  54  of the diaphragm carrier  6 , may have a deformation section  60 , preferably annular viewed in the vertical direction  16 , and having at least one outwards bulge. 
     The electrical drive means  4  provided in the embodiments of  FIGS. 1 to 11  expediently include in each case a spring device  57  which rests between the valve housing  2  and the diaphragm carrier  6  and which constantly presses on the diaphragm carrier  6  so that the latter is biased into the closed position referred to earlier. This closed position therefore defines the basic position of the diaphragm valve  1  for both embodiments. 
     To switch over into the open position, the drive means  4  contain in particular an electromagnetic device  58 , shown schematically, which contains an electromagnetically drivable drive member  63 , formed by an electromagnetically drivable armature of the electromagnetic device  58 . This armature is integral with the diaphragm carrier  6  in the embodiments of  FIGS. 1 to 11 . On activation of the electromagnetic device  58  a magnetic actuating force is generated, which moves the diaphragm carrier  6  into the open position, overcoming the restoring force of the spring device  57 . The spring device  57  is expediently part of the electromagnetic device  58 . 
     Naturally the drive means  4  may also be of another type than that described here. 
     In the embodiment of the diaphragm valve  1  depicted in  FIG. 12 , a single diaphragm body  5  is divided functionally into two sealing diaphragms  8 , each connected to a separate diaphragm carrier  6 , so that each may cooperate with a separate valve seat  47 ,  47   b.    
     Both diaphragm carriers  6  here are expediently plunger-like in form and guided to move linearly parallel to one another. They are so connected in drive terms that the one diaphragm carrier  6  approaches the assigned valve seat  47 ,  47   b  when the other diaphragm carrier  6  is lifted from the assigned valve seat  47 ,  47   b . The driving connection may be realised in particular by means of a rocker-like, pivotable operating lever  62 , which may be driven by the drive means  4  to a to-and-fro pivoting movement  65 , and which has two driving arms  67 ,  68 , each cooperating with one of the two diaphragm carriers  6 . Thus, in this embodiment, the pivoting movement  65  of the operating lever  62  is converted into the linear switchover movement of the two diaphragm carriers  6 . 
     The embodiment of  FIG. 12  differs from that of  FIGS. 7 to 11  in particular through an additional third fluid passage  45   c , which leads into a third passage opening  46   c  in the valve chamber  7  and which, like the first passage opening  46   a , is assigned a valve seat  47 , once again involving an annular valve seat  47   b . Over each of these two valve seats  47   b  extends one of the two sealing diaphragms  8  integrated in the one-piece diaphragm body  5 . In addition, lying opposite each of these annular valve seats  47   b  is one of the two diaphragm carriers  6 , to which in each case one of the two sealing diaphragms  8 , i.e. in each case one diaphragm section of the diaphragm body  5 , is fastened in a similar manner in the area of a mounting diaphragm section  36 , as in the embodiment of  FIGS. 7 to 11 . One may say that in the embodiment of  FIG. 12 , the functional unit described with the aid of  FIGS. 7 to 11 , comprising a diaphragm carrier  6 , a sealing diaphragm  8  and an annular valve seat  47   b , is present in duplicate while, by means of the operating lever  62 , actuation is effected in the manner described above, and wherein the two sealing diaphragms are combined in one piece to form the diaphragm body  5 . 
     Therefore, in the embodiment of  FIG. 12 , the second fluid passage  45   b  may be connected alternately to either the first fluid passage  45   a  or the third fluid passage  45   c  and at the same time isolated from the other respective fluid passage  45   c  or  45   a.    
     The drive means  4  in the embodiment of  FIG. 12  are also preferably electrically actuable, and expediently include an electromagnetic device  58 , indicated schematically, and an electromagnetically drivable drive member  63 . The drive member  63  exerts on the operating lever  62  a driving force which generates the pivoting movement  65 , wherein it expediently has to overcome the resetting force of a spring device  57 . 
     Visible at  66  are pivot bearing means, through which the operating lever  62  is mounted pivotably relative to the valve housing  2  to make possible the pivoting movement  65 . 
     Otherwise, components in  FIG. 12  which correspond to those of the embodiment of  FIGS. 7 to 11  are provided with the same reference numbers as in  FIGS. 7 to 11 . Also the statements made on  FIGS. 7 to 11  apply accordingly to this extent for the embodiment of  FIG. 12 . 
     As a variation from the above embodiment, one or two diaphragm carriers  6  may also be fixed components of an altogether rocker-like, pivotable actuating element. 
     In the embodiments the diaphragm carrier  6  is made in one piece. Varying from this, however, a multi-part and in particular two-part construction is also possible. Consequently the sealing diaphragm  8  may for example be so fitted to a multi-part diaphragm carrier that it is pushed into the diaphragm carrier and then fixed in place by a sleeve, which simultaneously forms a bearing means for an axle shaft serving for pivotable bearing of the diaphragm carrier. The sealing diaphragm  8  or the diaphragm body  5  may also be fixed between two parts o the diaphragm carrier  6  by clamping.