Abstract:
The invention relates to a controlled three-way proportional valve unit comprising: a valve assembly with two individual valves; an actuating device actuating valves of the valve assembly; and a control unit acting upon the actuating device and having a control signal input, the valves of the valve assembly being designed as poppet valves arranged on opposite sides and having counter-rotatable valve spindles. The valve spindles are prestressed relative each other in opposite directions by a prestressing element such that, when the actuating unit is inactive, a first poppet valve is open and the second poppet valve is closed. The actuating device comprises an actuator common to both poppet valves, acts upon the two valve spindles and changes the position of the valve spindles counter to the effect of the prestressing element.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation under 35 U.S.C. §120 of international Application PCT/EP2013/002598, filed Aug. 29, 2013, which claims priority to German Application 10 2012 017 714.3, filed Sep. 7, 2012, the contents of each of which are incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a regulated proportional three-way valve unit with a valve group comprising two single valves, an actuating device that actuates the single valves of the valve group and a regulating unit acting on the actuating device and having a control-signal input. 
       BACKGROUND 
       [0003]    In fluid engineering, valve units are used to influence the fluid flow selectively. This is the case, for example, of influencing the pressurization of a fluidically activated drive element, which in turn can be used, for example, to actuate a shutoff organ. In this connection, multi-way valve units with three ports are used for various applications, wherein typically one port—depending on the switched position of the multi-way valve unit—is in fluidic communication with one and/or other of the two remaining ports or else can be shut off relative to the other two ports. It is not only slide valves with such a function that are known, especially such in which a single slide, which can be displaced within a valve housing containing the three ports and which—depending on its position—opens or shuts off the said fluid communication paths. To the contrary, three-way valve units are also known that have a valve group comprising two structurally independent single valves, wherein the two single valves of the valve group can be actuated by means of an actuating device and typically one of three ports is in fluidic communication both with a valve chamber of the one single valve and also with a valve chamber of the other single valve (see EP 2133546 A1). In a particular manner—other than that according to EP 2133546 A1—these two single, valves can be biased in such a way that the one single valve—without pressurization of an actuator associated therewith—assumes a closed position, while the other single valve—without pressurization of an actuator associated therewith—assumes an open position. 
         [0004]    The object of the present invention is to provide a regulated proportional three-way valve unit having the features indicated in the introduction, characterized by a high degree of operating safety and reliability as well as by good regulation behavior in combination with a relatively simple design structure. 
       SUMMARY 
       [0005]    This object is achieved according to the present invention by the regulated proportional three-way valve unit specified in detail in the claims. In functional combination and synergetic interaction with the further features definitive for the inventive proportional three-way valve unit, it is therefore characteristic for the latter among other aspects that the two single valves of the valve group—preferably mounted in a common housing—are constructed as two poppet valves disposed opposite one another with valve spindles that can move in opposite directions and are biased in opposite directions by means of a biasing unit. This actuating device has an actuator, which is common to both poppet valves and acts on both valve spindles, and which—depending on its pressurization with an input variable—changes the position of the valve spindles against the action of the biasing unit. Under the action of the biasing unit—which biases the two valve spindles in mutually opposite directions—a first of the poppet valves is opened and the second poppet valve is closed while the actuating unit is inactive. Furthermore, according to the invention, this actuating unit and the biasing unit are matched to one another in such a way that, during steady changes of the input variable fed to the actor of the actuating device from a first operating value to a second operating value in a manner offset relative to one another (i.e. in a sequential actuating sequence), the first poppet valve is closed progressively over its entire operating travel at first and only then is the second poppet valve opened progressively over its entire operating travel, so that—when the said input variable is changed correspondingly—closing of the first poppet valve on the one hand and opening of the second poppet valve on the other hand take place in two different ranges for the input variable fed to the actor of the actuating device. In this way it is ensured that each value of the input variable for the actor is associated uniquely with precisely one particular position of both single valves of the three-way valve unit. As a further consequence, uniquely precisely one operating point of the valve group can therefore be associated in turn with each setpoint fed to the regulating unit. The switched state of the valve group is determined uniquely and exactly by a (single) sensor, which detects the relative distance of the two valve spindles from one another. The signal supplied by the sensor, which accordingly can provide information about the position of both poppet valves and thus about the current operating point of the valve group, is fed back in a manner that is particularly attractive as regards regulating systems—as an actual value—to the regulating unit, whereby matching of the actual operating point of the valve group with the setpoint fed to the regulating unit can be achieved in simple and reliable form. In particular, interdependences are precluded by the use of a single sensor common to both poppet valves, and so particularly stable regulation behavior is achieved. From the structural viewpoint, it is then particularly favorable when the sensor is disposed on a control platen, which in turn is disposed between the two valve spindles. 
         [0006]    Because of the proportional operation of the valve group, a particularly long useful life of the components—significantly longer than that of pulse-width-modulated activation of the fluidic load pressurized via the valve group—is achieved, and specifically not least because all valves experience predominantly a partial deflection during operation and only rarely are actuated over their entire range of movement. In addition, the inventive valve unit is characterized, in a manner different from that applicable for three-way valve units used for slide valves, by a valve group that is completely leak-free (or at any rate suffers negligible leakage), which is an outstanding advantage in particular from viewpoints of efficiency, because hereby true “shutoff” or “hold” of a connected load (see hereinafter) is possible without continuous admission of pressurized fluid. 
         [0007]    The advantages achievable by application of the present invention are particularly pronounced when, in the case of the change of the input variable depicted in the foregoing for the actor between closing of the first poppet valve and opening of the second poppet valve, a range (“shutoff range”) exists in which both poppet valves are closed. In other words: During a change of the input variable for the actor, opening of the second poppet valve preferably begins not more or less simultaneously, i.e. at the same value of the input variable, with complete closing of the first poppet valve. To the contrary, a more or less pronounced range within which both poppet valves are closed exists instead for the input variable. Particularly preferably, this shutoff range in question occupies between 10% and 30% of the range attainable on the whole by the input variable. This is of great advantage for stable operating behavior. This shutoff range can be used in particular to shut off or to hold a fluidic load (such as a pneumatic cylinder) being pressurized via an inventive valve group. Precisely this range within which the load is being shut off or held can be monitored via the sensor. Since disturbing influences related to operation are detected via the sensor and—by virtue of feedback of the measured value to the regulating unit—can be compensated by the regulating circuit, the hold or shutoff range need be executed with only small safety reserves, meaning that it can be relatively narrow. Consequently, correspondingly broader ranges are available for positioning of the two poppet valves, and so they can be constructed with relatively flat characteristic curves (at least in ranges), thus permitting particularly sensitive adjustment of the flow through the valve group. As a further consequence, leaks in the “hold” state can always be kept to a minimum regardless of the service conditions, since the hold state can always be guided to the optimum middle position via the regulating circuit. And, by virtue of the monitoring of the hold and shutoff range, expanded diagnosis options are created for early detection in particular of changes in the dynamics, the response behavior, any signs of wear or soiling o the valve seats and even impairments of the overall function. 
         [0008]    In a preferred improvement of the present invention, a fluidic, especially a pneumatic actuating device is provided, which has two pressure-displacement transducers pressurized from a common control chamber, a first of which acts (indirectly as the case may be) on the valve spindle of the first poppet valve and a second acts (indirectly as the case may be) on the valve spindle of the second poppet valve. Similarly, it is of advantage in particular when the fluidic actuating unit can be fed from the same fluid supply (such as a compressed-air source), which also supplies the working fluid to be influenced by the valve group. The matching of the two pressure-displacement transducers to one another used in the context of the present invention in the sense of the depicted hierarchy or actuation sequence can then be achieved by suitable engineering design of the area ratios of the two pressure-displacement transducers, on which the control pressure prevailing in the control chamber acts, and also by matching the biasing forces acting on the two poppet valves both relative to one another and relative to the respective associated effective area of the pressure-displacement transducer in question. Thus the biasing device in particular can act on the two valve spindles with different biasing forces. An effect of interest for operating safety then exists in the fact that pressure fluctuations developing—for whatever reason—in the control chamber, because they act on the two pressure-displacement transducers, can be detected via the sensor, and so the signal supplied by the sensor can also provide information on the operating state of the fluid supply. Conversely, because the sensor signal is fed back to the regulating unit, fluctuations of the operating pressure can be corrected, and so the desired fluid flow through the valve group can be maintained reliably even during possible fluctuations of the operating pressure. Nevertheless, the pneumatic construction of the actuating device explained in the foregoing is in no case imperative; to the contrary, other types of constructions of the actuating device may be advantageously considered—under different prerequisites—in the context of the present invention, for example actuating devices of electromagnetic type based on the coil-armature principle. 
         [0009]    According to another preferred improvement of the present invention, in the specific case of an actuating device of fluidic construction, the valve unit is constructed in two stages, i.e. the valve group explained in the foregoing is part of a two-stage valve unit, which further comprises an electrofluidic pilot stage, which is connected between the regulating unit and the valve group and which in turn comprises an electrical signal input connected with the regulating unit, a pressurized-fluid inlet, a control-pressure outlet in communication with the control chamber and a proportional pilot valve disposed between the pressurized-fluid inlet and the control-pressure outlet. Such a two-stage construction of the valve unit is particularly advantageous when—in the sense depicted in the foregoing—fluidic actuation of the two single valves via associated pressure-displacement transducers takes place from a common control chamber. In this regard it is also significant that, by virtue of the use of the working fluid switched by the valve group in the pilot stage also, i.e., for actuation of the two single valves, synergetic effects, which are manifested in particular in an equally compact and efficient system, can be achieved. In other words, the influence on the two pressure-displacement transducers in order to change the position of the valve spindles of the two poppet valves takes place selectively in this improvement via an electrical signal, via which the pilot stage is variably activated. The activation signal of the pilot stage is ideally generated via a regulating circuit, where the sensor signal is taken into consideration. 
         [0010]    In the foregoing improvement of the present invention, the electrofluidic pilot stage can operate successfully with precisely one electromechanical transducer and precisely one proportional valve actuated thereby. In conjunction with the unique correlation, which is characteristic of inventive valve units, of the operating point, defined by the switched status of the two poppet valves, of the valve group with the pressure in the one (single) control chamber, a position regulator designed using the inventive valve unit, for example, can be easily kept under control by regulating systems despite little structural and apparatus-related complexity, and so instabilities in particular can be avoided. 
         [0011]    According to yet another particularly preferred improvement, the units respectively comprising a poppet valve and the associated actor have a nonlinear variation of the characteristic curve of the opening cross section versus the input variable of the actor. Instead, the characteristic curve is preferably flat in the neighborhood of the respectively completely closed range of the poppet valve in question, in the sense that a given change of the opening cross section requires a larger change of the input variable than in a range further removed from the completely closed valve. In other words, for both poppet valves the gradient determining the ratio of the opening cross section to the input variable of the actor is flatter, particularly preferably when it is close to the respective closing point, than when it is further removed from the respective closing point. This permits, for example, particularly sensitive pressurization of a drive element of a positioning drive actuated via the inventive valve unit, in which case especially the fine-adjustment range bordering the hold range on both sides can be utilized particularly exactly by monitoring the positioning-regulator state, even at low required mass flows. This in turn is also a viewpoint of great advantage with regard to the stability of regulation. Corresponding matching of the components with regard to the said nonlinearity can therefore be applied not only to the respective actor (e.g. the pressure-displacement sensor). To the contrary, such matching is also possible at the poppet valve itself, specifically by constructing it with soft-sealing capability. To generate the said flat gradient of the characteristic curve, the sealing edges can be matched in such a way to the hardness of the respective valve seat that—by appropriate shaping—an opening gap is formed at first not over the entire circumference of the sealing edge but instead only over a partial extent of the sealing edge. It is particularly advantageous as regards the soft-sealing properties of the poppet valve explained in the foregoing when the valve seat is constructed on a captive seal, wherein the sealing edge is particularly preferably constructed on the movable valve member (closing member). 
         [0012]    According to yet another preferred improvement, the sensor characteristic of the inventive three-way valve unit can constitute a functional component of the biasing device, by the fact that it is constructed as an integral spring-sensor element. By this it will be understood that the said element not only supplies a biasing force acting on at least one of the valve spindles, preferably on both valve spindles, but at the same time generates a signal—to be fed back to the regulating unit—that corresponds to the relative distance between the two valve spindles. In this way a further engineering and design simplification of the inventive three-way valve unit is possible, as is also a particularly compact construction thereof. 
         [0013]    The inventive valve unit can be used with special benefits in the context of position regulators (for example, for valve positioning drives), wherein the drive element of the positioning drive then preferably has precisely one fluidic working chamber, which is in communication via a working outlet of the valve unit with respectively a first valve chamber of both poppet valves, wherein the second valve chamber of the first poppet valve is in communication with a pressurized-fluid supply and the second valve chamber of the second poppet valve is in communication with a pressurized-fluid vent. Such a design makes logical use of the options provided by the invention and makes available an efficient, compact, reliable positioning drive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The present invention will be explained in more detail hereinafter on the basis of the preferred exemplary embodiments illustrated in the drawing, wherein 
           [0015]      FIG. 1  shows a schematic diagram of a positioning drive, which is constructed using a first exemplary embodiment of an inventive valve unit, 
           [0016]      FIG. 2  shows a characteristic curve of the power stage of the valve unit according to  FIG. 1 , i.e. the opening cross sections of the two poppet valves versus the control pressure, 
           [0017]      FIG. 3  shows a second exemplary embodiment of the invention as a modification of the exemplary embodiment according to  FIG. 1 , 
           [0018]      FIG. 4  shows a third exemplary embodiment of the invention as a modification of the exemplary embodiment according to  FIG. 1 , 
           [0019]      FIG. 5  shows a fourth exemplary embodiment of the invention as a modification of the exemplary embodiment according to  FIGS. 1 , and 
           [0020]      FIG. 6  shows a fifth exemplary embodiment of the invention as a modification of the exemplary embodiment according to  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    The pneumatic positioning drive illustrated in  FIG. 1  comprises, for actuation of a valve  1 , a drive element  2  that can be pressurized with compressed air and a proportional position regulator  3  that regulates the pressurization of the drive element with compressed air. This drive element  2  is constructed in the form of a single-action pneumatic cylinder  4 , which in a manner known in itself comprises a housing  5 , a piston  7  plus piston rod  8  guided sealingly and displaceably therein and bounding a variable-volume working chamber  6 , and a biasing or restoring spring  9  acting on piston  7 . 
         [0022]    Proportional positioning regulator  3  is constructed in two stages with an electropneumatic pilot stage (upstream stage)  10  and a pneumatic power stage  11 . Both pilot stage  10  and power stage  11  are supplied by one and the same compressed-air supply  12 . 
         [0023]    Electropneumatic pilot stage  10  comprises an electrical signal input  13 , precisely one electromechanical transducer  14  in the form of a piezoelectric bending transducer  15  and precisely one proportional valve  116  that can be actuated thereby having a compressed-air inlet  18  connected—via pressure-reducing valve  17 —to compressed-air supply  12 , a control-pressure outlet  19  and a vent outlet  20 . In a manner known in itself, the pressure present at control-pressure outlet  19  depends on the specific geometry of piezoelectric bending transducer  15 , which in turn depends on the voltage present at electrical signal input  13 . Electrical input  13  in turn is connected via a regulating unit  21  with setpoint input  22 . 
         [0024]    Pneumatic power stage  11  comprises two poppet valves  24  and  25  mounted in the form of a valve group in housing  23  and disposed in diametrically opposite positions, each comprising a valve seat  26  and  27  respectively disposed in fixed relationship to the housing and a valve spindle  28  and  29  respectively with closing members  30  and  31  respectively disposed thereon. These valve spindles  28  and  29  respectively are joined sealingly and in fixed relationship with double-walled diaphragm units  32  and  33  respectively, while the space disposed within housing  23  between the two diaphragm units  32  and  33  forms a control chamber  34 , to which control pressure outlet  19  of piezoelectric pilot stage  10  is connected. In detail, valve spindle  28  of poppet valve  24  is joined in fixed relationship to a pressure plate  44 , which is a functional part of “control-pressure diaphragm”  32   a,  which in turn forms the wall of (double-walled) diaphragm unit  32  facing control chamber  34 . The second wall of diaphragm unit  32  forms a “chamber diaphragm”  32   b,  wherein the space between control-pressure diaphragm  32   a  and chamber diaphragm  32   b  is unpressurized and supplied by air. An analogous situation exists for second poppet valve  25 . Diaphragm units  32  and  33  seal control chamber  34  from a first valve chamber  35  or  36  respectively of poppet valve  24  or  25  respectively, wherein the two first valve chambers  35  and  36  respectively communicate with one another and with a common working outlet  37  of power stage  11 , which in turn is in communication with pneumatic working chamber  6  of drive element  2 . Second valve chamber  38  of first poppet valve  24  is then in communication with a compressed-air vent  39 , while second valve chamber  40  of second poppet valve  25  is in communication with compressed-air supply  12 . Pilot stage  10  can be integrated structurally in housing  23  of power stage  11  or can be built directly onto it, although this is not explicitly shown in the drawing. 
         [0025]    Biasing or restoring springs  41  and  42  respectively act on both valve spindles  28  and  29  respectively, and specifically in such a way that, of the two poppet valves  24  and  25  of power stage  11 —in the absence of pneumatic pressurization, i.e. when control chamber  34  is unpressurized (see hereinafter)—a first, namely first poppet valve  24  shown at the right in  FIG. 1 , is biased in an opened position, whereas the second, namely second poppet valve  25  shown at the left  1 , is biased in a closed position. For each of the two poppet valves  24  and  25 , the functional combination of diaphragm units  32  and  33  respectively and biasing or restoring springs  41  and  42  respectively form a pressure-displacement transducer—acting on the respective closing members  30  and  31  in question of the respective valve spindles  28  and  29  in question—in the sense that the position of the respective valve spindle  28  and  29  is guided by the pressure (control pressure) prevailing in control chamber  34 . The diametrically opposite arrangement of the two poppet valves  24  and  25  already mentioned in the foregoing then also extends to the two pressure-displacement transducers, by means of which, in other words, poppet valves  24  and  25  can be actuated pneumatically. This is important to the extent that the two pressure-displacement transducers are pressurized from a common control chamber  34 , which is in communication with control-pressure outlet  19  of pilot stage  10 . 
         [0026]    The pressure-displacement transducer associated with first poppet valve  24  is matched to the pressure-displacement transducer associated with second poppet valve  25  (see  FIG. 2 ) in such a way that, during a steady pressure rise in control chamber  34 , i.e. during steadily rising control pressure p via a limited—by a lower operating pressure B 1  and an upper operating pressure B 2 —working pressure range, first poppet valve  24  is progressively closed at first and second poppet valve  25  is then progressively opened only after first poppet valve  24  has closed completely. Both poppet valves  24  and  25  are closed within a partial range—constituting a shutoff range S—of the working pressure range for the control pressure, wherein the shutoff range occupies approximately 20% of the control pressure range attainable in total by the control pressure. The mean value of the control-pressure range therefore lies within shutoff range S. 
         [0027]    The working-pressure range makes up approximately 90% of the control-pressure range attainable in total by the control pressure, which means that the respective positions of the two poppet valves  24  and  25  do not change in the lowest 5% and in the highest 5% of the control-pressure range. As illustrated  FIG. 2 , the units respectively comprising a poppet valve  24  or  25  and the associated pressure-displacement transducer have a nonlinear shape of characteristic curve  24 ′ or  25 ′ of opening cross section Q versus control pressure p. In each case, a flat characteristic curve is present respectively close to or adjacent to shutoff range S, in the sense that a relatively large change—compared with the ranges of the performance characteristics further removed from shutoff range S—of control pressure p is necessary for a change of opening cross section Q of poppet valve  24  or  25  by a given extent. Such nonlinearities can be obtained in particular not only by suitable matching of valve seats  26  and  27  respectively and closing members  30  and  31  respectively to one another but also by adjustments on the part of the pressure-displacement transducers (e.g. of diaphragm units  32  and  33  respectively and/or of biasing and restoring springs  41  and  42  respectively). 
         [0028]    The design explained in the foregoing leads to the following mode of operation of the positioning drive: If the control pressure prevailing in control chamber  34  is gradually raised—starting from an initially unpressurized state—by appropriate pressurization of electropneumatic pilot stage  10  by setpoint input  22  and via regulating unit  21 , first poppet valve  24  begins to close after a pressure rise of approximately 5% (relative to the control-pressure range attainable in total by the control pressure), in which case the opening cross section of first poppet valve  24  changes relatively rapidly at first then much more slowly later, by virtue of the characteristic curve explained in the foregoing. At approximately 40% of the maximum control pressure, the first poppet valve is completely closed. As the control pressure continues to rise, the position of poppet valves  24  and  25  does not change until the control pressure reaches approximately 60% of the maximum value; at this point both poppet valves are shut off. It is only upon a further rise of the control pressure that second poppet valve  25  is opened, which actually happens gradually at first and then later more rapidly, specifically until it has reached its completely open position at approximately 95% of the maximum pressure. 
         [0029]    By virtue of this characteristic of position regulator  3  and of the interfacing of compressed-air supply  12  and drive element  2  therewith as described in the foregoing, working chamber  6  of drive element  2  is shut off at a control pressure within shutoff range S (40% to 60% of the control pressure), is in communication with compressed-air vent  39  within the pressure range located between 0% and 40% (for different opening cross sections of first poppet valve  24 ) and is in communication with compressed-air supply  12  within the pressure range located between 60% and 100% (for different opening cross sections of second poppet valve  25 ). Accordingly, depending on the control pressure prevailing in control chamber  34 , valve  1  is held (in the absence of internal air consumption of power stage  11 ), is closed more or less dynamically or else is opened—again more or less dynamically. 
         [0030]    The position regulator comprises a sensor  43 , which is disposed in control chamber  34  between the two poppet valves  24  and  25  and which measures the relative distance between the two pressure plates  44  and  45  joined in fixed relationship to valve spindles  28  and  29  respectively of poppet valves  24  and  25  respectively, A signal corresponding to the distance in question—and therefore characteristic of the current operating point of power stage  11 —is fed by sensor  43  as a feedback actual value to regulating unit  21 . Instead of the distance between pressure plates  44  and  45 , it would also be possible as an alternative for sensor  43  to measure the distance between other elements—between which it is disposed, possibly on a control platen—of the two pressure-displacement transducers that react to control pressure. In this respect, it must be ensured that the pressure-displacement transducers and/or valve spindles  28  and  29  associated with the two poppet valves  24  and  25  are not rigidly coupled with one another. 
         [0031]    Pilot stage  10  is constructed in such a way that control space  34  is unpressurized in the absence of an electrical input signal imposed on it, and so first poppet valve  24  is open and second poppet valve  25  is closed. As a consequence of this, working chamber  6  of drive unit  2  is unpressurized and piston  7  of drive unit  2  occupies the position dictated by biasing and restoring spring  9 . In this way, in the event of failure of regulating unit  21  (or of a comparable defect) on the side of pilot stage  10 , the position of poppet valves  24  and  25  of power stage  11 —and also the position of drive element  2 —is identical to that in the case of failure of compressed-air supply  11  Thus the positioning drive has a definite and unambiguous fail-safe behavior. 
         [0032]    The modification, illustrated in  FIG. 3  (only in a corresponding section), of the positioning drive according to  FIG. 1  differs from the embodiment explained in the foregoing primarily by a different type of configuration of the pressure-displacement transducer and of the sensor. And, in fact, the restoring forces acting on the two valve spindles  28  and  29  are supplied in this case by a common spring element  46 , disposed in control chamber  34  and preloaded in tension. The hierarchy actuation according to the invention, whereby actuation of the two poppet valves  24  and  25  as a function of control pressure takes place in offset manner, is accordingly achieved by different design of the two diaphragm units  32  and  33  with respect to their area pressurized by the control pressure and/or to their stiffness. Above and beyond this, common spring element  46  then simultaneously represents a sensor  47 , by the fact that a sensor function is integrated therein in order to measure the actual elongation of spring element  46  and to be fed back to regulating unit  21  as a variable characteristic of the operating point of the power stage, i.e. the position of the two poppet valves  24  and  25 . 
         [0033]      FIG. 4  illustrates specific engineering options for configuration of poppet valves  24  and  25 . In this case therefore, especially the use of soft-sealing poppet valves is illustrated, wherein valve seats  26  and  27  respectively are constructed on a captive seal  48  with a hardness between Shore 70 and Shore 85. And a well-defined sealing edge  49  is constructed on closing members  30  and  31  respectively of valve spindles  28  and  29  respectively. Hereby the nonlinearity of valve characteristic curves  24 ′ and  25 ′ already indicated in  FIG. 2  (opening cross section Q vs. control pressure p) can be predetermined even more accurately, in order to permit the most sensitive positioning possible of drive element  2 . 
         [0034]    Furthermore, it is evident in  FIG. 4  that a second diaphragm unit (chamber diaphragm)  50 , which seals the respective second valve chamber  38  or  40  of the respective poppet valve from the environment, is joined to spindle  28  or  29  respectively of each poppet valve  24  or  25  respectively. 
         [0035]      FIG. 5  illustrates an inventive valve unit in single-stage construction. Its structure and its function are evident directly from the foregoing explanation of the position regulator according to  FIG. 1  and its mode of operation, albeit with the proviso that in this case the actuator pressurized by regulating unit  21  and acting on the two valve spindles  28  and  29  is based on any desired functional principle that is suitable, e.g. of electromagnetic type. Accordingly it can be constructed as a coil  51 , which exerts, on plates  52  and  53  joined in fixed relationship to the ends of valve spindles  28  and  29 , increasingly repulsive forces—corresponding to the actual pressurization thereof—in which case the hierarchical, sequential movement is imposed, initially on first poppet valve  24  and only thereafter on second poppet valve  25  by appropriate matching of biasing and restoring springs  41  and  42  and/or of diaphragm units  32  and  33 , which in this case can have thin-walled construction. As a kinematic converse, it would obviously also be possible, by appropriate rearrangement of the poppet valves, to use a coil-armature configuration, in which valve spindles  28  and  29  are increasingly attracted by coil  51  in a manner corresponding to the pressurization thereof. 
         [0036]    The foregoing explanations about  FIG. 5  apply correspondingly for the embodiment schematically illustrated in  FIG. 6 , except in this case a combined spring-sensor unit  47  is used, by analogy with the embodiment according to  FIG. 3 .